Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/23/21

AREA FORECAST DISCUSSION

National Weather Service Albany NY

1031 PM EDT Sun Aug 22 2021

.SYNOPSIS...
Rain bands associated with Tropical Storm Henri will
continue to increase in intensity and coverage this evening. Heavy
rain is the primary concern for this evening into tonight, which may
result in both flash flooding and river flooding. Additional
showers, some with heavy downpours, will continue into the day on
Monday as well. Behind the storm, hot and muggy weather is expected
for much of the upcoming week.

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
.UPDATE as of 1020 PM EDT... Light rain associated with TD Henri
continues to fall across the Schoharie Valley and eastern
Catskills this evening. Storm total rainfall amounts range from
about 0.6" in Albany up to 2.75" at the Tannersville mesonet and
just over 3 inches in Litchfield county, CT. North of Albany,
only up to 0.25" fell today. Given the ongoing light rain, have
removed all mention of heavy rainfall and thunderstorms for the
overnight period.

.PREVIOUS DISCUSSION.
.UPDATE as of 750 PM EDT...Current radar analysis shows Henri
centered over northwest CT moving into the mid-Hudson valley.
Latest water vapor imagery shows an impressive area of dry air
wrapping into the storm which has cut off much of the heavier
rainfall for the forecast area. Heaviest rainfall looks like it
will be west of our region through this evening at least, before
a few bands wrap back northward towards Poughkeepsie during the
latter half of the overnight period. Therefore, rainfall totals
across the CWA overnight have decreased, prompting the removal
of the heavy rainfall wording in the forecast. Also have removed
the mention of thunder through 2AM.

.PREVIOUS DISCUSSION.
As of 520 PM EDT...In coordination with
NHC and neighboring offices, Tropical Storm Warning for
Litchfield County has been cancelled.

Tropical Storm Henri is now located inland over central Connecticut
and has been captured by the large upper level low located
south of area over the northern mid Atlantic States. As a
result, the storm has shifted direction and is starting to move
west-northwest across northern Connecticut for this evening,
while continuing to rapidly weaken. While there are some breaks
in the clouds across our far northwestern areas, most of the
region is seeing plenty of clouds as the storm`s circulation
moves towards the area.

Radar imagery shows the shield of steady rain has continued to
expand westward and has now overspread nearly the entire area
except for the Mohawk Valley and Adirondacks. Rainfall rates
have generally be around a quarter of an inch over eastern New
York, with rates up to a half inch per hour over the Berkshires
and NW CT. There are some heavier bursts over south-central
Mass and northern CT and this will be approaching our southeastern
areas over the next few hours.

Based on 3km HRRR and HREF, the heaviest rainfall will be
shifting across the southern half of our area between 6 PM and 2
AM tonight. Rainfall rates will be at least a half inch per hour
within these heaviest bands and some rates may reach close to
one inch per hour, especially across eastern facing slopes of
the high terrain, where upslope flow may locally enhance precip.
This rainfall will result in an increased risk for flash
flooding, as well as sharp rises on all streams, rivers and
creeks. Flooding of poor drainage, urban and low lying areas is
likely to occur. A Flood Watch remains in effect for a large
majority of the area.

The storm is rapidly weakening due to inland decay and is
already undergoing extratropical tranistion. Unlike other
tropical cyclones that have passed over the Northeast in recent
years, this storm doesn`t have strong jet dynamics in place to
transition it into a powerful extratropical storm. As a result,
it will continue to weaken and decay into a remnant low fairly
quickly. The winds have come down significantly. While some
gusts of 20 to 35 mph cannot totally be ruled out within the
heaviest rainfall over western New England over the next few
hours, winds will probably not reach tropical storm force over
our area. As a result, the threat for downed trees/limbs and
power outages has been significantly reduced for our area and
this is why the Tropical Storm Warning has been cancelled.

While the storm center may eventually get close to eastern
Upstate New York for tonight, it will likely slow down/briefly
stall before heading back to the east-northeast for Monday. By
this point, the actual storm center won`t matter much, as the
focus and impact will be due to the heavy rainfall occurring
across the southern half of the area. The remainder of the area
will see bands of showers, some of which may contain some
locally heavy downpours. By late tonight, several inches of
rainfall will have occurred for southern parts of the area, with
as much as five inches across the high terrain by late tonight.

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
The remnant circulation of Henri will be spinning back towards
New England for Monday. Model guidance, especially HiRes NAM
and HRRR, suggests that broken bands of convective showers will
likely be occurring across southern and eastern parts of the
region through the day. The highest coverage will be during the
late morning through afternoon hours, especially for western New
England. With the high PWATs still in place, any shower will be
capable of producing very heavy downpours. This will continue
the threat for flash flooding, especially for areas that already
see heavy rainfall overnight. WPC continues the moderate risk
for excessive rainfall for Monday for much of the area.
Otherwise, it will remain cloudy and muggy through the day with
highs in the 70s.

Some showers could linger into Monday night, but the bulk of the
precip will be ending. Skies will be clearing out, so some
patchy fog will likely form, as it will remain mild and muggy
for the overnight hours.

High pressure and weak ridging will build into the area behind
the departing storm for Tuesday into Tuesday night. It will
continue to be fairly humid, with dewpoints still in upper 60s
to low 70s. With a partly to mostly sunny sky returning, temps
should be fairly warm, with highs well into the 80s for many
areas. Heat index values will be reaching into the low 90s for
valley areas during the afternoon hours. With the high pressure
in place, no precip is expected, so areas should be allowed to
finally dry out and water levels should be receding.

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
A general westerly upper-level flow will ensue for Wednesday and
Thursday with a couple of passing upper-level shortwaves within the
flow. Both Wednesday and Thursday will feature warm and humid
conditions with possible heat advisory criteria being reached (heat
indices 95 degrees or higher) for valley areas. Surface high
pressure over our area Wednesday should result in a mainly dry day
with the first shortwave approaching late in the day and overnight
with a few lingering showers, especially for western areas. Shower
and thunderstorm activity looks to be more widespread on Thursday as
a second shortwave passes overhead and cold front approaches from
the north and west. Highs both Wednesday and Thursday will range
from the upper 70s to lower 90s.

A cold front looks to push across the region on Friday and stall
near the NY/PA border as an area of high pressure builds in from the
north. This will result in a cooler and less humid air mass for
Friday and Saturday. Pending on the position of the front, a few
showers and thunderstorms may be possible on Friday, mainly for
areas south of Albany. As the high pushes off to the east on
Saturday, a few showers and thunderstorms may be possible for areas
south and west of Albany along the lifting frontal boundary (warm
front). Highs Friday will be in the 70s to lower 80s with most areas
in the 70s on Saturday (except some upper 60s in higher terrain
areas).

Sunday will turn a bit warmer and more humid as an upper-level high
strengthens across the mid-Atlantic. The overall warm and humid
airmass could lead to some pop-up showers and thunderstorms, mainly
during the afternoon. Highs Sunday in the lower 70s to lower
80s.

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
The heavier rainfall that had been impacting the region through
the afternoon has lightened up as dry air wraps into TD Henri.
This should result in improved visibilities across most TAF
sites. However, ceilings will remain in the MVFR/IFR range
through the overnight period and into Monday morning.

It is possible heavier rain bands rotate northward back into
KPOU during the overnight period.

On Monday, steady rain will become more showery, however some
embedded heavier downpours, possibly with some thunder, could
occur Monday afternoon. Therefore, have included PROB30 groups
to account for the thunderstorm potential during the afternoon
hours.

Winds will become east to southeast at KALB and KPSF after
midnight tonight, and south to southwest at KPOU later this
evening as the weakening center of Henri approaches eastern New
York, possibly southeast or near KALB. Winds will decrease in
speed as the center ultimately weakens and approaches.

Low level wind shear will be possible through tonight,
especially at KPSF, as winds around 2000 FT AGL increase from
the southeast to 30-40 KT.

Outlook...

Monday Night: Moderate Operational Impact. Chance of RA...TSRA.
Tuesday: Low Operational Impact. Isolated SHRA...TSRA.
Tuesday Night: No Operational Impact. NO SIG WX.
Wednesday: No Operational Impact. NO SIG WX.
Wednesday Night: Low Operational Impact. Slight Chance of SHRA.
Thursday: Moderate Operational Impact. Chance of SHRA...TSRA.
Thursday Night: Low Operational Impact. Slight Chance of SHRA.
Friday: Low Operational Impact. Slight Chance of SHRA.

.FIRE WEATHER...
Bands of showers from Tropical Storm Henri will continue to
impact the region through Monday. With the rainfall and clouds,
RH values will remain elevated about 70 percent for most of the
time. Winds will be light for most places, although some gusts
of 20-30 mph are possible around the area of the storm`s
inner circulation for tonight into early Monday. All areas
should see a wetting rainfall, with some parts of the high
terrain seeing in excess of 5 inches of rainfall.

.HYDROLOGY...
Both flash flooding and river flooding continue to be the
primary hazards from Tropical Storm Henri through the day on
Monday. The storm system will move from southern New England
towards eastern New York for tonight, before heading back
eastward into New England for Monday. Although the storm will be
weakening, it will still be capable of producing very heavy
downpours, with rates in excess of 1 inch per hour, especially
for this evening into the first half of the overnight hours.
This may result in flash flooding, especially within small
stream and urbanized areas. Ponding of water will occur for poor
drainage and low lying areas as well. There will be a threat for
additional localized flash flooding again during the day on
Monday, as convective showers accompany the departing storm.
This will especially be true for far eastern New York into
western New England.

Total rainfall amounts from Henri have stayed fairly the same
from the previous update with 2 to 5 inches still expected for
areas in the flood watch. Higher amounts ranging 6 to 10 inches
in the eastern Catskills and Berkshires are still possible due
to favorable winds direction upsloping the terrain.

These amounts of rainfall will allow for a significant runoff
into the main stem rivers. Minor river flooding is expected to
occur for parts of the Schoharie, Hoosic and Housatonic Rivers.
We cannot rule out some moderate flooding, but the bulk of the
river flooding should be minor.

For details on specific area rivers and lakes, including observed
and forecast river stages and lake elevations, please visit the
Advanced Hydrologic Prediction Service /AHPS/ graphs on our
website.

.ALY WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch through Monday evening for CTZ001-013.
NY...Flood Watch through Monday evening for NYZ040-041-047>054-
058>061-063>066-083-084.
MA...Flood Watch through Monday evening for MAZ001-025.
VT...Flood Watch through Monday evening for VTZ013>015.

$$
SYNOPSIS...Frugis
NEAR TERM...Frugis/JLV
SHORT TERM...Frugis
LONG TERM...Rathbun
AVIATION...JLV
FIRE WEATHER...Frugis
HYDROLOGY...Frugis

Area Forecast Discussion

National Weather Service Denver/Boulder CO

842 PM MDT Sun Aug 22 2021

.UPDATE...
Issued at 821 PM MDT Sun Aug 22 2021

Satellite pictures are showing a tad of mid level cloudiness over
the CWA this evening, There are very boundaries around on the area
radars with a weak surge coming in from the northeast corner of
the CWA with upslope behind it. There was some smoke around over
the CWA this afternoon and evening from the fires out west. The
thickest smoke is north of the CWA and model data keeps it north
overnight and Monday. Made some minor cosmetic changes to the GFE
grids this update,; mainly to the sky cover and winds.

.SHORT TERM...(This evening through Monday)
Issued at 212 PM MDT Sun Aug 22 2021

Visible satellite this afternoon showing an boundary of developing
cu extending from around Limon to Cope. HRRR shows one storm
developing along the boundary this afternoon, then shifting east
by 23z. Will add isolated storms in the grids for the next 2-3 hrs
to account for this. For tonight, a dry southwesterly flow will
remain over the forecast area. A weak cool front will push into
the area from the north this evening. The HRRR smoke model
indicates that some of the smoke that has remained to the north
and west of Colorado this afternoon, will get pushed southward
into the plains as this front moves into the urban corridor and
plains overnight. As a result, areas of smoke have been included
in the grids tonight into Monday morning. On Monday, the flow
aloft will remain southwesterly, with the models indicating some
mid level moisture advecting into the region by the afternoon.
700/500 layer specific humidities in the 4-6 g/kg range at that
time. Forecast soundings in the afternoon show some limited CAPE
but DCAPE values will be around 1500 j/kg so gusty outflow winds
to 50 mph an increase in mid level moisture over the forecast area
southern and eastern CO by the afternoon. Precipitable water
values will be sufficient enough to support brief heavy rainfall
as well. Overall coverage of 10-20 percent for storms Monday
afternoon. Although the fire danger will be elevated in spots
due to the warm temperatures, no parameters are severe enough to
warrant any fire weather highlights through Monday at this time.

.LONG TERM...(Monday night through Sunday)
Issued at 212 PM MDT Sun Aug 22 2021

Persistent southwesterly flow aloft will be in place over
Colorado through the week with troughing to the northwest and
ridging to the southeast. A few shortwaves will pass through this
flow but models disagree on their timing and intensity which is
understandably difficult to specify in this pattern. Moisture
should be fairly limited early in the week anyway, but increase to
more significant quantities for the latter half of the week with
gradual southwesterly advection in the low to mid levels. This
will lead to an increase in coverage and intensity of
precipitation in the latter half of the week, peaking Thursday.

Monday evening, isolated storms and showers which developed over
the high terrain in the afternoon may continue to affect the
plains in the evening. I kept our slight chance PoP values across
the plains in the evening. Forecast soundings show deep mixing
which suggests high-based storms bringing light precipitation and
a primary threat of gusty winds. Best estimates are still for
gusts up to around 50 mph under the stronger storms, based mainly
on mixing heights. Tuesday should be yet warmer and drier as
heights continue to rise. Expect highs in the low to mid 90s on
the plains and 70s and 80s in the mountains, and no precipitation.
The GFS MOS is making a little more sense now with the high
temperature of the week shifted from a 98 on Wednesday to a 97 on
Tuesday. This is still a bit warmer than other guidance but the
pattern now matches much better.

A weak cold front will likely move over the plains Tuesday night
and Wednesday morning. It is unclear how much cooling the front
will bring for Wednesday, demonstrated by a spike in ensemble and
MOS variance. I have kept a consistent forecast for a few degrees
cooling over the plains to highs back in the upper 80s and lower
90s. Precipitation coverage should start to increase Wednesday,
probably already more scattered over the high terrain and still
isolated but across more of the plains. Coverage and intensity
will continue to increase Thursday with greater moisture. Models
currently show the trough advancing over northern Rockies on
Thursday but disagree on the timing and depth. Most of the forcing
should stay north of Colorado, but with enough vorticity at the
base of the trough to provide a slight dynamic boost to convection
as well. There is also uncertainty about how westerly the flow
will turn as the trough passes, and the more westerly it turns
will mean greater smoke advection from the west coast again.
Friday looks to be slightly warmer and drier than Thursday.
Overall, I moderated the increase in PoP and QPF in the grids for
the latter half of the week, allowing for a slight increase at
this time. There should also be enough instability and shear for
some isolated severe storms Wednesday and Thursday.

There is actually pretty good model consensus right now about the
synoptic situation next weekend, and it looks like yet more
southwesterly flow aloft with a few more shortwaves, likely still
too far northwest to have much impact for northeast Colorado.

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 821 PM MDT Sun Aug 22 2021

Weak drainage winds are expected at DIA late this evening and
overnight. There will be no ceiling issues.

.HYDROLOGY...
Issued at 212 PM MDT Sun Aug 22 2021

No thunderstorms this afternoon and evening. On Monday one or two
high based thunderstorms will be possible in the afternoon and
evening. The main threat will be gusty outflow winds. There may
still be enough moisture in the mid levels however to produce a
short burst of heavy rain, up to a quarter inch in less than 30
minutes. At this time will go with low/limited flash flood
potential for Monday.

Monday evening, there will be a very low flash flood threat from
weak and fast moving showers and storms. There is no flash flood
threat on Tuesday. Greater moisture and better forcing Wednesday
and Thursday will mean an increasing burn area flash flood threat,
though still limited. Precipitation should decrease in coverage
and intensity again for the weekend.

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

UPDATE.......RJK
SHORT TERM...Cooper
LONG TERM....EJD
AVIATION.....RJK
HYDROLOGY....Cooper/EJD

Area Forecast Discussion

National Weather Service State College PA

1132 PM EDT Sun Aug 22 2021

.SYNOPSIS...
The remnants of Tropical Storm Henri will linger over eastern
New York state or southwest New England into Monday, then move
east of New England Monday night. A building subtropical ridge,
centered just off of the east coast, will then dominate the
weather over central Pa the rest of next week.

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Latest guidance indicates the remnants of Henri will stall out
over the mid and upper Hudson Valley tonight. Radar trends and
latest hi-res models indicates the western edge of Henri`s rain
shield will continue to affect the eastern part of our forecast
area through 06-09Z. By late tonight, expect drying to work into
the eastern counties, as mid level trough axis pivots through.

Will maintain the current Flood Watch across the eastern edge of
the forecast area, where upper level divergence, combined with
a plume of anomalous pwats, should support periods of moderate
rain. The latest HRRR suggests the heaviest rain will remain
just to our east, where an upsloping westerly flow enhances rain
rates over the Poconos. However, wouldn`t rule out flooding
over the higher terrain of eastern Schuylkill Co or over spots
of Lebanon/Lancaster that have received heavy rain during the
last 24 hours.

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Scattered, diurnally-driven convection is expected Monday,
especially over the northeast part of the forecast area, closest
to departing upper level trough. Weak shear is anticipated with
little risk of severe weather. The latest HREF supports the
potential of spot afternoon rainfall amounts across the eastern
part of the forecast area of 1-2 inches. So, can`t completely
rule out some minor flooding issues in that area if tstorms
affect locations where the ground is already quite wet, such as
Sullivan County.

Model soundings support at least partly sunny skies Monday and
mixing through 850mb, which should support max temps ranging
from around 80F over the mountains, north of KIPT, to near 90F
in the valleys of the south central mountains.

Surface ridging will build into the region Monday night and
Tuesday, accompanied by fair and warm weather. Wet ground,
light wind and mostly clear skies will likely promote patchy
late night valley fog, especially over the western counties.
Model 850mb temps near 18C support hot conditions Tuesday.
However, humidity is likely to be a bit lower than recent days,
as drier air aloft mixes to the surface.

A building subtropical ridge off of the east coast will result
in increasingly hot and humid conditions by Wednesday, with the
chance of a late day thunderstorm. Temperatures will reach the
mid 80s to lower 90s under mostly sunny skies.

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Latest 2m/850mb plumes indicate heat and humidity will peak
Thursday ahead of a cold front approaching from the Grt Lks with
possible heat advisory concerns across the Susq Valley. A round
of tstorms could accompany the arrival of the front Thursday PM,
especially over northern Pa, closest to track of parent
shortwave.

The bulk of medium range supports warm, humid and unsettled
conditions Friday into next weekend, as stalled front slowly
returns northward through the area, providing the focus for
scattered, mainly PM convection. Cloud cover and PM convection
could hold daytime highs Fri-Sun to only a bit above normal.
However, all guidance points toward well above normal low temps
with plume of high pwats over the area.

.AVIATION /04Z MONDAY THROUGH FRIDAY/...
MVFR cigs and persistent showers are most likely across
Lancaster overnight. Elsewhere, VFR conditions in the evening
will transition to areas of fog and low clouds. LIFR is most
likely in BFD, and JST will likely go to IFR. IFR is less likely
elsewhere but cannot be ruled out.

Mainly VFR conditions on Mon. A few showers and thunderstorms
are possible, mainly in the east.

Outlook...

Mon-Thu...Restrictions possible in scattered afternoon showers
and isolated t-storms.

.CTP WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 8 AM EDT Monday for PAZ058-059-066.

$$
SYNOPSIS...Fitzgerald
NEAR TERM...Fitzgerald
SHORT TERM...Watson/Fitzgerald
LONG TERM...Fitzgerald
AVIATION...Ross/Colbert

Area Forecast Discussion

National Weather Service Des Moines IA

630 PM CDT Sun Aug 22 2021

.DISCUSSION.../Tonight through Sunday/
Issued at 228 PM CDT Sun Aug 22 2021

Key Points:
-Periodic storm chances overnight and through the upcoming week
-Heat builds with the hottest days of the week on Monday and Tuesday

Details:
The leading edge of a shortwave trough moving across the northern
and central plains has aided convective initiation across portions
of eastern South Dakota this afternoon. By 2 pm a small cluster of
storms had developed in far northwest Iowa at the South Dakota
border. CAMs have struggled with this system, as has been noted in
previous discussions. In fact, the ongoing convection is not
present in current runs with convection reaching Iowa after 06z in
most model solutions. Thus, confidence in convective trends this
evening and overnight is low. That said, the initial forcing with
the approaching shortwave may bring a few thunderstorms across
northern Iowa this afternoon, with additional activity through the
overnight as the low-level jet aid initiation. In favor of storm
development overnight is MLCAPE around 1500 J/kg and deep layer
shear around 30 knots. On the other hand, a strong cap will remain
in place and could limit development all together. The HRRR seems
to favor this solution with no convective development in Iowa
tonight while the NAMnest/RAP/NSSL-WRF favor a cluster of storms
moving across the state in the after midnight hours. Should
storms develop, elevated storms with hail would be the primary
threat.

Thermal ridging builds across Iowa Monday with the warm front
getting hung up across northern Iowa and southern Minnesota - a
scenario that remains in place through the upcoming week. This
results in warm air advection and moisture transport into the area
making for a hot and humid week. Monday and Tuesday will be the
warmest days with highs in the low to mid 90s and dewpoints
around 70 degrees. This will send heat indices into the upper 90s
north of I-80 to low 100s south of I-80. While just below heat
advisory criteria, those with outdoor plans should take
appropriate precautions to remain safe in the heat. The interplay
of convection and warm front placement will determine just how
hot and humid the area gets.

So what does the convective scenario look like? Convection on Monday
will depend on where the warm front stalls out overnight tonight
and will serve as the impetus for development. MLCAPE reaches
2000+ J/kg Monday with the advancement of a more unstable airmass.
Shear is weak however, around 20 kts, which will limit storm
organization and thus severe threat. SPC has added a marginal risk
to Monday which seems warranted based on the environment.

A shortwave will ride the ridge Tuesday, bringing better chances for
rain and a low end severe weather threat. With an unstable air mass
and a number of embedded disturbances in the flow, there are a
number of chances for convection throughout the week. While storms
are possible nearly everyday, it will not be a total washout and
most people will not see rain everyday.

.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 630 PM CDT Sun Aug 22 2021

Storm chances increase overnight, but coverage remains uncertain
across the region. Have added some VCTS to KFOD, KALO and KMCW
mainly aft 06z for 3 to 4 hour period. Overall VFR conditions
expected, though mid to high level clouds may be more prevalent
going forward to end of period. Light SSW winds expected through
period with minor wind gusts above ambient. Will evaluate trends
and update as needed for 06z package. /rev

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

DISCUSSION...Hagenhoff
AVIATION...REV

AREA FORECAST DISCUSSION

National Weather Service Eureka CA

257 PM PDT Sun Aug 22 2021

.SYNOPSIS...Seasonable temperatures and light winds have settled in
today and will continue through early this week. The coast is
expected to see nightly marine stratus with afternoon clearing.
Smoke is expected to remain near fires, flowing with daily diurnal
winds. Later this week, a warming and drying trend is expected with
marine stratus persisting.

.DISCUSSION...This morning, stratus blanketed the coast with
smoke aloft in the north. The marine layer was just a bit shallower
today, pulling its inland extent back from Saturday. Stratus has
mostly eroded this afternoon and smoke has pushed back east as
afternoon winds kick in. Temperatures have been mostly seasonable
where smoke allows, reaching into the low 80s early this afternoon
for the interior. Winds are mild with normal diurnal winds inland
and some gustier northerlies near shore. The evening should remain
calm and pleasant with areas west fires clearing of smoke before
haze moves back towards shore overnight.

Early this week, zonal flow aloft will continue allowing local,
diurnal effects to dominate. Along the coast this pattern entails
daily marine stratus with a weak inversion allowing for afternoon
clearing. Smoke will most likely ebb and flow with daily valley
winds moving west towards the coast overnight and east towards the
Sacramento Valley during the afternoon and evening. Weak winds
should keep the smoke near fires allowing the southern half of the
area to stay clearer. Temperatures will remain near seasonable
levels with highs in the high 80`s to low 90`s. Lows in valleys
could dip into the mid 40`s overnight.

Conditions should stay pretty consistent through Thursday. A weak
trough passage Wednesday morning may slighlty decrease temperatures
and allow for more marine influence, but its impact seems marginal
at this time. On Thursday, all clusters show an upper
level ridge building in the eastern Pacific. While specific
locations and intensity are still unclear, the ridge looks like it
will build through next weekend before breaking down. All clusters
currently keep the ridge mostly offshore, muting its impact. One
cluster keeps the ridge totally offshore, but most at least put NW
California under its influence. After Thursday, gradual warming and
drying is expected under the ridge. Peak temperatures are likely to
occur over the weekend with current guidance indicating highs
around 100 where smoke allows. Interestingly due to the ridge`s
position, most models currently have the coastal interior warming
more than the Sacramento valley. Early next week, the clusters
diverge with some showing more zonal flow and others showing a
troughing pattern.
/JHW

.AVIATION...As expected, the marine layer became shallower last
night, reaching around 2000 feet or just above. Stratus and fog
still extended inland up the adjacent river valleys, but these
clouds have pulled back to right along the coast this afternoon.
Stratus continues right along the coast from KCEC to KACV as S flow
piles up leftover moisture along the coastal terrain. This patch
continues to slowly shrink, but it is expected to expand once again
this evening and overnight. Stratus is more expansive S of Cape
Mendocino, and these clouds are hugging the coast as well. Smoke
blankets a large portion of Trinity and Humboldt counties. Smoke is
mostly aloft over the coastal areas, even this smoke is showing
signs of pushing E-SE per visible satellite imagery (as forecast by
the HRRR model).

The HRRR model predicts that smoke- both at the surface and aloft-
will continue to shift slowly E-SE away from the coast through the
evening hours. The model then shifts some smoke back toward the
coast from extreme N Humboldt County into Del Norte County. It
doesn`t appear that this smoke will affect either KCEC or KACV
through the end of the TAF period. Low clouds and fog are expected
to return later tonight along the N coast. Visibilities are
uncertain, but they may need to be adjusted downward in the next TAF
package. The marine layer doesn`t appear to be deep enough to
support stratus making it to KUKI from the W, but high resolution
model guidance does suggest that it may advect up the Russian River
valley by daybreak. Winds area-wide will be generally light, with
some gusts to 20 knots at KCEC late this afternoon and early this
evening. /SEC

.MARINE...Northerly winds will continue through the period, with
2 lobes of stronger winds through much of the period (downwind from
Pt St George and SW OR and downwind from Cape Mendocino). As a
result, advisory level wind speeds and short period seas will cover
more than 50% of each of the outer zones through the next 5 days,
and the Small Craft Advisory has been extended through midday
Wednesday. Have also hoisted a Small Craft Advisory for the N near
shore waters for late this evening through Tuesday afternoon. This
will be mainly for marginal sea heights, although winds will be
quite gusty near Pt St George.

Some periods of near gale force gusts are possible over the N outer
waters in the short term, and seas will approach hazardous seas
criteria as well, but the areal or temporal coverage doesn`t appear
to warrant a watch or warning at this time. There will be periods
when eddies in the surface winds produce more southerly winds near
the coast. /SEC

.FIRE WEATHER...Most areas today experienced modest drying and
warming, though smoke has limited heating near fires. Wind today is
relatively calm and terrain driven with few gusts on ridges over 10
mph. Conditions should stay relatively consistent through Tuesday
with seasonable temperatures, moderate recoveries, and afternoon RH
in the upper 10`s to low 20`s. Wednesday a weak trough may allow for
some cooling and extra marine influence, but little change in the
winds is expected.

Beyond Thursday, there is good agreement of gradual warming and
drying. This trend should peak next weekend. There is uncertainty in
the strength of warming by Saturday, but current models suggest
highs around 100 in the valleys and minimum humidities around 10
with moderate to poor recoveries. Winds are currently expected to be
mild. Depending on the position of the ridge, some models indicate
weak off shore synoptic flow. The specifics are still highly
uncertain, so future forecast refinement is expected.
/JHW

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory from 9 PM this evening to 3 PM PDT Tuesday
for PZZ450.

Small Craft Advisory until noon PDT Wednesday for PZZ470-475.

Visit us at https://www.weather.gov/eureka

For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png

Area Forecast Discussion

National Weather Service Grand Forks ND

915 PM CDT Sun Aug 22 2021

.UPDATE...
Issued at 910 PM CDT Sun Aug 22 2021

Severe thunderstorm watch has been allowed to expire with the
convection out running the instability axis and weakening. Will
continue to see the decreasing intensity and coverage of the
showers and storms as they move into NW MN. Precip will end or
lift out of the area in the 12 to 1am time frame.

UPDATE Issued at 638 PM CDT Sun Aug 22 2021

Line of strong and severe storms continues to spread to the
northeast across central ND this evening. Intensity is expected to
peak in the next hour or so then weaken as storms out run the
instability. Will continue to see the main threats of hail up to
2 inches and wind gusts to 60mph though given the low level shear
there remains a low tornado threat also as the storms move into
the central RRV.

.SHORT TERM...(This evening through Monday night)
Issued at 340 PM CDT Sun Aug 22 2021

Convective chances and strength remain the main challenges for the
period.

Strong upper low lifting from MT into southern Canada currently
seen on sat and radar rotating over western ND. The first round of
warm air advection showers and thunderstorms is continuing to move
through the Red River Valley this afternoon, but is not as
widespread for rain as Friday`s system. Further west, there has
been a bit of sunshine, and some storms are starting to develop in
central ND near the trough axis/frontal boundary. ML CAPE values
are not huge, in the 500-1000 J/kg range, but there is a good
amount of deep layer bulk shear. Much of the CAPE that is out
there is in the lowest levels of the atmosphere, along the strong
surface vorticity associated with the boundary. Will have to watch
cells that develop for some brief spin-ups as well as the chance
for some hail. Think there is a chance for the storms to maintain
themselves into our western counties, but the question is how far
east they will go. The HRRR has strong updraft helicity values
continuing into the evening as storms move east into the Red River
Valley. However, instability is pretty minimal over the Valley and
think this may be overdone. Kept POPs pretty high as there should
be at least some rain as showers and thunderstorms push east this
evening, but am not hugely excited about severe except in our far
west.

Winds will continue to be pretty high through the rest of the
afternoon and into the early evening, but will diminish and shift
to the west and then northwest as the surface low ejects into
Canada. Lingering clouds and precip should help keep lows tonight
in the 50s, but the far western tier should see a bit more
clearing and temps down into the 40s. Southwesterly flow aloft
sets up for Monday into Monday night ahead of the next approaching
system. Another surface boundary over ND will be the focus for
some convective development in central ND tomorrow afternoon and
evening. Some of those cells could move into our CWA after
midnight, so continued to keep pretty high POPs going. Elevated
CAPE values and deep layer bulk shear are pretty impressive during
the 06-12Z Tuesday time frame and a late night severe storm is not
out of the question.

.LONG TERM...(Tuesday through Sunday)
Issued at 340 PM CDT Sun Aug 22 2021

The low amplitude shortwave trough responsible for Monday
overnight`s convection will continue its trek eastward on Tuesday
into southern MB/ON. A surface low and attendant fronts are expected
to move through the Dakotas into Minnesota during the day Tuesday.
Ahead of the surface features will be a sufficiently moist and at
least weakly unstable warm sector. This will continue the chance for
showers and thunderstorms ahead of a cold front. While there is
still some uncertainty in exact timing of cold fropa, the currently
favored scenario depicts the front moving into Minnesota by
afternoon. This is where higher chances for afternoon thunderstorm
chances resides. Additionally, increased westerly flow aloft is
anticipated under the base of the shortwave. This will aid in
providing shear aloft introducing the potential of additional
organized convection by Tuesday afternoon, or perhaps transition
from elevated to surface based convection from ongoing morning
storms birthed the night before. In addition to the potential for
hail, daytime heating will dictate whether high wind gusts and
tornado potential evolves by Tuesday afternoon. There has been an
increasing trend in NBM CWASP values and its probabilities within
Minnesota, also backing up the thought that Minnesota holds more of
the chance for organized convection Tuesday afternoon.

Behind Tuesday`s shortwave and cold fropa, cooler and drier
conditions will dominate Wednesday and perhaps into Thursday.
Getting into Thursday and beyond, upper troughing in the PacNW will
promote southwesterly flow aloft over the Northern Plains. Ensemble
guidance is in fairly good agreement in at least one (perhaps
multiple) episode(s) of rain as one or more shortwaves eject out of
the PacNW trough over the region. During this Thursday - Saturday
period, high probabilities greater than 70% of QPF greater than 0.1
inches exists over the entire region each day. Notably on Friday-
Saturday period, there are already chance probabilities of a least
30% for 24 hour QPF amounts of at least 1 inch edging into west-
central Minnesota into the Red River Valley. This is notable in the
fact that most guidance during this range doesn`t handle high end
amounts well. Essentially this just backs the thinking that a
soaking rain event is likely in store for the Dakotas into Minnesota
Friday into Saturday. It is still too early to comment on severe
chances assoc with this late week event.

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 638 PM CDT Sun Aug 22 2021

Line of storms has cleared DVL and will move into the GFK and
possibly the FAR area between 7 and 9pm. Winds will remain
southerly and gusty though decreasing for the overnight with a
westerly wind shift and less wind tomorrow.

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$

UPDATE...JK
SHORT TERM...JR
LONG TERM...CJ
AVIATION...JK

AREA FORECAST DISCUSSION

National Weather Service Hastings NE

550 PM CDT Sun Aug 22 2021

...AVIATION UPDATE...

.DISCUSSION...(This evening through Sunday)
Issued at 305 PM CDT Sun Aug 22 2021

As of 2:45 pm satellite shows the remnants of a pesky, narrow, lower
level stratus deck breaking up over the northern portions of the
CWA. Under this cloud deck temperatures are struggling to reach 80
degrees. Clear areas are currently into the mid 80s across south
central NE, and mid 90s in KS. Breezy southerly flow at the sfc
today thanks to a tightening sfc pressure gradient from being wedged
between an approaching sfc low to the northwest and the departed
sfc high to the northeast. The main focus of the forecast is the
severe weather potential this evening and tonight, as well as the
heat the next two days. Then in the extended there are plenty of
off and on chances for more showers and thunderstorms and warmer
than average temps continue.

PoPs and the severe weather threat tonight:

Ahead of an upper level trof a sfc low is set to move across the
Northern Plains later this afternoon. This will push a weak cold
front through the area that will then stall around the state line
later tonight.

This looks to be one of those situations where development of
convection will be rather isolated in nature, but what does develop
has the chance of quickly going severe. The atmosphere is rather
primed for severe weather (though there is a slight cap in place,
but the frontal boundary should help with that). Most of our CAPE is
coming from daytime heating today, with most models showing around
2,000-3,000 J/kg of MLCAPE and 0-6 km bulk shear of 40-50 kts. Low
and midlevel lapse rates look fairly steep, and there is decent low
level curvature to the hodograph. This is certainly supportive of
supercell development with large hail, damaging winds, and
potentially an isolated tornado. Models generally agree that the
main timing is between 7pm and 1am, though we could still see a few
isolated storms outside this time period. With regards to location,
there is disagreement amongst models. The HRRR and the NAMNEST both
keep things a little farther south, around the state line, sweeping
across from west to east. The RAP shows development over the western
CWA that sort of stalls out and dies then redevelops with the LLJ
later tonight over the far eastern CWA. The EC and the GFS keep
storms focused around the I-80 corridor sweeping from west to east.
Even this close in time there is still too much uncertainty as to
how exactly this will play out later.

The remainder of the forecast is characterized by southwest flow
aloft, broad upper level high pressure to our south, and periodic
small waves pushing through that bring off and on chances for
showers and thunderstorms. Tomorrow and Tuesday look to be
uncomfortably hot, with highs well into the 90s and heat indices
from 100-105 degrees. Then tomorrow afternoon a weak midlevel wave
moves through and could help to spur some late afternoon to early
evening showers and storms, a few of which could be strong to
severe. Tuesday afternoon another quick shortwave moves through
along with a sfc cold front which could bring some showers and
storms to the eastern most portions of the CWA Tuesday evening.
Beyond Tuesday temperatures come down only slightly, still
remaining in the upper 80s and low to mid 90s. Several more
perturbations in the flow make their way across the area and bring
more off and on chances for rain to the forecast throughout the
week. On Thursday a broad upper level trof moves over the NW CONUS
and then gradually lifts over Canada on Friday, but a second and
more energized trof forms right on its heels and could be
something to watch in future forecasts.

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday)
Issued at 547 PM CDT Sun Aug 22 2021

Main concern is strong to severe storms forming across the outlook
area this evening and overnight. A few of these storms could
affect the terminals. Otherwise, VFR conditions are expected
through the end of the TAF period. Winds will become lighter over
the next several hours and will generally remain out of the south
and southeast.

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&

DISCUSSION...Shawkey
AVIATION...Shawkey

Area Forecast Discussion

National Weather Service Greenville-Spartanburg SC

741 PM EDT Sun Aug 22 2021

.SYNOPSIS...
An upper level trough will help kick off another round of mainly
afternoon and evening showers and thunderstorms today. Drier and
hotter conditions are expected Monday and Tuesday as the upper ridge
replaces the trough. The upper ridge over the western Atlantic will
control the overall weather pattern by the middle part of the week,
but daily showers and thunderstorms should prevail Wednesday through
the end of the week.

.NEAR TERM /THROUGH MONDAY/...
As of 730 PM EDT Sunday: A deep upper low hangs over the
Mid-Atlantic. The day`s weather has been driven by a series of weak
vort lobes traversing this low, and providing what meager synoptic
forcing we`ve been able to muster. Convection is ongoing, though
sparse and so far fairly weak. Later this evening, the influx
of some weak DPVA from another vort lobe may foster development
of some ridgetop showers over the Appalachians, with any activity
that does form progged to fizzle out by 03Z.

As ridging continues to build to our west and persistent northerly
flow continues strong dry air advection, the overnight hours will
see the dewpoint depression explode in the mid- and upper-levels.
Assuming the boundary layer is as moist as the CAMs are predicting,
this should allow for widespread fog and low stratus to form.
For now, have kept patchy fog across the Appalachians and foothills,
and somewhat less prominent fog in some areas of the Piedmont.

Tomorrow, with the upper low beginning to interact with Hurricane
Henri and meandering even farther east, QG forcing will all but
vanish as ridging pushes in. Model profiles depict continued dry
air through much of the troposphere and a strengthening subsidence
inversion, which should severely hinder convective chances
for tomorrow. The HRRR and NAMnest still depict very isolated,
shallow convection breaking out across the foothills and Piedmont,
but for the most part tomorrow afternoon should be warm and clear.

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 200 PM EDT Sunday: At the start of the short term forecast
period, Tropical System Henri will be tracking across the Northeast
United States. Meanwhile a ridge of high pressure to our west over
the Southern Plains and Deep South, will gradually build eastward
into northern Georgia and the western Carolinas. The Bermuda high to
our east in the western Atlantic will build west towards the
Southeastern United States. So throughout the short term period, the
western Carolinas and northeast Georgia will be situated between two
high pressure systems. While high pressure dominates over land, a
tropical wave will track through the Bahamas Tuesday into Wednesday,
nearing Florida late Wednesday. Since the Bermuda high is expected
to progress westward towards the East Coast, isolated shower and
thunderstorm chances will be a touch higher on Tuesday compared to
Monday. However, northerly and northwesterly flow continues on
Tuesday and allows dry air to remain in the low and mid-levels of
the atmosphere. So, there will only a slight chance for isolated
diurnal showers and thunderstorms. Wednesday the ridge to our west
retreats away from the forecast area and the Bermuda high takes over
leading to increased return flow off the western Atlantic Wednesday.
This will lead to flow becoming easterly and southeasterly,
increasing the low and mid-level moisture. As a result, PWATs will
increase ranging from 1.7 to 2.0 inches outside the mtns. With
increased moisture comes higher chances for showers and
thunderstorms, so have PoPs across the CWA ranging from high end
chance to low end likely for Wednesday. Tuesday has the potential to
be the warmest day with high temps 5 to 10 degrees above climo.
Wednesday will be slightly cooler but will remain several degrees
above climo.

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 230 PM EDT Sunday: The Bermuda high in the western Atlantic
will continue to be the main influence of the overall weather
pattern throughout the extended forecast period. This ridge will
lead to southerly and southeasterly flow which will act to stream
Atlantic tropical moisture into the region. PWAT values should
remain around 1.7 to 2.0 inches outside the mtns with values around
1.5 inches across the mtns. There remains a lot of uncertainty
regarding the tropical wave mentioned above in the short term
discussion. Forecast confidence will remain low through much of the
extended period regarding this tropical wave as models are not in
good agreement (more on this tropical wave below). Regardless,
shower and thunderstorm chances should remain elevated due to the
Bermuda high dominating the synoptic pattern. Capped PoPs to high
end chance to low end likely middle to end of next week. High temps
are expected to be cooler due to increased cloud cover and PoPs
throughout the extended period. However, highs will still run a few
degrees above climo.

The GFS has been fairly consistent the last few runs taking the
tropical wave across Florida late Wednesday night into Thursday
before tracking along or near the Gulf Coast late Thursday into the
weekend. The ridge in the western Atlantic could steer tropical
moisture associated with the tropical wave into the CWA Thursday
into Friday. Saturday into Sunday the GFS has the Bermuda high
building over much of the eastern CONUS, and shows another tropical
wave rounding the southwestern periphery of the ridge taking it into
the Carolinas. Meanwhile, the ECMWF has been flip flopping between
taking the tropical wave into the Carolinas and taking the tropical
wave into Florida late Wednesday night into Thursday. Currently the
12z run of the ECMWF has the tropical wave tracking across Florida
and then into the Deep South Friday. The ECMWF also shows the
Bermuda high building across the eastern CONUS this weekend and has
the tropical moisture associated with the tropical wave tracking
west of the CWA.

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: All TAF sites are VFR for now, and convection
is largely absent apart from a few stray showers across the NC/SC
state line. Notwithstanding the possibility of a couple more
showers in the mountains this evening, activity should die down
from here on out, and VFR conditions should prevail through the
first part of the night. Dry air aloft will allow the potential
for some morning fog/low stratus to creep in - but for now, have
only reduced restrictions to MVFR at KCLT and KHKY, and briefly
dipping to IFR at KAVL. Winds should remain light and variable,
becoming more northerly by the end of the TAF period. Tomorrow`s
convective chances should be suppressed much like today`s, if
not more so, and so have only included reference to VCSH at KCLT,
with no mention elsewhere.

Outlook: Slightly drier high pressure will continue over
the region early in the week the week, but expect isolated to
scattered diurnal showers and thunderstorms to increase by midweek.
Overnight restrictions can be expected in the mountain river valleys
and in any areas that receive heavy rainfall the previous day.

Confidence Table...

23-05Z 05-11Z 11-17Z 17-18Z
KCLT High 100% High 100% Med 72% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL High 100% High 100% Low 56% High 100%
KHKY High 100% High 100% High 100% High 100%
KGMU High 100% High 100% High 100% High 100%
KAND High 100% High 100% High 100% High 100%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables are available at
the following link:

www.weather.gov/gsp/aviation

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

$$
SYNOPSIS...AP
NEAR TERM...MPR
SHORT TERM...AP
LONG TERM...AP
AVIATION...MPR

Area Forecast Discussion

National Weather Service Gray ME

1004 PM EDT Sun Aug 22 2021

.SYNOPSIS...
A very tropical air mass remains in place, which is to be
expected as a tropical storm passes to our south. Showers will
cross the area in waves overnight as Henri drifts inland. The
storm will move back towards the coast tomorrow with showers and
thunderstorms popping up north of its track. Some of these may
produce torrential rain in the late afternoon and early evening.
After the remnants of Henri move out to sea our chances of rain
will drop off sharply but the summer-like weather will remain.

.NEAR TERM /TONIGHT/...
1000 PM Update... Ran through temperatures and dew points again,
this time through the overnight and for tomorrow according to
00Z model data starting to come in. Also went a bit more bullish
with fog overnight, not necessarily in severity but in
coverage... steady gradient flow should keep dense fog from
being an issue, however the soupy atmosphere and low clouds will
lead to at least patchy fog for most areas.

700 PM Update...
Incorporated HRRR guidance into the overnight temperature and
dew point forecast and tweaked PoPs according to the same. At
this hour, the primary stratiform rain shield associated with
Henri is positioned over the Hudson and upper Susquehanna Valley
after clipping the Monadnock region this afternoon. Rain
showers associated with a decaying feeder band are still pushing
into the Whites and western Maine mountains through the next
several hours but so far rainfall rates haven`t been spectacular
with surface stations thus far reporting around a quarter of an
inch thus far. Do suspect there are greater accums in the
mountains where observations are scarce however.

Previously...
Henri has moved inland and is beginning the weakening process.
Bands of showers will remain possible overnight...though I do
not anticipate any heavy rain at this time. The deep onshore
flow will support more fog and low clouds developing near sunset
however. Dense fog failed to really get going last night...but
hi-res guidance is in favor of it tonight. Given that was also
the case last night I have no issued a dense fog advisory at
this time. I could see some drizzle but given the already
complicated weather grids I figure a chance of showers will
cover it. Winds are not expected to be an issue overnight.

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
Primary concern for Mon will be where convection sets up in the
afternoon. The remnants of Henri are forecast to be somewhere
near Wrn MA with deep Sly flow over NH. Breaks in cloud cover
will support at least marginal CAPE...but of the tall...skinny
variety. This flow will also support very slow effective storm
motions as they back build. Given PWAT approaching 2 inches some
very heavy rainfall is possible in any convection. The greatest
chance for training cells will be over the flood watch area and
so I do not plan on expanding it at this time. Rainfall here
may be torrential...2 to 3 inches with locally higher amounts
entirely possible.

This will be in addition to rainfall closer to the low level
circulation of Henri. This is forecast to drift across Srn NH
and then along the Wrn ME coastline thru Mon night. Rainfall
rates look more reasonable with generally moderate
rainfall...but up to an inch with locally higher amounts.

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Due to active weather in the short term the extended forecast
beyond Tue is mainly the multi-model consensus.

Tue will see the remnants of Henri heading out to sea..and
scattered showers and thunderstorms possible in its wake before
the deep moist air mass is cleared out. Warm and humid
conditions will continue through the end of the week.

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Short Term...Deep...onshore flow will support plenty of low CIGs
again tonight and some areas of FG. SHRA coverage is expected to
be mainly scattered tonight. Convection is anticipated Mon
afternoon...mainly over NH...and IFR or lower conditions will be
possible in these storms. Henri will drift near Srn NH late Mon
into early Tue...with more RA and IFR or lower conditions before
heading out to sea.

Long Term...The tropical airmass over the area will support a
combination of low clouds and patchy fog Tuesday night and
Wednesday night. During the day, diurnally driven scattered
showers and possibly a thunderstorm may lead to localized IFR
conditions.

.MARINE...
Short Term...SCA conditions will continue tonight in NEly flow
to the N of Tropical Storm Henri. They are expected to gradually
diminish before possibly strengthening again early Tue as the
low level circulation emerges back off the coast. Seas will
continue to build a little this evening...with generally around
6 ft nearshore and 10 to 12 ft in the deeper waters. Areas of
dense fog are expected to form again tonight in the
moist...onshore flow.

Long Term...Winds and seas will remain below SCA thresholds
Tuesday night through Thursday. There may be periods of fog
reducing visibilities over the coastal waters with warm and
humid air in place. On Friday, a strong cold front will cross
the region from Canada. Winds may briefly be gusty with cold air
advection over the relatively warm waters.

.HYDROLOGY...
As TC Henri lifts north the moisture surge will spread into the
region with PWATs rising to 2.25" along southern ME/NH by this
time tomorrow. As TC Henri lingers to the southwest on Sunday
and Monday, scattered showers and thunderstorms are expected to
develop over the area with pockets of torrential rainfall. Given
how weak the forcing is showers and thunderstorms will be
closely tied to the diurnal cycle, with peak coverage this
afternoon/evening. At this time concern is not high for
widespread heavy rainfall, but these locally high amounts could
add up if repeated areas are impacted. The increased support in
the upslope regions of the Monadnocks and White Mountains are of
particular concern for repeat development. The final track of
TC Henri could also bring a swath of moderate to heavy rainfall,
with the latest forecast bringing it eventually over S NH and
ME. RFC/WPC QPF forecasts attempt to highlight the rainfall
enhanced by upslope, and do well for an overall rainfall
assessment. However we recognize there could easily be pockets
of locally higher amounts that could lead to flash flooding.
Soil moisture percentiles remain high in S NH due in part to
Fred`s passage a few days back. For now river flooding appears
to be a low threat as most rivers remain at or below normal
streamflows. Some lakes/reservoirs in S NH where heavy rains
have fallen over the last 6 weeks remain high, but there should
be enough storage to handle this storm. All of these factors
combine to support the Excessive Rainfall highlighting a slight
risk mainly over NH up to the White Mountains region.

.TIDES/COASTAL FLOODING...
Prolonged onshore flow is expected to continue through tomorrow
out of the E/NE before switching to the SE later in the day.
Looking at the ESTOFS/ETSS/PETSS guidance all models keep storm
surge values around .8 to 1.2 feet for tonight`s high tide.
Model bias has been about .3 to .4 feet too low on the past
tide cycle. Tweaked the model guidance to include the current
model bias forecast in the TWL grids. This will bring water
levels close to minor flood stage tonight, but should peak just
below, Hampton gage could touch 11 ft though. In addition, surf
conditions will increase slightly or maintain with 5 to 7 feet
near shore wave heights with is a combination of two wave
groups. There is the shorter period local NE wave group and the
longer period swell coming around the Cape from Henri to the
south. Overall high surf conditions could linger into tomorrow,
but splash-over and minor beach erosion should be concentrated
to tonight`s HAT cycle. The tide cycle will begin to trend down
tomorrow, so should help limit minor coastal flood issues.

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...High Surf Advisory until 8 AM EDT Monday for MEZ023>028.
NH...Flood Watch through late Monday night for NHZ007-008-011-015.
High Surf Advisory until 8 AM EDT Monday for NHZ014.
MARINE...Small Craft Advisory until noon EDT Monday for ANZ150-152-154.

UPDATE...Casey
NEAR/SHORT TERM...Legro
LONG TERM...Casey/Legro
AVIATION...Legro
MARINE...Legro
HYDROLOGY...Jamison
TIDES/COASTAL FLOODING...Dumont

Area Forecast Discussion

National Weather Service Wilmington NC

1021 PM EDT Sun Aug 22 2021

.SYNOPSIS...
A weak inland trough will persist into the first part of
next week with some unsettled weather possible especially late
tonight into Mon along the Carolina Coasts. Atlantic high
pressure, surface and aloft, will begin to build westward by
the mid to late week period. A more typical summertime pattern
will ensue with a lower chance of tstorms by the late week
period.

.UPDATE...
Not much changes from the 7 pm update where POPs were lowered
considerably. The latest HRRR model continues this trend from
earlier with the main threat along the immediate ILM CWA Coast
and the adjacent Atlantic waters during the pre-dawn Mon hrs and
extending into Mon daytime morning prior to the Upper trof axis
moving off the Carolina Coasts. Still some weak pieces of
energy dropping down on the back-side of the upper trof that
could instigate a tstorm/shower overnight across inland
locations but with an atm overall stabilizing, will keep this
POP threat low chance at best inland. Min temp fcst just needed
a few tweaks but overall integrity aok. Included patchy fog
across much of the CWA with plenty of stratus possible. Will
need to monitor for dense fog especially if majority of the
debris convective clouds scour out completely prior to low
stratus becoming the dominant cloud cover.

The tightest sfc pg to remain just offshore of the Carolina
Coasts as depicted by the latest models. Enough of a sfc pg to
support 15 kt wind speed range overnight, directions SSW backing
to W overnight. Weak sfc low developing off Cape Fear then
tracking NE could push winds briefly toward 20 kt across the
Outer Coastal waters during Mon morning. Seas generally 3 to 5
ft with a few 6 footers possibly bleeding across the outer
waters off Cape Fear due to swell/wave direction becoming SSE-S.
Dominant periods will run 6 to 7 seconds.

.NEAR TERM /THROUGH MONDAY NIGHT/...
Latest sfc analysis shows a weak frontal boundary over the
local area as Tropical Storm Henri advances northward into
southern New England. The front in conjunction with deep
moisture and an upr- level trough will lead to scattered to
numerous shras/TSTMs through this evening, trending more towards
the coast tonight. No severe wx expected, however minor
flooding is possible especially over the southern half of the
cwa in low-lying areas, so will continue to highlight this in
the HWO. Due to the moist environment and light winds overnight,
areas of fog are again expected inland. Mon will feature
isolated to scattered shras/TSTMs, but the coverage is expected
to be less than today as the upr-level trough axis pivots
offshore and drier mid-level air moves into the area. Highest
rain chances (30-40%) near the coast. Temps near normal...highs
in the upr 80s to lwr 90s. Similar low rain chances continue
along the coast into Mon night coinciding with the axis of
highest moisture. Low temps in the mid 70s.

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
It is possible the H5 deformation may linger just enough off
the coast during Tue to help align the deepest moisture (PWAT
>2.2 inches) just east of the coastal areas. This would prevent
any widespread convection, especially across the far inland
zones. However, given PWATs lingering around 2 inches, the
inland trough, and the sea breeze to provide some lift will
maintain 30-40 POPs across much of the forecast area but closer
to 50% far southern zones. Convection would be able to carry
into the evening before coverage would diminish some with the
loss of heating. Favor a blend of guidance leaning toward the
slightly warmer ECWMF guidance for Tue`s high temperatures,
while low temperatures Tue night

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
During Wednesday the axis of highest PWATs will shift westward
across the forecast area as the mid-level subtropical ridge
shifts westward. As a result, the focus for convection will
shift farther inland as well during Wed aftn/evening. Also
during this time a TUTT will approach FL helping to keep the H5
ridge axis in place across NC into Thursday. It remains to be
seen how much of an influence the TUTT will have on rainfall
chances this far north. Ultimately, it may lead to an increase
in showers/tstms by Thu than what is currently advertised,
especially across the southern forecast area. By the end of the
week the H5 subtropical ridge should be the dominant feature
across the region with more typical summertime weather
expected and high temperatures back above climo.

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
VFR/MVFR to dominate tonight into daylight Mon with periodic
IFR/LIFR from low stratus and/or fog mainly during the pre-dawn
hrs. Sfc low to develop along the sfc trof boundary as it
pushes briefly to the ILM CWA Coast during the pre-dawn Mon hrs
thru daylight Mon. Will see convection fire up, mainly over the
adjacent Atl waters but a few storms could back-build or back-
peddle to the coastal terminals and there4 have indicated VCTS.
Upper trof axis to slide SE and off the ILM CWA Coast Mon aftn
which should negate the overall convective threat. However,
plenty of pieces of energy remain within the NW flow aloft for
isolated tstorms to occur during the remainder of the 24 hr
period, enough to mention here but not place in the aftn/evening
TAF period. Winds 0 to 4 kt tonight thru Mon morning, with
directions SW veering to W-WNW. Winds become N-NE around 5 kt
inland terminals and WSW backing to S around 10 kt across the
coastal terminals.

Extended Outlook...Mainly VFR except periodic MVFR/IFR from
daily diurnally induced isolated to scattered convection, and
the possibility of early morning fog and/or low stratus.

.MARINE...
Through Monday night...Sub-SCA conditions continue early this
week. Expect 10-15 kt SW winds on avg, and 3-5 ft seas. A weak
frontal boundary lifts north and then gets pushed offshore late
tonight. Henri swell has faded away and the dominant wave
periods will transition to wind-seas, thus a bit bumpier early
this week as lower periods (5-7 sec) dominate.

Tuesday through Friday...The pressure gradient between the weak
inland trough across the Carolinas and high pressure far
offshore will result in S-SW flow across the coastal waters
Tue/Tue night. Wind speeds Tue are expected to be around 15
knots with gusts to 20 kt. The fetch will likely be even
stronger farther offshore in the vicinity of the Gulf Stream. As
the high builds westward on Wed Sly flow will gradually
diminish. By Thu/Fri the ridge axis may build across the
Carolinas promoting an E-SE fetch with speeds generally 10-15
kt or less. Seas will be highest Tuesday given the
aforementioned fetch (choppy 3-5 footers), then 3 ft Wed, and
2-3 ft Thu/Fri. Chance of storms expected Tue/Wed, with lesser
chances across the waters by Thu/Fri.

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...Coastal Flood Advisory until 1 AM EDT Monday for NCZ107.
MARINE...None.

$$
SYNOPSIS...SRP
UPDATE...DCH
NEAR TERM...MAS
SHORT TERM...SRP
LONG TERM...SRP
AVIATION...DCH
MARINE...ILM

Area Forecast Discussion

National Weather Service Northern Indiana

1204 AM EDT Mon Aug 23 2021

.SYNOPSIS...
Issued at 1156 PM EDT Sun Aug 22 2021

Dry conditions are expected through Monday evening. It will
remain warm on Monday, and humidity levels will be on the increase
for Tuesday and Wednesday. Peak afternoon heat index values are
expected to reach into the 95 to 100 degree range during the
afternoon hours Tuesday through Thursday. There will also be some
additional periodic chances of showers and thunderstorms during
this time period.

.SHORT TERM...(This Evening through Monday)
Issued at 320 PM EDT Sun Aug 22 2021

Convection has expectedly struggled to this point today to develop
along a weak cold frontal boundary. Narrow axis of good low level
moisture pooling is evident in RAP analyses this afternoon from
west central Indiana into southwest Lower Michigan with
precipitable water values into the 1.5 to 1.6 inch range and
MLCAPEs of 1000-2000 J/kg along this axis. Surface
observations/satellite imagery do indicate a couple of favored
convergent axes at 18Z, one extending from just east of Three
Rivers, MI to west of Huntington IN associated with sfc
trough/weak cool front, and another extending from southwest Lower
MI, through Elkhart IN, and back southwest to Rensselaer, IN.
This second convergent axis appears to be tied more to some lake-
enhanced convergence with some stronger onshore post-frontal flow.
Water vapor imagery does indicate a very weak upper level short
wave trough shifting east out of northeast Illinois, which may aid
in some uptick in coverage along these convergent zones over the
next hour or two. Overall, conditions remain very marginal for
convective development due to weak mid level lapse rates/warm mid
levels, very shallow nature to frontal forcing, and lack of
significant large scale forcing with prevalence of the mid level
ridging. Expecting quick diminishment early this evening of any
isolated showers with loss of peak heating.

Dry weather expected for the remainder of the night as some drier
low level air advects in behind the weak front. This weak front will
not be effective in scouring out near sfc moisture however, and
would expect patchy radiational fog will develop once again for
Monday morning, with some possibility of some localized patchy
dense fog.

Subtle upper height rises and relatively dry low levels will allow
for another dry day on Monday with possibility of some high cloud
debris drifting across northern Indiana from decaying Mid MS
Valley convection. Afternoon should feature mostly sunny/partly
cloudy skies and continued warm conditions as westerly low level
flow advects warmer low level temperatures back into the area. Not
expecting heat indices to be a major concern for most areas on
Monday, although some mid 90s peak heat indices are possible
across the southwest where some better moisture recovery is
expected in the afternoon.

.LONG TERM...(Monday Night through Sunday)
Issued at 320 PM EDT Sun Aug 22 2021

More robust low level theta-e advection is expected for Tuesday
night into Wednesday as fast moving eastern Pacific wave draws a
warm front northward. Best low level moisture convergence during
the day Tuesday should be across southern MN/southern-central
Wisconsin, but will have to watch for potential of this convection
to propagate southeast through time later Tuesday into Tuesday
night/Wednesday. Flow profiles will remain weak across the area
and given fairly strong upper ridge remaining intact, still too
early to have much confidence in resolving convective chances with
any fine detail. Early indications would suggest that Tuesday
night-Wednesday may represent best chances given passage of
eastern Pacific short wave across the Great Lakes. Additional
chance of showers and storms toward end of this period as more
ridge riding Pacific waves move across northern tier states.

Maintenance of broad mid/upper level ridging will pose a concern for
heat/humidity this week, particularly Tue-Thu. Extent of heat
indices will of course depend on coverage/timing of any
convection/cloudiness during this period, but the potential does
exist for heat indices to reach around 100 degrees Tue-Thu
afternoons. Above normal temperatures to persist through the end
of this forecast period with little change in longwave pattern
anticipated.

.AVIATION...(For the 06Z TAFS through 06Z Monday Night)
Issued at 1203 AM EDT Mon Aug 23 2021

A weak pressure gradient was over the area with very light wind
flow. Mentioned MVFR fog given the likelihood of ground fog with a
strong conditional climatology signal around or above 50%
(09-13Z) at both sites. Otherwise, conditions will remain VFR.

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

SYNOPSIS...Marsili
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...Skipper

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Area Forecast Discussion

National Weather Service North Platte NE

618 PM CDT Sun Aug 22 2021

.SHORT TERM...(This evening through Monday night)
Issued at 225 PM CDT Sun Aug 22 2021

Currently, Nebraska is located just SE of a closed low centered over
the Montana/ND border. Some lee troughing dips SE through to W
Kansas. A warm front has passed, but soon a dry line and
subsequent cold front are expected to move through. Also at lower
levels is a LLJ located in the SW portions of the CWA. This
feature doesn`t really seem to move largely, and may provide
convective support in the short term.

Ahead of this boundary, CAMs advertise steep lapse rates, and decent
CAPE. Dwpts are widespread in the 60s to low 70s across the region
(minus portions of the Panhandle), signifying a slight surplus of
moisture...also identifiable via above avg PWATs of 1.25". Once the
boundaries move through, isolated thunderstorms are possible. Not
expecting widespread as a decent cap still exists, and instability
starts to move east with the boundaries. However, for those storms
that are able to overcome any inhibition, there is ample CAPE
available for them to tap into. The HRRR advertises widespread
MUCAPE of 1000J/kg, with patches of up to 3000J/kg. The RAP
advertises higher widespread values near 2000J/kg. However, shear
and SRH look fairly limited. At best thinking a storm or two may
become severe at best, with large hail and damaging winds as the
hazards.

Behind these boundaries, expecting a clockwise wind shift to
eventually be southerly tomorrow. Mostly clear skies and 850 Temps
in the 30s will allow for daytime highs in the 90s. Although the
system moves out of our area for precip/storms tonight, most of the
instability will remain tomorrow. Daytime heating steepens lapse
rates, and ~1500J or so of MUCAPE is available for north central.
Given support from the remaining LLJ, another chance for isolated
storms is possible tomorrow, with large hail as the primary threat.
However, this threat will be limited by lack of stronger forcing.

.LONG TERM...(Tuesday through Sunday)
Issued at 225 PM CDT Sun Aug 22 2021

At upper levels, there will be some broad scale ridging come Tuesday
over south central CONUS, but it is pretty low amplitude and
generally flat isobars across the Plains. As the previous fcst
mentioned, a closed low centered over the PACNW will enhance the
amplification of the ridge a bit. Just north of the broad scale
riding, an UL jet will be centered over the Dakotas/Canada border.
At lower levels, the LLJ remains, located just to the southwest of
western Nebraska. This feature looks to remain centered here for
Tuesday and Wednesday AM, but strengthen and center itself over
Nebraska by Thursday. It looks as though it will pretty much stay in
place through the weekend.

The ridging looks to allow for above normal (~5-10 degrees) highs
Tuesday and beyond. 850 temps will be generally above 30 and allow
for sfc highs generally in the 90s.

Behind the system affecting the short term, a bit of dry air tries
to work its way in, but looks limited to the Panhandle at best. This
will make Tuesday likely the most comfortable day as dwpts will be
in the 40s (Panhandle) to 50s range (Sandhills and southwest Neb).
This will be short lived though as moisture builds a bit Wednesday.
PWATs are advertised as 1" with patches of 1.25" Wed, and widespread
1.25"+ for Thursday. This is approx normal to above normal for this
time of year. The ample moisture will allow for precipitation
chances as the LLJ begins to center over W Nebraska mid-week.

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 618 PM CDT Sun Aug 22 2021

Gusty south or west winds will wane this evening by sunset, giving
way to light and variable winds overnight. In the meantime,
isolated thunderstorms may affect central Neb terminals (KMCK to
KBBW) and some patchy surface smoke to the northwest (KGRN).
Additionally, patchy fog may develop toward sunrise, most notably
in the Platte River Valley (KLBF).

.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&

SHORT TERM...Sinclair
LONG TERM...Sinclair
AVIATION...Snively

Area Forecast Discussion

National Weather Service Marquette MI

743 PM EDT Sun Aug 22 2021

.SHORT TERM...(This evening through Monday)
Issued at 343 PM EDT SUN AUG 22 2021

Latest water vapor imagery and RAP analysis show a vigorous
shortwave over nw ND lifting nne into south central Canada. This
feature is expected to weaken as it continues to lift ne into
Ontario on Monday but its associated sfc trough could push far
enough east to bring some showers and perhaps a thunderstorm into
western portions of the cwa later tonight. Weak shortwave ridging
and sfc high pressure over the Upper Great Lakes has resulted in
mostly sunny skies across the U.P. this afternoon with temps ranging
from the mid 60s to lower 70s north and mid 70s along the WI border.

Tonight, the vigorous shortwave currently over the Northern Plains
will lift into southern Manitoba on a very similar track to
yesterday`s system. Not surprisingly, the best forcing/dynamics with
this wave will again stay north and west of Upper MI. Models do show
some differences with regard to potential pcpn for Upper MI. Showers
and storms that move into MN this evening ahead of the associated
sfc trough will weaken as they approach Upper MI overnight. The
question is how fast will they weaken and dissipate. Given the
antecedant dry air mass over the area combined with weakening
forcing and weakening 850-700mb transport, leaned fcst toward the
drier end of model solutions. Fcst will reflect only schc pops as
far e as Gogebic/Ontonagon counties late tonight. To the e, sfc high
pres ridge will be drifting e, but will allow for calm conditions
under lingering clear skies. Favored the low end of guidance for min
temps across the e half. Mid 40s F should be quite common in the
interior. Temps will range up to 55-60F far w.

Monday, The surface trough associated with the system moving north
into Ontario stalls out just west of the area. After the weak
shortwave ripple moves through in the morning, heights rise again in
the afternoon. Mid-levels look dry and stable so no pcpn expected.
However, WAA in a southwest flow ahead of the trough will bring 850
mb temps of 16C or higher across the area and dew points will climb
back into the upper 50s and lower 60s by afternoon make for another
warm and somewhat muggy day. Mixing through 850 mb will result in
max temps in the lower to mid 80s most areas, except for mid to
upper 70s near the Lake Mi shoreline with onshore southerly wind.
Fcst soundings suggest steep low-level lapse rates and rising dew
points could lead to some diurnal cu formation.

.LONG TERM...(Monday night through Sunday)
Issued at 438 PM EDT SUN AUG 22 2021

Expect another calm night to start the extended period Monday night
as slight height rises, a strong temperature inversion near 900 mbs,
and dry air near 700 mbs should help keep convection and cloud cover
from developing. Low temperatures look to be mostly in the mid 50s
to low 60s across the area. Weak WAA Tuesday should bring another
warm day over Upper MI as a sfc low approaches western Lake
Superior. Skies should become more cloudy as the low approaches
Tuesday afternoon.

Some model guidance suggests that we could be dry Tuesday night, as
the better synoptic forcing associated with the low goes north of us
into northern Ontario (ON) Tuesday night, and an MCS could
simultaneously develop just south of the WI border and clip our
southern counties. This makes sense, as an MCS would prevent
convection from developing over Upper MI during the overnight hours
Tuesday. However, I`m not completely sold on this solution, as other
model guidance does not show this MCS complex developing in WI.
Therefore, I`ve kept chance pops for Tuesday night. If we do see any
thunderstorms develop Tuesday night, there are marginal conditions
for severe weather given MUCAPEs ranging from 1000-2000 J/kg (NAM
has up to 3000 J/kg, but it likes to overestimate), and 0-6 km bulk
shear around 30 to 40 kts. However, I`m doubtful for severe weather
given that this would occur during the overnight hours, as the
better synoptic forcing is expected to be in northern MN/ON, and the
better instability would be south in WI. Some showers and
thunderstorms are expected in the east half Wednesday as the low in
northern ON looks to bring a cold front SE across the area as it
goes from traveling northeast to east. Again, not expecting severe
weather potential Wednesday too, as the better rain chances would
happen in the morning hours, instability would be lower, and 0-6 km
bulk shear would still be rather marginal (even if the forcing is
better).

Thursday looks to be a fairly nice day, as weak CAA and height rises
drops high temperatures to the 70s across most of the area. Near the
end of the week, we should see ourselves get stuck under a fairly
tight pressure gradient and height falls as a troughing pattern sets
up to our west. This should bring us successive shortwaves this
upcoming weekend that could bring some widespread, soaking rainfall
IF the model guidance verifies. Also, some weak CAA and WAA is
expected over the area this upcoming weekend. Winds could also
become breezy, as the NBM is even picking up on gusts becoming over
20 mph across some of the U.P. this upcoming weekend. Would not be
surprised to see these winds increase as the weekend approaches, as
currently the mid-range guidance differs on the timing of the
strength and turning of the winds. However, what they do agree on
are some winds over 20 mph moving across the U.P. and the Upper
Great Lakes sometime this upcoming weekend. Perhaps the winds will
amount to nothing more than breezy conditions, but wanted to include
in the discussion just in case wind speeds increase with each
successive fcst, and wind related threats become more probable in
the future.
&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 743 PM EDT SUN AUG 22 2021

High pressure ridge sliding off to the east tonight and tomorrow
will keep TAFs VFR. A cold front passing by to the northwest could
bring a few showers and possibly a weak thunderstorm into IWD late
tonight. Did not feel confident enough to go with more than a VCSH
at this point as showers/storms will be limited in coverage and
weakening as they approach the area. Fair weather cu with bases
around 3000-5000 ft is expected by early afternoon tomorrow.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 343 PM EDT SUN AUG 22 2021

High pres ridge building over the Upper Great Lakes has resulted in
winds diminishing blo 20 knots this afternoon. Expect winds to
remain generally under 20kt across Lake Superior thru the midweek
period. E to ne winds may gust to 20-25kt over western Lake Superior
on Thu as pres gradient tightens btwn high pres over northern
Ontario and broad low pres developing over the western Plains.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

SHORT TERM...Voss
LONG TERM...TAP
AVIATION...RJC
MARINE...Voss

Area Forecast Discussion

National Weather Service San Francisco Bay Area

827 PM PDT Sun Aug 22 2021

.SYNOPSIS...Cool temperatures with a deep marine layer persisting
through mid week. Chance for patchy drizzle and fog along the
coast Monday morning. Continued onshore flow helps push smoke east
of the bays. Gradual warming trend through the week, with chance
for warmer temperatures Friday and Saturday for inland areas and
higher terrain.

.DISCUSSION...as of 08:11 PM PDT Sunday...Marine layer has
compressed slightly this evening and is now hovering near 2000 ft
deep. Onshore flow will continue through midweek as we stay under
the influence of a trough aloft. Expect winds to get breezy in the
afternoons.

Looking at models and satellite, the marine stratus deck is well
established along the coast so we expect another inland push
tonight into tomorrow morning. Have added slight chance of drizzle
to the forecast for coastal areas as well as into some inland
areas such as from Petaluma up to Santa Rosa (in Sonoma County),
potentially over towards the Napa Airport, East side of the SF Bay
including Oakland and Hayward, along with the northern part of the
Salinas Valley including the Salinas Airport. Otherwise, no other
changes made to the forecast package this evening. Models continue
to show a slight warming trend by the end of the work week which
should be a little more pronounced Friday into the weekend. At
this time, the temperatures do not look to trigger any significant
heat risk for the general population.

.PREV DISCUSSION...as of 01:27 PM PDT Sunday...

..Short Term...Tonight and Monday..
A fairly deep marine layer holds over the immediate central CA
coast line up to the North Bay today. The Fort Ord profiler has
shown a deep inversion around 2500ft this morning. Cooler ocean
air will be able to advect inland today keeping the coastal areas,
higher terrain (below 2,500ft), and most of the inland areas
below normal for high temperatures today and Monday. An upper
level trough persists over the area, with a weak short wave
passing through Monday which is allowing for the cooler
temperatures to push so far inland. These lower heights aloft will
also help continue this deeper marine layer through mid week. With
onshore winds persisting, most of the smoke from fires around CA
should stay out of our area. If anything, elevated haze might be
seen over the North Bay in the afternoon hours. Slight chances
for some light drizzle along the immediate coast Monday morning as
the short wave moves through.

..Long Term... Monday night through Sunday...
After the short wave rotates through the area along the axis of
the upper level trough overhead, the patter stays fairly stagnate
mid week. Upper level troughiness will remain over the area
through Wednesday night. With no synoptic scale forcing, local
climate regimes will build back and dominate through the end of
the week. Onshore winds build during the afternoon hours, with
terrain driven drainage winds overnight for most areas.
Temperatures will gradually warm back up to normal by Wednesday.
Models have had some uncertainty run to run, but with the 12Z run
the GFS and ECM agree on deepening the trough down the CA
coastline Thursday and Friday, keeping lower 500mb heights over
the area. This should keep Thursday temperatures around normal for
most of the area as well.

Upper level high pressure over the Pacific to our west
will inch towards the coast Friday and Saturday. There is still
uncertainty with how close it will get. However, this could advect
some drier air into the marine layer over the waters Friday, as
well as strengthen some of the winds over the waters. 850mb
temperatures look to warm back up to 25C by Friday afternoon,
which could keep higher elevation areas around 5 degrees warmer
than normal. Impacts don`t look alarming as of now for heat
concerns this next weekend, but we will keep an eye on how the
models trend.

.AVIATION...As of 6:48 PM PDT Sunday...For the 00z TAFs. The
marine layer depth has compressed a little, currently 2,000 feet
on profiler data. A moderately deep marine layer supports stratus
/MVFR/ ceilings along the coast and nearby coastal valleys early
this evening, however mid to late evening ceilings lowering to a
mix of MVFR and IFR with onshore winds ushering stratus and patchy
fog inland. LIFR-IFR due to further lowering of stratus ceilings,
patchy fog and light drizzle along the coast late tonight and Monday
morning.

An ongoing, favorable for stratus/fog formation, upward flux of
heat and water vapor from sea surface to air (at the interface)
and feed of water vapor from the northwest continues coupled with
surface based cooler air arriving from the north, blending into
the marine layer, and reinforcing this process tonight and Monday
morning; hi-res and global model forecasts show patchy light
coastal drizzle. Light amounts of cool air advection reach the 925
mb level Monday morning before stabilizing then warming slightly
Monday afternoon.

Only minor adjustments made to timing ceilings tonight in the 00z
TAFs, otherwise TAFs look good and href model is in-line with
current areal extent of stratus. The hrrr near-surface smoke
model output concurs with current satellite imagery showing light
amounts of smoke mainly on the back edge of the stratus, however
northwest winds and stationary surface troughing wind field will
feed the smoke into the marine layer tonight and Monday; smoky to
hazy conditions likely in the slant range and possibly adding to
lowering surface visibilities to IFR-MVFR, even farther inland.
Conditions otherwise MVFR-VFR Monday, coastal stratus continuing
with an inland intrusion Monday night/Tuesday morning.

Vicinity of KSFO...VFR, northwest wind 12 to 15 knots until mid
evening, 5 to 10 knots tonight and Monday morning. Ensemble (href)
model output forecasting MVFR ceiling by 11z Monday, preceding this
with tempo MVFR 09z-11z. MVFR lifting to VFR 18z Monday. Afternoon
to mid evening west wind near 20 knots. Slant range visibility likely
lowering Monday.

KSFO Bridge Approach...similar to KSFO.

Monterey Bay...VFR, southwest to west winds are bringing stratus
/MVFR/ ceilings over much of the Monterey Peninsula and eastward
across the Monterey Bay to the northern Salinas Valley. West-southwest
wind at KMRY may temporarily delay stratus ceiling an hour to two
longer than 0230z-0300z MVFR-IFR advertised in the TAF. Otherwise
as mentioned overall favorable conditions for lowering stratus
ceilings, patchy fog and light coastal drizzle tonight and Monday
morning. Conditions lifting to MVFR-VFR by late Monday morning and
afternoon. Slant range visibility likely lowering Monday.

.MARINE...as of 08:11 PM PDT Sunday...Continued light to locally
breezy west to northwest winds over most of the coastal waters
through the early part of the week. Stronger winds will persist
over the far northern outer waters through much of the forecast
period, creating hazardous conditions for smaller vessels. Gusty
onshore winds also expected through the Golden Gate gap and into
the Delta this afternoon and evening. A long period weak
southerly swell will continue through midweek along with shorter
period northwest waves at 8 to 10 seconds.

.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...SF Bay until 9 PM

PUBLIC FORECAST: Bingaman/Dhuyvetter
AVIATION: Canepa
MARINE: Lorber

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Area Forecast Discussion

National Weather Service Las Vegas NV

800 PM PDT Sun Aug 22 2021

.SYNOPSIS...Southwest flow will continue to spread smoke across
portions of Inyo and Esmeralda counties through Tuesday. Seasonal
temperatures are expected through Tuesday then warming to above
normal Wednesday through Sunday. Thunderstorm activity could make
a return to Mohave County next weekend as monsoonal moisture
increases.

.UPDATE...French and Walkers wildfires just west of Inyo County
continue to impact that area with lower visibility`s and poor air
quality, although the visibility is not as limited as 24 hours ago.
Elsewhere, skies are clear with much drier air in place across the
Mojave Desert and northwest Arizona with surface dewpoints generally
in the teen and 20s.

A dry southwest flow will prevail over the region through Tuesday
with temperatures near normal. Latest HRRR Smoke does suggest that
smoke/haze from the California fires will become more prevalent
across the area Monday night and Tuesday.

No update this evening.

.DISCUSSION...Tonight through Wednesday night.

A low pressure system over southern British Columbia is forecast
to just brush the northern parts of Oregon, Idaho, and Montana as
it heads east through Tuesday. This system should have no direct
weather impacts for us but troughing extending down along the
West Coast will keep a dry southwest flow over our area through
Wednesday. High temperatures forecast by the NBM which have been
fluctuating slightly cooler or slightly warmer depending on the
model run time, now appear to have settled on the slightly cooler
forecast. Highs Monday and Tuesday will be right around normal and
slightly above normal on Wednesday. Under the southwest flow,
smoke could remain an issue at times for portions of Inyo and
Esmeralda counties through mid week.

Remnants of the now dissolved tropical system Grace emerged over
the Eastern Pacific near the west central coast of Mexico earlier
today. NHC forecasts an 80 percent chance of this tropical
disturbance forming into a tropical depression within the next 48
hours. This system will have no direct impact on weather in our
area as it is forecast to be well south of Baja as it moves away
from land and heads WNW over the ocean. What it has done already
is deepen the moisture pool in the southern Gulf of California with
dewpoint temperatures from the upper 70s to low 80s as far north
as Los Mochis Mexico. Ensemble guidance has this pool of deeper
moisture continuing northward to about the Baja Spur by midday
Tuesday. This brings the one inch PWAT line to near our southern
CWA border midday Tuesday and to the southern tip of Nevada by the
end of the day on Wednesday. This will likely be mid to upper
level moisture that is not expected to result in any shower
activity for us.

Thursday through Sunday...

The trough along the coast moves east across the Great Basin on
Thursday and extends far enough south to lower heights over our
area. Thus, the NBM has dropped temps a couple of degrees from
what was forecast yesterday morning. This moves us further away
from records on Thursday and Friday and this is indicated in the
lower values in heat risk. As such, heat risk in the high
category is more localized than what we were seeing just 24 hours
ago and based on this, heat related headlines are not needed at
this time. An uptick in surface moisture over the weekend is still
forecast along with a gradual increase in thunderstorm chances,
primarily in Mohave County. Temperatures over the weekend are
forecast to be a few degrees above normal.

.AVIATION...For McCarran...Breezy southeast winds will continue
through the afternoon, with gusts to around 20 KT expected through
the evening. Gusts will end early tonight, though southerly winds
speeds 8-10KT could persist through around midnight. After a lull in
the winds Monday morning, breezy south winds are expected again
Monday afternoon with gusts 15-20KT developing in the afternoon.
Clear skies and dry conditions will continue through Monday. Skies
will continue to be mostly clear, although haze from distant
wildfire smoke will reduce slant range visibility at times.

For the rest of southern Nevada, northwest Arizona and southeast
California...Expect breezy south to southeast winds to continue
through the evening with gusts around 20 knots. Higher gusts to
around 25KT are likely through the Colorado River Valley. Winds
will decrease around 03-04Z with typical overnight wind patterns
expected overnight. Skies will continue to be mostly clear, although
haze from distant wildfire smoke will reduce slant range visibility
at times. South winds will increase again on Monday, with speeds the
same or slightly lower than what occurred today.

At BIH, wildfire smoke will continue to bring visibilities down at
times. Some improvement has been noted early this afternoon, with
visibilities around 4-5SM likely through the early evening. Some
additional improvement is possible this evening and early tonight,
with low confidence in a period of VFR conditions sometime tonight
before a return of thicker smoke results in visibilities reducing to
3SM or less again by Monday morning.

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.

UPDATE...Pierce

DISCUSSION...Salmen
AVIATION...Nickerson

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