Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/18/21
AREA FORECAST DISCUSSION
National Weather Service Albany NY
1008 PM EDT Tue Aug 17 2021
A warm and humid, tropical airmass will move into the region
tonight with scattered showers and a few thunderstorms.
Tomorrow, showers and thunderstorms will be most numerous north
and west of the Capital Region. The remnants of Tropical Cyclone
Fred will bring a more widespread, and possibly heavy rainfall
Wednesday night through Thursday with humid conditions
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Heaviest, most persistent rain has been staying west of Albany
Forecast Area. Parts of Central New York saw 3-5 inches of rain
this evening. Scattered showers now occurring over most of our
New York zones, but mainly dry over western new England zones.
Winds are light an variable. Temperatures are in the mid 60s in
the terrain to the mid 70s in the mid Hudson Valley. Latest run
of the HRRR has periods of showers over the Adirondacks
continuing overnight with showers over the rest of the area
PWATs are on the rise on the transitional air mass
with the latest SPC RAP Mesoanalysis showing 1.6-1.9". The 12Z
KALY sounding was 1.91". Forecast area will get into better
tropical environment into tonight. The 1.91" PWAT is in the
90-100% of climo for this time of year. Intense rainfall rates
will be possible with any convection.
Weak elevated instability is noted so an isolated thunderstorms
or two is possible. The heaviest rainfall will be north and
northwest of the Capital Region. A lull is likely to continue to
the south and east. FFG values remain high due to the recent
dry spell since Aug 1st, so any hydro issues look minimal
through the afternoon. Some ponding of water and poor drainage
flooding is possible. An isolated FFG may be possible near the
western Mohawk Valley if intense rainfall rates are realized due
to high PWATs.
Low-level theta-e advection continues overnight with some
scattered showers possible or maybe an isolated thunderstorm.
Synoptic forcing becomes nebulous the with warm front drifting
through. Better chances of showers continue from ALY north and
west. A sticky night is expected with dewpts in the 60s to
spotty lower 70s. Lows will be in the 60s to around 70F.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
Tomorrow...The guidance continues to vary on the track of the
remnant circulation of TC Fred. The circulation lifts northeast
of the TN Valley into the OH Valley and wrn PA. In the confluent
zone northeast of Fred, enhanced low-level convergence will
allow for periods of moderate to heavy showers to occur west of
most of the forecast area but then to slide eastward during the
day. In the tropical environment, PWATs will be in the 1.7-2.0+
range range. Low stratus will likely linger over the region
into the late morning into the afternoon. A conditional
thunderstorm threat is possible if any heating occurs during the
day. Low-level shears increases with low to moderate
instability. An isolated tornado may be possible or damaging
wind gusts as a Marginal Risk is in place southwest of Albany
along the eastern Catskills, Schoharie and western Mohawk
Valley. Some locally heavy rain is possible, but the guidance
(majority has shifted north and west) with the low and mid level
ridging building in off the coast. Highs will only get into the
70s to spotty lower 80s in the valleys. Some 60s will linger
over the higher terrain.
Wed night to Thu...A subtle shift in the rainfall with TC Fred
with the EC/NAM trending north and west to the GFS and some of
the CAMs. The NAM is the furthest west slamming the Adirondacks
and western Mohawk Valley northward with the heaviest rainfall.
The EC and GFS hit the northern Catskills/Capital
Region/northern Berkshires north and west with 1-3" of
rainfall. We had an extensive collaboration call with WPC with
neighboring WFOs to shift the QPF north some and move the SLIGHT
Risk for excessive rainfall north of the mid Hudson Valley in
Day 2. The Marginal Risk was expanded in Day 3. See the hydro
discussion with more details. PWATS are +2 to +3 STDEVs above
normal so intense rainfall rates with local orographic
enhancement are possible. The timing and placement of the
rainfall is uncertain but locations north and west of the
Capital Region may get the higher QPF at this time. 1-3" with
locally higher amounts are possible. Low to modest amounts of
instability will exist some isolated to scattered thunderstorms
are possible in the tropical air mass. Lows WED night will be in
the 60s. THU highs will be in the 70s with some 60s over the
mtns. It will likely be a gray day with temps below normal.
Thursday night...showers diminish with the remnant circulation
of Fred moving downstream of New England. Have kept a chance of
showers in prior to midnight with a slight chance of
thunderstorms. Lowered PoPs after 06Z with some weak ridging
building in the wave of the trough. Some patchy fog may also
occur with lows in the 60s still in most locations.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
The long-term forecast period will continue to feature warm and
humid weather conditions with day-to-day chances for showers and
thunderstorms as eastern New York and western New England sits in
the warm sector of a storm system well off to our northwest with an
associated frontal boundary to our north, a cold surface frontal
boundary to our west, and upper level ridging/higher geo-potential
As far as precipitation chances, there`s been better continuity
amongst forecast guidance overall over the past few days, but still
some uncertainty in the spread. In general, the deterministic
solutions are showing more spread than the ensembles. Given the
abundance of moisture that`s forecast to be over the area with PWAT
values still ranging 1-2 STDEVs above normal, weakness in the mid-
levels with a weak mid level low and associated impulses, and an
unstable environment, afternoon/evening scattered showers and
thunderstorms will be possible each day of this long-term period.
Have 30-40% PoPs each day of the extended during the afternoon and
Given that 0-6km bulk shear values are low and there`s weak flow
aloft, not expecting any thunderstorms to become organized. That
said, thunderstorms (diurnally-driven) will be of the garden/pulse
variety. Rainfall could become moderate to heavy under any
convection given the high moisture environment with PWATS 1-2 STDEVs
above normal and dewpoint values in the upper 60s to lower 70s.
There`s still uncertainty in the timing of the cold fropa. Right
now, it appears to be in the Tuesday evening into Wednesday
timeframe given how slow the system is moving. Once the cold front
passes the region, it will being a cooler and drier airmass into the
region mid to late next week.
As far as temperatures, high temperatures are forecast to be in the
lower to mid 80s along the river valleys with 70s over the higher
terrain. Nighttime will remain warm and humid with overnight lows
holding in the mid to upper 60s (upper 50s and lower 60s higher
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Light rain or rain showers should overspread all the TAF sites
this evening. Ceilings will gradually lower overnight to MVFR.
IFR ceilings are also possible By 09-12UTC with some
restrictions to visibility in fog down to 1-2 miles with very
moist airmass in place.
Any fog should lift tomorrow by 13-15UTC. MVFR ceilings look to
linger through at least 15 UTC tomorrow at most TAF sites and
could struggle to improve to VFR even by 18 UTC.
Some isolated showers or thunderstorms are possible after 18UTC
tomorrow, but coverage looks limited and locations too
uncertain to include in TAFs at this time.
Southeasterly winds turn light and variable tonight before
shifting to the south - southwest by 12 UTC becoming sustained
at 5 - 10 kts during the day.
Wednesday Night: High Operational Impact. Definite SHRA...TSRA.
Thursday: High Operational Impact. Likely SHRA...TSRA.
Thursday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Friday: Moderate Operational Impact. Chance of SHRA...TSRA.
Friday Night: Low Operational Impact. Slight Chance of SHRA.
Saturday: Moderate Operational Impact. Chance of SHRA...TSRA.
Saturday Night: Low Operational Impact. Slight Chance of SHRA.
Sunday: Moderate Operational Impact. Chance of SHRA...TSRA.
A warm and humid, tropical airmass will move into the
region tonight with scattered showers and a few thunderstorms.
The showers and a few thunderstorms will be most numerous north and
west of the Capital Region tomorrow. The remnants of Tropical
Cyclone Fred will bring a more widespread rainfall Wednesday night
through Thursday with some thunderstorms and humid conditions
A moist, tropical air mass will be over the area through
Thursday with periods of rain and elevated RH values. Winds will
be south to southwest for much of the period.
Localized hydro issues may arise Wednesday night through
Thursday across the ALY HSA.
A warm front will move through the region early tonight.
Some late afternoon and evening, slow- moving showers and
thunderstorms may move back into this area north and west of the
Capital Region. This may result in an isolated flash flooding
threat mainly over the Mohawk Valley into the southern
Adirondacks. A slight risk of excessive rainfall is in place in
this area per WPC guidance.
The remnants of TC Fred will approach late Wednesday night into
Thursday. An area of heavy rainfall will likely accompany the
remnant circulation. There is uncertainty as to the timing and area
of heavy rainfall, but the risk is maximized has shifted
northward and is from the northern Catskills, Capital Region
north and west, where a slight risk of excessive rainfall
exists per WPC collab this pm. Rainfall amounts will be in the
1 to 3 inch range.
Fairly dry antecedent conditions should mitigate the flood
threat somewhat, but areas of urban/poor drainage flooding and a
few flash floods cannot be ruled out especially north and west
MMEFS and NERFC guidance shows no main stem river flooding at
this time. However, the trends will continue to be monitored. A
Flash Flood Watch may be needed later in time especially for
Chances of rain persists Friday into the weekend, but will be
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
Area Forecast Discussion
National Weather Service Gaylord MI
1123 PM EDT Tue Aug 17 2021
Issued at 959 PM EDT Tue Aug 17 2021
Main concern is the patchy fog, and how much it will obscure
locations. At this point the fog will probably lower the
visibility to about a mile. There could be some location that
could see lower visibility, but generally things should be decent.
So, not much to change on the forecast for the night.
.NEAR TERM...(Through Tonight)
Issued at 325 PM EDT Tue Aug 17 2021
High Impact Weather Potential...Minimal
Pattern Synopsis/Forecast...18z surface analysis shows high
pressure centered off the New England coast ridging back west into
the Great Lakes. A cold front sits off to our northwest from far
northwest Ontario into North Dakota. Remnants of Tropical
Depression "Fred" are lifting northeast across north Georgia.
Water vapor imagery shows a nice little spiral north of Georgian
Bay spinning away from Michigan...part of a positively tilted PV
anomaly that stretches back southwest across Iowa and into Kansas.
Departing circulation over northeast Ontario has been throwing
bits of mid/high cloud back into eastern Upper throughout the day
along with some diurnal Cu across Chippewa county...and a couple
areas of Cu across far northwest Lower as well as south of a CAD-
APN line...both areas where surface dew points have managed to
hang on around 60+F.
No real changes in the pattern tonight as surface ridging/
anticylonic flow holds...with a PV "filament" lingering over
northern Lower as part of the overall elongated short wave trough
Primary Forecast Concerns...Pretty minimal concerns and mostly
reflect the concerns from the past several nights revolving around
fog possibilities. As winds remain on the light side and clouds
remain clear/thin will probably see some fog develop especially in
interior low lying areas especially around lakes and rivers which
is typical for cool nights this time of year. Overnight lows
should be mostly in the 50s...but some interior cold spots could
dip into the 40s.
.SHORT TERM...(Wednesday through Friday)
Issued at 325 PM EDT Tue Aug 17 2021
High Impact Weather Potential: Minimal...
Pattern Synopsis/Forecast: Last 48 hours have seen large scale,
upper-level pattern across the CONUS go from more or less zonal to
more positively tilted... with additional shortwave energy
digging into the broad troughing in the Pacific northwest. Bermuda
high is retrograding westward into the southeastern US as Fred
meanders northward on the inland side of the Appalachians...with
that same weak troughing/PV anomaly action across the inner half
of the country/Great Lakes region as has been noted the last few
days (best noted on water vapor satellite imagery today by a long
swath of dry air ahead of some cloud activity extending from a
little niblet to our northeast this morning...back into the
southern central Plains). Will look for this overall pattern to
continue...with Fred attempting to make its way northward...but
ultimately unable to do much to our weather here in Northern
Michigan beyond some increased cloud cover and perhaps
(perhaps....) some small rain/storm chances by Wednesday
afternoon. Loosely split flow across the center of the country
seems to favor the Great Lakes for subsidence and high pressure,
on the north side of that PV anomaly, however. As upstream
troughing digs eastward through the middle/end of the week...will
look for it to build ridging in the northern stream...only further
reinforcing the split flow idea. Depending on the exact position
of the pattern...this could mean we remain overall dry and quiet
even into the end of the short term...though some uncertainty yet
Primary Forecast Concerns: Rain chances...or a lack thereof...and
possible smoke effects...
Welllll....17/12z HRRR vertically integrated smoke guidance
continues to keep the bulk of the smoke to our west/northwest,
caught up in the more active part of the flow as stronger shortwaves
pass well north of us. Weakly split flow here in the Great Lakes
looks like it will continue to keep the majority of the smoke from
moving in, at least through 12z on the 19th (Thursday morning).
Looking at today`s visible satellite imagery...can see diurnal cu
popping across central WI/E central UP ahead of the smoke...with
cloud development under the smoke limited to activity driven by a
cold front/dryline crossing the northern Plains. Given that smoke
guidance suggests some higher concentrations filtering into the UP
Wednesday and Wednesday night (looks to have a tough time making
it into Northern Michigan, at least initially)...and given
upstream trends and prior experience with smoke this summer...
first loose guess is that highs across the UP Wednesday (and
perhaps again Thursday) will not reach their full potential as the
smoke blocks out some of the better heating, despite minimized
cloud cover there. Did lower max temps for Wednesday across the E.
UP, though we`ll see if it was enough or not. Otherwise, it
should be warmer with more diurnal Cu across most of Northern
Lower. Will have to wait and see how things turn out for Thursday
and beyond regarding smoke...but I suspect the plume may primarily
miss Northern Lower, encroaching at times here and there...adding
extra wrenches into the forecast for the upcoming week.
By Wednesday, there are some signals for increased moisture into
especially southeastern Michigan...perhaps getting as far north as
our southern/southeastern CWA? Whether this is totally from remnants
of Fred...or related to some of that PV action to our southwest
lifting into the area...is not entirely clear. Either way...there is
perhaps somewhat of a better chance of showers and maybe a rumble of
thunder Wednesday afternoon than the last couple days, given a
little more potential for instability as we become a little warmer
and more more moist in the boundary layer than we`ve been the last
few days...and some slight steepening of lapse rates is possible
aloft as the PV anomaly to our southwest tracks up into the area,
bringing some slightly cooler 500mb temps in with perhaps little
change to the lower level temperatures. Even so...guidance still
seems to want to keep things drier and push better precipitation
chances out farther into the end of the week. Model derived
soundings suggest the cooling aloft Wednesday may lead to mainly
elevated instability over a weak but somewhat deep cap in the mid-
levels, so it could go either way, depending on how warm we get in
the afternoon. Additionally...soundings suggest a pretty deep layer
of dry air aloft...which could further mitigate precipitation
With this somewhat more warm and moist atmosphere in
place...Thursday and perhaps even Friday may end up seeing some
isolated shower/storm development. Ridging looks to strengthen to
our west ahead of the approaching upstream trough Thursday into
Friday...while the same PV anomaly mischief seems to linger across
the Great Lakes into end of the period. Depending on exactly
where these features end up, either one could ultimately serve to
instigate some precipitation, whether due to the weak perturbations
aloft or lake breeze development...though there is still a lot of
uncertainty surrounding precipitation chances through the remainder
of the period.
Bottom line: stereotypical summer weather ahead -- warm,
increasingly humid, and isolated showers and storms possible at
times, probably especially in the afternoons and especially inland
along the lake breeze(s), though many locations should stay dry.
.LONG TERM...(Friday night through Tuesday)
Issued at 325 PM EDT Tue Aug 17 2021
High Impact Weather Potential: Minimal attm...
At this point in time...looks like the best chance for showers/
storms (which may or may not also be dwindling...?) should be
Saturday (ish) as that upstream trough swings through. Current
model runs look less impressive with this for us compared to
yesterday at this time...so things appear to be less certain yet
again...though they do seem to be getting on board with the
overall pattern a little better now. Would guess this uncertainty,
and continuing uncertainty into the remainder of the period,
relates at least in part to the Atlantic basin tropical systems --
Grace and Henri -- both of which will be affected by that
retrograding ridge across the southern US. Even so...will still
have to keep an eye on the weekend as it could be somewhat active
as far as storms go...especially considering that this is still
peak outdoorsy- camping season across our beautiful Northern
Michigan CWA. Either way, it`s always good to remember to include
the weather in your vacation plans.
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1113 PM EDT Tue Aug 17 2021
The main issue is still the fog potential for the TAF sites. TVC
should remain fog free overnight with the very light south flow.
The rest of the sites (MBL, PLN, APN) all will probably see some
type of restriction, with MBL expected to fall to around 4sm
prevailing, and tempo restrictions to 3/4sm or maybe 1/2sm FG.
After 12 or 13z, the fog should lift and diurnal Cu will form over
the region, so CIGs should maintain VFR if they form at all.
Issued at 325 PM EDT Tue Aug 17 2021
High pressure ridging in from the west should keep winds on the
lighter side and allow for lake breezes to dominate things
Wednesday and Thursday. Increasing signals for some fog and haze
to develop over the next several days...lake waters are warm so
will take some decently high dew points for that to occur. Fog on
the St. Mary`s River is possible tonight with some cool air
Area Forecast Discussion
National Weather Service Bismarck ND
942 PM CDT Tue Aug 17 2021
Issued at 940 PM CDT Tue Aug 17 2021
Fire weather danger conditions are starting to improve across the
CWA late this evening, although lingering hot temperatures are
making for some low RH in the southwest. Light southeast breezes
continue for some areas in the south, with a northeast flow across
the north. Overall improving fire weather conditions are expected
through the night, thus have let the Red Flag Warning expire. Made
some minor adjustments to PoPs based on current radar trends.
Surface low in MT will strengthen the low level jet tonight. Where
this jet meets the low a few showers and thunderstorms are
possible. Atmosphere is fairly capped, and these storms should be
mostly elevated. Thus severe weather is not expected at this time.
HRRR Smoke Forecast also showing easterly flow should improve
smoke tonight, so have reduced mention of this later tonight. Surface
front will then slowly make its way across the region tomorrow.
Initial passage looks to be fairly dry, and have lowered daytime
PoPs. Wednesday night could see some increased moisture along and
behind the front, perhaps returning isolated to scattered showers
and thunderstorms. Look for another generally warm day as well on
Wednesday, with upper 90s expected across central portions.
UPDATE Issued at 658 PM CDT Tue Aug 17 2021
Minimal updates needed early this evening. A few weak returns are
currently showing up on radar across the west and across the James
River Valley. Although a few showers may come out of these
returns, especially in the west, dry air at the surface will limit
chances for showers and thunderstorms this evening. Made some
adjustments to PoPs based on latest trends. Winds have increased
slightly early this evening, bringing warm temperatures and low
RH values to much of the state. Will let the Red Flag Warning
continue until at least 8 PM CDT for the time being as a result.
.SHORT TERM...(This evening through Wednesday)
Issued at 142 PM CDT Tue Aug 17 2021
Cloud cover, along with smoke, have inhibited temperatures so far
today for central North Dakota. It seems unlikely many of these
locations will reach originally forecast highs, thus have lowered
highs a bit along the eastern half of the forecast area. Winds are
not quite picking up as expected in the southwestern part of the
state either as the surface low center has already nudged into the
state. Weaker winds along with the aforementioned reduced
temperatures for the eastern counties may prevent much of the
area from fully reaching Red Flag criteria. Still, with how dry
the area has been, it wouldn`t take much for any fires that may
develop to spread rapidly, thus will allow the Red Flag Warning to
remain in place.
Could see a few showers this afternoon into tonight for the
western and northern forecast area. Overall though, with so much
dry air present, expect coverage to remain isolated and rain
amounts to be low. Besides precipitation chances, HRRR Smoke
indicates an improvement in near-surface smoke this evening and
overnight, although more elevated smoke will likely remain in
place for Wednesday.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 142 PM CDT Tue Aug 17 2021
The extended period begins with a west CONUS trough and east CONUS
ridge in place. Through Friday night, the west CONUS trough will
gradually lift northeastward through the region producing some of
the better shower and thunderstorm chances in a while. While
precipitation will be possible throughout the majority of the
period, presently the best chances of seeing more widespread
moderate precipitation are Thursday night through Friday. For the
most part, instability looks to be limited, so rain showers are
likely to be more prevalent than thunderstorms, although rumbles
are thunder are certainly expected at times. Even a severe
thunderstorm or two Thursday evening is not completely out of the
question further southeast towards the southern James River
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 658 PM CDT Tue Aug 17 2021
Overall look for VFR conditions through the forecast period.
Through tonight, a few isolated showers and thunderstorms are
possible across the west and north. Confidence is low that this
will impact any TAF sites, and ceilings should generally remain at
VFR levels. A breezy south southeast wind may also be found at
times through tonight, with some low level wind shear possible for
a few TAF sites. Wednesday then looks to see mainly dry and VFR
conditions. A breezy south wind looks to be found for more sites,
although a switch to a northerly wind may be found from KXWA to
KDIK and KXWA to KMOT on Wednesday afternoon.
Area Forecast Discussion
National Weather Service Des Moines IA
633 PM CDT Tue Aug 17 2021
.DISCUSSION.../Tonight through Tuesday/
Issued at 359 PM CDT Tue Aug 17 2021
-- Warm, humid through Thursday.
-- Smoke aloft Wednesday in Northwest and Northern IA.
-- Thunderstorm chances return later in the week, severe storms
TODAY THROUGH WEDNESDAY: A few clouds in central to eastern Iowa
along with the return of wildfire smoke to northwest Iowa can be
seen on GOES-16 Satellite this afternoon. With a weak mid-level
ridge in place and the remnants of the upper-level trough pushing
off to the east through the day today, mainly quiet weather
continues. Moisture return this afternoon aided by southerly low
level flow has caused dew points to surge into the 70s in western
Iowa with mid to upper 60s dew points elsewhere as of 2pm. The
return of the humidity has pushed heat indices back into the 90s in
western Iowa as of 2pm. High temperatures this afternoon are
expected to climb into the mid to upper 80s with heat indices
topping out in the upper 80s to low 90s across the area.
With a thermal ridge continuing to build off to the west and moving
eastward into tomorrow and Thursday, a stronger push of theta-e
advection will raise temperatures a few degrees on Wednesday with
high temperatures near 90 and heat indices topping out in the low to
mid 90s on Wednesday afternoon. Breezy southerly winds are expected
on Wednesday afternoon as the pressure gradient tightens with 10 to
20 knot wind gusts becoming common. Some scattered convection could
still be possible on Wednesday afternoon, mainly associated with
peak heating and in southern Iowa, but any storm chances look to be
isolated at best. The formation of diurnal cumulus is likely with
with the warm and humid airmass in place and an unstable boundary
layer, but forecast soundings in southern Iowa remain mostly dry at
the surface and mid levels so any updrafts that do form will be
difficult to maintain. With all these caveats and scattered/isolated
nature of any possible convection, kept forecast dry for Wednesday.
The return of smoke from western wildfires today in northwest Iowa
will continue into Wednesday with the higher concentrations aloft
moving somewhat east overnight into tomorrow impacting northwest
into northern Iowa through the day on Wednesday and with smoke aloft
making its way towards central Iowa overnight into Thursday, as of
the latest HRRR model output. Added additional sky cover to account
for smoke aloft Thursday in the sky grids, but no visibility impacts
expected as of current model trends.
THURSDAY AND BEYOND: The mid-level trough that will bring our next
system pushes east from the the Inter-Mountain West Thursday into
Friday. An associated surface cold front will be move through the
area on Friday into Saturday with precipitation chances ramping up
late Thursday into Friday morning ahead of the aforementioned cold
front. Although scattered showers and a few storms are possible
throughout the day Friday, the best chances for storms looks to be
Friday afternoon into early Saturday morning. Some strong to severe
storms are possible with most models suggesting the trough will take
on a negative tilt allowing for the surface cyclone to deepen as it
approaches the area. A ribbon of high instability will be ahead of
the cold front though deep layer shear may be a lacking ingredient.
0-6km shear away from the boundary is 20-25 knots but higher shear
values could be along, but more likely behind the boundary. The SPC
has introduced a 15% probability of severe storms over much of the
northwest half of the state, so we will continue to monitor these
trends over the coming days to further evaluate the severe weather
In terms of temperatures, Thursday will be similar to Wednesday with
the warm and humid conditions continuing. High temperatures will
once again be near 90 with heat indices climbing a degree or two
warmer across the area, but again in the low to mid 90s. The
precipitation/storms and cloud cover on Friday will provide some
temperature relief dropping temperatures back into the 80s and the
cold front passage helping to drop temperatures a bit more on
Saturday with locations in northwest Iowa dropping back into the
upper 70s with low to mid 80s elsewhere. There are additional
chances for precipitation late Sunday into early next week, but
details will continue to be ironed out in the coming days.
.AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/
Issued at 632 PM CDT Tue Aug 17 2021
Widespread VFR conditions for much of the forecast period. Only
concern would be some low lying fog early morning Wednesday, but
this will be mostly patchy. Surface winds to remain from the south
to southeast for the period.
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1049 PM CDT Tue Aug 17 2021
.SHORT TERM...(This Evening through Wednesday)
Issued at 342 PM CDT Tue Aug 17 2021
A breezy afternoon across the area with low pressure over the
Rockies and high pressure over the Mississippi Valley resulting in a
decent SPG through the region. Even with temperatures in the mid 80s
to mid 90s, along with the gusty winds, relative humidity values
have remained in check so there have been no fire weather issues.
Winds will fall off overnight, though not light by any means, and
with the southerly low level flow it will be a mild night with lows
in the mid 60s to around 70.
Not much change in the weather for Wednesday. With the
aforementioned surface pressure gradient and soundings indicating
momentum transfer winds of around 15 to 20 kts, it will be another
breezy day. Latest HRRR smoke model continues to indicate smoke
aloft for tomorrow, which could impact temperatures slightly, though
with model 850 mb temperatures of 19 to 25C consecutively from east
to west across the area, we will again see highs in the upper 80s to
.LONG TERM...(Wednesday Night through Tuesday)
Issued at 342 PM CDT Tue Aug 17 2021
Another nearly carbon copy day on Thursday will little change in the
overall pattern. It will be breezy with highs in the upper 80s to
As for Thursday night and Friday, an upper level trough situated
over the western CONUS begins to shift eastward, landing in the
Northern/Central Plains by Friday evening. The GFS continues to be
the most progressive and generally stronger with the system than the
NAM/ECMWF/GEM, though still a bit slower than previous model runs.
The GFS still brings a leading cold front/surface trough into our
far western CWA by 03Z Friday, while other deterministic models have
it farther to the west. Because of this, GFS develops precipitation
quicker on Thursday evening - and the resultant NBM pop grids look
to bring higher pops in too quickly on Thursday night. Models do
indicate a low level jet developing through central SD in the late
evening, and this could aid in thunderstorm development. While there
will be instability in place, effective bulk shear does not look
that impressive over our area during that time period, so think the
severe threat would be on the low end but enough that an SPC
marginal risk is appropriate in our west for that night.
The main surface trough/cold front begins to push eastward across
the area by late Friday afternoon or evening - though again there
are model differences in the timing of this feature, with the GFS
continuing to be the fastest. While thunderstorm activity will be
likely sometime during the day on Friday, it is still difficult to
say how much of a severe potential there is because of the
differences in frontal timing and strength of upper level forcing.
In any event, cannot completely rule out some severe storms on
Friday afternoon as supported by a 15% prob of severe weather per
SPC on Day 4.
By Saturday models show the upper level wave tracking off into the
northern Great Lakes region so we should dry out for that day. With
cold air advection behind the system it will cool down to below
normal levels with highs mainly in the 70s. Another shortwave is
progged to slide into the Northern Plains sometime in the Sunday to
Monday time frame, but models are differing in handling this
feature, so confidence is low in precipitation chances. Overall, it
appears that near normal temperatures will be the rule for the
beginning of the week.
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1048 PM CDT Tue Aug 17 2021
For the most part, will be a repeat of conditions from last
night and earlier today, for tonight and tomorrow. Surface winds
will remain sporadically gusty for KFSD/KHON areas overnight.
Very small chance that could see a few shards of cloud between
1000-2500 ft AGL into KSUX/KFSD 11z-14z as increased moisture
feeds in beneath the inversion aloft. Slight stronger winds with
gusts around 25 kts will develop again by 17z Wed.
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
618 PM CDT Tue Aug 17 2021
.DISCUSSION...(This evening through Tuesday)
Issued at 345 PM CDT Tue Aug 17 2021
Warm and dry conditions through Thursday afternoon,
then chance for shwrs/storms with next cold front Thursday night
into Friday. Brief cool down expected behind the cold front,
before hot temperatures return for second half of the weekend and
into early next week.
Somewhat "busy" upper level pattern noted on aftn WV imagery
consisting of the remnants of Fred over Southeast/Mid-Atlantic,
remnant weak troughing from S Plains into Lower MO Valley,
shortwave ridging from Four Corners NE into central High Plains,
and finally, a strong upper trough digging SE through the Pac NW.
We have some fair wx CU over SE half of CWA, but not expecting
this to bubble up to any shwr/tstm activity owing to broad
subsidence/mid level dry air noted on WV. Can see a slight haze to
the sky this aftn, and true color sat imagery confirms a nearly
stationary swath of smoke stretching from SE Colorado, across
central Nebraska, northeastward into Upper MS Valley. Sfc vsbys
are nearly perfect in the region, however, which suggests this
smoke layer is elevated in nature. Have maintained a haze-free
forecast as HRRR shows main impacts W/NW of the area.
It looks to be mainly a persistence forecast for the next 36-48
hours, with little in the way of upper forcing to support
organized pcpn, or even much cloud cover for that matter. NAM has
backed off on it`s temps for Wed, so now nearly all guidance,
sans the GFS, is in good agreement in temps being similar or only
slightly warmer than yesterday/today for Wed/Thu. Looks like a
decent pressure gradient (by late summer standards) will continue
to provide breezy conditions thru Thu, so overnight lows will be
mild in the upper 60s to near 70F.
Our weather should eventually turn more active later on Thu as
the western trough gradually shifts E and pushes a cold front onto
the Plains. Still have some uncertainty on exact timing on
certain features, with GFS still faster than other model
solutions, but I think the general evolution of Thu eve to Fri
night time frame is becoming more clear. Models are in good
agreement that the primary zone of initial tstm development late
Thu aftn will be W/SW of the area over the higher terrain of CO/WY,
in an area of upslope flow, along and ahead of the cold front.
Some models (namely some NAMNest runs) develop activity further E
in two zones: across NW/W KS along apparent dry line feature
and/or across N KS in zone of enhanced WAA. Have a feeling these
solutions are overdone given modest capping amidst weak
ascent/lapse rates, and fairly dry mid to upper levels. Can`t
completely rule these solutions out, but think our primary tstm
chcs will come during the overnight as tstms attempt to roll
eastward off the High Plains, possibly supported by incr low level
jet. However, it`s uncertain how successfully this activity will
be at holding together owing to decr shear and incr CINH with time
and eastward extent. Also, models are a bit unclear as to where
best low level convergence will be on nose of veering LLJ. Agree
with SPC that if storms can organize, W portions of CWA would have
a non-zero chc for severe (mainly dmg wind) during the late eve
and early overnight, with activity probably weakening further E.
Some NAM/EC runs point towards W/NW/N portions of CWA standing
best chance for a potential MCS Thu night.
Evolution on Fri will likely depend on how activity unfolds Thu
night. Could easily envision a scenario where Thu night convection
is just strong enough to sweep the outflow/effective cold front
thru most of the CWA Thu night/Fri AM, such that the best aftn
instability and chc for redevelopment would be over far E portions
of CWA, or even just to the E. On the other hand, NAM and EC
maintain a slower trough progression that would give at least
central and eastern portions of CWA a chance to destabilize by mid
to late aftn and support new tstm development along the advancing
cold front. IF this were to happen, would think svr chcs (both
hail and wind) would be higher than Thu eve due to stronger shear,
better timing with peak instability, and better upper level
support. Have seen these scenarios play out both ways, so will
just need to watch trends, esp. regarding tstm organization Thu
night and overall system timing.
Still expect cooler conditions behind the front, esp. for Sat,
with highs mainly in the 80s. This cooldown looks to be short-
lived, though, as both EPS and GEFS bring upper 80s and 90s back
to the forecast area for Sun, and perhaps more widespread 90s for
early next week as heights build. Another shortwave is forecast to
track from central Rockies into northern Plains late Sun into Mon
that may try to drag a cold front into Neb., but rising heights
suggest this front will stall or washout somewhere in the area
early next week.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Thursday)
Issued at 617 PM CDT Tue Aug 17 2021
Skies are expected to be clear through the period. Winds from the
south will continue through the night and into the daytime on
Area Forecast Discussion...UPDATED
National Weather Service Gray ME
934 PM EDT Tue Aug 17 2021
High pressure over the Gulf of Maine will continue to slide
southeast tonight. Humidity and chances for showers and some
thunderstorms increase Wednesday with showery and humid weather
expected through the end of the week as the remnants of Tropical
Depression Fred advance northward. Temperatures will generally
run in the upper 70s to low 80s each day.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Update...Minor changes to reflect latest observational trends.
There is a small break in more widespread shower coverage for
the time being...which will give way to more showers moving out
of NY in several hours.
Previous discussion...Showers that have been located over
western New England and Upstate New York today will spread north
and east during the overnight hours. The latest HRRR suggests
that the best chance for showers will be over New Hampshire and
the western mountains of Maine. PWs rapidly increase tonight
across the region topping out at 2 inches by morning in some
areas. The increasing surface dew points and deep layered
moisture may allow for a couple of the showers to be heavy,
mainly along and near the Connecticut River Valley.
The cloud cover and increasing moisture will make for relatively
uniform temperatures during the overnight hours. Lows will
mainly be in the lower to mid 60s.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
A few showers will form on Wednesday ahead of the approaching
remnants of tropical cyclone Fred. CAPE values will be on the
increase as the atmosphere destabilizes during the day. This
will allow for scattered thunderstorms as well, some of which
could contain locally heavy rains.
High temperatures will climb to the mid 70s to lower 80s across
the region with the warmest temperatures across southern New
Hampshire and interior southwest Maine. It will feel rather
muggy however as surface dew point values climb to around 70.
The 12Z model suite suggests the remnants of TC Fred will begin
to cross the region late Wednesday night. There is considerable
uncertainty as to how much rain will fall and the location for
this precipitation. However this will need to be monitored for
the potential of locally heavy rains.
Plentiful low level moisture will allow for patchy fog to
develop overnight. It will be a mild night with lows mainly in
the mid to upper 60s. A few locations across southern New
Hampshire may not fall below 70 degrees.
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Overview: The forecast will begin with a large western Atlantic
ridge in place as Tropical Storm Henri loops around Bermuda. Deep
southwest flow will allow for increased humidity as tropical
moisture begins to move northeastward from the Gulf. The remnants of
what is now Tropical Depression Fred will bring an increased chance
for rainfall to the area late Wednesday night through Thursday
Impacts: The potential exists for locally heavy rainfall on
Thursday as the remnants of Tropical Depression Fred interacts
with a shortwave trough to our north. There remains differences
in model guidance for the placement and magnitude of the
heaviest rain axis but currently southern NH is favored. In
addition, dewpoints will once again climb to near 70F with
overnight lows only into the 60s, which although they will not
be accompanied by temperatures into the 90s it will still feel
Forecast Details: While there remains some differences between the
GEFS and global model spaghetti plots, there is now moderate to high
confidence that the remains of what is now Tropical Depression Fred
will move northeastward through the Ohio River Valley before moving
east across New England by early Friday. This will occur as an upper
level shortwave passes to our north, which will supply Fred
with some additional energy and thus increase our rain chances.
Deep tropical moisture will be advected northward under deep
southwest flow, which will allow PWATS to approach 2.00",
especially across southern portions of the forecast area. Using
the SPC sounding climatology, these would be about 200% of
normal. In terms of QPF, there remains differences between
individual forecast models as well as between their operational
and ensemble means. Today`s forecast runs have trended further
northward with the heaviest rainfall axis but this could once
again shift south in future runs and therefore confidence
remains low. The control runs are generally higher than the
ensemble means with the ECMWF ensembles the most bullish on
rainfall amounts of between 1.00-2.00", especially across
southern NH. The ECMWF is also notably slower than the GFS and
CMC with having the low not pass through the area until later on
Friday. Should these heavier rainfall amounts be realized in a
few hour time period, then some flash flooding would be
possible, especially across urban and hilly areas. The latest
day 2 and day 3 excessive rainfall outlooks released by the
Weather Prediction Center places extreme southwest NH as well as
York County ME into the Marginal risk category.
Rain will end from north to south on Friday with skies gradually
clearing, especially towards the international border. Saturday and
Sunday will be a warm and muggy with high temperatures into the
upper 70s to lower 80s as dewpoints remain near 70F. Skies will be
partly cloudy each day and given the humid airmass that will be in
place a few mostly diurnally driven showers and thunderstorms will
be possible during the afternoon and early evening hours. Upper
level ridging will try to build into the eastern CONUS through the
middle of next week but a few shortwaves will likely ride under the
northern periphery and provide at least some chances for scattered
showers and thunderstorms each afternoon.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Scattered SHRA and lowering cigs may bring periods of MVFR
tonight before a return to mostly VFR Wednesday outside of SHRA
and a few TSRA. Patchy fog late Wednesday night will lead to
localized IFR conditions.
Long Term...VFR conditions expected outside of any SHRA/TSRA.
While more widespread showers and isolated thunderstorms are
expected on Thursday, the remainder of the forecast period will
mostly feature diurnal showers/thunderstorms across interior
Patchy fog may form over the eastern waters tonight. Otherwise,
winds and seas remain below SCA threshold through Wednesday
night as high pressure over the waters slides to the southeast
Long Term...Winds and seas are expected to remain below SCA
criteria through Saturday. Some marine fog/stratus will be
possible as moist warm air moves over the relatively colder
Area Forecast Discussion
National Weather Service Louisville KY
920 PM EDT Tue Aug 17 2021
Issued at 920 PM EDT Mon Aug 17 2021
Convection has dissipated across the forecast area this evening.
Back edge of rain shield from the remnants of Fred continues to
straddle our border with WFO JKL. The back edge is pivoting back to
the west slightly, but should continue to pull more back to the east
over the next several hours as the remnants continue to push off to
the northeast. Will hold on to some isolated/scattered showers over
our far eastern sections through about 18/06-7Z or so and then go
dry after that.
Out to our west, some isolated convection was beginning to fire from
Evansville south to near Hopkinsville. HRRR runs had been hinting
at that, but those solutions keep that activity west of our area and
then dry it up around midnight or so.
For the overnight period, we expect low stratus to redevelop across
the region. The most stratus will be located east of the I-65
corridor with some potential for fog. More widespread fog
development will be possible out west of I-65. Widespread fog
threat is not overly high. However, areas and/or pockets of dense
fog will be possible, similar to last night. Areas that saw
appreciable rainfall this afternoon will likely be the areas that
see the most dense fog. Will go ahead and throw out a Special
Weather Statement for the western half of the CWA to highlight the
.Short Term...(This evening through Wednesday)
Issued at 222 PM EDT Tue Aug 16 2021
Isolated to scattered showers have developed this afternoon across
the region. The bulk of the showers have generally been confined to
locations between the I-65 and I-75 corridors, where weak
convergence has aided in convective development. Up to this point,
there has been very little to no lightning activity with this
precipitation. Visible satellite shows a modest cu field west of the
I-65 corridor where upper level clouds have been a little thinner
today and allowed for surface heating to reach near convective
temperatures. Additional shower and occasional storms may fire off
in these areas this afternoon and early evening.
Once the sun sets, we should see precipitation activity taper down
in coverage. Clouds associated with Tropical Depression Fred will
move off to the northeast overnight, and should allow for a good
period of clearing for a decent portion of the region. With high
moisture content in place near the surface and light to calm winds,
this should be a good setup for fog/stratus to develop around or
shortly after midnight. If we had widespread rains today, would be
concerned about dense fog potential... but think that dense fog
should be limited to concentrated areas and isolated in nature.
Fog and stratus should slowly burn off after sunrise tomorrow, with
it lingering the longest toward the Kentucky Bluegrass where it will
likely be thickest. The morning and early afternoon hours should
start out dry, with PoPs increasing toward the mid and late
afternoon hours ahead of a weak wave moving in from the west-
southwest. There will be a very marginal amount of shear
associated with the wave moving into a modestly unstable
environment, so some organized clusters and/or broken lines of
convection could move into central Kentucky after 21z. SPC has
highlighted portions of central Kentucky in a Day 2 Marginal Risk
for severe weather, which seems appropriate given the
.Long Term...(Wednesday night through Tuesday)
Issued at 200 PM EDT Tue Aug 17 2021
A weak upper level low drifts northeast across Lower MI Wednesday
night into Thursday. Particularly 06-12z Thursday, central KY and
southern IN will be beneath the right entrance region of a very
modest 55 kt 250 mb jet streak. A mid-level shortwave trough draped
south across the mid-MS Valley will be favorably positioned just
upstream, but height falls look quite weak. In addition, a subtle
mid-level ripple in the flow does look to lift ENE from the Memphis
area Wednesday night. HREF members point to the possibility of a
band of convection moving east, just ahead of the TN wave. Stronger
convection looks most likely across Middle TN, but certainly enough
confidence to go high chance/likely hourly PoPs across south-central
KY around and shortly after 00z Thu. Convection will diminish in
coverage and intensity overnight. ML/MUCAPE already looks somewhat
modest by 00z and steadily diminishes overnight. Surging PWATs from
the southwest will support occasionally heavy or even torrential
At least scattered showers are likely to be ongoing at 12z Thursday,
and hi-res models suggest the best chance across southern IN and
northern KY in proximity to a weak sfc trough and the axis of
deepest moisture. Weak plenty of moisture and the weak upper trough
still overhead, diurnal scattered convection will be possible
Thursday. However, the moist profile and cloud cover will likely
limit sfc heating. Wind fields will remain weak, but given the
moisture, some locally heavy rain will be possible. Highs should be
in the upper 70s to lower 80s for most.
Moisture depth diminishes Thur night into Fri as the primary upper
trough axis shifts further east, but the upper low will be trapped
over Ohio with high pressure off to the north and east. Despite the
continued cyclonic flow aloft, precip coverage should be lower Fri
with more isolated activity. There could be a window Fri night into
Sat with a better chance for rain/storms with warm, moist air
advection ahead of a sfc trough. This occurs just before the broad
subtropical ridge across the southern tier of the US strengthens and
expands northward this weekend into early next week. This does look
to bring a stretch of hot, humid conditions with generally more
sparse precip coverage.
.Aviation...(00Z TAF Issuance)
Issued at 723 PM EDT Tue Aug 17 2021
-Fog impacts in areas mainly west of I-65 (KHNB/KBWG)
-Low clouds and some fog possible over at KLEX
Scattered showers continue to move through the region this evening
as we remain on the northwest periphery of the remnants of tropical
cyclone Fred. Expect convection to wind down over the next hour or
two across the area with the main rain shield remaining just east of
the I-75 corridor. Models still have a good fog signal for
KHNB/KBWG. Hit KHNB harder with fog on this package and kept a
similar forecast for KBWG. Some patchy fog is possible at KSDF, but
vsbys should remain around 6SM or above through the period. KLEX
will see a gradual build down in cloud cover overnight with winds
shifting from the east-southeast to the northeast, then to the
northwest as the remnants of Fred pass by. Some patchy fog and low
stratus are likely to affect that terminal late tonight and into
Medium to high on all elements at all sites.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
538 PM PDT Tue Aug 17 2021
.SYNOPSIS...Cooling trend has begun in our region as an upper-
level trough tracks across NorCal. Dry, gusty offshore winds will
result in critical fire weather conditions across the interior
North Bay Mountains and portions of the East Bay Hills from
tonight into Wednesday. Smoky and hazy conditions will also return
to the Bay Area with the arrival of northerly winds through
.DISCUSSION...as of 03:00 PM PDT Tuesday...It`s a cool afternoon
today. Many observation sites are reporting current temperatures
ranging 3 to 14 degrees cooler than 24 hours ago. The upper level
trough is currently over NorCal and it rapidly increased the
marine layer depth this morning to about 2000 ft. Much of the
marine stratus has scattered out along the North Bay coastline but
we have some lingering low level clouds along the SF Peninsula
and around portions of the Monterey Bay area.
Biggest concerns are the elevated fire weather risk tonight into
Wednesday due to gusty offshore winds along with impacts from
higher concentrations of smoke near the surface. The forecast is
still on track as hi-res models continue to show enhanced N to NE
winds moving into the Napa County hills tonight. The enhanced
winds are likely to spread into the interior hills of Sonoma
County and into the East Bay hills. Peak gusts are still within
the range of 30-45 mph with highest peaks potentially reaching up
to 55 mph. Also, relative humidity values will be lower due to the
drying impact of the offshore winds. Thus, the Red Flag Warning
remains in effect from 11 pm tonight through 3 pm Wednesday. NOTE:
enhanced winds may develop in far NE Napa County a little earlier
(around 9 pm). The models do indicate that there could be a
secondary round of N to NE winds Wednesday night into Thursday
morning, but at this time it looks to be weaker than the first
round. However, we will be monitoring that in case the Red Flag
Warning needs to be extended.
Another impact of the N to NE winds is that they will transport
the smoke from NorCal wildfires down into our region. The timing
is the same as the Red Flag Warning....near surface smoke
concentrations will increase in the North Bay tonight and then
spread southward overnight into Wednesday which will impact the
rest of the Bay Area including South Bay and may even reach into
Santa Cruz County. If you notice higher levels of smoke, take
precautions by keeping your windows closed or wearing masks if
outdoors to prevent you from breathing in the particulates.
As we get into Thursday, the trough will linger over the Great
Basin to our east. Our temperatures are expected to be fairly
seasonable for the rest of the week as we get back into our
typical marine influenced summer pattern. In the extended
forecast, the ECMWF and GFS show another trough moving into the
west coast on Saturday with the potential for a third trough early
next week. That means no significant heating events in the long
.AVIATION...as of 05:30 PM PDT Tuesday...For the 00z TAFs. VFR
conditions presently prevail at all terminals, with marine
stratus having now cleared entirely aside from areas near the
shoreline of Monterey Bay. Expect overnight redevelopment to be
more limited than last night, at least from around the San
Francisco Bay Area northward, as drier offshore flow develops.
However, latest HRRR smoke forecast continues to show these N/NE
winds will advect both near surface and total column smoke to the
region. This will result in worsening surface and slant range
visibility tonight in the North Bay and Wednesday across the SF
Bay Area, with some smoke potentially making it down to Monterey
County by Wednesday afternoon.
Breezy onshore winds into this evening, though less so than
yesterday. Gusts of about 20-25 kt along the coast anticipated
before winds diminish overnight. N/NE winds aloft at about 1,500
to 2,000 feet will increase over the interior North and East Bay
later tonight. This may result in some minor LLWS issues.
Vicinity of KSFO...VFR. Some scattered low clouds may return
later tonight, but moderate confidence in forecast of no ceiling
development. Breezy onshore winds through mid-evening with peak
gusts into the 25-30 kt range, but not as windy as yesterday.
Slant range visibility issues by late tonight as smoke drifts in
from various wildfires. Some reduced surface vis may occur
KSFO Bridge Approach...similar to KSFO.
Monterey Bay...Latest satellite images show just one area of
marine stratus still persisting, over the coastal plain and hills
adjoining the central portion of Monterey Bay. Low clouds are
anticipated to return this evening as the marine layer remains in
place. Winds aloft will shift offshore late tonight drifting
wildfire smoke over the area on Wednesday, potentially resulting
in some reduction of slant range visibilities.
.MARINE...as of 02:00 PM PDT Tuesday...Strong north to northwest
winds today with gale force gusts will continue over the northern
and outer waters through Wednesday morning. Winds are forecast to
peak tonight before diminishing on Wednesday. These strong winds
will generate locally steep waves and result in hazardous seas
conditions. Winds will ease across most of the waters on
Wednesday, but locally breezy conditions will persist over the
northern outer waters. Seas remain mixed with a light southerly
swell as a result of tropical cyclone activity to the south along
with a weak northwest swell. Steeper short period northwest waves
also continues at periods of 7 to 9 seconds.
.Tngt...Red Flag Warning...CAZ507-511
SCA...SF Bay until 9 PM
SCA...Mry Bay until 9 PM
SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 9 PM
GLW...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
GLW...Pt Arena to Pt Reyes 0-10 nm until 3 AM
SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
PUBLIC FORECAST: Bingaman
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...Updated Aviation Forecast Discussion...
Issued at 225 PM CDT Tue Aug 17 2021
Quiet weather continues across the area for the next couple of
days, with active weather returning by Friday as a frontal
boundary moves into the area.
Geocolor satellite imagery shows a smoke layer aloft continues to
affect northeast NE, and recent HRRR smoke model output suggests
this may remain status quo tonight but may thin a bit Wednesday.
At least the smoke doesn`t appear to be impacting air quality or
surface visibility at this time.
Wednesday will be similar to today, with mostly sunny skies,
southerly breezy winds, and highs again in the upper 80s to lower
90s. When combined with the humidity, heat index values will again
range in the lower to mid 90s. This temperature trend continues
into Thursday. And a few locations along/south of I80 could make a
run for heat index near 100 Thursday afternoon.
Precip chances may begin increase Thursday afternoon south I80,
but really increase Thursday night ahead of a cold front that
moves into the area Friday. Scattered to numerous storms will be
eventually become possible Friday into Friday evening. SPC placed
a good portion of the area in a 15% probability of severe on their
day 4 outlook this morning, so severe weather potential is
something we`ll be looking at more closely as we get closer.
For Saturday, we`ll probably cool down slightly in the lower to
mid 80s with dry weather. But the heat returns for Sunday with
highs back into the mid 80s to lower 90s. There will also be
spotty storm chances in the extended period, but honestly
confidence is pretty low in the details as models are generally
out of sync on the timing.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 554 PM CDT Tue Aug 17 2021
LLWS threat appears to be focused at KOFK after 06Z tonight.
Otherwise VFR conditions will prevail through the period.
AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
945 PM EDT Tue Aug 17 2021
The remains of Tropical Storm Fred will track slowly north
through the southern Appalachians through early Wednesday.
After this system moves north and away from the area, typical warm
and humid summertime weather will return to the region later in the
week, with a daily risk of scattered storms.
.NEAR TERM /THROUGH TONIGHT/...
As of 945 PM Tuesday...
TD Fred`s center is located over far E central TN, near the NC
border, at this hour, and it will continue to track northward over
the S Appalachians overnight, reaching W WV toward daybreak. The
anticipated relative lull in precip over central NC continues this
evening, with only isolated to scattered disorganized showers in the
last several hours. While this low-pop period should persist for
another hour or two, attention then turns to the line of strong and
potentially tornadic storms E of Fred, over the NC Foothills into W
and central SC. The latest HRRR runs take this line into our W
shortly after midnight and drift it slowly eastward (although
individual convective elements will be moving nearly due N)
overnight, reaching the Triangle region toward sunrise. While
nocturnal stabilization with loss of heating would seem to be in our
favor here, the current RAP-estimated MLCAPE remains 1000-1500 J/kg,
with the better effective deep layer shear and 200+ m2/s2 SRH both
expected to continue to ease slowly from W NC northeastward across
the NW Piedmont overnight. So, we are not yet out of the woods in
terms of both a severe threat (mainly in the NW Piedmont overnight)
and a heavy rain threat (with training cells and still-anomalously-
high PW likely to lead to higher totals). Have made some pop
adjustments to account for this timing and threat heading through
tonight and into early Wed morning. Still expect lows mostly in the
low to mid 70s. -GIH
Earlier discussion from 325 PM: Fred has weakened to a tropical
depression, with its circulation center approaching the southern NC
mtns. The weakening remnants of Fred will continue to track north-
northeast through the NC mtns during the late afternoon and evening
hours. With the 2.0-2.3" tropical moisture centered over central NC,
intermittent shower activity will continue through tonight, with
some daytime enhancement of some thunderstorms through the
In the wake of the broken convective band that`s currently moving
north through the northern Piedmont and northern coastal plain
counties, latest radar trends suggest central NC will experience a
late afternoon/early evening lull. Rain chances are then expected to
increase after midnight as the primary rain tropical rain
band(currently over central SC and eastern Ga moves through the
area. Additional rainfall amounts through daybreak are expected to
range from a half inch across the NW Piedmont to around a tenth of
an inch across the NE coastal plain.
Despite the recent increase in rain that central NC has seen over
the past several days, rainfall amounts have been hit and miss.
Antecedent hydrological conditions are still rather dry, with 1 to 3
hr FFG still in the 2.5-3.5" range. Thus, do not think a Flash Flood
watch is warranted, with only isolated instances of minor flooding
possible, mainly in poor drainage and/or urban areas.
Additionally, close proximity to Fred`s stronger low-level wind
field will provide some favorable low-level kinematics to support
some rotation within any strong updrafts that develop, mainly during
peak heating and across western NC.
Lows tonight in the 70s.
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 325 PM Tuesday...
The remnants of Fred will race newd away from the area, moving
through the central Appalachians through the afternoon, and reaching
the NE US by the evening. The tropical moisture plume of 2-2.25"
will shift eastward over eastern NC by late morning/early afternoon,
with slightly drier filtering into western piedmont counties.
Scattered showers and thunderstorms will continuously re-develop
within this axis of anomalously high PWATs, with diurnal
destabilization allowing for some isolated/widely scattered re-
development back over the western Piedmont. Could still see some
locally heavy rain that could result in some minor flooding.
Otherwise, weak shear and lapse rates should preclude a severe
threat. Highs ranging from mid 80s west to upper 80s east.
Cannot rule out some isolated showers Wednesday evening, but
otherwise it should be mostly dry Wednesday night with areas of fog
possible. Lows 70 to 75. -CBL
A negatively-tilted mid-level trough will approach the region on
Thursday, resulting in decent height falls and forcing for
precipitation. Thus, have high chance POPs on Thursday. A
subtropical ridge will also extend across the western Atlantic on
Thursday, which will pump warm and very humid air into our region,
with highs in the upper-80s to lower-90s and dew points in the mid-
to-upper-70s. This could bring heat indices up to 105F in portions
of the eastern Piedmont, Sandhills, and southern Coastal Plain, and
a Heat Advisory may be needed for this area on Thursday. -JD
.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 945 PM Tuesday...
Fri/Fri night: A surface frontal zone to our NW, on the SE side of
the baggy closed low over OH/WV/PA, will slowly drift southeastward
into central NC. This weak low level mass convergence plus incoming
DPVA aloft, increasing upper divergence in the LFQ of a 60+ kt
northwesterly jetlet over the Ohio Valley, and 2-2.25" PWs streaming
over much of our area (esp E) all support high pops, peaking in the
afternoon/evening. Thicknesses will still be a bit above normal but
temps should be modulated by considerable cloudiness. Highs around
90 to the lower 90s. The combination of incoming surface high
pressure drifting over WV, the surface circulation around Henri as
it moves northward well off the NC coast, and SE-moving convection
outflow Fri evening and night should help push the surface front to
our E and S sections overnight. Lows 70-76 with decreasing pops and
partial clearing W late.
Sat through Sun night: The surface front should hold over our SE CWA
Sat, prompting better convection coverage there in the afternoon in
contrast to the slightly drier NW sections. Then, as so often
happens with summertime fronts over NC, the front should quickly
lift north and effectively wash out by Sunday, as mid level ridging
builds anew from TX/OK across the lower Miss Valley and Mid South to
the interior Southeast states. But Henri may still affect our
weather as it is expected to drift N or NNW over the NW Atlantic
toward the New England coast over the weekend: Depending on its
exact location and the degree to which it merges with the mid level
low, there is a chance that the surface front could hold up across
our far NE, if the Henri circulation prompts frontogenesis in that
area. Will retain mostly diurnally-favored pops Sun, highest in our
E half (SE and along the front in the NE), where low level moisture
should be most abundant. Expect highs both days close to normal, in
the upper 80s to around 90, with lows in the upper 60s/lower 70s.
Mon through Tue: Tough forecast as NC will be the battleground
between the Southern Plains / Lower Miss Valley mid level ridge and
the baggy trough / shear axis extending along the East Coast, with
any surface features very weak. The ECMWF keeps pops high, esp E
(assuming warmer mid levels and lower CAPE further W). The latest
few GFS runs are drier but have trended toward less ridging
extending into the Carolinas and a greater number of ridge-riding
MCSs or MCVs tracking from the Midwest and Ohio Valley through VA
and NE NC. Without a clear signal favoring one way or the other,
will stay the course with temps near to slightly above normal, esp
W, and pops close to climatology, chances of mainly afternoon
storms, higher SE. -GIH
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 815 PM Tuesday...
The remnants of TS Fred will continue to move north through the NC
mountains tonight and early Wednesday. While there is a lull in
showers across central NC this evening, a line of showers and
isolated storms in upstate SC will move gradually north-northeast
overnight, impacting GSO/INT between roughly 04-08Z, with scattered
showers possible further east toward RDU/RWI/FAY overnight. Very
heavy rain and low vsbys will occur within the showers and storms.
The line of showers will continue to move east during the morning
hours and may increase again during the day on Wednesday. Ceilings
will lower to MVFR/IFR overnight and only gradually lift to VFR
through Wednesday afternoon as winds shift from SErly tonight to
SSWrly on Wednesday.
Outlook: Afternoon showers and storms will return Thursday and
continue each day through the weekend. Sub-VFR conditions from
fog/low stratus will be possible each morning.
Area Forecast Discussion
National Weather Service San Diego CA
847 PM PDT Tue Aug 17 2021
A low pressure system moving into the West will bring stronger
onshore flow with gusty westerly winds in the mountains and deserts.
The marine layer will deepen and should produce some drizzle or a
few light showers for the coast, valleys, and foothills, mainly late
nights and mornings into Thursday. Clearing may be difficult in many
areas west of the mountains on Wednesday. High pressure to the east
will bring warmer weather and less extensive coastal clouds next
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING
ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN
Low clouds had already blanketed much of the immediate coast by
sunset and are now surging inland. Skies were clear inland except
for some smoke aloft. The onshore sfc pressure gradients have turned
sharply onshore, reaching 11 MBS from San Diego to SW NV early this
evening. West wind gusts peaked at 50 MPH through the San Gorgonio
Pass and remain around 30 MPH with gusts to 45 MPH. These gusty
winds will continue through tomorrow night, building the marine
layer clouds onto the lower coastal slopes and into the passes.
The forecast has been updated this evening to remove the isolated
thunderstorm threat and to modify POPS/QPF through 36 hours to more
closely mirror the 00Z HRRR guidance. With the aid of upslope, HRRR
forecast QPF now exceeds 1/3 to 1/2 inch on favored coastal slope
locations of the Santa Ana and San Bernardino Mts through Thursday
morning. Some coastal areas have between 1 and 2 tenths of an inch
From previous discussion...
A low pressure trough is amplifying across the West today and
Wednesday. This is rather unseasonal for this time of year and will
extend our deepening marine layer while shoving monsoonal moisture
to the east. A coastal eddy will also develop to contribute to all
this deepening. This is expected to thicken the clouds as well as
extend them into most if not all of the valleys overnight. Areas of
drizzle or a few light showers are expected late tonight into
Wednesday and again Wednesday night into Thursday, most likely in
the foothills or near the coast. Temperatures near normal today will
dip below normal Wednesday through about Saturday. For folks in the
inland valleys, waking up to low clouds overhead and high
temperatures in the 80s will be quite a change from what most of our
summer has featured. The trough moving through the West will also
boost onshore westerly winds through mountain passes and desert
slopes the next few afternoons and evenings, with gusts exceeding 40
mph in the favored passes. The trough departs Friday, but another
trough fills the void by Saturday across the West. This one is
weaker, so the onshore breezes, marine layer cloudiness and
temperatures will not respond as profoundly as with the bigger
trough. Next week, ensembles show some rebuilding of a high pressure
ridge over the West, but with differing strengths. Some solutions
also show the monsoon door opening a crack sometime next week, for
now beyond our forecast window. There will be a warming trend, which
could return temperatures back to near normal Monday or Tuesday,
while restricting coastal clouds nearer to the coast.
180345Z...Coast/Valleys...BKN-OVC stratus with bases 1000-1500 ft
MSL and tops to 4000 ft MSL will spread rapidly inland through the
valleys by 07Z with areas of higher terrain obscured. SCT -SHRA will
will occur mainly 09Z-19Z Wed especially over higher terrain, with
local vis 2-4 miles in -SHRA/BR. Clearing will be slow and partial
Wed with BKN-OVC clouds becoming SCT-BKN 18Z-21Z Wed and bases
rising to 1500-2000 ft MSL with tops locally to 5000 ft MSL. BKN-OVC
stratus is likely again Wed night with more SCT -SHRA.
Mountains/Deserts...Areas of west/southwest winds 15-25 KT gusts 30-
45 KT will occur from the mountain crests east/north through the
desert slopes and into the deserts with strong up/downdrafts through
Wed evening, with strongest winds Wed afternoon/evening. Areas of
terrain obscurations will occur on the coastal slopes below 4000 ft
MSL tonight and below 5000 ft MSL Wed/Wed evening due to clouds and -
No hazardous marine conditions are expected through Sunday.
A south-southwest swell of 3 ft/17-19 sec from 200 degrees will
build Wednesday evening, peak Thursday and Friday, then slowly lower
this weekend. This will generate surf of 4-6 ft with sets near 7
feet along south-facing beaches of Orange County Thu and Fri.
Strong rip currents and dangerous swimming conditions are expected.
Above average high tides peaking near 6.5 feet will also occur,
which may lead to coastal beach erosion and minor flooding. Please
see the Beach Hazards Statement for the latest details.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
CA...Beach Hazards Statement from Wednesday evening through Friday
evening for Orange County Coastal Areas.
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
857 PM MDT Tue Aug 17 2021
Issued at 853 PM MDT Tue Aug 17 2021
Thunderstorms that were located over parts of far western South
Dakota have now ended.
UPDATE Issued at 453 PM MDT Tue Aug 17 2021
Isolated high based thunderstorms have developed along a N-S
surface trough currently located near the SD/WY border. Expect
little or no rainfall from these storms so may see a couple of
wildfires develop due to the lightning.
.DISCUSSION...(This Evening Through Tuesday)
Issued at 217 PM MDT Tue Aug 17 2021
Upper air analysis shows upper ridging over the northern plains and
an upper trough digging into the western CONUS. As the trough slides
eastward, an associated surface low approaches western SD, expected
to pass through later Wednesday. Ahead of the low, a tighter
pressure gradient will bring in breezy conditions today. Coupled
with temps reaching into the 100s today and RH values nearing 10
percent, a red flag warning is in effect for northeastern WY and
western SD. Smoke aloft and near surface continues to restrict
visibility throughout the forecast area. Have kept mention of smoke
in through Wednesday based off the HRRR model.
As we progress towards mid-week, ridge slides eastward and upper
trough shifts over the rockies. Timing of frontal passage Wednesday
will be key in high temperatures, as models still differ a bit on
timing, but expect passage during heating hours. Ensembles still
have a 12 degree spread based off differing timing. Following
frontal passage, winds will shift out of the north and the region
cools down. Highs for Thursday are only expected to get up to the
mid 60s for northeastern WY and the black hills, with warmer temps
in the 80s closer to central SD. CAMs all agree on potentially
widespread showers/storms late wednesday into Thursday following the
front. With increased buoyancy and moderate shear in the region, SPC
has us in a marginal risk severe. High PWATs also point to at least
some areas seeing some locally heavy rainfall.
A more active pattern is expected approaching the weekend, as the
upper trough slowly slides eastward into the midwest. Models show
the upper low moving through the northern plains around
Friday/Saturday, bringing more potential for precipitation.
.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 522 PM MDT Tue Aug 17 2021
Areas of MVFR visibility due to smoke will continue tonight with
some improvement during the day on Wednesday. Isolated
thunderstorms, with locally gusty winds, are possible over parts
of northeastern Wyoming and far western South Dakota through 03Z
Issued at 853 PM MDT Tue Aug 17 2021
A cold front will slide into northeastern Wyoming tonight and western
South Dakota Wednesday. Elevated fire weather conditions are
expected in the warmer air ahead of the front on Wednesday
Area Forecast Discussion
National Weather Service Las Vegas NV
832 PM PDT Tue Aug 17 2021
.SYNOPSIS...Low pressure dropping into the Great Basin will bring a
cooling trend to the region while also limiting monsoonal
thunderstorm activity to eastern Lincoln, Clark and Mohave
counties through Thursday. Breezy conditions can be expected as
well. Temperatures will remain slightly below average through the
weekend with generally dry weather.
.UPDATE...Thunderstorms have been very isolated and relegated
to Lincoln County and northern Mohave County. Am tracking an outflow
boundary moving west across Coconino and just starting to enter
Mohave County over the Grand Canyon/Kanab Creek region. Question is
just how far west this may go to support convection the rest of this
evening. camPops suggest the threat for isolated thunderstorms will
remain across parts of Lincoln, as well as parts of Mohave County
Trough dropping south into the Great Basin will continue to support
gusty south-southwest winds the rest of tonight through Wednesday.
The Lake Wind Advisory remains in effect through tomorrow evening.
Another issue tonight will be the continued smoke/haze and lower
visibilities across parts of Inyo, Esmeralda and Nye Counties. A
storm spotter in Goldfield reported the visibility down to about a
half mile. Populated grids using the 00Z HRRR Smoke with NBM showing
area of lower visibility in the previously mentioned counties.
Sent out an update for the rest of tonight.
.SHORT TERM...through Thursday night.
Main focus of the short term period will be around thunderstorm
chances and gusty winds as a large trough develops into the Great
Basin. Ahead of this trough, rich monsoonal moisture continues to
stream north, up the Colorado River Valley and into mainly eastern
Lincoln county en route to the eastern Great Basin. Its mainly
along and east of this axis where thunderstorm chances will be
confined. This afternoons RAP analysis suggests 1000-2000 j/kg of
mixed layer CAPE is present across northern and eastern Lincoln
county along with 20-25 knots of deep layer westerly shear. While
not expecting widespread thunderstorms as the the stronger forcing
will be further north into Utah, a few isolated storms forming in
this environment through the evening may pose a risk for strong
downdraft winds and isolated hail to nearly a quarter size. The
Storm Prediction Center has highlighted the northern Panhandle of
Lincoln County in a Slight risk of severe storms through the
The aforementioned trough will dig southward Wednesday, reaching
into the Great Basin by the afternoon. Mid level temps will be
cooling through the day, though moisture will remain limited to
our eastern zones. Expecting a similar overall outcome with
thunderstorm activity on Wednesday, though overall forcing will be
a little stronger while instability will trend weaker. The trough
will push east into Utah on Thursday, with thunderstorm chances
shifting to our far eastern border before drying out completely
for the remainder of the week.
Outside of storm chances, areas of smoke have been prevalent
across the region as the flow aloft shifts more westerly and blows
California wildfire smoke our direction. This will continue to
occur for the next several days as the trough to our north
dominates our local wind flow patterns. Greatest reductions in
air quality and visibility will be across Inyo, Esmeralda, and
central Nye counties, with more of a pesky haze elsewhere.
Breezy south winds have also been noted as pressure gradients
increase in response to the incoming Great Basin trough. These
winds will stick around overnight and into Wednesday before easing
on Thursday. Winds have been strongest on the Nevada National
Security site in Nye county where gusts over 40 mph have been
reported, though most areas have seen gusts in the 25-30 mph
range. Gusty winds have also been ongoing across Lake Mead and
Mohave, and the Lake Wind Advisory through tomorrow still looks
On the plus side, the deep trough will result in a cooling of
regional temperatures, with afternoon highs falling a few degrees
below normal Wednesday and Thursday.
.LONG TERM...Friday through next Tuesday.
As the Great Basin trough lifts eastward Friday, another trough is
likely to drop south in its wake for the weekend, keeping the West
in a somewhat cool and breezy pattern. This will keep monsoonal
moisture at bay and also maintain fairly moderate temperatures by
August standards. Temperatures will gradually rebound closer to
normal next week as low amplitude high pressure begins to rebuild
across the Southwestern US.
.AVIATION...For McCarran...Breezy south to southwest winds will
continue through the early evening. Expecting a stronger period of
winds 23Z-04Z this evening, with gusts over 25KT likely and gusts
over 30KT possible. For tonight, moderate confidence gusts will
decrease to 20-25KT after 06Z but continue through the night. There
is a low chance that gusts end at 06Z. Either way, elevated south
winds at 10-15KT will continue through the night. Winds may vary 150-
180 degrees 09Z-14Z before increasing again out of the south-
southwest late Wednesday morning. Gusts to around 25KT are likely
through Wednesday afternoon. Other than winds, no impactful clouds
are expected with dry conditions persisting through the period.
For the rest of southern Nevada, northwest Arizona and southeast
California...Isolated thunderstorms are possible across south-
central Nevada and western Arizona this afternoon and evening. Best
chances will be through Lincoln County into southwest Utah.
Otherwise, Gusty south to southwest winds will continue across the
region through the evening before diminishing early tonight.
Winds will increase again late Wednesday morning and afternoon,
with the strongest winds on Wednesday likely up the Colorado River
Valley. Smoke will spread south through the southern Great Basin
tonight and Wednesday morning, with visibilities around 5-6SM
possible at BIH after 09Z tonight through 15Z.
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
For more forecast information...see us on our webpage:
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