Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/25/21
Area Forecast Discussion
National Weather Service Charleston SC
1018 PM EDT Tue Aug 24 2021
A broad area of low pressure will develop over the near shore
waters off the Georgia and South Carolina coast today. This low
will drift west across the region tonight into Wednesday
morning. Atlantic high pressure will build towards the region
late this week, then prevail into next week.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Evening composite analysis reveals a deep moisture plume with
PWAT values in excess of 2 inches extending across Florida to
just offshore from the SE states. Low level trough axis also
appears to reside along the SC coast and down into SE Georgia
per GOES derived motion winds. Some convection continues just
off the coast, some of which is spreading northward along the
SE Georgia and parts of the SC coastal waters, apparently along
a northward propagating gravity wave/impulse emanating from
earlier convection in northern Florida. Further east, upper
level circulation is noted east of the Bahamas on water vapor
imagery and 1.5 PV streamline analysis and making westward
Still quite a bit of uncertainty over the forecast through
Wednesday morning. Aforementioned upper level circulation will
continue to shift westward toward the SE coast helping to drive
deep moisture axis back inland and tighten the low level
trough/convergence axis along the coast. Most CAM guidance
solutions continue to develop showers and storms to varying
degrees within the coastal waters. However, guidance has
trended much less bullish with pushing convection inland toward
morning and certainly less bullish with a heavy rain threat
along the coast. In fact, it`s possible that convection remains
largely offshore through Wednesday morning as suggested by the
the latest HRRR runs and 00Z NAMNEST.
Will see. Again, quite a bit of forecast uncertainty to be had.
But at this juncture I`m not inclined to trim pops/QPF
forecasts too dramatically, but will trim them back some.
Convection is quickly fading early this evening with just a few
showers/storms in the western portions of the CWA at this
juncture. Have tweaked/refined pops accordingly for the next
several hours. A fair amount of convection ongoing in the
Atlantic, especially off the Georgia and Florida coasts,
associated with an larger scale upper level cyclonic circulation
SE of Miami...noted on the 1.5 PV streamline analysis. This
feature is still expected to migrate westward toward the SE
coastline overnight pushing showers/storms back into the region
Radar returns from KCLX show scattered showers and
thunderstorms throughout the forecast area. These will continue
into the evening but dissipate after nightfall.
A fairly complicated forecast is in store for the overnight. At
the surface MSAS is analyzing a trough along the SC and GA
coast. Aloft, mid- level water vapor imagery shows a TUTT east
of Florida in addition to an inverted trough just off the SC and
GA coast. Through much of the day showers and thunderstorms
have been plentiful well offshore in association with this
inverted trough. As the TUTT continues its west northwestward
progression towards Florida, the inverted trough will be pushed
westward and towards the forecast area. Nearly all guidance has
been consistent in showing numerous showers and thunderstorms
forming in the offshore waters late evening, before moving
inland late tonight into the early morning hours.
There is the potential for heavy rain, especially over the
Charleston Tri-County. While 12Z guidance has come down a tad
in QPF in comparison to earlier runs, the consistency between
different models and model runs is cause for concern. Soil
saturation is over 90% in most of the Charleston Tri-County
area, leading to a higher than average risk of minor flooding
with any heavy rainfall. PWATs are forecast to be just over 2
inches in addition to CAPE values around 1000 to 1500 J/kg.
Numerous to widespread showers and thunderstorms should develop.
The potential for heavy rainfall and minor flooding is outlined
in the HWO.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Wednesday: The mid-levels in the morning will consist of weak
ridging over our area, while areas of high pressure prevail far to
our east and west. Additionally, a low will be over the Bahamas. The
low is forecasted to move over FL into the night, causing the ridge
to weaken a bit. At the surface in the morning, a trough will be to
our west with high pressure in the Atlantic. The trough will be
pushed further to the west with time as the high approaches from the
east. Abundant moisture will be in place across our area, with a
band of PWATs peaking in the 2-2.25" range. This is around the 90%
mark for CHS sounding climatology per the SPC. Though, the NAEFS
seems less impressed, barely having us in the 1-2 standard deviation
range for part of the day. Either way, there will be moisture in
place. Both the synoptic models and the HREF indicate
showers/thunderstorms will be ongoing at the start of the day,
especially along the coast. The expectation is for them to gradually
move inland into the afternoon, which much of the focus being far
inland. While there is the potential for locally heavy rainfall the
could prompt flood advisories, the models seem to vary quite a bit
on the QPF amounts, the placement of the highest amounts, and the
timing. For this reason, we kept the POPs and QPF broad, with the
details getting ironed out with the overnight forecast. The overall
severe risk is low due to the moisture limiting the DCAPEs. The
convection will move out of our area in the evening, while
dissipating. Overnight should be mainly dry. Temperatures will be
Thursday and Friday: Mid-level ridging overhead on Thursday will
give way to high pressure building in from the Atlantic on Friday.
The surface pattern will reflect this somewhat with troughing to our
west, getting pushed away as high pressure move in from the
Atlantic. Moisture doesn`t look quite as impressive as previous
days. But the models still vary quite a bit on the precipitation
potential each afternoon/evening. Given numerous variables regarding
this along with the timing/location, the best approach with this
package was to run with the forecast blends for now, and let the
details get ironed out more with future forecasts. Temperatures may
actually be slightly above normal, assuming rainfall isn`t too
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
A ridge will be over the Southeast U.S. this weekend, then gradually
weaken next week. The WPC surface forecast has high pressure to our
north most of the time, with periods of troughing inland. The
forecast reflects the NBM, which is chance POPs at times/locations
each afternoon for our area with temperatures perhaps rising a few
degrees above normal.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Showers and storms have fizzled out across the region this
evening with no threat for convection at any of the terminal
sites over the next several hours. Thus overall VFR conditions
are anticipated through much of the night.
Heading into Wednesday morning, showers and storms are expected
to develop over the coastal waters and push inland after 08Z or
so. CHS/JZI may have the biggest impact during the morning push,
with showers/storms potentially producing MVFR conditions, and a
risk for IFR conditions as the heaviest precip moves through.
SAV will also see some precip, although the heaviest and higher
impact precip is looking to occur along the South Carolina
Precip continues to move inland through the morning with VFR
weather returning late morning and through the afternoon.
Extended Aviation Outlook: Flight restrictions are possible with
scattered showers and thunderstorms mainly in the
Broad low pressure will push onshore tonight, bringing southwest
winds 10 to 15 knots. Seas are forecast to range between 2-4
ft. Numerous to widespread showers and thunderstorms are
forecast to develop over the marine zones tonight. Some of these
storms may produce strong wind gusts and frequent cloud to
Extended Marine: Atlantic high pressure will build towards the
region late this week, likely moving inland this weekend. On
Thursday, seas are forecasted to build due to an incoming SE swell.
Seas are expected to peak in the 5-6 ft range across the GA waters
beyond 20 nm Thursday night into early Friday, so a Small Craft
Advisory may be needed for this zone. Seas gradually subside Friday
into the weekend.
Area Forecast Discussion
National Weather Service Des Moines IA
706 PM CDT Tue Aug 24 2021
.DISCUSSION.../Tonight through Tuesday/
Issued at 307 PM CDT Tue Aug 24 2021
-Hot and humid through the end of the work week.
-Continued convection through tonight into Wednesday.
-Additional storms possible Thursday into Saturday.
Rest of today into Wednesday...convection continues to develop
over west-central to north-central part of the CWA within the
Severe Thunderstorm Watch. Outflow boundary from severe convection
in northern Iowa may also help trigger further development in
very unstable airmass across central Iowa. There remains a bit of
a cap in place but with LCL heights around 1500m, may likely be
dealing with elevated convection through the afternoon. Especially
with the mid-level lapse rates of 7.5-8 C/km and good instability
(DCAPE values in the 1000-1500 J/kg range), the potential remains
for hail and damaging winds between the Highway 20 to Interstate
80 corridors. Deep layer shear remains great for thunderstorms to
persist but the low level shear is very weak and with the high
LCLs, low confidence with any tornado threat. The majority of the
CAMs are not handling current convection and thus not trustworthy
going into the future through Wednesday. Confident however
convection should continue within the watch area, especially
within the vicinity of the outflow boundary. With the LLJ
increasing later tonight into Wednesday morning along with the
strong moisture transport, confident in the overnight convection
to develop just uncertainty remains in the location. More than
likely along and south of the Highway 30 corridor to the MO
border. Certainly potential for heavy rain, wind, and hail
overnight into Wednesday morning. The HRRR keeps convection going
through a good portion of the day but look sub-severe.
Thursday through Tuesday...large upper level ridge builds into the
southeast portion of the CONUS later this week. Boundary looks to
drape across southern Minnesota into South Dakota Thursday into
Friday and might sag south enough for convection to impact
northern Iowa during this time. The ECMWF is further south with
the surface low developing out of the Central Rockies while the
GFS keeps any convection to the north. The WAA remains decent on
Thursday into Friday and thus much of the area should remain in
the 90s and even into Saturday before a decent cold front moves
through Saturday night into Sunday. Temperatures look to be a bit
more tolerable by early next week.
.AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/
Issued at 705 PM CDT Tue Aug 24 2021
TAFs are VFR through the period with non-convective visibility or
ceiling degradations not anticipated. Confidence in convective
trends is low however so have a generic period of VFR VCTS
overnight as at least weak convection is expected to advance into
IA from NE overnight. MVFR or less periods are certainly possible
near storms, but confidence on timing and location is too low to
include. Winds should be fairly light outside of any storms.
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
424 PM PDT Tue Aug 24 2021
.SYNOPSIS...Seasonable temperatures will occur across the interior
through mid week, while coastal areas experience nightly stratus
development followed by afternoon clearing. Thereafter, a warming
trend is forecast to occur across the region with the approach of
.DISCUSSION...The weak upper-level trough remains temperatures
generally seasonable across the interior with highs in the mid 80s
to low 90s through Wednesday. Stratus blanketed the coastal waters
and adjacent land areas this morning. Areas of stratus along the
Redwood coast will gradually clearing into the evening, but is
expected to redevelop during the evening. Otherwise, the low
level inversion will be fairly week to aid a partial clearing
by late afternoon on Wednesday.
Smoke from the active wildfires in the Trinity and Siskiyou
counties continues to be pushed toward northeast with the
southwesterly breezes aloft to bring some improvement in the air
quality for areas in and around Trinity, Mendocino and Lake
counties. HRRR model indicates smoke will spread south to
southeast as the winds shift to the north-northeast across the
interior into the weekend.
A series of weak upper- level troughs are forecast to move east
across the PACNW during the remainder of the work week into the
weekend. Upper troughing will initially aid in seasonable high
temperatures across the interior. However, a slightly more
vigorous upper disturbance ejecting east on Saturday is forecast
to initiate an offshore component in low- level flow over NWRN CA.
Temperatures will subsequently moderate across interior valleys,
with highs ranging from the mid 90s to low 100s. Low pressure
developing offshore will also aid in clearing marine stratus away
from the coast this weekend into early next week, which may yield
mild temperatures at sea level. Otherwise, the probability of
precipitation is forecast to be zero during the next seven days,
with the exception of localized drizzle development occurring
along the windward facing slopes of the King Range.
.AVIATION...Eddies along the North Coast earlier in the day kept
coastal locations socked in with stratus and some visibility
reductions in haze and fog. The stratus field has cleared over land
except along the Mendocino County coastal plain, but a narrow band
of stratus lingers along the North Coast. The W edge of this stratus
is steadily eroding as the E edge continues to pile up along the
immediate coast. Expecting these clouds to mostly dissipate later
this afternoon, but this will still be several hours later than on
Monday. Clouds are more expansive offshore S of Cape Mendocino, but
there may be some breaks along the coast before stratus expands
again later this evening. The marine layer bottomed out just below
2000 feet at the McKinleyville and Bodega Bay profilers late last
night, but it has deepened a bit through the day today.
Low clouds advected up the Russian River Valley again this morning.
The latest HRRR guidance is not as bullish with moisture advection
toward KUKI on Wednesday morning, so have just put a low scattered
deck in the latest TAF package. Winds will be generally light. /SEC
.MARINE...Northerly winds will continue through the period. There
will be enough of a lull in the winds across the N waters to
allow for the Small Craft Advisory to end there Wednesday morning.
Have also let the Small Craft Advisory for the N inner waters
expire. Winds are forecast to increase once again later in the work
week, with gale force gusts likely by Friday morning, and watches
may need to go up tonight or tomorrow. /SEC
.FIRE WEATHER...The weak upper-level trough over the region remains
temperatures generally seasonable through Wednesday. Winds will
continue to be light and terrain driven. Otherwise, a brief period
of increasing wind is expected today and Wednesday by late afternoon
with westerly to northwesterly breezes. More wind prone areas could
sees gusts up to 25 mph. Warming and drying trend is expected on
Thursday into the weekend as the high pressure build in, with high
temperatures across the interior valleys peaking in the 90s to low
100s on Saturday. The afternoon RH values will likely be in the
teens across Trinity, Lake and eastern Mendocino counties. Humidity
recoveries will gradually diminish through the weekend, with locally
poor recoveries by Sunday.
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 6 AM PDT Wednesday for PZZ470.
Small Craft Advisory until noon PDT Friday for PZZ475.
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AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1049 PM CDT Tue Aug 24 2021
.SHORT TERM...(This Evening through Wednesday)
Issued at 253 PM CDT Tue Aug 24 2021
Complicated and low confidence set up across the region for the
rest of today through tonight, with CAM guidance continuing to
struggle as well. Earlier elevated convection across southwestern
MN and northwestern IA has left a boundary across portions of
northwestern IA (noted by a subtle wind shift from KSUX to KFOD).
Earlier convection and cloud debris has limited the diurnal
heating thus far, with 1 pm temperatures in the 70s for areas
which experienced convection. To the south, water vapor imagery
and RAP analysis show a wave ejecting to the northeast across NE,
with some convection developing ahead of the main wave (impacting
Woodbury/Ida/Monona/Crawford/Sac counties in northwestern IA and
trailing to the southwest). Finally, shifting our focus to the
north and west, a cold front associated with a wave along the
International Border remains in place across the central/east
central portions of SD, evident by the calm winds and subsequent
shifts to the west/northwest after the fropa. Temperatures across
our area that have not been impacted by either a boundary or
previous convection have warmed into the 80s to near 90, with dew
points in the 60s to mid 70s.
Despite all the uncertainty and questions regarding when/where
convection may from this evening, guidance from this morning and
early afternoon does support severe weather potential if storms are
able to develop. Latest (24.17z) HRRR runs show quite a bit of
instability and a fairly robust, but are not sampling the current
environment well. Temperatures are cooler than models suggest, with
higher dew points (which would increase the cap). Satellite/radar at
19z shows some agitated clouds and showers across northern NE
struggling at this time and decreases confidence in something
breaking the cap in our area. Do think that if something were to
develop later today, it would likely be in our far south (near
Highway 20 or further south) in the area of the boundary from today
and as the wave passes over providing additional forcing. Main
threats with any severe storm would be gusty winds to 70 MPH, hail
to half dollar size and locally heavy rain. DCAPE values from the
earlier samples are around 1500 J/kg, with MUCAPE values over 2000
J/kg and 0-6 bulk shear over 30 knots. Given fairly high LCL
heights, tornado threat seems fairly low - although can`t be
discounted given boundaries.
Wednesday may provide a very short break in the active weather
pattern, although confidence in this is fairly low. Model guidance
shows weak surface high pressure to the north of our area, and more
northerly flow behind this evening/tonight`s frontal passage.
Temperatures look cooler than today, closer to normal. WAA slides
into the area ahead of the next trough, which could form some early
morning or afternoon elevated showers or convection. CAMs hint at
this potential, but show a wide variety of solutions. Have just
slightly adjusted pops from previous forecast, given uncertainty.
.LONG TERM...(Wednesday Night through Tuesday)
Issued at 253 PM CDT Tue Aug 24 2021
Bottom Line Up Front: active pattern remains in place through
much of the extended, with the general quasi-zonal flow across the
Northern Plains, and high pressure to the south and east. A
series of waves ejecting from the Rockies traverse through the
main pattern, with models progging the deeper wave to move through
for the weekend (although guidance varies on this feature`s
timing). Guidance also hints at weak upper ridging returning to
the region for the early part of next week.
Wednesday night: WAA begins to build into the area ahead of the next
wave, which will likely enter our CWA on Thursday (with minor
timing/location differences in today`s guidance). Model guidance
doesn`t show quite as much instability across the area for later in
the day Wednesday but shear does not appear to be lacking with this
wave. Would likely see elevated convection again, with some storms
possibly strong to severe.
Late Week: Models do show a slight bit of uncertainty in Thursday
night`s wave but do seem to agree on strong WAA over the region with
strengthening south/southwesterly flow. Initial flow looks to be
perpendicular to the boundary, shifting to parallel as the boundary
as it moves across (thus isolated storms initially with the
potential to grow upscale). Could see some heavy rainfall as well,
as moisture return and low level jet increase. Will need to keep an
eye with any potential flooding concerns, particularly for areas
which have experienced convection today.
Weekend/Early Next Week: Guidance shows a deeper trough moving
through over the weekend, which will likely bring additional
shower/storm chances for late Saturday into Sunday. Given this is
still a few days out, models differ in the solutions at this time.
Behind the trough, northwesterly winds and CAA return, which should
bring temperatures near to below normal. Another wave may move
through early in the work week but confidence remains low.
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1049 PM CDT Tue Aug 24 2021
Remainder of scattered showers and thunderstorms should remain well
south of the Highway 20 corridor overnight. Some high-res models are
starting to hint that some fog and low stratus could be possible
across portions of SW MN and NW IA, though not expected to impact
any of the TAF sites. Otherwise, a cold front is moving through the
region overnight and shifting winds to be out of the north, with
winds becoming east/northeasterly by the afternoon.
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
637 PM CDT Tue Aug 24 2021
.DISCUSSION...(This evening through Tuesday)
Issued at 405 PM CDT Tue Aug 24 2021
Hot/warm and humid conditions and occasional thunderstorm chances
are the main themes of this forecast.
Hot and humid conditions this afternoon will give way to slightly
cooler, but still warm and humid, conditions for Wed. Temps look
to tick back up for Thu and continue into the weekend until a cold
front moves through at some point Sat eve/night. Thunderstorm chcs
appear fairly limited in coverage and intensity for at least the
next 24-36 hrs. Better chcs arrive Thu eve/night and again Sat
night with the next cold front.
For the rest of today into tonight...the forecast remains largely
on track from this morning. Heat indices have risen into the
100-104 from the Tri Cities S and E...but even ODX has climbed to
around 102F. We still have another 1-2 hrs of heating, but we may
wind up a bit short of 105F for NW portions of the ongoing Heat
Advisory. However, still believe it is warranted as winds are
pretty lgt at 10 MPH, or less, under full sunshine. So feeling the
full brunt of the heat and humidity with nothing but sunset to
provide much relief through this eve.
We`ve had some iso/weak, elevated convection near and N of BBW to
OLU line much of the day...but even this has largely shifted N of
the CWA over past hr. Tstms chcs going forward thru tonight are
pretty uncertain/conditional, owing to weak upper forcing and very
warm mid level temps (~14C at H7). There remains a pretty large
spread in short-term, hi-res model guidance regarding tstm
coverage and intensity, further illustrating the low
confidence/nebulous forcing environment we`re in right now (which
is common for late summer). Think best chcs (relatively speaking)
for some iso tstms over next 6 hrs will be over far NW portions of
CWA, near a weak confluence zone/trough axis, as it shifts ever
so slightly SE towards the primary low level moisture axis. Tds,
for example, range from 58 at BBW to 73 at GRI. Another potential
area would be near MCK near sfc low/triple point. Both these areas
could be somewhat supported by weak shortwave seen on WV moving
from CO into W NE. However, as mentioned above, warm mid level
temps could suppress activity altogether, and latest SPC
mesoanalysis shows strong CINH remaining in place. Thus, only slgt
PoPs in forecast thru the eve. IF something could fire, there
would be chc for severe given strong instability and 30-35kt of
deep layer shear. Later tonight, may see a slight uptick in
elevated convection over NE/E portions of CWA in response to
strengthening LLJ. However, guidance is all over the place with
latest HRRR runs mainly dry, compared to more aggressive HRW FV3
and 12Z NAMNest. Think these models are overdone, but carrying
20-30 PoPs to cover this potential.
Wed will see NE to E winds much of the day behind a cold front.
This will help keep sfc temps cooler than today, for most areas,
with perhaps the far S/SE still seeing 95-100F. This will probably
keep most heat concerns just S/SE of the CWA, but if push of
cooler air is any less than may need a Heat Advisory from Osborne
toward Beloit as the Erly wind will help compensate the lower
temps with higher low level moisture. Have a dry forecast for the
The next chc for tstms could come as early as Wed night with
convection spreading N/NE from W KS, aided by LLJ. Once again,
model spread remains pretty high. Didn`t go too high on PoPs given
SREF probs for measurable rain only around 30%. Lowest chcs would
be SE third or so of CWA.
Wednesday`s cold front looks to lift back N Wed night into Thu AM,
allowing for hot/humid conditions once again...that probably last
thru the daytime hrs Sat. A shortwave tracking across N Plains
could bring better chcs for tstms by late in the day Thu into Thu
night. Looks like initial devpmnt favors areas NW of the CWA, with
some eastward component expected thru the eve. How far S/SE this
activity progresses remains uncertain, though, as primary LLJ
convergence could remain just N/NE of the CWA per latest NAM/GFS.
EC is further S/SE with QPF...so some forecast adjustments are
A stronger cold front is forecast by med range models to move into
the area Sat night as a stronger trough moves E across N Plains.
EPS and GEFS are in good agreement for decent drop in temps for
1-2 days (Sun-Mon). Still too soon to go into great detail
regarding tstm details, but pattern recognition and EC ensemble
QPF progs suggest this is the best area-wide-chc for rain over
the next 7 days.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Thursday)
Issued at 618 PM CDT Tue Aug 24 2021
VFR conditions are forecast for this TAF period. Decided to remove
the VCTS mention from KGRI later this evening/tonight, latest hi-
res models have been trending toward keeping better chances off
to the north and east of the terminal. Have variable winds through
much of the overnight hours, turning more easterly with time
through the end of the period and increasing in speed to around 10
NE...Heat Advisory until 8 PM CDT this evening for NEZ041-047>049-
KS...Heat Advisory until 8 PM CDT this evening for KSZ005>007-017>019.
Area Forecast Discussion
National Weather Service Goodland KS
547 PM MDT Tue Aug 24 2021
.SHORT TERM...(This evening through Thursday night)
Issued at 340 PM MDT Tue Aug 24 2021
Overview: An expansive upper level ridge, centered over the
Southern Plains and southern MS River Valley, will persist through
mid-week.. downstream of a persistent trough along the Pacific
Coast. The Tri-State area will remain situated on the N-NW
periphery of the ridge.. at the far southern fringe of the mid-
latitude westerlies. In the lower levels.. a weak/broad thermal
low will persist in the lee of the central Rockies.
In a rather stagnant synoptic pattern one would generally expect
little change in sensible weather conditions, however.. in such
close proximity to the mid-latitude westerlies, the Tri-State area
will, nevertheless, remain within the `sphere of influence` of
small amplitude waves progressing northeastward from the
Intermountain West into the Northern Plains -- whether that
influence be direct or, more-likely.. indirect (upstream
With the above in mind, well-above normal temperatures and dry
conditions are anticipated to persist. Isolated late afternoon and
evening convection cannot be ruled out.. generally in far
northeast Colorado and southwest Nebraska (in relative closer
proximity to the mid-latitude westerlies).
Interestingly.. simulated reflectivity forecasts via numerous
runs of the HRRR and NAM NEST suggest that scattered diurnal
convection will develop in southwest KS (beneath the ridge aloft)
~21Z Wednesday afternoon.. presumably in association with low-
level convergence invof a weak surface cyclone /thermal low/.
While this is certainly possible, confidence remains low.. as
convection allowing guidance tends to be less reliable in weak
forcing regimes. While organized convection is unlikely.. strong
insolation, near dry-adiabatic SFC-H5 lapse rates, and extreme
DCAPE suggest that any high-based updrafts would be capable of
producing severe downbursts.
.LONG TERM...(Friday through Tuesday)
Issued at 338 PM MDT Tue Aug 24 2021
At the beginning of the long term period, forecast models depict the
CWA being underneath the bottom portion of trough base over the
Northern Plains region yielding a mostly westerly flow aloft.
There appears to be some redevelopment and strengthening of the of
the trough occurring out near the ID/MT area during Friday as
well. On Saturday, the flow over the CWA turns southwesterly as
the redeveloped trough starts to move eastward with the ECMWF
showing a quicker progression than that of the GFS. The base of
the trough appears to pass north of the CWA late Saturday
according to the ECMWF while the GFS shows the base passing the
same area Sunday morning. By Sunday, models show a ridge following
the passing trough leaving a westerly flow over the CWA. On
Monday, model guidance shows the westerly flow aloft turning
northwesterly by the evening hours while upper air lows move into
western Canada. On Tuesday, the CWA returns to a mostly westerly
flow aloft as models still show the ridge residing over the
At the surface, the CWA looks to see some precipitation chances
during the weekend. On Saturday, the eastern portion may see chances
for showers and thunderstorms with a surface low looking to move
into eastern CO. Due to this low, the CWA may see some increased
wind gusts around 30 mph in the southern portions due to a
tightening pressure gradient. On Sunday, a cold front is expected to
pass through the CWA during the day bringing chances of showers and
thunderstorms ahead of it. The remaining days of the long term look
to be relatively dry at this time along with Friday. Elevated fire
weather conditions are possible for the Colorado counties of the CWA
on Friday, Saturday, and Tuesday with minimum RH values around 20%
or a little below are seen on these days. Maximum wind gust values
do not appear to support fire weather at this time, but these
conditions will be monitored should they change.
The Tri-State area should see high temperatures on Friday and
Saturday between the lower and upper 90s. On Sunday, daytime highs
cool to the lower to upper 80s followed Monday`s highs being in the
upper 80s to lower 90s and Tuesday`s highs in the lower to middle
90s. Tri-State area overnight lows for Friday expect to be between
the lower 60s and lower 70s with Saturday seeing overnight lows in
the middle 50s to upper 60s. Overnight lows for Sunday and Monday
look to be in the middle 50s to lower 60s.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 534 PM MDT Tue Aug 24 2021
VFR conditions are expected over the KMCK and KGLD terminals
through the 00Z TAF period. Winds are expected towards the NE
over the next few hours, becoming light. Around 06Z tonight, winds
over KGLD are expected to shift towards the east through sunrise.
Around 12Z, the winds will begin shifting variably from N to NE,
increasing to ~10 kts. Wednesday afternoon, winds are once again
expected to shift towards the east at 10-15 kts. There is
potential during the late afternoon/evening hours for isolated to
scattered showers/storms to develop. Current confidence is low in
terms of timing and impact to the terminals, so there is no
mention in the current TAFs.
Area Forecast Discussion
National Weather Service Gray ME
1038 PM EDT Tue Aug 24 2021
Very warm and humid continues through Thursday before a cold
front will usher in a cooler and drier Canadian airmass for
Friday through Sunday. Some heat remains along the coast on
Friday, but temperatures return to the 70s for the weekend.
Southwesterly flow will return early next week, likely bringing
seasonable warmth and increased humidity.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
1035 PM...No real changes to the current forecast for
overnight. Only thing worth mentioning is that Tds continue to
run higher /low 70s/ than models are suggesting, and this may
keep mins up along the SW ME coast and in srn NH around 70
rather than upper 60s.
715 PM...Most changes were just to keep the grids current based
on obs. Did bump up mins a degree or two in many spots, given
the currently high Tds. Places that fog should be able to fall
through the Td, but only by a couple degrees.
Previously...Any remaining diurnal showers will dissipate with
loss of daytime heating. Clouds will also scatter out to leave
us with clear skies overnight. Ridge axis nosing into the region
from the SW will allow for the boundary layer to decouple and
lows dropping into the lower 60s to upper 50s in the interior
valleys. This will also likely lead to quite a bit of radiation
fog. I have added some patchy dense wording to the favored Nrn
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
A true hazy hot and humid day expected on Wed. Temps once again
will climb into the 80s and low 90s...with dewpoints helping to
push the apparent temps to between 90 and 95. In addition to the
humid haze...latest runs of the HRRR show that some wildfire
smoke may try and work down to the surface in subsidence across
the region. At this time it looks most favorable from Seacoast
NH NNEwd into Wrn ME. Concentration does not look quite as high
as earlier this summer...but enough that it may be noticeable.
SW flow ahead of the approaching cold front should keep temps
overnight more mixed and a little warmer than tonight. That
should preclude widespread valley fog. Some isolated showers may
try and sneak into far Nrn zones towards morning.
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Thursday will be the last day of this stretch of warm and humid
conditions, but likely will also be the worst of the conditions.
Highs will push to near 90 degrees again across southern areas and
the coastal plain, with dew points hovering in the low to possibly
mid 70s during the morning and early afternoon hours. This will send
heat indices into the mid 90s for many southern and coastal areas. A
cold front will be pressing southward through Canada and likely
won`t pass through northern New England until Friday. Some relief
may come sooner to northern areas in the form of some showers and
thunderstorms late in the day, but at this point the forcing
doesn`t appear robust enough to support widespread activity.
The cold front will continue to push south of the area on Friday,
with cool Canadian high pressure building across the area. Highs
will likely still warm into the mid 80s along the coastline on
Friday, but with dew points continuing to drop during day the change
of airmasses will be quite noticeable. High pressure will
continue to build on Saturday and Sunday, bringing widespread
highs in the 70s.
Despite the dramatic change in air masses across northern New
England, the front will largely dissipate south of New England. This
means that even as high pressure extends across our area, weak areas
of low pressure and clusters of thunderstorms will be developing and
passing south of the region. With this set up, it`s likely that
periods of high to mid level cloudiness will pass across the area
through the weekend, with the best chance for the most sunshine
across northeastern areas. Furthermore, the models have been showing
remnants of a decaying MCS from the northern Plains drifting
into our area late Saturday, but there is some disagreement on
just how robust it will be by the time it actually arrives in
the area. With this in mind the forecast has a period of
increased POPs for late Saturday, but it would likely be short
lived and the confidence on extent of it remains low.
By Sunday night and Monday the flow will return to a southwesterly
direction ahead of a cold front extending southwestward through the
Great Lakes. This will return temperatures back to near or slightly
above normal, and bring increasing humidity again. There will also
be an increased threat of showers and thunderstorms as a warm front
passes through on Monday. During this time period the ensemble
members are in fairly good agreement that ridging will continue to
build in the mid to upper levels, likely weakening and delaying
the cold front in the Great Lakes by at least a day or two. So
early to mid next week looks increasingly likely to be our next
period of seasonably warm and humid conditions.
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Short Term...Widespread VFR conditions this afternoon will give
way to IFR and LIFR in typically radiation fog valley locations.
This will include LEB and HIE...and perhaps CON and AUG as well.
VFR returns for Wed and Wed night.
Valley fog is possible Thursday morning, limiting visibilities.
Otherwise VFR conditions will be predominant through Friday, except
for some isolated showers or thunderstorms across primarily
northwestern areas late Thursday. VFR to MVFR conditions will be
predominant Friday through early Sunday, with primarily mid to high
level clouds. Low ceilings are possible by Sunday with increasing
cloudiness. VFR conditions likely return early next week,
outside of scattered showers and thunderstorms.
Short Term...Winds and seas will remain below SCA thresholds.
Offshore flow will finally clear out fog and stratus...though it
will likely take a couple hours longer in the Penobscot Bay
region before that takes place early this evening.
Southwesterly winds will freshen to near 20kts late Thursday
ahead of an approaching cold front. Conditions ease late
Thursday night and Friday as the front crosses the waters.
Northeasterly winds will then freshen to near SCA criteria
Friday night and early Saturday. High pressure will then bring
more tranquil conditions later Saturday and Sunday.
Area Forecast Discussion
National Weather Service North Platte NE
640 PM CDT Tue Aug 24 2021
Issued at 438 PM CDT Tue Aug 24 2021
A forecast update is in place for isolated showers and
thunderstorms forming along a cold front moving through the srn
Sandhills. The risk of upscale growth appears low at this time.
.SHORT TERM...(This evening through Wednesday night)
Issued at 334 PM CDT Tue Aug 24 2021
A cold front drifting through Nebraska this evening will drop south
into KS overnight, remain stationary during the day Tuesday and then
begin lifting north Wednesday night. The sfc front will likely
remain over KS during this time, but aloft winds at the 850-700mb
become southerly with increasing moisture and instability. The 850mb
front in the RAP model remains across nrn KS while the NAM and GFS
lift the front slowly into swrn Nebraska after midnight. The warm
front, low level moisture and the northward migration of a
subtropical moisture plume across nwrn Texas should provide
excellent focus and moisture for showers and thunderstorms across
wrn and ncntl Nebraska Wednesday night. Precipitable water should
rise to over 1.25 inches.
500mb winds are 20 to 25 kts which increase to 30 to 50 kts at
300mb. The resulting modest midlevel and deep layer shear could
support strong to severe storms but the NAM is relative slim on QPF.
It is possible the models are not picking up on what appear to be
weak h700mb trofs moving through or off the Colorado Rockies and
the nrn Plains. Perhaps these disturbances are too weak. A fairly
strong h700 cap will be in place with temperatures at that level
between 13C and 15C. The rain forecast Wednesday night leans on
the SREF but limits rain chances to 20 to 40 percent. The new
forecast is similar to the previous forecast but WPC is keeping
wrn and ncntl Nebraska mostly dry Wednesday night. The better rain
chance will be across the nrn states.
The temperature forecast leans on the short term model blend plus
bias correction for post-frontal highs in the 80s Wednesday. This
forecast is in the middle of the guidance.
.LONG TERM...(Thursday through Tuesday)
Issued at 334 PM CDT Tue Aug 24 2021
A fairly strong upper level disturbance near the coast of Washington
state will traverse the nrn Plains Thursday and Thursday night.
Across wrn and ncntl Nebraska, the disturbance will be interacting
with subtropical and Gulf moisture. This appears to be the best
rain chance during the next 7 days. The models continue to favor
the Dakotas and upper Midwest for the best rain chance.
Wrn and ncntl Nebraska will be in the warm sector by late Thursday
with a warm front located near the SD border. The NAM and NAMnest
suggest subtropical dynamics will move out of Colorado and reach
into Nebraska setting off strong thunderstorms late in the afternoon
and during the evening. These are the wettest models.
Chance to likely POPs are in place for this system with the best
chance across the north. Precipitable water in the NAM, SREF and GFS
rises above 1.25 inches
A second disturbance will move through the nrn Plains Saturday
night. This disturbance will mainly affect ncntl Nebraska-closer to
the upper level dynamics. Once again, the ECM and GFS show a plume
of subtropical moisture advancing north into Nebraska which could
lead to locally heavy rainfall in some areas. WPC will maintain the
best rain chance across the upper Midwest for this system.
Otherwise the forecast is basically dry. Friday and Saturday will
the warm days with a cold front stationary across SD. Highs in the
80s and 90s are in place these days. H700mb temperatures across
Nebraska will be around 14C which could support warmer highs. The
storm activity Saturday night will send a fairly strong cold front
through the region. Sunday and Monday are cooler and post-frontal.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 640 PM CDT Tue Aug 24 2021
VFR conditions expected to prevail through tomorrow evening. A few
thunderstorms will continue across portions of the Sandhills this
evening, though any impacts to terminals looks to remain
minimal. Some guidance hints at an area of low stratus roughly
along and south of an ONL to AIA line tomorrow morning, though
confidence is too low for inclusion at LBF for now. Otherwise,
winds will transition from northerly to easterly to southeasterly
through the day tomorrow, at around 10 to 15kts.
Area Forecast Discussion
National Weather Service Reno NV
308 PM PDT Tue Aug 24 2021
Moderate summer temperatures along with breezy afternoon winds
are on tap through Wednesday. Lighter breezes and some warming
are expected late in the week and for the weekend. Westerly winds
will continue to push wildfire smoke into the Sierra and western
Nevada through Wednesday. There is a chance for a bit less smoke
influx late in the week into the weekend for western Nevada.
Not much change to the forecast with this package.
A broad trough with a dry southwest flow will promote continued
southwest-west afternoon breezes through tomorrow before a low-
level wind shift and reduction in wind speeds occurs as the trough
slides by Wednesday night and Thursday. The flow will continue to
bring influxes of smoke through Wednesday from the Caldor Fire
across western Nevada while Dixie Fire smoke continues to spread
across Plumas, Lassen, eastern Modoc, and far northern Washoe
The troughing pattern will help give a boost to our afternoon and
early evening winds with gusts generally in the 20-30 mph range
through Wednesday. While the bump in winds can could result in
short lived and modest air quality improvements via afternoon
mixing, it could on the other hand allow for more smoke production
from upwind wildfires. As a result, air quality is likely to
degrade again overnight and into the morning. For additional air
quality resources, check out the links below:
- Air Quality Readings: fire.airnow.gov
- Air Quality Forecast: airnow.gov
The winds may bring slightly increased concerns for fire weather
(see the fire discussion for more details) but widespread and
longer duration critical conditions are not expected.
Lighter winds return Thursday through much of Sunday although some
increase in northerly flow is possible north of I-80 by Friday
night and Saturday morning. With lighter winds from the northwest
to northeast at the low levels, there should be less smoke influx
for western NV, and northeast CA north and east of the Dixie Fire,
starting Thursday. Now this does not mean there won`t be some
smoke particulates/haze leftover as the flow looks light; however,
it may bring some improvement in air quality as new smoke influx
is held mostly in the Sierra. Note that there could be a brief
return to west-northwest flow Friday afternoon and evening between
shots of northerly flow for the Basin so that may muddle the
improved air quality somewhat. Anyway, fingers crossed in at least
Temperatures will remain a couple of degrees below season averages
through Thursday before high pressure starts a modest warming
trend through the weekend. Temperatures look to warm roughly 5
degrees above average with mid 80s to lower 90s for valleys over
the weekend. -Snyder/Fuentes
* Through Wednesday: South-southwest flow aloft into Wednesday
morning will veer around to southwest-west in the afternoon and
evening as a trough axis moves overhead. Due to the flow aloft
and with surface winds kicking up from the SW-W today and again
Wednesday afternoon, the HRRR smoke is still transporting
copious amounts of smoke into the the Tahoe Basin and western
NV. The longest-lived IFR VIS is simulated downwind of the
Caldor Fire including KTVL/KTRK/KCXP/KRNO tonight, although
KTVL, KMEV, KCXP may again see increased VIS late tonight and
early Wednesday as smoke retreats with southerly flow up through
~700 mb. Smoke is simulated to shift more to the Hwy 50 corridor
southward (KTVL, KCXP, KMEV) Wednesday afternoon/evening as flow
veers around to westerly with the trough passage. Even outside
these "worst" areas, expect widespread haze and smoke to limit
slantwise visibility. Some turbulence is possible as well
through Wednesday as ridge level winds gust to 40+ kts.
* For Thursday, surface winds shift around to the NW/N/NE as the
upper air pattern changes some. That could yield some
improvement in flight conditions for portions of western NV as
well as northeast CA to the north and east of the Dixie Fire.
*Slightly elevated speeds this evening and Wednesday afternoon;
gusts 20 to 30 mph.
*Wind direction change Friday afternoon into early Saturday.
No major changes were made this cycle with troughing expected to
move inland tonight and Wednesday. Surface gusts 20-30 mph remain
likely this evening and Wednesday afternoon. This could result in 1-
3 hours of critical conditions mainly east of Susanville and along
the Sierra Front from Reno through Mono County.
Breezes along ridges remain likely tonight with elevated speeds
expected along upper slopes as well. While temperatures will run a
little cooler than recent conditions, instability associated with
the trough axis over the region may result in increased ventilation
and promote enhanced fire activity.
Temperatures warm through the end of the week with highs ranging in
the low/mid 80s for Sierra locations and low/mid 90s for western
Nevada. These temperatures will keep surface instability higher
although the smoke inversion may keep ongoing fire activity tamped
until the afternoon hours. Also, another dry trough is expected
sometime Friday into Saturday. This will likely result in wind
switch from westerly flow to out of the north/northeast late Friday
and Saturday. Otherwise, poor mid-slope and ridge top recoveries are
expected through the weekend.
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