Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/27/21
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
925 PM CDT Thu Aug 26 2021
.UPDATE...
Issued at 918 PM CDT Thu Aug 26 2021
Severe Thunderstorm Watch has been issued for the southern part of
the CWA near a stalled out frontal boundary and in association
with a strengthening low level jet. Increased POPs in that area
and included a mention of possible severe storms. No other changes
made to the forecast at this time.
&&
.SHORT TERM...(This Evening through Friday Night)
Issued at 251 PM CDT Thu Aug 26 2021
We remain under a persistent and messy weather pattern with
off and on showers and thunderstorms that remain a little difficult
to time. Southwesterly flow remains at 500mb with several embedded
waves. The main shortwave is over MT/WY this afternoon and will move
into the western Dakotas tonight. Will continue to monitor rounds of
showers and thunderstorms that are being enhanced by an area of high
shear. We`re still looking at the chance for more storms over our
southwestern counties this evening into the overnight hours. Just
how the storms evolve is in question, mainly on how far north the
storms will move. The HRRR continues to be on the more
aggressive/farther north solution, with the potential of storms
mainly near the Missouri River around 05-06Z (mainly south of
Mobridge). HREF keep much of the more significant UH values over our
southern counties, but can not rule out the HRRR. Expect whatever
develops to shift east-northeast overnight and exit into
northeastern SD/western MN by around 12Z. This will be while the
surface low over NE pushes northeast into portions of southeastern
SD. While that feature moves into southwestern MN Friday evening,
yet another low will be moving into southwestern SD. At this point
expect mainly dry weather for Friday afternoon, before storms near
from the northwest Friday night and expand across the forecast area
overnight. Any storm that does develop will have the potential to
produce strong winds, hail, and heavy rain. PW values remain over
1in through the period.
.LONG TERM...(Saturday through Thursday)
Issued at 251 PM CDT Thu Aug 26 2021
A somewhat active pattern will continue across the northern CONUS
through the extended time period. To start the period, an upper trof
will be advecting across the Dakotas Saturday and Saturday night.
The main low level boundary associated with the upper trof will
stretch from ne-sw across eastern South Dakota by afternoon.
Moderate instability is expected to develop along this feature with
daytime heating, particularly over far eastern SD, and western
Minnesota. So, expect most activity that develops over eastern SD to
likely move into MN quickly in the evening. Moderate instability and
strong deep layer shear suggests some severe weather is likely.
Later Saturday night and Sunday should be mostly dry as sfc high
wafts over the forecast area. Return southerly flow begins in
earnest Monday through Tuesday, with convection chances returning to
the forecast. Mid-level ridging builds across the region for
midweek, but with a sfc boundary in the vicinity, pcpn chances will
continue. The end of the week may bring a lesser chance of pcpn as a
front settles out to the south of the forecast area. Temperatures,
overall, will favor near to slightly below normal for the period,
except for mid-week when the ridge aloft may allow for warmer than
normal temperatures.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 628 PM CDT Thu Aug 26 2021
Terminals KABR,KATY,KPIR,KMBG
Scattered showers and thunderstorms will affect the northeastern
part of the area this evening, with additional showers and
thunderstorms expected to develop during the overnight hours and
spread eastward through early Friday morning. Cigs will fall to
IFR/MVFR levels with the precipitation development, then will
remain at those levels into early Friday afternoon before lifting
to VFR levels.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&
$$
UPDATE...Parkin
SHORT TERM...KF
LONG TERM...TDK
AVIATION...Parkin
Area Forecast Discussion
National Weather Service La Crosse WI
1100 PM CDT Thu Aug 26 2021
.SHORT TERM...(Tonight)
Issued at 329 PM CDT Thu Aug 26 2021
...An Active Night Of Weather Expected...
A complex but potentially impactful weather scenario is shaping up
across the region for tonight. Current storm and rain activity
moving through is reinforcing the cool stable layer which extends
across all of northern Iowa. There is still some MUCAPE available
above the surface there /1500-2000J/Kg/. Surface-based CAPE pool
is growing and impressive but still far southwest in SW IA. Using
RAP guidance and surface observations, the front between the very
unstable mT air and the "cooler" stable air to the north should be
roughly NW>SE Iowa by early evening. This low-level thermal
boundary orientation and isentropic lift zone extends from
southern MN into eastern IA.
After about 9 pm, the low-level jet amps up into the isentropic lift
zone to erupt storms over southwest MN and nrn IA. These storms,
quickly forming into a line, tracking southeast, would have the
best chances of being severe with damaging winds as they shift in.
It seems the trajectory and low-level front and CAPE pool should
provide NERN IA with the highest probability of damaging
winds...and closer to I-35 or southwest of the area. That would
likely end the damaging wind threat.
However, heavy rain and flash flooding is now the greatest concern
overnight with moderate moisture transport convergence via low-level
jet inflow /850 mb/ at 35 kts isentropically lifted over the entire
thermal gradient - northeast of the surface front. The entrance
region of the upper jet also provides a favorable larger mesoscale
lift boost. This looks like it will cause cause widespread storm
eruption by late evening across southern MN into northern IA with
storms shifting east into WI and repeating over some of the same
areas. There could 3 to 7 inches of rain with this rich air mass
of 170-190% normal precipitable water, 3.5-4km warm cloud depth,
and propagation vectors east-southeast along the
front...suggesting some training. While it is concerning, soils
can take some rain, but really the character of the waves of
storms and if they can concentrate on one area is still a bit in
question. So, have decided to wait a bit longer on a Flash Flood
Watch, possibly until early evening. Right now, it appears NERN IA
and SERN MN would be the target. But widespread rain/storms are
expected with 1-3 inches by morning for many, higher in training
storm regions.
Any assistance from our TV/media partners in suggesting people
stay weather aware overnight, keeping their phones on, is
appreciated! Campers near streams/smaller rivers will want to be
alert overnight as well - they likely wont sleep much with hours
of storms.
.LONG TERM...(Friday through Thursday)
Issued at 330 PM CDT Thu Aug 26 2021
After any lingering Friday morning convection clears, the 850mb
boundary should be on the move northward into central WI. The
models have been hinting at this every day, but each day we see
that the boundary does not actually move. Friday may be another
day where that happens. If the boundary stays put, we could see
more showers and thunderstorms develop right over us and
increase our risk of flash flooding. The 850mb moisture transport
will actually be pushing right into our area (or to our north) all
day Friday.
The more amplified upper trough will approach the Upper Midwest
Friday night with an embedded shortwave crossing MN Saturday
afternoon. Each wave will bring a renewed chance for storms and
those storms will be focused along the 850mb frontal boundary and
nose of the low level jet. The upper trough and associated
surface cold front will finally swing through sometime on Sunday,
although the upper wave will become removed from the surface front
by the time it moves into southern WI. Therefore, models are
showing a weakening trend in precip along the front.
Quiet and less humid weather will finally return early next week
as high pressure settles over the Upper Great Lakes. There will
continue to be shower and isolated thunderstorm chances toward
northeast IA on the edge of the surface high as weak ripples in
the upper flow move overhead.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1051 PM CDT Thu Aug 26 2021
Widespread showers and thunderstorms overspread the area tonight,
which will taper off in coverage during the morning hours. Expect
restrictions to IFR or even LIFR with the regions of heaviest
rainfall overnight. MVFR to IFR fog is also likely in areas that
clear out from the rain before sunrise. Winds will generally be
from the east to southeast at 5-10 kts, with locally higher gusts
around any thunderstorms. Ceilings during the day on Friday may be
slow to lift above MVFR during the morning to early afternoon.
Additional showers and storms will affect the area late in the
afternoon and evening hours.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Flood Watch until 7 AM CDT Friday for MNZ079-086>088-094>096.
IA...Flood Watch until 7 AM CDT Friday for IAZ008>011-018-019-029-030.
&&
$$
SHORT TERM...Baumgardt
LONG TERM...MC
AVIATION...Skow
Area Forecast Discussion
National Weather Service Bismarck ND
912 PM CDT Thu Aug 26 2021
.UPDATE...
Issued at 850 PM CDT Thu Aug 26 2021
Slightly slowed the eastward progression of PoPs tonight based on
model guidance and latest radar trends. Past couple runs of the
HRRR make for a potentially more interesting night with more
widespread stronger cells in the southwest and south central parts
of the state. Plenty of shear is available, however, instability
is limited. Thus while a severe storm or two cannot be completely
ruled out this evening, still thinking severe weather is less
likely than likely to occur.
UPDATE Issued at 610 PM CDT Thu Aug 26 2021
Removed PoPs from the western forecast area and lowered them
slightly over the eastern forecast area over the next few hours
to reflect current radar and model trends. With fairly light winds
tonight and a very low stratus deck expected at times after the
fresh rainfall, added patchy fog to much of the forecast area.
Locations most likely to see fog for an extended period are primarily
those in more elevated terrain.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 247 PM CDT Thu Aug 26 2021
Widespread scattered showers and thunderstorms are possible through
the short term forecast, with some strong to severe thunderstorms
possible on Friday.
This afternoon, flow aloft was turning southwesterly across the
Northern Plains as a shallow trough was based over the western
CONUS. Broad high pressure was centered to the northeast of the
forecast area, with a moderate pressure gradient between the high
and relative low pressure over northeast Wyoming. A surface trough
extended northeast-southwest across central Minnesota, with a few
isolated thunderstorms ongoing in the wake of it across the southern
James River Valley. We are expecting some widely scattered shower
and non-severe thunderstorm activity across the area through the
afternoon from elevated warm advection.
Chances for showers and thunderstorms will increase late this
evening and through the overnight hours as another shortwave moves
through the southwesterly flow, ahead of the approaching trough
base. At this point, we are not expecting any of these storms to be
severe, with marginal instability during the overnight hours. The
highest chance for a strong to severe storm would be in the
southwest, where there is the best overlap of shear and instability.
Lows tonight will be in the upper 40s to mid 50s.
The main concern in the short term is the potential for severe
thunderstorms on Friday. Precip chances from tonight`s shortwave
taper off from west to east through Friday morning, but PoPs quickly
increase again in the afternoon and evening as the trough base moves
over central Montana. Development is expected in south central
Montana during the afternoon on the nose of an upper jet, with
storms then moving east into the western Dakotas. Instability
around 1000-1500 J/kg and 0-6 km shear on the order of 35-45 knots
will be enough to support discrete cells forming along a frontal
boundary moving through Friday evening. Main hazards will be ping
pong ball sized hail and 60 mph wind gusts, as well as locally
heavy rainfall with PWATs still around the 90th percentile. Expect
the threat to start in the evening, with the storms moving east
through the late evening and overnight.
.LONG TERM...(Saturday through Thursday)
Issued at 247 PM CDT Thu Aug 26 2021
A slow warming trend and various chances for showers and
thunderstorms highlights the extended forecast.
Precipitation chances linger through the day on Saturday, especially
central and east, as the base of the upper trough moves overhead and
eventually off to the northeast by Saturday night. It will be
another pleasant day, with clearing skies from west to east and
highs generally in the 70s, although winds will be breezy in the
west.
Sunday will finally be a dry day, with zonal flow aloft and broad
high pressure at the surface. Temperatures will slowly be warming as
upstream troughing deepens over the western CONUS and ridging
develops over the Northern Plains in response. Highs will warm to
the mid 70s to mid 80s by Tuesday, when low but relatively
persistent chances for showers and thunderstorms begin in the
evening. Multiple shortwaves look to move through southwest flow
aloft through much of the work week, with uncertainty then emerging
in how long the trough persists out west before it breaks down.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 610 PM CDT Thu Aug 26 2021
IFR and MVFR ceilings are expected at all locations at times
throughout the TAF period. Patchy fog is also possible at most
TAF sites at some point, although KDIK is the site most likely to
see longer lasting fog that will reduce visibilities to IFR
levels. Finally, showers with the occasional rumble of thunder are
expected to work into the area from the west tonight and linger
into Friday morning. These could further reduce visibility, lower
ceilings, and/or create erratic wind gusts while showers and
thunderstorms are ongoing.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Telken
SHORT TERM...MJ
LONG TERM...MJ
AVIATION...Telken
Area Forecast Discussion
National Weather Service Birmingham AL
705 PM CDT Thu Aug 26 2021
.UPDATE...
Evening Update and 00Z Aviation.
&&
.SHORT TERM...
/Updated at 0648 PM CDT Thu Aug 26 2021/
Central Alabama is positioned between two subtle easterly waves
early this evening. Precipitable Water values are near 1.5 inches
per the latest RAP analysis. This is a relative minimum with 2+ in
southern Mississippi and southern Georgia. Therefore, a limited
cumulus field this afternoon with mixing and little vertical
growth. A few small scale boundaries were here and there plus
another outflow in west central Georgia. Left a token 15 pop for a
few hours this evening but a majority of the locations will be
high and dry. Some low clouds may try and inch into or develop
over southeast areas just after sunrise and will monitor this
potential development before mixing begins. Due to lack of rain
today and no particular boundary or convergence, fog should not be
a widespread problem overnight.
The big news is that Tropical Storm Ida has formed in the
northwest Caribbean Sea. The initial path and intensity forecast
from NHC has Ida moving into the central gulf coast as a
hurricane Sunday afternoon. Parts of west central Alabama are in
the error cone as the storm moves inland. Much more on the tropics
in later forecast. If you have interest along the gulf coast, pay
particular attention to the latest forecast and updates for the
NHC.
75
Previous short-term discussion:
/Updated at 1247 PM CDT Thu Aug 26 2021/
Today through Friday.
Features of Interest.
Broad ridging remains over much of the Southeast while lower-
level ridging remains to our east and northeast. Surface east to
southeasterly flow was continuing to support humid conditions. The
26/12z BMX sounding contains a subtle subsidence inversion around
900 mb with saturated low-level conditions. This has allowed
persistent low-level clouds to remain across much of our northern
and central counties through late morning.
Hazard Assessment.
The wet microburst risk is moderate today, which is similar to
yesterday`s outlook. We will monitor the potential for some of the
heavier thunderstorms to produce strong winds.
Today.
The lower clouds are mixing out and expect partly cloudy
skies this afternoon with isolated showers and thunderstorms
developing over the next few hours. The better chances will be
northern and northwest counties today with the lowest chance
across our far southeast counties. Highs will range from the upper
80s in the higher elevations east to the lower 90s elsewhere.
Winds will remain from the east to southeast 6-12 mph.
Tonight.
Partly to mostly cloudy skies are forecast overnight with some
lower clouds expected toward daybreak. Chances for lingering
showers will be widely isolated at best with the best potential
north and west. Lows range from around 70 north and east to
readings in the lower 70s south and west. Winds will be light from
the east 3-6 mph.
Friday.
Morning clouds look to begin the day Friday with scattered showers
and thunderstorms developing from late morning through the
afternoon hours. The best chances will be across the eastern and
southern portions of the forecast area in association with a mid
level disturbance that is progged to move into the area from the
east during the daytime hours. Highs will range from the upper 80s
in the higher elevations east to readings in the lower 90s
elsewhere. Winds will be out of the southeast 6-12 mph.
05
.LONG TERM...
/Updated at 400 PM CDT Thu Aug 26 2021/
The main tweaks in the extended are based on the latest guidance
for TD 9. While official tracks may vary some over the next couple
of days, we will likely have some affects from being on the right
side of the storm as it moves northward across the Gulf of Mexico
onshore late Sunday into the beginning of next week as the
tropical system moves around the SE US upper ridge. It will
encounter the main upper flow causing it to turn NE Monday into
Tuesday some. To what extent as to how much remains to be seen.
With that said, there will be a threat for tornadic activity in
the right front quadrant across C AL on Monday as of now. The W
half of the area will likely have the better chance. Heavy rain at
times and some flash flooding will be possible in any training
feeder bands. Will add a low confidence 1 in the HWO for Monday to
account for this. Other changes include tweaking down highs for
Monday and Tuesday due to more cloud cover and tropical rain
bands.
08
Previous long-term discussion:
/Updated at 300 AM CDT Thu Aug 26 2021/
Friday night through Wednesday.
Friday`s diurnal convection will weaken and lingering into the
evening hours. Overall, coverage should not be that great with most
of the activity gone by midnight. An upper ridge off the Carolina
Coast will produce a moist southeast flow across Alabama over the
weekend. On Saturday, sea-breeze initiated storms will likely be
main focus for storms across south Alabama, and carried likely rain
chances for areas south of I-85. By Sunday a low level convergence
zone will likely set-up along the MS/AL state line between the ridge
over the Carolinas and the approaching tropical system in the Gulf
of Mexico, so better rain chances west of I-65. Beyond Sunday, the
models are in fairly good agreement in moving the tropical system
northward along the MS river. Based on model consensus, feel fairly
confident in raising rain chances across west and northwest Alabama
Monday and Tuesday. This track would also place Central Alabama in
the favored region for the potential for tornadoes.
58/rose
&&
.AVIATION...
00Z TAF Discussion.
VFR conditions will be forecast outside of convection through the
period. Much drier conditions through the atmospheric column today
than yesterday. Expect light and variable winds overnight with
little cloud cover for most. Some MVFR clouds may approach or
develop near TOI around daybreak and will have to monitor for
possible inclusion on later forecast. Due to lack of rainfall and
convergence, fog has not been mentioned at the terminals
overnight. Although there may be a few locations where vis drops
some, not expecting anything widespread. On Friday, another
easterly wave and increased mean moisture move over Central
Alabama. Therefore, there should be more convection than there was
today. Started with PROB30 in the afternoon at all terminals.
Winds maintain an easterly component at 5-7kts.
75
&&
.FIRE WEATHER...
An increase in rainfall coverage is expected Friday and Saturday.
An additional increase in shower coverage can be expected by next
week, but will be dependent on activity in the Gulf of Mexico and
direction during the first of next week. Weak low level winds
remain out of the east to southeast through the end of the week,
with elevated humidity values keeping min RH values above 50
percent range.
&&
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 70 91 71 91 71 / 20 40 20 30 10
Anniston 71 90 73 90 73 / 20 50 20 30 10
Birmingham 73 92 73 91 73 / 20 40 30 40 10
Tuscaloosa 74 92 73 91 74 / 20 40 30 40 10
Calera 72 89 73 89 74 / 20 50 30 40 10
Auburn 72 89 73 88 73 / 20 60 20 50 10
Montgomery 73 91 73 92 74 / 20 60 30 50 20
Troy 72 91 73 90 73 / 20 60 30 60 20
&&
.BMX WATCHES/WARNINGS/ADVISORIES/...
None.
&&
$$
Area Forecast Discussion
National Weather Service Cheyenne WY
525 PM MDT Thu Aug 26 2021
.SHORT TERM...(This evening through Friday night)
Issued at 151 PM MDT Thu Aug 26 2021
Current radar imagery indicates some cells developing in northern
Carbon County and to the south across Colorado. Fairly slow start
to the Convection today, with some model inconsistencies with the
later runs. NAM-NEST and the HRRR models have picked up on a line
of convection developing just off to the west traveling eastwards
across the CWA. However, it seems the HRRR is a bit more bullish
as this line of convection travels downstream towards the
Panhandle. Main concerns today exist with severe potentials. Low
level winds are expected to turn near zero just east of state
line between Wyoming and Nebraska. NAM-NEST has picked up on this
feature, shearing the convective cells and effectively decreasing
their intensity. Already seeing signs of this occurring with a
cell developing over Morrill County. In addition, the SREF CAPE
probabilities indicate a near zero percent chance for greater
than 1000 J/kg of CAPE for southeastern Wyoming and around a 30
percent chance across the Nebraska Panhandle. Most of the better
energy appears to be northward, with a good bullseye close to our
northern region of the Panhandle. Could see some outflows develop
from the north that could cut southwards towards Dawes County.
Nevertheless, main threats today include strong damaging winds
from any storms able to develop in the Panhandle with a good
inverted V signature and will likely be similar to yesterday. Due
to the model inconsistencies, confidence for tonight severe
potentials is low. Looking ahead into tomorrow, a series of
shortwave disturbances is expected to dig to the east/southeast
across the region, kicking up the wind speeds along the way.
Overall, dry and windy conditions expected from these features,
with most of the moisture advection to the east of the CWA,
raising fire weather concerns. Went ahead and upgraded the current
Fire Weather Watches to Red Flag Warnings.
.LONG TERM...(Saturday through Thursday)
Issued at 151 PM MDT Thu Aug 26 2021
An upper level trough will begin to dig east/southeastward from
the Pacific Northwest towards the Rockie Mountains through late
Saturday night. Could see some showers and thunderstorms develop
late Saturday night into early Sunday morning. However, the
likelihood of any convection during that period is decreasing.
Current model runs are picking up on the moisture advection into
the region that now seems poor with Tropical Depression Nine
coming on board towards the Gulf of Mexico, effectively cutting
off the flow from the Gulf and tilting the moisture advection
eastward. Looking into next week, mostly quieter weather ahead
with near zonal flow developing overhead and bringing drier
conditions across southeastern Wyoming and the Nebraska Panhandle
beginning on Monday. Daytime highs are expected to increase,
relative to the cooler weekend, with highs in the mid-90s east of
I-25 and in the mid to low 90s to the west on Monday, and climbing
on Tuesday. With the increase in daytime highs across the Great
Plains and the drier conditions will inevitably raise fire weather
concerns as the afternoon RH values drop to the mid-teens.
However, winds are expected to remain below warning criteria level
at this time. Next round of precipitation is expected to return
by mid-week, as the next system comes on board.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 523 PM MDT Thu Aug 26 2021
VFR. Thunderstorms in the vicinity at all terminals except Rawlins
until 03Z. Wind gusts to 25 knots at Laramie, Cheyenne and Sidney
until 02Z, then to 35 knots at Rawlins, Laramie and Cheyenne after
15Z Friday.
&&
.FIRE WEATHER...
Issued at 151 PM MDT Thu Aug 26 2021
A series of shortwave disturbances is expected to dig
to the east/southeast across the region, kicking up the wind
speeds along the way. Overall, dry and windy conditions expected
from these features, with most of the moisture advection to the
east of the CWA, raising fire weather concerns. As a result, went
ahead and upgraded Converse, Niobrara from a Fire Weather Watch
to a Red Flag Warning, in addition to including Carbon County for
the warning. Fire weather concerns will remain elevated through
the weekend with low humidity values and gusty winds. Will need to
evaluate later model runs for any headlines needed on Saturday,
Monday, and Tuesday where wind speeds inch closer to critical
thresholds.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning from noon to 8 PM MDT Friday for WYZ301>304.
NE...None.
&&
$$
SHORT TERM...MD
LONG TERM...MD
AVIATION...RUBIN
FIRE WEATHER...MD
Area Forecast Discussion
National Weather Service Quad Cities IA IL
643 PM CDT Thu Aug 26 2021
...AVIATION UPDATE...
.UPDATE...
Issued at 606 PM CDT Thu Aug 26 2021
Have issued a flash flood watch for the northern third of the
area.
Satellite trends show new convection developing further south
than expected. The concern is that this is the effective boundary
that the expected MCS will develop and move along. This first
round of storms may prime the ground for when the very heavy rain
occurs overnight.
The potential for storms to repeat over the same area may be
increasing given trends in more recent RAP runs. Regardless, an
extremely heavy band of rain looks very possible and it will be
mesoscale in nature; potentially 1-2 counties wide and 4-6
counties long.
If storms repeat over the same areas then amounts over 4 inches
are very possible.
&&
.SYNOPSIS...
Issued at 327 PM CDT Thu Aug 26 2021
18Z surface data has in inferred low in southwest Wisconsin. A warm
front ran east from the low across southern Wisconsin while an
outflow boundary moved toward the Mississippi river in eastern Iowa.
Dew points were in the 70s from the Ohio Valley west into the
central Plains. Dew points in the 40s and 60s were across the
northern Plains and upper Midwest.
&&
.SHORT TERM...(This Evening through Friday)
ISSUED AT 327 PM CDT Thu Aug 26 2021
The situation through sunrise Friday is a continuous nowcast where
surface, satellite and radar data along with conceptual models are
the inputs to the forecast.
The boundary from the overnight storm complex is providing the focus
for new storms in southeast Iowa. Satellite also shows an implied
air mass boundary so additional storms are expected to develop
across the southern third of the area through sunset. Outside of
some light rain and a possible thunderstorm north and west of Cedar
Rapids through sunset, the rest of the area looks to remain dry.
The question is what happens during the late evening and overnight
hours. Here the situation is not entirely clear.
Satellite data shows another upper level disturbance moving through
Nebraska. Given the agitated cumulus cloud field in the area
surrounding KFSD, the next organized storm complex will likely
develop in this area late this afternoon and evening.
Conceptually this storm complex should move east along the elevated
boundary seen in satellite along the IA/MN border toward Wisconsin.
A gradual southward sag to the storm complex is expected with it
reaching the northern parts of the area after midnight.
Given the high moisture levels in the atmosphere heavy rainfall is
likely. However the ground may soak up much of the rain given the
moderate to severe drought conditions across the northern parts of
the area.
If storms repeat over the same areas late tonight then excessive
rainfall is possible that `could` result in flash flooding. Right
now we will not be issuing a flash flood watch but that could change
later this evening depending upon on how the storm complex develops
and evolves.
On Friday lingering nocturnal convection will dissipate during the
morning hours followed by new diurnal convection in the afternoon.
Again locally heavy rainfall will be possible from the stronger
storms.
Cloud cover and precipitation will dictate how warm it gets on
Friday. The potential does exist for another heat advisory with
areas south of I-80 being favored. Again this will depend upon cloud
cover during the day.
.LONG TERM...(Friday Night through Thursday)
ISSUED AT 327 PM CDT Thu Aug 26 2021
Continued hot and humid through the weekend with some relief next
week. Potentially active weather will continue. Heat headlines will
be assessed on a day by day basis.
Friday night
Assessment...low to medium confidence
Storms that develop Friday afternoon will continue into the evening
hours followed by dissipation. Boundaries from these storms will
then dictate where the next round of nocturnal storms will develop.
Right now the area north of I-80 is favored for the nocturnal storms.
Saturday
Assessment...medium confidence
Right now the model consensus has hot and humid conditions with no
rain expected during the daylight hours. Based on forecast high
temperatures and dew points, heat index readings of 100+ are
expected which would necessitate another heat advisory.
Saturday night/Sunday
Assessment...medium confidence
The models have slowed down the arrival of the next cold front.
Several model solutions keep Saturday night dry with the front
moving through on Sunday. Other solutions bring the front in very
late Saturday night and slowly move it through the area on Sunday.
Right now the model consensus has slight chance to chance pops
across the northwest half of the area Saturday night with chance
pops across the entire area on Sunday.
Monday through Thursday
Assessment...low to medium confidence
The cold front pushes through the area and then stalls/dissipates.
The models are, for the most part, in a cycle of daily diurnal
convection occurring with the highest pops in the afternoon and
evening. However the models also have several upper level
disturbances moving through in the flow aloft that may cause
convection to persist through the night and into the morning hours.
Right now the model consensus has slight chance to chance pops
Monday and Monday night, chance pops Tuesday and slight chance pops
Tuesday night and Wednesday. Wednesday night the model consensus has
mainly dry conditions followed by slight chance pops on Thursday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 640 PM CDT Thu Aug 26 2021
Satellite/radar trends shows new convection has developed further
south than what the models indicated. This suggests that this is
where the nocturnal TSRA complex will develop and track east.
Through 06z/27 VFR conditions are expected outside of SHRA/TSRA.
After 06z/27 KDBQ has a high probability of IFR conditions with
TSRA. The rest of eastern Iowa and northern Illinois south of
Interstate 80 can expect mainly VFR conditions with patchy MVFR
conditions around sunrise Friday.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flash Flood Watch from 10 PM CDT this evening through Friday
morning for Benton-Buchanan-Delaware-Dubuque-Jackson-Jones-
Linn.
Heat Advisory until 8 PM CDT this evening for Des Moines-Henry
IA-Jefferson-Lee-Van Buren.
IL...Flash Flood Watch from 10 PM CDT this evening through Friday
morning for Carroll-Jo Daviess.
Heat Advisory until 8 PM CDT this evening for Hancock-Henderson-
McDonough-Warren.
MO...Heat Advisory until 8 PM CDT this evening for Clark-Scotland.
&&
$$
UPDATE...08
SYNOPSIS...08
SHORT TERM...08
LONG TERM...08
AVIATION...08
Area Forecast Discussion
National Weather Service Grand Forks ND
1036 PM CDT Thu Aug 26 2021
.UPDATE...
Issued at 1036 PM CDT Thu Aug 26 2021
Showers have ended in our CWA, and main impact into the overnight
hours is related to smoke advecting in from fires in the MN
arrowhead from the east. HRRR smoke model indications this may
linger until the next cluster of showers/thunderstorms arrives
Friday morning. There is increasing consensus with this cluster
and timing favors southwest to northeast progression after 6AM
through midday and eastward through the afternoon (additional
development still possible after this cluster). I adjusted timing
of PoPs/thunder tonight into Friday including increasing coverage
to reflect numerous showers/embedded thunderstorms Friday. There
is enough instability advertised to support thunderstorm mention,
but not enough to message strong/severe convection. Higher
moisture content and embedded storms do raise the possibility for
localized heavy rain amounts. So far the consensus would favor 0.1
to 0.25" amounts with pockets of 0.5-0.75" possible where
thunderstorms occur (outliers in guidance and very low probs in
NBM 24hr QPF).
UPDATE Issued at 707 PM CDT Thu Aug 26 2021
Cluster of showers and embedded thunderstorms is lingering in our
south with isolated showers further north. Current consensus of
CAMs supports trends for this activity to shift east-southeast
through the evening hours with a lull overnight before next round
of showers/embedded thunderstorms arrive (southwest to northeast)
Friday morning. Adjustments were made to reflect current
radar/satellite trends and to tweak timing overnight. Impacts
will be lighting and brief heavy rain where thunderstorms track.
Elevated instability 500 J/KG or less and stabilizing low levels
with sunset lower chances for any stronger storms the rest of the
night.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 256 PM CDT Thu Aug 26 2021
Near term impacts through the remainder of the day are expected to
be minimal, with scattered showers and thunderstorms generally south
of Interstate 94. A few of these storms could produce brief wind
gusts and small hail. The late evening period into the early
overnight hours will remain quiet, with a slight chance for an
isolated thunderstorm, mainly along the SD border.
For Friday, additional showers and thunderstorms are in the forecast
along a pre-frontal trough and associated theta-e gradient boundary.
This will move through the area during the mid-morning through mid-
afternoon period. Periods of heavier rain are possible during the
overnight hours as PW values continue increasing ahead of the main
cold front.
.LONG TERM...(Saturday through Thursday)
Issued at 256 PM CDT Thu Aug 26 2021
Scattered strong to severe thunderstorms should move out of the area
late Saturday evening with cold frontal passage. Behind the front
expect a dryer, cooler, and more stable pattern for the early week
period. A warmer and more unstable pattern then develops for the mid
to lake week period.
Saturday night into Sunday...
An unstable pattern with southwest flow aloft looks to move eastward
and out of the northern plains region from Saturday night into
Sunday morning. Consensus guidance now depicts a lead cold front and
deep convection moving well east of the FA by early evening, with a
lower risk of a secondary cold front and isolated showers impacting
mainly far northern portions of the FA during the overnight into
early morning hours. On Sunday, a building H5 ridge aloft and drier
west-northwesterly blayer flow should overspread the area bringing
generally fair skies and temperatures just a bit cooler than long
term averages, ranging from the upper 60s north to mid 70s south.
Monday through Tuesday...
A transitory H5 shortwave ridge continues to build in aloft
from Monday into Tuesday, while a southerly return flow develops
near the surface. With that, temperatures should edge back back to
near seasonal normals and daytime highs range through the middle to
upper 70s. While morning low temperatures ramp up from the lower 50s
on Monday into the upper 50s by Tuesday. The increasing low level
flow and warming blayer temperatures will likely struggle with the
capping affect of warming temperatures aloft, thus isolated to
scattered showers and thunderstorms are possible each day.
Wednesday through Thursday...
By midweek, ensembles favor an amplifying trof/ridge pattern over
the western and central NOAM with a strengthening southerly blayer
flow. From mid to late week a return to a more unstable southwest
flow aloft pattern looks quite probable, with an increased risk for
more widespread string to severe thunderstorms and wetting to
soaking rains. Temperatures through this period look to remain near
long term averages, with highs 70s and lows in the 50s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 707 PM CDT Thu Aug 26 2021
MVFR ceilings have improved, however low stratus eventually
overspreads all of eastern ND and northwest MN after 09-11Z
tonight/early Friday and IFR appears likely through the daytime
period Friday. Most showers and isolated thunderstorms have
transitioned to southeast ND and west central MN and should end
this evening, however another round of showers/embedded
thunderstorms is likely to spread southwest to northeast Friday
morning. Coverage may remain scattered and thunderstorms isolated,
so I held off on introducing thunderstorm mention during this
update. Winds should generally remain from the east-southeast
8-13kt through Friday based on current trends and expected
surface pattern. Erratic winds are still possible due to
shower/thunderstorm activity.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$
UPDATE...DJR
SHORT TERM...Lynch
LONG TERM...Gust/Lynch
AVIATION...DJR
Area Forecast Discussion
National Weather Service Grand Rapids MI
1148 PM EDT Thu Aug 26 2021
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 330 PM EDT Thu Aug 26 2021
-Heat/humidity with storm potential through Sunday
-Dry with more comfortable conditions starting Monday
&&
.UPDATE...
Issued at 1148 PM EDT Thu Aug 26 2021
I have updated our forecast grids for showing the highest pops
overnight to be mostly on the east side of US-131. We have a
stationary front (overnight) from near MKG to near GRR to near
LAN. It is not forecast to move much until after 10 am Friday.
It now seems a low level jet (weak but there) develops just east
of US-131 early this morning and where it crosses the front
generates showers. This is were the RAP model shows the 80 to 95
percent 850 to 700 rh to be between now and 10 am. Just about
every run of the HRRR since 18z has shown nearly no precipitation
west of US-131 overnight. East of US-131 it has pockets of 1 to 2
inches of rain between now and noon. Locally heavy rainfall is
possible east of US-131 during the early to mid morning hours. So
I have updated the forecast to show this largely.
&&
.DISCUSSION...(This evening through next Thursday)
Issued at 330 PM EDT Thu Aug 26 2021
--Heat/humidity with storm potential through Sunday--
Heat indices will continue to peak in the mid 90s to around 100
in the absence of any clouds/convection through Sunday with dew
pts remaining in the lower 70s and H8 temps holding near 20C.
We expect isolated showers and storms through early evening,
particularly along the lake breeze front near and north of GRR.
Some of these could produce localized higher wind gusts and
torrential downpours. ML Capes are around 2000 J/KG with mid level
lapse rates around 7 C/KM and DCAPES around 1200 J/KG, although
really no shear to speak of. Diurnally driven activity should fade
with sunset, then attention turns to the upstream convection
currently in ern MN and IA.
Based on extrapolation of the upstream convective clusters (which
are associated with a shortwave and also contain a couple MCVs),
the shower and storm risk should ramp up again after midnight into
early Friday morning. In addition to the shortwave approaching
from the west we also have a warm front lifting north toward the
area tonight, supporting a period of higher pops.
Then it looks like a diminishing trend in convective coverage
should develop by Friday afternoon with the warm front lifting
farther north and subsidence/NVA moving in behind the
aforementioned shortwave. However our capes will soar again on
Friday to at or above 3000, and can`t rule out a few additional
storm clusters riding our way from the SPC SLGT risk area over WI.
Several of the CAMS support this notion, showing decent coverage
of convection across our area on Friday evening.
Saturday and Saturday night appear to be fairly quiet at this
point as we`ll be fully in the warm sector with lack of trigger.
Cant rule out some isolated diurnal convection though on Saturday
afternoon/early evening inland from Lake Michigan.
Coverage of storms expected to ramp up on Sunday
afternoon/evening as a sfc cold front approaches from the west.
Some of these could be strong/severe since deep layer shear
should increase due to the shortwave passing east across the nrn
GrtLks Rgn.
--Dry with more comfortable conditions starting Monday--
Cooler temperatures and drier air/lower dew pts pour in behind
the cold front Sunday night, ushering in a stretch of dry weather
with more tolerable dew pts in the 50s and highs near 80.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 739 PM EDT Thu Aug 26 2021
The short story is largely VFR through Friday. Now there are a few
lake breeze generated thunderstorms near US-131 this evening, one
storm came over GRR and dissipate over GRR around 23z. A few more
storms will develop and dissipate early this evening before the
sun sets but other than than expect partly cloudy skies overnight.
It would not be out of the question that the storms currently near
the Mississippi River in MN and IA (23z) could make it into our
western TAF sites in the 09z to 11z time frame. However, there is
little low level jet support for this. The RAP model (22z) has
the feeble low level jet axis that is forecast in this area at
that time. It is centered near TVC (at 09z) and moving northward
at that time. Also the moisture transport is aimed at northern
lower Michigan at that time too. This sort of set-up is typically
not good for thunderstorms to do well over Southwest Michigan. I
am thinking whatever is coming this way will die before reaching
here. Since there is a low level jet and some moisture convergence
north of our CWA early Friday morning, maybe the storms will
cross our northern CWA at that time but I do not see them
impacting our TAF sites. As a result I took the mention of it out
of the TAFs.
During the day light hours of Friday I do not seem much happening
either. It is true the stationary front will still be near I-96 in
the morning and it wills start lifting north later in the day.
Even so, most of the push for the warm front is near and west of
the Mississippi River over MN. It would seem to me any storms
would largely stay north of our TAF sites even then. So at this
point I feature no VCTS in any of our TAFs for the next 24 hours.
If it becomes more clear that storms will impact our TAF sites, we
will update those impacted TAFs.
&&
.MARINE...
Issued at 330 PM EDT Thu Aug 26 2021
Increasing southerly flow over the weekend may lead to hazardous
winds and waves developing, especially north of Holland from
Saturday night into Sunday. A brief period of stronger northwest
flow may also occur on Monday behind a cold front which comes
through on Sunday night. Scattered thunderstorms will impact Lk MI
on and off through the weekend and may occasionally pose a threat
to mariners.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&
$$
UPDATE...WDM
SYNOPSIS...Meade
DISCUSSION...Meade
AVIATION...WDM
MARINE...Meade
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
959 PM CDT Thu Aug 26 2021
.UPDATE...
947 PM CDT
Evening updates include lowering pops overnight across parts of
the cwa. Convective evolution overnight continues to be unclear,
though it appears the best focus for much of the night will be
west and northwest of the forecast area across parts of IA and MN.
Have eased pops to generally slight chance across our far east and
southeastern counties and kept chances in the west, mostly after
midnight for the majority of the area.
Had a few isolated weak thunderstorms develop along the lake
breeze this afternoon, and along outflow boundaries across our
southeastern cwa. These have faded with the loss of diurnal
heating. Currently, local air mass is generally capped with
respect to near-surface based parcels. South-southwesterly low
level jet back to our west across central/western IA and MN will
likely be the driving feature for renewed convective development
overnight, with RAP mesoanalysis depicting the best organized
deep moist convergence from far northern NE across northwest IA
and southern MN. Some recent convective development noted across
northwest IA in fact within the low level jet axis. While CAM
guidance has not been very helpful of late, latest 00Z 3km NAM and
recent HRRR runs do focus on the IA/MN border region overnight for
best thunderstorm coverage. The LOT cwa will be on the far eastern
periphery of the low level jet, thus not expecting significant
coverage for the most part. Elevated showers/embedded thunder with
MCV across eastern IA will likely move into northwest/north
central IL later this evening/overnight, though better potential
for stronger convective development looks to remain off to the
west. Some potential may exist for remnants of southern
MN/northern IA MCS to push into the area Friday morning in a
decaying form. Based on this have maintained going chance pops
across north central IL from late evening into the overnight
hours, while have decreased pops across the east/southeast to
slight chances.
Otherwise, no significant changes made to forecast through Friday
morning.
Ratzer
&&
.SHORT TERM...
302 PM CDT
Through Friday night...
Main concerns are low confidence convective trends (especially
tonight into Friday morning) and heat and humidity on Friday
afternoon.
In the near term, main areas of concern are near the lake breeze
convergence and in the vicinity of the remnant MCV over the
east and southeast CWA. Have seen pulse convection into our
southernmost counties, with the somewhat more organized
convection farther south over ILX and IND CWAs. Recent AMDAR
soundings, visible satellite, day cloud phase RGB, and radar
trends indicate the cap has eroded or is in the process of eroding
near the lake breeze. Still think that coverage and organization
will be less than yesterday but expect a few widely scattered
storms until sunset. Lack of deep layer shear today vs the more
supportive shear with MCV yesterday will make lightning, heavy
downpours/localized flooding, and brief likely non-severe
downbursts the main threats.
Turning to the thunderstorm threat tonight, unfortunately
confidence continues to be quite low. Thus far, the upstream
convection from central IA to southern MN hasn`t really taken off
this afternoon. There appears to be a weak short-wave near the
southeast IA/southeast MN border assisting the ongoing convection,
with the RAP initializing this and passing it north of us through
Wisconsin this evening. If organization doesn`t increase with
signs of MCS development and cold pool formation from this
activity this evening, the chances of organized convection
tonight drop off drastically given modest height falls focused
north of the area.
It`s possible thunderstorms to the northwest from one of the
various waves over the Upper MS Valley and northern Plains
congeals and pushes in later overnight, but confidence is too low
to put stock in this scenario. Due to the low predictability
nature of convection evolution tonight, lowered PoPs a bit from
previous and show them increasing to mid to high chance overnight.
If any organized/semi-organized convection moves in tonight, main
threat would be wind gusts strong enough to down tree limbs. High
PWAT air mass and large MUCAPE reservoir would also be supportive
of at least localized flooding in the presence of deep moist
convection. Trends *should* become more clear with time by this
evening.
Held onto chance PoPs Friday morning for the possibility of
showers and thunderstorms lingering from overnight activity to the
extent that it occurs. Thereafter, Friday afternoon will be hot
and humid but otherwise could turn out more quiet as low level
winds will increase and likely keep lake breeze development at
bay, with unidirectional south-southwest winds also limiting low-
level convergence across the area. In addition, modest mid-level
height rises are forecast and a majority of the models advect in
some pretty dry air in the 700-500 mb layer. Forecast low level
thermal progs from 925 to 850 mb support highs near low to the
lower 90s, with some upside potential if the afternoon ends up
mostly sunny. With dew points back up in the lower to mid 70s this
yields forecast maximum heat indices of the upper 90s to lower
100s (with overperforming temps bringing values closer to 105F
advisory criteria).
Friday night, the support for thunderstorms will primarily be
across the Upper MS Valley and central and northern Wisconsin
closer to the stalled frontal boundary and where short-wave
forcing will be focused. Most locations have a dry forecast,
except the Wisconsin state line counties where some slight chances
are indicated to account for wiggle room if storms form a bit
farther south than expected. Any thunderstorms that form later
tomorrow-tomorrow night would have a lower end threat to become
strong to severe (mainly wind threat) over far north central
Illinois with up to 20-25 kt of deep layer shear forecast.
Castro
&&
.LONG TERM...
305 PM CDT
Saturday through Thursday...
Forecast thinking for the long term period has not changed.
Hot and humid conditions will persist through the weekend then
trending "cooler" next week with periodic shower and thunderstorm
chances through at least Monday.
The upper ridge continues to amplify in advance of an approaching
upper shortwave trough. In response to this, 850 temperatures
around 20C move overhead again, and this will support surface
temps into the lower 90s areawide. This combined with yet another
day of dewpoints in the lower to mid 70s will result in heat
indices around 100 degrees. There will be some breezes out there
which should help some with the heat. A few isolated to widely
scattered thunderstorms are possible on Saturday afternoon.
Details for Sunday into Monday are a little less certain and will
depend greatly on the timing of the arrival of the upper wave and
associated surface cold front. At this time, this looks to move
through late Sunday night into Monday. Thus have another warm day
forecast with highs in the upper 80s. Model guidance has
development out ahead of the main cold front Monday afternoon and
early evening with additional storms moving through with the cold
front overnight.
Once the cold front moves through, temperatures through at least
the first half of next week will be closer to normal in the lower
80s with east northeast winds off the lake keeping lakeside areas
in the upper 70s. The front does look to stall out somewhere
across central IL/IN on Monday with showers and thunderstorms
possible mainly south of I-80. We then trend cooler with generally
low chances for thunderstorms. Will note that uncertainty in the
upper pattern and precip chances increases by midweek with
potential influences from a tropical system in the Gulf.
Petr/KJB
KJB
&&
.AVIATION...
For the 03Z TAFs...
Update at 03Z:
Observational and forecast model trends have backed away from
convection overnight, favoring expansive thunderstorms along the
IA/MN border. Accordingly, we removed the TEMPO groups for
thunder at all terminals. Depending on how organized convection
becomes upstream overnight, some form of remnants may try to sneak
in late Friday morning or early afternoon, but will withhold on
any mention in favor of watching trends overnight.
Borchardt
Previous Discussion issued at 00Z:
The primary forecast concerns through the next 24 to 30 hours are
as follows:
* Isolated thunder chances through the next few hours
* Chances for additional thunderstorms overnight
* Potential for an easterly wind shift Friday afternoon
Isolated showers and a few storms continue to percolate along a
lake breeze stretching from near DPA/ORD/MDW to IGQ. With waning
instability (e.g. setting sun), coverage should continue to wane
over the next few hours, but opted to hold onto VCTS at the
Chicago terminals through 01Z just to be safe.
Attention then turns toward Iowa where thunderstorms are
developing along the intersection of the nose of a 30+ kt 850mb
low-level jet and a residual outflow boundary. Forecast model
guidance continues to perform poorly with convective evolution
tonight, though with continued low-level forcing (aided by the
approach of a subtle upper-level wave over the central Plains),
convection will likely continue to develop if not "grow upscale"
with time with eastward motion into at least southern Wisconsin.
The greatest uncertainty lies with how far south the convection
will develop, so for now opted to maintain the inherited TEMPO
for thunder at all terminals, but slide the timing back toward the
predawn hours of Friday. Should a more organized system develop
tonight, strong northwesterly winds would become an increasing
concern, especially at RFD.
Finally, depending on convective coverage tonight and whether the
brunt passes to the north into Wisconsin, a northeasterly wind
shift off Lake Michigan cannot be ruled out particularity during
the early afternoon hours of Friday at ORD/MDW/GYY/DPA. After
collaboration with CWSU ZAU, opted to withhold formal mention for
now in place of watching convective trends over the next few
hours. Otherwise, light winds will prevail tonight, with a
southerly to southwesterly direction preferred tomorrow during
daylight hours.
Borchardt/Doom
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service San Francisco Bay Area
435 PM PDT Thu Aug 26 2021
.SYNOPSIS...An interior warming trend will continue into Friday
and Saturday under strong high pressure as dry northerly winds
pass over the region. A few degrees of cooling by Sunday afternoon
as onshore winds return then a West Coast trough brings
temperatures back closer to seasonal values early next week. The
forecast remains dry through the end of the month and likely into
Labor Day weekend.
&&
.DISCUSSION...as of 01:50 PM PDT Thursday...The region-wide
warming trend is well underway this afternoon as high pressure
builds over the region and temperatures aloft warm. This has
compressed the marine layer to between 1,200- 1,500 feet in depth
with morning fog and stratus having quickly dissipated except for
along the immediate coastline. Temperatures at this hour are
running a few to as much as 15 deg F warmer compared to 24 hours
ago.
Overnight, look for a shallow marine layer to persist with low
clouds to develop near the coast and potentially over the Monterey
Bay and locally into the Salinas Valley. Elsewhere, stratus will be
less widespread with the HRRR forecast model indicating very little
to no clouds over much of the greater San Francisco Bay Area
(including the North Bay). Warm and very dry conditions will also
prevail in the region`s hills, ridges and peaks given the warming
air mass aloft not only tonight but also through the upcoming
weekend. Smoky/hazy conditions are also forecast to be transported
across the region on Friday and potentially into the upcoming
weekend as winds aloft remain northerly. Will have to monitor the
amount of smoke and any impacts it may have on forecast maximum
daytime temperatures.
Speaking of temperatures, the warming trend will continue on Friday
and into Saturday as 850mb temperatures reach to around 25 deg C.
This will translate to more widespread mid/upper 90s to around 105
deg F across the interior. The interior East Bay Valleys and
region`s typical hot spots are the most likely to approach or exceed
the 100 deg F mark in the coming days. Elsewhere, light onshore
winds are likely to hold temperatures in the 60s/70s near the coast,
70s to 80s around the San Francisco Bay Shoreline and 80s/90s for
other inland areas both Friday and Saturday afternoons. This said,
Heat Risk analysis keeps most populated areas across the interior in
a Moderate Risk with some sparsely populated higher elevation
locations reaching into the High Risk. While heat products are not
anticipated at this time, any added smoke may exacerbate health
concerns for sensitive populations during the peak heating during
the coming days.
The mid/upper level ridge is forecast to begin to weaken by Sunday
along with a slight increase in onshore flow. Thus, look for
temperatures to cool by a few degrees across the interior albeit
remaining well above seasonal averages. Forecast ensembles are in
decent agreement with another mid/upper level trough to develop
along the West Coast early next week. This will bring a region-wide
cooling trend early next week and likely return of a deeper marine
layer. Longer range outlook leans toward continued warm and dry
conditions into the Labor Day weekend.
&&
.AVIATION...as of 04:35 PM PDT Thursday...For the 00z TAFs. The
marine layer continues to compress this afternoon, with the latest
coastal profilers reporting a depth that is running at around
1000ft. Onshore winds (15-20kt) are also peaking this afternoon
along the coastal gaps and passes. These winds will gradually
subside this evening, but given the shallow nature of this marine
layer, and in accordance with the latest surface smoke values on
the HRRR-smoke, are on track for winds aloft to loft smoke into
portions of the inland North and East Bay terminals (e.g.
STS/LVK/CCR) through tonight and into tomorrow. As such, have
added HZ to the terminals, while using FU for LVK to account for
greater concentrations expected over the East Bay. The compressed
marine layer will also result in cig reductions at the coastal
terminals (e.g. MRY/SNS/WVI) where IFR/LIFR conditions are on
track to develop in the overnight. Moderate confidence (TEMPOs
OAK/APC) in patchy marine stratus developing along the Bay
Shoreline, with higher likelihood of stratification developing
along the East Bay Hills and coastal portions of the Napa Valley.
Cigs that do develop will lift and clear by 16-18Z tomorrow
morning. Will then see a return of onshore flow along the coast
and bays by Friday afternoon.
Vicinity of KSFO...VFR through the period. 20-25kt gusts will be
possible at times this afternoon as onshore flow streams in from
the gaps and passes. These winds will gradually subside by early
evening. While stratification is possible tonight within the OAK
vicinity, the chances for patchy stratus reaching SFO tonight and
into Friday morning are rapidly decreasing due to a shallow
marine boundary layer. Are expecting a relatively quiet night with
light onshore winds (5-10kt). Winds will then pick up once again
tomorrow afternoon as onshore flow streams back in to the vicinity
from the gaps and passes.
KSFO Bridge Approach...Similar to KSFO.
Monterey Bay...VFR cigs this afternoon with breezy onshore winds,
and slightly stronger winds in the Salinas Valley. IFR/LIFR
ceilings with patchy FG will return late Thursday night and
lasting through Friday morning due to a shallow marine layer.Cigs
will then lift by 17-19Z.
&&
.FIRE WEATHER...as of 3:30 AM PDT Thursday...Nighttime drying
event is currently underway above the marine inversion layer. Were
seeing humidity values as low as 3% at Ben Lomond and 4-8% at
Rose Peak in the Diablo range and even down to 12% Mallory Ridge
over in the East Bay hills just below 2000 feet. Elevations above
1500 feet showing significant warming trend with readings already
in the lower 70s or about 15 degrees warmer than yesterday at this
time. Marine layer is compressing as forecast.
Fuels are climbing back to the 97th percentile across the North
Bay with values 90 percent Bay Area hills and near normal below
1000 feet due to the recent persistent marine layer influence.
However given the long term drought and late summer conditions the
fine fuels will dry rapidly as the next warming and drying trend
starts. Expect to see that by this afternoon for inland areas.
Expect little or no humidity recovery in the hills the next
several nights and perhaps even night time drying like were seeing
early this morning. Minimal smoke today but increasing from north
to south Friday and likely into Saturday as smoke from the NorCal
fires drifts south. The incoming smoke will literally be a smoke
signal that the dry north winds are working down the Sac Valley
and arriving. Expect this to occur overnight into Friday for the
North and East Bay.
Widespread 90s and lower 100s Friday afternoon and then Saturday
looks to be the hottest day for inland areas. The coast will
remain mild. Expect light offshore winds at night peaking early
Saturday morning for the Napa hills. Criteria will be near
critical but at this time we look to fall short of Red Flag
criteria as no moderate/strong offshore winds are forecast.
On Weds afternoon we saw heavy initial attack fires erupt across
the state as well as continued activity for the large ongoing
wildfires. The hot/dry conditions will now be over the Bay Area
the next several days so any new starts will likely exhibit rapid
growth. Essentially the marine layer has been our safety shield
for much of August. The ridge will minimize its impacts and we are
rapidly approaching September which signals the start of our
climatological offshore wind season and peak fire season for the
Bay Area.
&&
.MARINE...as of 02:44 PM PDT Thursday...Winds out of the
northwest increase over the waters this afternoon growing strong
and becoming more widespread over the waters by Friday. These
winds will have the potential to generate steep waves and produce
hazardous seas conditions, particularly for smaller vessels. Seas
remain wind drive at a period around 8 to 10 seconds with a
lighter, longer period southerly swell embedded it.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...GLA...Pt Arena to Pigeon Pt 10-60 nm from 3 AM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
SCA...Pt Arena to Pt Reyes 0-10 nm
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
&&
$$
PUBLIC FORECAST: RGass
AVIATION: Diaz
MARINE: Diaz
FIRE WEATHER: RWW
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Area Forecast Discussion
National Weather Service Shreveport LA
941 PM CDT Thu Aug 26 2021
.UPDATE...
No wholesale changes are needed to this afternoon`s forecast
package at this time. Updated the 00Z-03Z PoPs to reflect the
diminished convective activity as of 02Z, and updated the QPF and
Wx grids accordingly. RAP13 and HRRR are in agreement that no
further convection is expected throughout the overnight hours,
thus maintaining minimal PoPs through 12Z. Otherwise, ingested the
last several hours worth of temperature and dewpoint observations
and interpolated through to morning lows in the low to mid 70s
areawide. /26/
&&
.PREV DISCUSSION... /issued 639 PM CDT Thu Aug 26 2021/
AVIATION...
For the 26/00Z TAFs, a line of thunderstorms is tracking westward
across our southern zones, primarily south of the I-20 corridor,
thus TEMPO for TSRA at LFK. Carrying VCTS for GGG, SHV and TXK.
Storms will dissipate after sunset, with VFR conditions prevailing
through the nighttime hours. Some brief MVFR conditions resulting
from patchy fog are possible near dawn at MLU, ELD, LFK and TYR.
VFR conditions will then prevail at all terminals into the
afternoon. Winds will be generally from the east/southeast with
peak sustained speeds of 5-10kts. /26/
PREV DISCUSSION... /issued 240 PM CDT Thu Aug 26 2021/
SHORT TERM.../Tonight through Friday Night/
Temperatures this afternoon have climbed into the lower to mid 90s
across the area with heat index values ranging from the lower to
mid 100s. A Heat Advisory will remain in effect this afternoon
through 6:00 PM CDT this evening. Starting to see some showers and
thunderstorms develop this afternoon across deep east Texas and
southwest Arkansas. Expecting this activity to increase and move
into our Louisiana Parishes during the afternoon hours before
coming to an end shortly after sunset.
Overnight lows will range from the lower to mid 70s across the
area with generally clearing skies. We could see some patchy fog
overnight for a few locations, but definitely not widespread.
As we move into Friday, the good news is that temperatures and
dewpoints will be slightly lower than what we have seen over the
past few days, which in turn means no need to issue another Heat
Advisory. Afternoon highs will generally range from the lower 90s
to near 95 degrees across most of the region. Showers and
thunderstorms will once again be possible Friday afternoon, with
the best chances coming for areas along and south of I-20.
Overnight lows Friday night will generally range from the lower to
mid 70s across the area. /33/
LONG TERM.../Saturday through Wednesday Night/
The first 24 hours of the long-term forecast, mainly Saturday
through sunrise Sunday, will continue to be characterized by a deep
southerly flow around a strong deep layer ridge centered over the
Carolinas. This should continue to bring chances for diurnal showers
and thunderstorms associated with the sea breeze northward into the
forecast area. Low-level moisture will be rapidly surging northward
into the area. Given the cloud cover and a relatively high amounts
of convective coverage, this should help to hold daytime high
temperatures in the lower 90s for Saturday.
Now...onto the big story. Tropical Depression Nine has developed in
the Western Caribbean Sea. Very early Saturday morning, TD #9 should
move across Cuba and into the very warm waters of the Southeast Gulf
of Mexico. There will be a very favorable environment in place for
strengthening into an eventual hurricane. The flow around the ridge
over the Carolinas will steer this storm northwestward towards the
Louisiana coast, with an expected landfall either very late Sunday
or very early Monday morning. Most of the operational model guidance
continues to trend with a more eastward track, generally towards
Southeast Louisiana, followed by a more northward turn either
generally up the Ouachita or Mississippi Rivers, and eventually
northeast into Northwest Mississippi by Tuesday morning.
There is still enough uncertainty in the track that a shift eastward
or westward will significantly change the impacts to our area, both
in terms of wind and rainfall. At this time, the areas most likely
to be impacted by this storm appear to be Louisiana...especially
east of Interstate 49, and South Central Arkansas. The western side
of a landfalling tropical system tends to be the "dry" side. Thus,
there will be very tight gradient in the rainfall amounts. Potential
rainfall amounts should range from 3 to 6 inches east of a line from
El Dorado to Colfax, with totals increasing with eastward extent.
Rainfall amounts decrease quickly to the west.
While the main impacts appear to be focused on Louisiana and
Arkansas, this storm still has a long way to travel. The remainder
of the forecast area is still not out of the woods. Everyone is
encouraged to continue to monitor the latest forecasts over the next
few days.
Beyond Tuesday, the forecast is very uncertain. The NBM continues to
hint that a moisture plume trailing southwest from the remnants of
this tropical system will continue to provide chances for mainly
diurnal showers and thunderstorms through the midweek time frame.
Therefore, chance PoPs were maintained, with the highest rain
chances across the southeast half of the forecast area close to this
tropical moisture plume.
CN
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 75 95 75 91 / 10 30 0 40
MLU 73 94 74 91 / 10 30 10 50
DEQ 74 93 73 91 / 0 10 0 20
TXK 75 93 75 90 / 0 20 0 30
ELD 72 93 72 91 / 0 20 0 40
TYR 75 93 74 91 / 10 30 0 30
GGG 73 93 73 90 / 10 30 0 40
LFK 74 94 73 89 / 20 30 10 60
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&
$$
26/33/CN
Area Forecast Discussion
National Weather Service Sacramento CA
238 PM PDT Thu Aug 26 2021
.SYNOPSIS...
Winds shift to the north today, and will become locally breezy
Friday and Saturday. This along with low humidity and dry fuels
will bring critical fire weather, so a Red Flag Warning has been
issued. Smoke and haze from the wildfires will continue to impact
portions of the area.Temperatures will warm to above normal
levels by late week, though the smoke may keep it from getting as
hot as it otherwise could be.
&&
.DISCUSSION...
A building high pressure ridge will increase the north to south
pressure gradient late tonight into Friday. The HRRR smoke model
shows near surface smoke levels increasing across the Valley and
Delta as northerly winds increase with this gradient. Air quality
will likely worsen. For more details on this, go to AirNow.gov or
check with your local air quality district.
There north winds over the northern and central Sacramento Valley
will increase further early Friday morning and become gusty.
Winds could gust to 35 mph during the strongest winds mid day and
afternoon. Relative humidity recovery will be moderate to poor in
the morning, with afternoon humidity dropping to single digits to
teens from around Chico northward. The Fire Weather Watch in that
area has been upgraded to a Red Flag Warning from 5 am Friday
morning to 11 am Saturday morning. The earlier start is due to
winds picking sooner than previously expected.
The ridge strengthening offshore will also lead to warming over
the next several days. Triple digit high temperatures are
forecast for northern Sacramento Valley on Friday, with chances
expanding south down the Valley for Saturday and continuing
Sunday. Wildfire smoke may reduce solar heating, so have reduced
forecast high temperatures by a few degrees, with highs projected
to peak around 100-101, bringing moderate heat risk.
Monday Valley highs cool down into the low to mid 90s as an upper
trough approaches, bringing cooler onshore flow. This should act
to shift the smoke eastward, bringing clearer air. Gusty southwest
winds over Sierra ridges could enhance fire weather concerns
there. EK
&&
.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Ensembles are in good agreement with dropping an upper level
disturbance south along the British Columbia coast toward Oregon
itno Tuesday. Locally, this would lower geopotential heights and
allow temperatures to moderate closer to normal by around Tuesday.
This would also bring gusty southwest winds, which could increase fire
weather concerns over the Sierra.
&&
.AVIATION...
VFR with gusts generally under 12 kts. By 00 UTC Friday,
conditions begin to degrade starting in the northern Sacramento
Valley terminals due to area wildfires smoke. Widespread MVFR to
locally IFR conditions develop southward overnight due to the area
wildfire smoke. Northerly winds increasing after around 10 UTC
with surface gusts 15-30 kts.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 5 AM Friday to 11 AM PDT Saturday for
Central Sacramento Valley in Glenn, Colusa, Yuba, Northern
Sutter, and Butte County Below 1000 Ft-Eastern Mendocino NF-
Eastern Portion of Shasta/Trinity NF-Northern Sacramento Valley
to Southern Tehama County Line Below 1000 Ft-Northern Sierra
Foothills from 1000 to 3000 Ft. Includes portions of Shasta-
Trinity and Butte Units-Southeast Edge Shasta-Trinity NF and
Western Portions of Tehama-Glenn Unit.
&&
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