Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/16/23
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
622 PM CDT Fri Sep 15 2023
.UPDATE...
Issued at 620 PM CDT Fri Sep 15 2023
Increased sky cover based on the HRRR smoke to account for the
elevated smoke over the region. It`s expected to affect the region
into Saturday afternoon. Otherwise, the forecast remains on track
this evening.
&&
.SHORT TERM...(This Evening through Saturday Night)
Issued at 106 PM CDT Fri Sep 15 2023
The primary forecast concerns involve potential stratus cloud
influence on temperature over northeast South Dakota and west
central Minnesota on Saturday, as well as near surface smoke
potential.
At 1 PM CDT, skies are mostly sunny on light northwesterly component
winds, while surface high pressure gradually builds into the
northern plains. Temperatures are warming through the 60s and 70s.
Surface obs in conjunction with HRRRsmoke output supports the idea
that any haze/near surface smoke is down over the
southern/southwestern forecast zones. Visibility has only been down
to between 6 and 10 miles today at KPIR and points south, suggesting
concentrations of near surface smoke are not very high.
The HRRRsmoke model does advect another slug of both near surface
smoke and smoke aloft down through the region overnight into the
first half of the day on Saturday. But, when fed through the
forecast building process, it resulted in just a few patches of haze
later tonight through Saturday, and a slight uptick (maybe ~20
percent) in skycover values (smoke aloft) tonight through Saturday.
The other concern is low stratus potential, trying to sneak into the
northeastern corner of the CWA early Saturday morning and persisting
throughout the day. The low level thermal advection pattern is CAA
on northerly winds from now until early Saturday evening, when the
surface high translating through the region finally begins to center
itself east of the CWA, resulting in the development of return flow
southerly winds out west Saturday night. The RAP model, along with
some other short term guidance(s), is hinting at some low clouds
developing/moving down in these low level northerly mixing layer
winds. If this happens, and the clouds take most of the day to mix
out, high temperatures could be in jeopardy. Although, looking at
the going forecast high temperatures along/east of the Prairie
Coteau (60s) on Saturday, the gap between what is forecast and what
ends up being observed might not be too far off.
.LONG TERM...(Sunday through Friday)
Issued at 106 PM CDT Fri Sep 15 2023
Warmer air will be the theme to start this period, with daytime
temperatures warming into the 80s for Monday and Tuesday. A few 90
degree readings will be possible over portions of central SD Monday,
and south central SD Tuesday.
Looking at the surface weather map, we`ll start out at 12Z Sunday
with a ridge of high pressure stretching from Ontario through much of
MN and eastern SD. However, a trough will be over Alberta and
eastern MT through the western third of SD. The 500mb ridge to our
west with northwesterly flow over our forecast area at 12Z Sunday
will become surpressed as it moves over the Central and Northern
Plains states, with zonal to northwesterly flow continuing as the
ridge shifts overhead by 06Z Monday. We`re still monitoring the
trends for early next week with the lows over western Canada and off
the CA coast, and how that will impact our weather for much of the
work week and especially the latter half of the work week into next
weekend. There is pretty good agreement with the warm and dry air in
place until about Wednesday. This is when several unknowns come into
better view on whether we have a faster/slower more northerly or
southerly couple of systems move through. Either way, it will be a
change from our dry and warm weather, with at least a slight chance
of precipitation (20%)returning as early as early Wednesday morning
and continuing through Friday. After 80s being common for Monday and
Tuesday, 70s look to be more realistic for the latter half of the
work week. 60s are possible as well, especially as we wrap up the
work week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 620 PM CDT Fri Sep 15 2023
Terminals KABR,KATY,KPIR,KMBG
VFR conditions are expected through the next 24 hours.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&
$$
UPDATE...Wise
SHORT TERM...Dorn
LONG TERM...KF
AVIATION...Wise
Area Forecast Discussion
National Weather Service Amarillo TX
648 PM CDT Fri Sep 15 2023
...New AVIATION...
.SHORT TERM ...
(This evening through Saturday night)
Issued at 242 PM CDT Fri Sep 15 2023
Another round of conditional afternoon thunderstorms is possible
again today thanks to some clearing skies after morning
convection. Areas in the SW and central TX Panhandle have had a
chance to destabilize ahead of a subtle lead impulse preceding the
main upper disturbance over Colorado. This minor leading
perturbation within zonal flow is already trying to initiate weak
convection along the TX-NM border and northern Panhandles. Our 18z
special sounding and RAP mesoanalysis show MUCAPE in the
1000-1500 J/kg range for the southwest and central Panhandles,
which might be enough to support this earlier convection. There is
also an east-west oriented boundary visible on radar and
satellite marching south through Amarillo as of 2 PM that could
come into play later. However, with weak MLCAPE, mediocre bulk
shear, and less than ideal lapse rates, storms may struggle to
sustain themselves until the main upper trough approaches later
this evening. As better dynamics arrive and shear is able to
improve, CAMs suggest an isolated cell or two could traverse NW
to SE through the west/southwest Panhandles between 7 PM to
midnight. This activity could be strong to severe with damaging
winds and large hail the primary threats. Additional
showers/storms will linger in the south overnight until the wave
drives moisture out of the area. PWATs are still over 1.00" across
the CWA, and rainfall totals exceeded 1-2 inches in some spots
from this morning`s storms, leading to a continued flooding threat
from additional heavy rainfall this evening.
The rest of Saturday looks to stay quiet as drier air settles in.
Clouds will finally vacate the area, making for a beautiful
Saturday with light north winds and high temperatures comparable
to today (mid to upper 70s). These clearing skies and light winds
will also allow for more radiational cooling overnight Saturday,
leading to Sunday morning lows being noticeably cooler in the
upper 40s to low 50s.
Harrel
&&
.LONG TERM ...
(Sunday through next Thursday)
Issued at 242 PM CDT Fri Sep 15 2023
The long term message consist of warmer temperatures next week
along with isolated chances for storms that mostly favor the
southern and eastern portions of our CWA. The upper trough across the
eastern CONUS will advance out into the Atlantic this weekend.
Meanwhile, high pressure will build back into southwestern parts
of Texas. Heights are expected to rise at the forefront of the new
week, thus allowing temperatures to rise as well. The initial
pattern consists of northwest flow aloft that should shift to
zonal flow by Tuesday. By the midweek timeframe, a new closed
upper low will develop in the western CONUS. At this point, long
range models show divergence in where they set up the closed low
as it progresses towards the Great Plains. Then heading into next
weekend some of the long range deterministics hint at a cold front
entering through the Panhandles, but that outcome will be
contingent on how our synoptic pattern pans out in the front half
of the week.
Our forecasted high temperatures should range in the mid to upper
80`s for the majority of the extended, with a few lower 90`s in
place for areas near the Canadian River Valley and the Palo Duro
Canyon. As previously mentioned, there are slight chances for
isolated storms in the southeast Texas Panhandle for Monday and
Tuesday; but then, those chances relocate further east Wednesday
onward. The potential for severe storms still looms over the
eastern and central Panhandles by the midweek. However, due to
model inconsistencies, it is difficult to pin point areas of
interest and the potential strength of this system at this time.
Rangel
&&
.AVIATION...
(00Z TAFS)
Issued at 637 PM CDT Fri Sep 15 2023
A thunderstorm southwest of KDHT is moving southeast to start the
00z period, and may eventually approach KAMA . While the bulk of
the storm isn`t directly impacting KDHT and could miss KAMA
later, showers and lightning from this storm may still be in the
vicinity of these sites. MVFR CIGs should settle in behind the
showers and storms overnight, clearing out from north to south
Saturday morning. Winds will stay out of the north/northeast
around 10 kts throughout the period.
Harrel
&&
.PRELIMINARY POINT TEMPS/POPS...
Amarillo TX 57 77 53 82 / 60 10 0 0
Beaver OK 56 77 49 82 / 40 10 0 0
Boise City OK 52 75 47 83 / 40 10 0 0
Borger TX 59 80 54 86 / 40 10 0 0
Boys Ranch TX 57 79 53 83 / 50 10 0 0
Canyon TX 57 77 54 81 / 60 10 10 0
Clarendon TX 61 76 56 81 / 60 20 0 10
Dalhart TX 52 76 47 82 / 50 10 0 0
Guymon OK 54 77 48 84 / 30 10 0 0
Hereford TX 57 77 53 82 / 60 20 10 0
Lipscomb TX 56 77 52 83 / 40 10 0 0
Pampa TX 58 75 52 81 / 40 10 0 0
Shamrock TX 59 78 55 83 / 40 20 0 0
Wellington TX 61 79 55 84 / 40 20 0 0
&&
.AMA WATCHES/WARNINGS/ADVISORIES...
TX...None.
OK...None.
&&
$$
SHORT TERM...38
LONG TERM....55
AVIATION...38
Area Forecast Discussion
National Weather Service La Crosse WI
952 PM CDT Fri Sep 15 2023
.UPDATE...
Issued at 950 PM CDT Fri Sep 15 2023
Guidance and surface/satellite trends continue to support the
development of widespread fog for much of the area after midnight,
with the best consensus for dense fog being from the Charles City
to La Crosse to Black River Falls areas. This fog forms in what
might be best described as a Goldilocks corridor where conditions
will line up just right. To the north, low stratus developing
over northwest Wisconsin may keep visibilities from falling too
far while high clouds may not clear the eastern forecast area
until after 08-09Z. Over south-central MN, the influx of drier
air and stronger winds behind the surface trough will help to
erode the fog late tonight, but to what degree is uncertain.
Finally, we may see elevated showers towards sunrise that could
through a wrench in the forecast.
That all being said, this fog event has both advective and
radiative components driving its development, which is why the
models are so lock step in its development. Have issued a dense
fog advisory along the corridor of highest confidence of seeing
quarter mile or less visibilities, but expect that the coverage
of the advisory will need adjusting later tonight--possibly
further west as the latest RAP/HRRR are indicating.
UPDATE Issued at 415 PM CDT Fri Sep 15 2023
Latest trends in the observations and near-term model guidance is
that fog should develop overnight as the mid to high cloud deck
departs and an already pre-conditioned near-surface airmass
rapidly saturates. A 50-70-mile wide ribbon of 60+ degree
dewpoints stretches from south-central Minnesota to west-central
Wisconsin ahead of a pre-frontal trough dropping southeast through
the region. T-Td spreads within this corridor are only 3-5
degrees owing to the extensive clouds and precipitation earlier
today.
Extrapolation of this axis matches well with the output from the
near-term guidance--bifurcating the forecast area from northeast
Iowa into central Wisconsin between 06-12Z, with drier air
infiltrating the western forecast area towards south-central
Minnesota. Therefore, the probabilities for the densest fog will
be within the aforementioned corridor where the 12Z HREF
visibility progs have a 30-60 percent chance of visibilities
falling below a quarter of a mile. Will need to monitor conditions
through the evening for a potential dense fog advisory.
&&
.DISCUSSION...(This evening through Friday)
Issued at 235 PM CDT Fri Sep 15 2023
Key Messages:
- Northeast-southwest running band of light showers will continue to
progress east for the rest of the afternoon, with a decrease
in areal extent as they combat drier air over WI. Most should
end by early evening with only minimal amounts.
- A few more showers for parts of northeast IA/southwest WI
Saturday with, again, minor accumulations expected.
* SHOWERS END THIS EVENING - a few more possible across northeast IA
and southwest WI Saturday
A northeast-southwest running band of mostly light rain showers ran
from northeast WI into southwest IA early this afternoon. Broad low
level warming, ripple in the upper atmosphere, a sfc trough and a
ribbon of low level moisture transport were all playing rolls in
firing up the showers. There has been some decrease in intensity and
areal coverage as the pcpn has worked east into WI where a bit of
dry air was helping counter the rain. Latest CAMS support a
continued decrease and gradual end as the band continues to slowly
shift east this evening.
Before it does though, the CAMS also continue to spark isolated
showers/storms along a cold front hanging southwest-northeast across
MN - separate from the primary band. The meso models wait until late
day to get them going, tapping into ~500 J/kg of MUCAPE. If the
activity gets going, it would be short lived with instability
quickly dropping off with sundown. Model trends also favor keeping
them west/northwest of the local area...IF they develop.
Working into Saturday, another upper level shortwave trough is
progged to drop across the dakotas from Canada this evening,
spinning over the mid mississippi river valley Sat night. The
feature should have enough saturation to fire off more showers while
a RAP suggested 1000+ J/kg of MUCAPE helps with storm development.
Questions locally is how far northward the pcpn will extend. Short
term and medium range guidance keep the bulk of related QPF just
south of the local area, but would stretch rain chances into
northeast IA/southwest WI. Main thunder threat would be across
southeast IA. Will lean into the model blend for rain chances with
all this in mind.
* LOOKING AHEAD
As an upper-level ridge builds east towards the Upper Midwest early
next week above-normal temperatures are likely. NAFES guidance is
1.5 standard deviations above normal for high temperatures Tuesday
in parts of Minnesota and Wednesday area wide. So, while it will be
noticeably warmer with most locations at or above 80 on Wednesday,
record-breaking heat is not expected. Well-organized rain chances
appear unlikely until later next week, but we will have to wait on
the details as there are still major differences exhibited by the
global models that far out.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 645 PM CDT Fri Sep 15 2023
Widespread fog develops after 06Z with the highest probabilities
(50-70 percent) of seeing IFR to LIFR conditions along a 70 to 100
mile wide line from CCY to MDZ. Brought LIFR visibilities to LSE
as it falls along this line, with lesser confidence towards RST
resulting in the inclusion of an LIFR stratus deck but higher
visibilities. Winds will be light and variable overnight, veering
to the northwest for Saturday at 5 to 10 kts under a 4-6 kft
cloud deck.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory from 4 AM to 9 AM CDT Saturday for WIZ033-034-
041-042-053.
MN...Dense Fog Advisory from 4 AM to 9 AM CDT Saturday for MNZ088-095-
096.
IA...Dense Fog Advisory from 4 AM to 9 AM CDT Saturday for IAZ008>011-
018-019-029.
&&
$$
UPDATE...Skow
DISCUSSION...KAA/Rieck
AVIATION...Skow
AREA FORECAST DISCUSSION
National Weather Service Bismarck ND
1015 PM CDT Fri Sep 15 2023
.UPDATE...
Issued at 1015 PM CDT Fri Sep 15 2023
Smoke continues to linger across much of central and eastern
portions of the CWA tonight. Although visibilities have improved
some, expect smoke to linger through the night. Latest HRRR smoke
runs even lingers at least patchy smoke across the west and some
central areas tomorrow morning, thus extended patchy smoke mention
in these areas through tomorrow morning. Cool temperatures are
still expected tonight. Slightly lowered temps in the west based
on current trends, lowering dewpoints, and the latest NBM runs
coming in a little cooler. Even so, the mention of frost has
still remained in the southwest and still looks to be too patchy
for any highlight at this time. These cooling temperatures and
expected light winds could bring some patchy fog to central areas
tonight. Added in patchy fog for some areas higher resolution
models are highlighting lowering visibilities. Removed mention of
smoke for any areas with patchy fog, although smoke may also
continue for some of these areas as well.
UPDATE Issued at 655 PM CDT Fri Sep 15 2023
Main update is for the abundant wildfire smoke that has return
across much of the CWA. Visibilities are currently being reported
as low as 2 miles at times. Expect this smoke to stick around
through the evening hours. Although the HRRR Smoke model, at least
at the surface, is not particularly handling the current smoke
well it is handling the overall trend for the movement of smoke.
Based on this extended smoke coverage through the night for much
of the CWA, with some improvement in the north expected.
Otherwise some weak returns in the far north could bring a
sprinkle or brief light rain shower early this evening.
Temperatures tonight could be quite cool in some areas and
approach frost criteria. Current forecast in some areas is
slightly higher than NBM 50th percentile. This would indicate
perhaps some areas, mainly the west, could get cooler than
currently forecast. Even lowering to the NBM 50th would still
isolated frost possibilities in the far southwest. For now left
the temperatures as is and will continue to monitor.
&&
.SHORT TERM...(This Evening through Sunday) Issued at 305 PM CDT
Fri Sep 15 2023
The wildfire smoke continues to stream in from Canada, reducing
visibilities below 3 miles in some locations. The HRRR and the RAP
smoke models have been not been performing well today. The smoke
has mixed to the surface faster and more widespread than modeled,
so most of the CWA is blanketed in "areas of smoke" until 2z.
After 2z I`d imagine the boundary layer will stop mixing the smoke
down. Winds will continue to gust around 20-25 mph this evening
until sunset, then calm winds and clear skies. With this the
concern of FROST in the southwest is real. Forecast lows are in
the mid 30s for Adams, eastern half of Bowman, and most of
Hettinger counties TONIGHT. The rest of the weekend will be
quiet weather still with a ridge moving in through Sunday.
.LONG TERM...(Monday through Friday) Issued at 305 PM CDT Fri Sep
15 2023
The work week will start warmer than average with zonal flow
setting up and a warm thermal ridge in the southwest. With these
warmer temperatures and breezy winds, there are some fire weather
concerns Monday in the northwest for a few hours. Tuesday the
flow pivots to the southwest which is our active pattern. There
chances of showers all day Wednesday through the end of the week.
With temperatures in the upper 60s and lower 70s, the
possibilities of thunder are very low.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 655 PM CDT Fri Sep 15 2023
Areas of smoke will bring MVFR to brief IFR visibilities through
tonight, with VFR conditions generally expected to non-smoke
covered sites. Wildfire smoke has moved into much of western and
central ND, reducing visibilities to as low as 2 miles at times,
especially from KMOT to KBIS and eastward including KJMS. Expect
this trend through this evening, with perhaps some slight
improvement tonight, although smoke may still linger through the
night. Patchy smoke could then be found across the west on
Saturday, although confidence is not high enough to include at
this time. Otherwise look for lingering clouds to dissipate
tonight, as well as today`s breezy winds. Saturday then sees
mainly clear skies, light winds, and VFR conditions.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Anglin
SHORT TERM...Smith
LONG TERM...Smith
AVIATION...Anglin
Area Forecast Discussion
National Weather Service Grand Forks ND
948 PM CDT Fri Sep 15 2023
.UPDATE...
Issued at 948 PM CDT Fri Sep 15 2023
Still a little bit of patchy haze/smoke and a smell in the air
even though visibilities have improved over Grand Forks. Will
continue to keep smoke mention a bit longer, then push it off to
the southwest after midnight. Cloud cover has been continuing to
move in from the north even as showers fizzle out this evening.
Temps seem on track to bottom out in the 40s. A this point think
there will be more stratus than fog, but will continue to keep an
eye on things as the night goes on.
UPDATE Issued at 659 PM CDT Fri Sep 15 2023
Still getting quite a few sites reporting smoke/haze across
portions of our northern forecast area. Extended mention a bit
further east and south. Models show some improvement later on this
evening into the overnight, but neither the HRRR or RAP are doing
very well with this plume of smoke so will take with a grain of
salt. Still getting a few showers moving into our northern
counties, so will keep 20-30 POPs going until sunset.
&&
.SHORT TERM...(This evening through Saturday night)
Issued at 317 PM CDT Fri Sep 15 2023
Key Messages:
1)Smoke aloft and at the surface for the rest of the day
2)Showers along the international border, as far south as HWY 2
Current satellite shows clouds moving south from Canada, and
associated showers are popping up on radar. Light rain is being
reported with these returns, so falling in line with the forecast.
For the rest of today, Showers will continue along the international
border as this upper low moves east to our north. Winds will calm
around sunset, and smoke that has been reported at the surface at
many sites should hopefully mix out as well. This smoke is more
Canadian wildfire smoke, and models are not handling its presence
too well. Thus, a lot of guesswork and not high confidence on the
time of dissipation from our skies.
Tonight, temperatures will dip into the 40s, with some locations in
the Devils Lake Basin possibly able to dip into the upper to mid
30s. In these locations, patchy frost will be possible on Saturday
morning. With skies staying more cloudy overnight, it will take some
unexpected clearing or advection to reach the upper to mid 30s but
it remains a possibility, although unlikely (<20% chance of
occurrence).
Into Saturday, winds will be lighter and from the north. Highs will
be cool, in the mid to upper 60s. Besides the clouds, looks to be a
quiet weekend in store.
.LONG TERM...(Sunday through Friday)
Issued at 317 PM CDT Fri Sep 15 2023
Key Messages:
1) Near-critical fire weather possible Mon & Tue.
2) Rain chances possible mid-week, specifics uncertain.
Brief UL ridging will be responsible for the WAA, and this will send
our high temperatures back into the 80s to start the work week. With
these temperatures, RHs will be low around 30%. If winds increase
from where they currently are, we could see near critical fire
weather conditions Monday and Tuesday.
Mid-week, when a trough with weak synoptic and mesoscale forcing
dips into the area. In recent guidance, it looks like mesoscale
forcing may be trying to make more of an appearance with this
system. Right now, it is still classified as weak forcing, but this
is something to watch considering yesterday there was nothing in the
guidance so this is an increase. Current QPF amounts look to have
increased since yesterday, with more spatial consistency. WSUP Probs
have increased as well. Over a 72 hour period (Wednesday morning
through the end of the period), Probabilities for greater than an
inch are 20 - 50%, with highest amounts along the SD border. There
is a chance for greater than or equal to 2", around 10 - 30%, again
with highest amounts along the SD border. This system could be a
significant rain maker, and bears watching with this large increase
over 24 hours. Still, timing, location, exact amounts, and other
parameters remain of low confidence.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 659 PM CDT Fri Sep 15 2023
Some MVFR conditions at KGFK, KDVL, and KTVF thanks to wildfire
smoke that is limiting vis down into the 4-6SM range. Should see
some improvement in visibility later this evening, but some MVFR
stratus and even IFR stratus on the MN side will start moving into
the region during the early morning hours. Some improvement to VFR
possible by the end of the period. Winds have mostly lost their
gusts, and should remain mostly out of the northwest at 10 kts or
less.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
&&
$$
UPDATE...JR
SHORT TERM...AK
LONG TERM...AK
AVIATION...JR
Area Forecast Discussion...Updated
National Weather Service Lincoln IL
932 PM CDT Fri Sep 15 2023
.SYNOPSIS...
Issued at 902 PM CDT Fri Sep 15 2023
Cloud cover increases overnight, with mostly cloudy skies by
Saturday morning. Areas of light rain are possible Saturday
morning mainly west of I-55, then scattered thunderstorms are
expected to move in from the west during the evening. Showers and
storms will linger east of I-55 during the day on Sunday.
&&
.UPDATE...
Issued at 930 PM CDT Fri Sep 15 2023
An elongated trough/frontal zone will approach IL from the west
overnight. Mid and high clouds will thicken from west to east late
tonight into Sat morning, with a few sprinkles possible by sunrise
for areas west of the Illinois River. The increased cloud cover
will hold low temps a little warmer in our western counties, with
around 60 for early morning temps. Areas east of I-55 will have
more time under clearer skies to dip in the lower 50s. No
adjustments were done to the precip timing on Saturday, but HRRR
is painting a drier scenario/less coverage of showers through the
day. Even the line of potential storms in the evening appear less
structured in the HRRR. Overall the current forecast database is
in reasonable shape, and no formal update will be needed this
evening.
Shimon
&&
.DISCUSSION...
Issued at 223 PM CDT Fri Sep 15 2023
---------- Key Messages ------------
1. A cold front will bring two rounds of rain and storms on
Saturday. The first round is expected to be light rain, while the
second round will be scattered showers and thunderstorms. There is
a low, but non-zero, chance of a strong thunderstorm west of the
IL River tomorrow evening.
2. Scattered showers and storms will linger east of I-55 through
the day Sunday.
3. Warmer temperatures are expected next week, with highs in the
low to mid 80s after Monday.
------------------------------------
It`s been another beautiful day across central IL, with very few
clouds in the sky, but that will change tonight. A sfc low
pressure system was positioned over Ontario Friday afternoon, with
an attendant cold front draped across WI, IA, and KS, and as this
system approaches tonight mid/high cloud cover will increase,
resulting in mostly cloudy skies by Saturday morning. That cloud
cover will keep low temps a bit warmer than previous nights, in
the mid to upper 50s.
** Saturday **
As this system progresses into central Illinois on Saturday, it
will provide two chances for rain. The first will be light rain
along a leading, weakening cold front, likely reaching the far
western portions of the CWA around or just after sunrise and
progressing eastward through the day, impacting areas west of I-55
through midday then areas east of I-55 in the afternoon. Forecast
soundings show limited instability and dry low-level air ahead of
this precip activity which supports the expectation of only light
precip.
Into the afternoon, thunderstorms are expected to bubble along a
secondary cold front/theta-e gradient. CAMs have trended
west/slower with this aspect of the system, largely keeping
t-storm activity out of the ILX CWA until 5 or 6 PM (22-23z), as
opposed to mid-afternoon like previous model runs suggested.
Forecast soundings still show some low-end potential for strong
storms, but for the most part are unimpressive, with only around
1000 J/kg of MUCAPE and lackluster deep layer shear. Another
factor to consider here is how much the atmosphere recovers after
the morning rain. The morning rain will likely be light enough to
not have too much of a suppressive effect on the instability, but
it`s possible the modeled instability is overdone for tomorrow
afternoon. The trend toward a slightly later storm arrival also
makes the diurnal timing less favorable, at least within the ILX
CWA. The 15.12z run of the HREF shows scattered gusts to 40-45 mph
with the afternoon storms, but almost entirely to the west of the
ILX CWA. Ultimately, those west of the IL River will need to keep
an eye out for an isolated strong storm or two tomorrow evening,
but the severe weather chances have trended downward.
Much like the first round of precip, these storms will progress
eastward in time, although CAMs show the coverage becoming fairly
sparse as daytime heating is lost, leaving some question as to how
much, if any, of this t-storm activity makes it into eastern IL
overnight. With PWAT values expected to be over 1", rainfall
amounts within t-storms will likely exceed 0.50", but such totals
will be very hit or miss. This will be a beneficial rain given
the dry antecedent conditions and the fact that excessive
rainfall/flash flooding are unlikely.
** Sunday **
By Sun morning, an upper level vort max is forecast to be over
central IL, slowly tracking east during the day. With cool temps
aloft (H5 temps around -16 degC) and forcing from the vort max,
scattered showers and storms are expected to be present across
the eastern half of the CWA during the day. With the combo of the
cool temps aloft and the vort max, it would not be a surprise if
cold air funnels were spotted on Sunday. These showers will once
again capable of producing isolated rainfall amounts over 0.50".
** Next Week **
The vort max in place over the area on Sun will shift east, while
upper ridging builds across the Plains. A broad sfc high pressure
centered over Ontario will keep things dry across IL for Mon/Tues
with minimal weather impacts.
There is still a good deal of uncertainty surrounding any specific
precip chances beyond Tues, as consistency of the upper level
pattern evolution has been poor from run-to-run of the
deterministic models. There is signal that a weak shortwave will
lift across the Midwest Wed into Thurs, which would provide a rain
chance. Ensembles show a gradient in rain chances across the ILX
CWA from that system, highest in the west (20-30%) and lower in
the east (10-15%). That seems to be a common theme during the
latter half of next week and into early next weekend: rain chances
will be highest west of the area and diminish with eastward
extent. This pattern shows up in the CPC 6 to 10 day precip
outlook (valid Sep 20-24), with greater chances for above normal
precip across IA/MO compared to IL.
Above normal temps remain on track for next week, as IL sits
between a sfc high pressure to the northeast and a sfc low to the
northwest, resulting in a period of continued southerly flow.
Highs are expected to climb into the low to mid 80s after Mon,
while lows will be mild, right around 60 degrees.
Erwin
&&
.AVIATION... (For the 00z TAFs through 00z Saturday Evening)
Issued at 700 PM CDT Fri Sep 15 2023
VFR conditions will prevail for the majority of this TAF period
through 00z tomorrow. Satellite imagery shows mid and high clouds
positioned west of Illinois this evening, ahead of an approaching
cold front. Those clouds will overspread the area from west to
east later tonight, with mostly cloudy skies by Saturday morning.
Light rain is possible Saturday morning, primarily at KPIA
although perhaps reaching KBMI/KSPI toward 18z/19z. Spotty showers
could linger for our western terminals through the afternoon, but
confidence is low on any terminal site having rain for more than
30 mins to an hour at any one time tomorrow. Better chances of any
thunderstorms will come at the end of this TAF period, but a
decreasing threat is indicated in the latest model runs. If a
storm hits a TAF site, brief MVFR vis could develop. However,
confidence is not high enough to put in this round of TAFs.
Shimon
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$