Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/24/24
Area Forecast Discussion
National Weather Service Boston/Norton MA
1115 PM EDT Tue Apr 23 2024
.SYNOPSIS...
Wednesday brings scattered showers and a thunderstorm or two as
a cold front sweeps across the region. Very chilly Thursday
morning with a Freeze Watch in effect. More seasonable
conditions develop for the weekend. Another chance for showers
comes mid to late weekend.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
11pm Update - Made an adjustment to hourly temps as sites on the
mid Cape and Vineyard have decoupled and radiated. Places like
MVY reported a ten degree drop from the low 40s to low 30s in
the last three hours. The area around the airport is known to
cool quickly do to the soil type, do think this is a localized
occurrence. Have looked at sites like WXFLOW and do see else
where winds are still out o the south around 5-10 mph. Given the
localized nature of this quick cool off, will hold off on any
short-fused Frost/Freeze headlines.
Previous Discussion...
Only minor tweaks to the forecast this evening. Trend of the
latest HRRR, RAP and NationalBlend guidance was for a slower
onset to the measurable showers. This was only by a couple of
hours at most. Still have large surface dew point depressions of
20+ degrees F. It will take some time for humidity to increase
enough to permit rainfall to reach the ground.
Previous Discussion...
Dry and tranquil conditions persist this evening into much of
the overnight hours. Low pressure well to our south will
continue to filter some high clouds across southeastern MA and
the Islands as high clouds stream in from the west ahead of an
approaching cold front.
Winds from the south overnight advecting increased moisture over
southern New England, combined with increasing cloud cover will
keep temperatures considerable warmer than the last few nights,
with lows generally ranging from the upper 30s to low 40s. Rain
showers associated with aforementioned cold front may begin to
push into western MA and CT by daybreak, but expecting dry
conditions through the night for most.
Not expecting to decouple overnight in most locations which will
preclude any radiation fog formation, but winds may slacken just
enough by daybreak for some patchy advection fog to form across
the Cape and Islands.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Cold front sweeps across southern New England during the
daylight hours of tomorrow as trailing shortwave follows suit
late afternoon/ early evening. Expecting two rounds of potential
precipitation tomorrow, the first between 12-18Z with
katafrontal showers tapping into SWerly flow enhanced PWATs,
between 3/4 and 1". These showers are not expected to bring
significant precipitation to the region, perhaps a tenth of an
inch in any locality.
The second round of showers comes, at least as defined by the
CAMs, as a very "stubby" line of potentially convective showers
initiate by the trailing shortwave aloft between 18-23Z. CAMs
remain varied both in the position and geographic spread of
these isolated to scattered convective showers, but all 5 of the
main HREF members derive their existence tomorrow afternoon. Any
convection will remain elevated, and sub severe. Surface CAPE
will be near zero as cold air rushes in on W/NW flow, but breaks
of sunshine during the PM hours will allow a few hundred joules
of MUCape to develop above the surface inversion. All in all,
expecting a few rumbles of thunder, but confidence is rather low
in who will see a passing thundershower. At present, our best
guess is somewhere in central/eastern MA or in southeastern
MA/RI as the shortwave pivots east. Given the potential for
convective showers, a few localized rain totals in excess of
0.25" are possible.
Conditions clear very quickly after sunset across the area as
winds shift to the north overnight. Expected a very chilly
night across southern New England, but there are two scenarios
as to how we may achieve our morning lows. First, in a situation
where we are unable to decouple and radiate, anomolously cold
air aloft, for late April, with 925mb temps as cold as -5C, will
partially mix to the surface, which will derive lows in the mid
20s to low 30s region wide. The second scenario, and perhaps
the less likely scenario, is if we are able to completely
decouple overnight, which would yield radiating under clear
skies to dewpoints, which will be dismal in the mid 10s to 20s.
In reality, we may see somewhat of a mix of these solutions,
with the best chance for a period of slack winds across the far
interior of MA. Given uncertainty in the potential for
radiational cooling, utilize rather "middle of the road"
guidance, the MAV, depicting temperatures dropping to the lower
20s in far NW MA and mid to upper 20s outside of urban
centers. Given the potential for widespread temperatures in the
mid 20s, we have hoisted a Freeze Watch for portions of
Connecticut, northern RI, and interior SE MA where the
frost/freeze program is now active.
With that said, the potential for a widespread freeze is
stronger across the interior, but because the frost/freeze
program does not start in these locations until May 1st, or
later, based on the climatological last freeze, there is no
Freeze Watch in effect. Winds are expected to stay high enough
along the immediate coastline to preclude a hard freeze. Will
note, given the potential for a breeze overnight, this is a
likely a "freeze or nothing" scenario, with frost unable to form
given the winds.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Key Points...
* Dry Thu through Sat. Chance of showers Sat night and Sun.
* Cool Thu, then milder Fri into Mon. Turning cooler Tue.
* Chance of showers Sat night and Sun. Another round of showers
Mon night into Tue.
Details...
Latest guidance suite was in rather good synoptic agreement into
this weekend. Then some differences start to appear, but
nothing profoundly unusual for this forecast time range.
High pressure will remain in control of our weather Thursday
into Saturday. Temperatures will be modulated based on our
relative location to this high center. With the high pressure
moving overhead Thursday, that should be our coolest day of this
stretch. AS this high pressure moves offshore into this
weekend, we begin a warm up to above normal temperatures. Some
question on whether southerly flow will be strong enough to
completely preclude a seabreeze Monday. As high as temperatures
are expected to be, seabreezes are likely, which would mean a
significant temperature gradient between the coast and farther
inland.
A passing warm front should provide a risk for showers some time
late Saturday into Sunday. Monday is looking mostly dry, with a
stalled front to our north. Increasing risk for showers some
time late Monday into Tuesday as a cold front approaches from
the west. Stayed close to the NBM timing for now, but do not
have much confidence in the timing.
&&
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Tonight... High Confidence
VFR through 09Z Wednesday, with MVFR cigs possible across
western terminals through 12Z. Rain showers develop ahead of
advancing cold front during the pre-dawn hours and may creep
east into BAF/BDL prior to 12Z, but terminals farther east will
remain dry through the period. Winds shift further to the SW by
sunrise. Winds generally 10 to as high as 15kt, though some
gusts to 20kt possible along the south coast through sunset
tonight.
Wednesday...High confidence.
Generally low end VFR to MVFR, with lower cigs in showers
between 12-20Z. Localized IFR possible. Rain will trend showery
over stratiform in first surge of cold frontal precipitation.
A secondary round of widely scattered showers will develop after
20Z and may contain isolated TSRA. Uncertainty remains too high
to include a PROB30 or prevailing TSRA group at any terminal,
but the best chance for any sort of thunderstorm remains between
20-23Z.
Southwest winds shift to the west behind the frontal passage mid
day, winds gusting to as high as 20kt.
Wednesday night... High Confidence.
Rapid clearing expected from west to east, widespread VFR with
nearly clear skies. Winds shift to the north and will range
between 5 and 10kt.
KBOS TAF...High Confidence
Cold frontal passage brings showers to the terminal between
15-20Z Wednesday. Low risk for TSRA between 20-23Z before rapid
clearing occurs. Winds ESE this afternoon become SW overnight
and W behind the frontal passage tomorrow afternoon. Winds
eventually become N by late Wednesday night. Uncertainty in
strength of winds on Wed night, but winds will be greatest for
coastal terminals, up to 25kt.
KBDL TAF...High Confidence
Cold frontal passage brings showers to the terminal between
13-21Z Wednesday. Winds become SW overnight and W behind the
frontal passage tomorrow afternoon. Winds eventually become N by
late Wednesday night.
Outlook /Thursday through Sunday/...
Thursday through Friday Night: VFR.
Saturday: VFR. Breezy. Slight chance SHRA.
Saturday Night: Mainly VFR, with local IFR possible. Breezy.
Chance SHRA.
Sunday: Mainly VFR, with local IFR possible. Breezy. Slight
chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight...
Tranquil conditions persist for the waters with southeasterly
winds becoming more southwest overnight. Gusts to 25kt diminish
slightly overnight, but resurges to around 20kt by early AM.
Wednesday and Wednesday night...
Cold front sweeps across the waters Wednesday afternoon bringing
showers and a wind shift from the SW to the W. Low chance for a
thunderstorm across the inner waters late Wednesday
afternoon/early evening but would be localized. Winds further
shift to the north overnight Wednesday, with gusts in excess of
25kt possible across the northeastern waters.
A small craft advisory is in effect for the outer and eastern
waters from 12Z Wednesday to 12Z Thursday for seas in excess of
5 feet and gusts in excess of 25kt.
Outlook /Thursday through Sunday/...
Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft.
Thursday Night through Saturday: Winds less than 25 kt.
Saturday Night: Winds less than 25 kt. Slight chance of rain
showers.
Sunday: Low risk for Small Craft Advisory winds with gusts up
to 20 kt. Areas of seas approaching 5 ft. Slight chance of rain
showers.
&&
.FIRE WEATHER...
Thursday...Potential Elevated Fire Weather Concerns.
Fire weather may again be a concern on Thursday depending on how
much rain falls on Wednesday, and how quickly winds subside as
high pressure builds in by Thursday mid-day. Further shifts will
need to evaluate this risk based on observations and model
guidance.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Freeze Watch from late Wednesday night through Thursday
morning for CTZ002>004.
MA...Freeze Watch from late Wednesday night through Thursday
morning for MAZ017-018.
RI...Freeze Watch from late Wednesday night through Thursday
morning for RIZ001>004.
MARINE...Small Craft Advisory from 8 AM Wednesday to 8 AM EDT Thursday
for ANZ231-250-251-254>256.
&&
$$
SYNOPSIS...Belk/KS
NEAR TERM...Belk/Dooley/KS
SHORT TERM...KS
LONG TERM...Belk
AVIATION...Belk/KS
MARINE...Belk/KS
FIRE WEATHER...KS
Area Forecast Discussion
National Weather Service Green Bay WI
1025 PM CDT Tue Apr 23 2024
Updated aviation portion for 06Z TAF issuance
.KEY MESSAGES...
- Elevated fire weather conditions are likely Wednesday and
Thursday due to relative humidities ranging from 15 to 25
percent. However, relatively light winds and cool temperatures will
keep conditions below critical levels.
- Two systems will bring periods of showers and thunderstorms to
the forecast area Friday through Monday. Watching the
potential for severe weather on Saturday, although it is still
too soon to tell.
&&
.DISCUSSION...
Issued at 224 PM CDT Tue Apr 23 2024
Short Term...Tonight and Wednesday
The latest RAP analysis and satellite/radar imagery show a dynamic
upper trough moving across the western Great Lakes early this
afternoon. The trailing cold front is entering far northern
Wisconsin. Showers and thunderstorms developed by late morning
across north-central and far northeast Wisconsin and continued to
expand in coverage into the early afternoon hours as temps reached
their convective temps. Due to deep mixing (estimated at up to
600mb!!), the showers were high based and produced gusty winds
upwards of 40 mph. Have not received any reports of hail, but
storms in the Upper Peninsula produced three quarters inch hail.
The showers and storms will continue to move southeast for the
rest of the afternoon. Even light showers will be capable of
producing gusty winds to 40 mph as the lower atmosphere will be
supportive of evaporative cooling. Small hail will also be
possible in the strongest storms, but this threat is will be more
confined to central and east-central WI where precip has been more
widely scattered.
Clouds and precipitation: Showers and a few storms will rapidly
exit east- central Wisconsin this evening. Gusty winds and small
hail will be possible but the threat should wane rapidly as
nocturnal cooling sets in. Most showers will exit by the 8-9 pm
hour.
Then a very dry airmass (pwats 20-30% of normal) will move into
the region from the north for the rest of the night. After a
period of mostly cloudy skies behind the front, skies should
rapidly clear late this evening into overnight. Clear skies are
then expected for Wednesday.
Temperatures: No significant changes to the previous forecast.
Don`t think winds will fully decouple tonight, so remained close
the NBM. On Wednesday, low level temps are colder over eastern WI
due to north winds and the previous forecast already showed this
well.
Long Term...Wednesday Night Through Tuesday
An active pattern is expected to set up toward the end of the
work week and persist through early next week. Multiple chances
for rain and thunderstorms will accompany several systems that are
progged to track from the central Plains into the upper Midwest
through Monday. Watching potential for severe weather on Saturday,
although currently too far out in the forecast period to discern
any details. Temperatures will begin a steady incline through the
end of the week before peaking in the mid 70s (~15 degrees above
average) on Saturday given favorable placement in the warm sector.
Friday/Saturday precip... Main focus for the extended is an end of
week system that will bring rain and storm chances to the forecast
area, including potential for some severe weather on Saturday. A
robust upper-level shortwave will spin up a surface low over the
central Plains before trekking into the upper Mississippi Valley
Saturday morning. Current model guidance seems to be targeting
portions of northeast Wisconsin to receive the bulk of the QPF
(~0.6 to 1") from this system, although there is still some
disagreement about when precip arrives on Friday. Suspect that QPF
may trend on the higher end of what ensembles are currently showing
given deep Gulf moisture placing around 1.3" PWATs across most of
eastern Wisconsin. Some elevated storms would be possible Friday
afternoon/evening out ahead of the warm front, although most
convective elements look to come together on Saturday. A trailing
cold front is progged to move east across the warm sector during
peak heating Saturday afternoon, providing a source of lift for
surface-based convection. Additional ingredients (CAPE, lapse
rates, shear) also look to be in relatively good shape for
Saturday, although it is still too soon to tell for certain.
Southeast winds will begin to ramp up Friday afternoon as the
pressure gradient tightens between the leading edge of the
approaching surface low and departing high pressure to the east.
Sunday/Monday precip... A brief lull in precip is expected to set
in Saturday night to Sunday morning before a second system trails
from the Four Corners region into the upper Midwest by Monday
morning. There are still timing issues this far out in the
forecast period, although there is a strong signal for periods of
moderate to heavy rainfall across northeast Wisconsin.
Thunderstorms look to be possible across eastern Wisconsin Monday
afternoon, although this could change as models hone in on timing.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 1018 PM CDT Tue Apr 23 2024
MVFR ceilings still covered a large portion of the forecast area
late this evening. The low clouds should erode early in the TAF
period, except along the lakeshore, where they may persist until
daybreak.
Canadian high pressure will bring clear skies and light and
variable winds to the region for most of Wednesday and Wednesday
evening.
&&
.FIRE WEATHER...
Issued at 224 PM CDT Tue Apr 23 2024
Another period of elevated fire weather conditions is likely on
Wednesday and Thursday due to a very dry airmass that will move
into the region. Afternoon RH values of 15 to 30 percent are
likely on Wednesday, but cooler temps are anticipated in the
lower 40s lakeside to the low 50s inland. On Thursday, RH values
will be slightly higher between 25 to 35 percent, but temps and
winds will both be slightly higher. While RH`s will be near to
below critical criteria, winds and temps should remain below
criteria each day.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION.....MPC/Goodin
AVIATION.......Kieckbusch
FIRE WEATHER...MPC
Area Forecast Discussion...Updated
National Weather Service Lincoln IL
850 PM CDT Tue Apr 23 2024
.KEY MESSAGES...
- Temperatures will fall into the 30s Thursday morning. There is a
around a 50-80 percent chance along and north of I-74 for temps
to fall to 37 or below with frost formation a possibility.
- A warm front will lift north across central Illinois Friday
ushering in much warmer temperatures with highs near 80F over
the weekend. There will also be periodic chances for showers and
storms Friday through Sunday, some of which may be severe.
&&
.UPDATE...
Issued at 850 PM CDT Tue Apr 23 2024
A cold front continues to edge southeastward this evening...with
01z/8pm obs showing it along the Illinois River. The front will be
accompanied by little more than a few mid-level clouds and a shift
in the wind over the next few hours. Based on the latest RAP/HRRR,
it will cross I-55 by midnight...then exit the KILX CWA into Indiana
overnight. Low temperatures will drop into the lower to middle 40s.
Barnes
&&
.DISCUSSION...
Issued at 237 PM CDT Tue Apr 23 2024
Today and Tonight...
This afternoon, a diffuse cold front stretches from central
Wisconsin into northeastern Missouri. A prefrontal band of
showers and a few storms in the warm advection continues across
central Illinois, but will gradually taper off from the north,
ending north of I-72 around 22Z/5pm CDT and north of I-70 around
01Z/8pm CDT. Meanwhile, the aforementioned cold front will push
through the area through the evening with southwest winds veering
to the northwest and eventually northeast in its wake. Meanwhile,
the latest RAP continues to advertise a narrow ribbon of around
200 J/kg MLCAPE along the front, but weak frontal convergence and
displacement from the upper wave digging into the Great Lakes will
result in little if any development across most of central
Illinois. The best chance for an isolated shower or storm will be
along and north of the I-74 corridor. Temperatures are expected to
fall into the lower to mid 40s overnight.
Wednesday and Thursday...
High pressure will build across the Great Lakes midweek resulting
in northeast to east winds across central Illinois with below
normal temps Wednesday to near normal temps Thursday. Temps will
bottom out Thursday morning with lows in the mid 30s to lower
40s, coldest along the I-74 corridor. There is some potential near
and north I-74 for frost development as temps approach the
freezing mark, but a modest breeze will be a mitigating factor.
There is a small (20-40 percent per NBM) chance for temps to fall
below freezing along the I-74 corridor.
Friday through the weekend...
Two separate areas of low pressure will lift from the central
Great Plains to the upper Great Lakes Friday though Sunday. A
broad corridor of southwesterly flow and a favorable fetch off of
the Gulf of Mexico will be in place ahead of the low across the
Midwest. This will result in a surge in temps and humidity
starting Friday and temps will peak with highs near 80F over the
weekend and dew points rising well into the 60s. This more summer-
like heat and humidity coupled with strong spring kinematics will
set the stage for at least a couple rounds of severe weather
during this time frame.
The first low is set to lift across northeastern NE/northwestern
IA Friday evening. Instability will be strongest across IA/MO
but will bleed into western Illinois. Storms should ramp up to our
west as the low level jet strengthens Friday evening with storms
riding the instability gradient east into Illinois. The severe
threat may extend into portions of west central Illinois Friday
night but should diminish with eastward extent and time as storms
outrun stronger instability and the LLJ veers/weakens.
Shortwave ridging moving overhead Saturday should result in a lull
in precip chances during the day, but temps warming to near 80
degrees alongside dew points into the lower to mid 60s will
contribute to moderately strong instability (MLCAPE 1500-2000
J/kg) Saturday afternoon and evening. Moderate flow aloft will
result in 35-40kt deep layer shear. Forcing appears weak/nebulous
Saturday, but so does CINh by mid afternoon, so isolated to widely
scattered thunderstorms could be possible with shear/instability
parameter space favorable for any storms to be severe.
Sunday`s low will take a slightly more easterly track compared to
the Friday low, with the attendant severe weather threat likewise
shifting east further into Illinois. There remains some
uncertainty on the amount of instability owing to ongoing
convection and cloud cover in the region. Timing of cold frontal
passage also appears to be late at night which will limit
instability along the front. If we are able to realize some
stronger instability, deep layer shear and forcing all appear
favorable for a severe weather threat to once again materialize.
Deubelbeiss
&&
.AVIATION... (For the 00z TAFs through 00z Wednesday Evening)
Issued at 637 PM CDT Tue Apr 23 2024
Skies have cleared at the central Illinois terminals early this
evening: however, a cold front currently approaching the Illinois
River will produce SCT mid-level clouds and a shift in the wind
later. Based on current trends and HRRR/RAP forecast, have veered
winds to NW at KPIA by 03z...then further southeast to KDEC/KCMI
by around 05z. Winds immediately behind the front have gusted
25-30kt across Iowa/far western Illinois through the afternoon.
Once the sun sets and the atmosphere decouples, the gusts will
decrease, but am still expecting a few gusts of 15-20kt along/west
of I-55 after FROPA. After a couple hours of gustiness, winds
will decrease and veer to the NE late tonight into Wednesday.
Despite FROPA, skies will not become completely clear tonight as
SCT mid-level clouds across Minnesota/Wisconsin drift southward
into central Illinois through Wednesday.
Barnes
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Indianapolis IN
1028 PM EDT Tue Apr 23 2024
.KEY MESSAGES...
- Afternoon/evening rain expected. Total QPF under a half inch;
Cooler
- Becoming Partly Cloudy on Wednesday.
- Cooler mid-week, with some frost possible Wednesday night for
northern portions of Central Indiana
- Active pattern returns Friday into next week with above normal
temperatures and frequent rain chances
&&
.FORECAST UPDATE...
Issued at 1028 PM EDT Tue Apr 23 2024
Made minor adjustments to account for the location of rain and
current surface observations. Radar shows that the rain has almost
completely moved out of the forecast area. The front itself still
hasn`t made it`s way through central Indiana but it sits just off to
the NW and will move through overnight. Until then, the majority of
clouds have also exited with the rain but while we still sit in a
humid and relatively warm sector, a patchy stratus deck is forming
over the area. Satellite shows that much of the stratus is
currently over the NE counties, but there are some spots of
stratus forming over the Indy metro and areas both north and NE.
Can`t rule out shallow patchy fog in low lying areas as well.
&&
.SHORT TERM (This evening through Wednesday)...
Issued at 235 PM EDT Tue Apr 23 2024
Synopsis:
Surface analysis early this afternoon shows low pressure over the
Central Great Lakes and a second area of low pressure was in place
over OK and the TX panhandle. A cold front across WI, SE IA and
eastern KS connected these two lows. Broad and elongated high
pressure was found across the east coast and stretching west across
the gulf coast. This was resulting in southerly flow across Central
Indiana, however the high pressure system was effectively blocking
moist gulf flow from reaching the Ohio Valley. Aloft, a moderate
short wave was found over WI and MN, with a trough axis extending SW
across IA. This was resulting in moderate westerly flow aloft across
Indiana. This short wave was being influenced by the broader
cyclonic flow across northeast North America as a deep upper low was
anchored near Hudson Bay. Water Vapor showed moisture ahead of the
trough over IL and Indiana and MI. GOES16 shows abundant cloud cover
ahead of the frontal boundary, pushing toward Central Indiana. An
area of rain was found over North Central Indiana, sagging
southward. Dew points ahead of the line have reached the 40s, but
current dew point depressions of 15-20F still exist.
Tonight...
Models suggest the forcing with the approaching short wave will pass
across Indiana this evening as the trough axis and the associated
surface cold front lag behind, passing overnight. Given the recent
radar trends showers over the northern parts of the forecast area
and the expected southern progression of the upper trough, the band
of showers will sag southward to nearly the I-70 corridor by 4-5pm
and farther south by 8p-9p. Forecast soundings through this time
period continue to a saturated column through the late afternoon and
early evening hours. Thus will continue with the ongoing near 100
pops with this band as it sags southward late this afternoon and
evening.
After the forcing clears, residual lingering clouds will be left in
the wake of the rain, as clearing skies will hold off until the wake
of the front overnight. HRRR Suggests lower level saturation toward
12Z hence some lingering lower clouds may still remain during the
late overnight and early morning hours.
Cold air advection will be in place overnight as winds become
northerly. Ongoing lows in the lower to middle 40 appear on the
mark.
Wednesday...
Models on Wednesday show the upper trough departing. Strong ridging
is shown to build across the Rockies, leading to NW flow aloft and
lee side subsidence over the upper midwest, Great Lakes and Ohio
Valley. A strong area of surface high pressure is shown to build
behind the front, reaching the Great Lakes by Wednesday afternoon.
This appears to be a large area of high pressure, extending its
influence from Ontario across the Ohio Valley to the Gulf of Mexico.
Models show relatively high RH within the column in the area as the
day begins, but as heating and mixing resumes, a dry column is
realized. Hence we will look for skies to become partly cloudy as
the day progresses and the surface high builds across the area.
Given the ongoing cold air advection highs will only reach the lower
to middle 50s.
&&
.LONG TERM (Wednesday night through Tuesday)...
Issued at 235 PM EDT Tue Apr 23 2024
Wednesday night and Thursday...
Quiet weather can be expected during this period with high pressure
in control at the surface and rising upper heights.
The main question is frost potential Wednesday night. Winds will be
light, and the cooler airmass will remain in place. However,
uncertainty remains in how much cloud cover there will be. There
will be likely some high clouds moving in over the ridge, but they
may be initially thin.
Will go with lows in the mid 30s north and continue to mention some
frost. Lows will be in the upper 30s elsewhere. On Thursday,
filtered sunshine will boost temperatures into the upper 50s to mid
60s.
Friday and beyond...
A couple of upper systems will eject out of the southwestern USA
during this period. The first on Friday will bring a warm front
northeast through the area. Good southwest flow aloft will bring in
moisture for the front to work with. Will go with likely PoPs most
areas on Friday and Friday night.
Forcing weakens on Saturday but there will still be some around, so
will keep chance PoPs then.
The next upper system will begin influencing the area on Sunday,
with better forcing arriving with a front on Sunday night into
Monday. Continued southwest flow will keep moisture available, so
will go with likely PoPs again.
Of course, some uncertainty in timing of the best forcing remains
this far out, so details could change.
CSU Machine Learning is hinting at some potential for strong to
severe storms at times, but feel that the better threat will remain
west of central Indiana (closer to stronger forcing and better
instability) at least through the first half of the weekend. Will
have to watch the Sunday/Monday system to see if things align better.
Temperatures will be above normal through much of the period. With
the stronger southwest flow aloft, mixing will allow some breezy
conditions through much of the long term period.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 845 PM EDT Tue Apr 23 2024
Impacts:
- Rain is exiting the area
- Winds shifting from SW to out of the north, sustained at 7 to 10
kts
- MVFR ceilings possible at a few sites tomorrow morning under a low
stratus deck
Discussion:
The rain is moving out of the area at the top of the forecast period
leaving behind VFR conditions for much of the night. Then expecting
a low stratus deck to move in from the NE bringing MVFR ceilings
early in the morning and lasting into midday. These clouds will
likely reach LAF and IND but could also get to BMG and HUF briefly.
Winds will shift from SW to NW to N behind the front which will pass
through the region near to after midnight. Expect sustained winds of
7 to 10 kts through the period.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...KF
SHORT TERM...Puma
LONG TERM...50
AVIATION...KF
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
700 PM CDT Tue Apr 23 2024
.KEY MESSAGES...
- There is a 50-70% chance for a freeze Wednesday night into
Thursday morning outside the Metro, with the highest chances
generally west of I-57. Tender vegetation may be damaged if
protective actions are not taken.
- Multiple rounds of thunderstorms late Friday through the
weekend will pose a risk for severe weather and heavy rain.
Damaging wind gusts, large hail, localized flooding, and a
tornado are all concerns, though confidence is low in when and
where chances will be highest at this time. Have multiple ways
to receive warnings, and a plan for where you`ll seek shelter.
&&
.DISCUSSION...
Issued at 149 PM CDT Tue Apr 23 2024
Through Wednesday Night:
At 145pm, current radar imagery shows showers with a few
embedded thunderstorms roughly south of an El Paso to Valparaiso
line. Over the next couple hours, the pockets of sunshine
behind this wave of precip will result in steepening low level
lapse rates for some weak instability favoring isolated showers
and thunderstorms ahead of the cold front slated to reach I-55
around 6-7pm. The stamps from the 12z HREF are looking a little
less aggressive than they did in the 00z iteration, though still
around 50-60% of HREF membership generates 500 J/kg or more of
SBCAPE at some point between 3 and 8 pm along a narrow corridor
extending from roughly Chicago- Waukegan southwest to Galesburg.
Given low LCLs and 30-40 kt of 0-3 km wind shear along the
front, there`s a nonzero (though very small) chance for a
landspout tornado with this activity. However, the steep lapse
rates and dry mid level air would seem to favor more of a
momentum transfer wind concern with the stronger cells; the HRRR
shows this in its wind gust field, with pockets of 40+mph gusts
under showers this evening. In other news, it`s turning quite
warm behind the front given the drier airmass fostering
efficient radiational warming with the anticipated sunshine; the
last few iterations of the HRRR suggest a few locations will
top out around 70 degF for highs before the evening`s over.
Short term guidance suggests northerly winds will stay 5-10 mph
tonight, except quite a bit higher near the Lakeshore, which
should in theory prevent frost from developing and
simultaneously offset radiational cooling to diminish chances of
a freeze (NBM gives 10-20% probabilities north of a Georgetown
to Waukegan line) as well.
The cool advection in the wake of the front will suppress
tomorrow`s highs, most notably near Lake Michigan where the
Lake-chilled boundary layer airmass will be advected inland
throughout the afternoon to keep temps in the 40s in many
locations, including the Chicago Metro. Tomorrow night, there is
a higher chance of widespread frost as high pressure building
into the region leads to light/calm winds allowing for more
optimal radiational cooling. The lowest temps will occur away
from the Lake and west of I-57; further east, the weak
northerly/northeasterly flow will advect southward a shallow
marine layer and attendant stratus which should offset nocturnal
cooling. The NBM suggests west of the I-57 corridor there will
be a 50-75% chance for a freeze, with a 15-30% chance for a hard
freeze (temps < 28 degF) north of Rockford, so frost and/or
freeze headlines will likely become necessary.
Bumgardner
Thursday through Tuesday:
As the high pressure ridge axis reaches northern IL, winds will
veer to southeast on Thursday, advecting into the region a
warmer airmass that will bring afternoon highs into the low 60s
inland, mid 50s Lakeshore. All signs indicate Friday will be
even warmer, though it`ll come with a price: The deterministic
GFS and ECMWF each show a pronounced theta-E gradient lifting
north into the area at some point Friday, and while they
disagree on timing each model suggests precip riding along that
front. Fortunately for us, the associated sfc low will be
displaced well to our west - across the central Plains - though
locally backed winds enhancing low level shear and low LCLs
along and south of that front could prove sufficient for a
couple severe storms, especially across our south and west CWA
where the NAM suggests around 1000 J/kg MUCAPE materializes by
00z Sat (7pm Friday). We`ve still got several days before that
system arrives, so a lot is subject to change, though the CSU
MLP paints a 15%+ probability area across virtually the entire
CWA (save northwest IN).
Convection will certainly have an effect on the warm front`s
movement, but at this point there`s fairly good agreement in the
extended range models and their respective ensembles that
Saturday will be much warmer; the NBM, in fact, gives a 50-65%
chance for highs over 80 degF. This, of course, could be a bust
if there`s more cloud cover than currently forecast or
thunderstorms develop during the day. Instability will certainly
be higher on Saturday compared to Friday, with 50-60+% chances
for more than 1500 J/kg SBCAPE during the evening west of I-55.
However, it`s uncertain whether there will be any trigger for
storm initiation with the warm front expected to be so far
north; it might come down to outflow boundaries from nocturnal
convection Friday night into Saturday morning. CSU again depicts
a 15% contour for severe weather on Saturday, so we`ll be
watching carefully.
Another sfc low will spin up in the southern Plains Saturday
night and lift into IA Sunday afternoon/evening, increasing wind
shear across our area and potentially favoring another round of
thunderstorms which, once again, could turn severe. The SPC has
highlighted our area with a level 2 of 5 (slight) risk for
severe weather on Sunday, with all hazards (damaging wind gusts,
large hail, and tornadoes) seemingly in play; of course, this
will be conditional on Saturday night-Sunday morning convection,
afternoon cloud cover, the precise track of the sfc low, and
the strength of the low - all of which are difficult, if not
impossible, to pin down at this time step. We`ll continue to
monitor.
Bumgardner
&&
.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 700 PM CDT Tue Apr 23 2024
Aviation concerns:
- A few showers linger through mid-evening (~1-2Z)
- Sharp northeast wind shift with backdoor front late evening
- Period of MVFR cigs at ORD/MDW/GYY overnight into Wednesday AM
The earlier thunderstorm potential has mostly waned. Spotty
showers (and perhaps a lightning strike or two out over Lake
Michigan) will remain possible for the next couple of hours as
they continue to redevelop just east of a surface boundary
extending from Peru, IL to near ORD.
Winds to the south of this boundary (ORD/MDW/GYY) are SSW to SW
and are W to NW to the north of this boundary (DPA/RFD) with
gusts in the mid 20kt range. As this boundary gradually sinks
southward winds may turn northwest at ORD/MDW over the next
couple of hours. A sharp wind shift to northeast is anticipated
late in the evening as a backdoor front dives down the lake
during the 4-6Z timeframe, earliest at the Chicago area
terminals. Winds then ease with time during the daytime hours on
Wednesday
There remains the potential for a period of MVFR stratus to
push inland in the wake of the backdoor front overnight near the
lake (ORD/MDW/GYY) and is expected to scatter out during the
morning on Wednesday.
Petr
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 10 PM CDT Wednesday for the IL and
IN nearshore waters.
&&
$$
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