Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/18/22
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
902 PM CDT Sat Sep 17 2022
Issued at 859 PM CDT Sat Sep 17 2022
Convection has departed the area, thus have updated the forecast
and text products to remove any thunderstorm mentions. Focus then
turns to the expected fog development after midnight tonight. High
resolution guidance continues to point towards fog development in
the James River Valley and into the Prairie Coteau, as high
pressure builds overhead and winds weaken. An earlier update
trended the forecast towards the latest coverage and intensity and
will need to watch for the potential for some dense fog in spots
late tonight into tomorrow morning.
UPDATE Issued at 629 PM CDT Sat Sep 17 2022
Updated for 00Z Aviation Discussion below.
UPDATE Issued at 541 PM CDT Sat Sep 17 2022
No significant changes to the going forecast initially this
evening. Surface low is near KVVV at this time and the surface
boundaries extend southwest and northeast from there. Instability
has increased along the boundaries, with MLCAPEs in the 1000-1400
J/kg range (along and southeast of a line from KETH to KATY)
based on RAP and SPC MesoA data. We`ve had a few isolated showers
develop thus far, with the strongest being elevated and behind the
sfc/850mb cold front in Marshall County. With less instability to
work with, don`t expect them to become severe. Still watching
weak development along the front and north of the sfc low in
Traverse county. It`s in better instability and has added
sfc/925mb convergence/FGen, but haven`t seen too much development
thus far on satellite. That being said, there is an area of high
cirrus on satellite and WV imagery approaching that area, likely
associated with a weak upper level disturbance, which could help
lead to additional development. There`s a good chance any
significant development will be beyond our CWA based on when they
.SHORT TERM...(This Evening through Monday Afternoon)
Issued at 203 PM CDT Sat Sep 17 2022
Deterministic models are in good agreement in the synoptic setup
through the short term. A large troughing pattern with the axis of
the trough is noted from western Canada through the Pacific Coast
with a closed low that will develop through the weekend. Within this
main flow, a shortwave trough will continue to push northeast across
the upper Midwest and Northern Plains through this evening. Another
shortwave is noted to our southeast, which is also pushing northeast
through MN/WI. We are on a shortwave roller coaster as another
shortwave moves into the upper Midwest overnight into Sunday morning
and will push east. Winds at 500mb will continue out of the
southwest becoming more zonal overnight through Sunday (couple of
the models have it more overnight). By late Sunday into Monday, a
ridge will amplify over the area with a 500mb high over much of the
central Midwest and Southern Plains.
At the surface by 00Z the center of low will be over central-
northern MN with the cold front along the SD/MN boarder. Through the
overnight hours as this low pushes east/northeast, a surface high
pressure system will move in and be centered over SD for Sunday.
This high moves east early Monday with our next system moving in
from the west.
With this setup aloft and at the surface, precipitation chances, in
the form of showers and thunderstorms, shift towards northeastern SD
into western MN, ahead of the cold front this afternoon and evening.
ECMWF is holding on to parts of the LLJ in the eastern CWA that
could help aid in convection. Most of the stronger storms will be in
central MN but there is a chance of isolated strong to severe in our
CWA, mainly in Traverse and Big Stone counties who are on the
western edge of this marginal threat. HREF model indicates SB/ML
Cape values around 1000-1200 J/kg across the eastern/ northeastern
CWA around 20Z with that threat pushing east by late this evening.
Bulk shear values increase to 30-40kts. Isolated tornadoes are not
out of the question in the marginal risk, especially early on in
storm development. Cams/HREF note cell formation with a couple UH
tracks with some of these storms, suggesting supercells around 22Z.
0-1km SRH indicate values 50-75m2/s2. RAP sounding between 19-22Z
has a STP of 0.2-0.5 across western MN. The time window will be
fairly short with CAMs/HREF reflectivity indicating storms pushing
through between 4-7PM. Behind the system skies will clear a bit but
will be back on the increase with possible fog in the am over
northern ND and around the Prairie Coteau.
For Sunday, the shortwave mentioned above, does bring moisture aloft
in the western and southwestern cwa. However a surface high will be
just to the east which could evaporate a lot of that moisture (and
keeping any rain from falling anywhere else.)Overnight lows in the
upper 40s/mid 50s with cooler air moving in with winds out of the
northwest. Highs for sunday ranging in the 70s/lower 80s.
.LONG TERM...(Monday Evening through Saturday)
Issued at 203 PM CDT Sat Sep 17 2022
A somewhat amplified mid-level pattern is forecast to take shape
during the long term. To start the period deterministic/ensemble
data are pretty similar in depicting a cutoff low just off the
California coast, with another trof digging toward the northwest
CONUS. The main difference between today`s model runs and previous
ones is that the northern trof appears to be more progressive, and
brings a front through the Northern Plains earlier. Some rain
chances exist for Monday as WAA pattern shifts from southwest to
northeast across the state. However, along with the WAA comes
increasing warm air aloft with H7 temps pushing to near or above 10C
over a large part of the region. The result being increasing MLCIN
over the forecast area. For now will keep low pops in place.
Forecast is then pretty much dry until near next weekend. At that
time, the old cutoff near California is expected to eject northeast
into the Northern High Plains region, and then track slowly east
over the Northern Plains. Most long term guidance is onboard with
this scenario. As for temperatures, 2m temp anomalies suggest above
to well above normal readings for the early part of the period. But,
behind a front for Wednesday-Friday, temperatures are expected to
fall back to near or even below normal.
.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 629 PM CDT Sat Sep 17 2022
A couple of concerns for the first half of the TAF forecast.
First, have some lingering MVFR ceiling behind the cold front over
the James River Valley and have been seeing KABR bouncing between
VFR/MVFR ceilings over the last few hours. Expect that to continue
this evening and eventually see the shallow/thin clouds dissipate.
When/If that occurs, expect winds to be light under high pressure
and should see some fog development over the James River Valley
and Prairie Coteau after midnight and continue into tomorrow
morning. Guidance indicates KABR being the site that has the
lowest visibility and have indicated LIFR conditions for now. Then
the focus turns to an upper level disturbance approaching from the
Rockies. This will bring the potential for light rain to central
SD tomorrow morning, but at this time, expect conditions to remain
Area Forecast Discussion
National Weather Service La Crosse WI
1102 PM CDT Sat Sep 17 2022
.DISCUSSION...(This evening through Saturday)
Issued at 242 PM CDT Sat Sep 17 2022
- Shower/Storm chances increase this evening
- Warm start to the week/Much cooler for the first day of
Autumn(Thursday)/end the week
- Fog potential Monday morning
- Rain/Storm chances Monday night into Tuesday and Tuesday night
into Wednesday with the cold front
Early afternoon satellite water vapor imagery showed the first
subtle shortwave associated with this morning`s cloud cover and
scattered showers/sprinkles pushing out of the area to the
northeast. A second subtle shortwave follows behind just entering
central Iowa. Radar imagery shows the associated weakening MCS
moving through southeastern Iowa entering far northwestern Illinois.
This cluster of showers/isolated storms appears to be nearly aligned
with the latest RAP analysis of the moisture transport field.
Showers are expected to redevelop and expand in coverage across the
forecast area heading into this evening with additional moisture
advecting into the region from an increasing southwesterly low-level
jet. Cannot rule out some isolated thunder with 1000-1500 J/kg of
MLCAPE being available. Any storms that do develop, are anticipated
to be elevated and the overall risk for severe storms is greatly
Overnight as high pressure builds into the Dakotas and a cold front
sweeps east/southeastward through the area, precipitation chances
are anticipated to exit a majority of the region by sunrise Sunday
morning. Quiet weather will persist throughout the day with
afternoon temperatures reaching into 70s and a few locations
topping out near 80.
Sunday night through Tuesday...
The 500 mb pattern through Tuesday is for a piece of the
broad area of low pressure over Canada near Ontario to slide
toward New England with another...deeper trough pushing toward
Montana and North Dakota. Heights increase for Monday and begin to
decrease again by 21.00Z.
Depending on how far south the 850mb front makes it Sunday night,
a few showers/storms could linger across southern areas. Behind
the cold front, surface high pressure settles in with decreasing
surface winds. Forecast soundings show an inversion setting up in
the low levels with surface winds decoupled, but winds above the
surface in the 10 to 15kt range. Low level dewpoints spreads
appear to be close to zero, thus looks like a good potential for
valley fog and more widespread fog if the winds aloft drop down
early enough. The low level dewpoints mix out during the morning
with highs topping out in the 70s to lower 80s.
Monday night into Tuesday, the 500 mb longwave trough is still well
to our northwest and into Canada, however, there is good agreement
with a lead wave heading toward the upper Mississippi Valley.
Although the bulk of the organized precipitation with the wave is
north of the International Dateline, the low level jet is forecast
to strengthen over Iowa with the potential for scattered
showers/storms across parts of the forecast area. MUCAPE is around
2500 J/kg with 40 to 50kts of deep layer shear/0-3km shear of 35-
45kt. Although not the most favorable time of day, could support
elevated storms with hail before they shift east if the
forcing/shear is this strong. The forcing shifts the storm chances
east during the afternoon with warmer temperatures aloft
arriving, but will have to watch this with lingering 850mb
moisture. Tuesday`s highs should continue to be well above normal
with highs in the 70s and 80s.
Turning Colder For the First Day of Autumn/End of the Week...
The 500mb trough swings through with lowering heights and
convergence along the front. Showers/storms increase overnight
Tuesday and Wednesday as the cold front pushes south. After highs
in the 70s Wednesday, sharply cooler temperatures arrive Wednesday
night. Lows for the first morning of Autumn are forecast to be in
the 40s and 50s, with 50s and 60s for highs Thursday. Still cool
Friday with highs in the 50s and 60s with rain chances returning.
.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1100 PM CDT Sat Sep 17 2022
Main cluster of showers and storms expected to largely stay south
of the TAF sites overnight. Isolated convection is starting to
develop at this hour as the low level jet ramps up, but most of
the activity is expected to stay over northeast Iowa and far
southwest Wisconsin. Very small chance that anything would graze
LSE. That low level jet will lead to marginal LLWS at LSE for
several hours overnight, with a lesser chance for impacts at RST
early in the period.
Main aviation concern continues to be potential for developing low
ceilings towards daybreak. Low pressure and a weak cold front
dropping into central Minnesota now are already producing MVFR to
IFR ceilings up that way, and that stratus is likely to spread
into the TAF sites as the front eventually approaches with MVFR to
IFR conditions. Winds shifting to the northwest behind the front
will bring in some drier air that should scour out the low
ceilings by mid to late morning with VFR conditions thereafter.
Winds will generally be light through the period.
Area Forecast Discussion
National Weather Service Grand Rapids MI
1201 AM EDT Sun Sep 18 2022
Issued at 808 PM EDT Sat Sep 17 2022
I have increased the risk for getting wet tonight to between 70
pct and 80 pct in a triangle area from near Whitehall to Mount
Pleasant to South Haven. The timing of the showers and a few
thunderstorms would be between 10 pm and 5 am.
This update is based what every run of the HRRR since 15z is
showing. The latest NAMNEST and RAP models also show this.
Considering there is an MCV over Iowa heading this way, I have
increased the pop significantly in the area I wrote about above
and adjusted the area of heavier precipitation and pop farther
As for severe potential tonight, that is limited at best. The
effective bulk is negligible. However the mix layer and most
unstable cape is between 500 and 700 j/kg by 2 am over our western
CWA, north of I-94. This suggests some thunderstorms are possible
overnight. Several runs of the RAP model show a 25 to 35 knot low
level jet amid at MKG by midnight. Model sounding look fairly
moist through 200 mb,, the precipitable water forecast to be near
1.5 inches and RH over 80 pct. This would tell me the rain should
have no problem getting to the ground. I could see some isolated
locations getting over a half inch of rain tonight. Most of the
storms should be north of a line from Holland to Lansing. Most
areas should see at least a few hundredths of an inch of rain
tonight, if you live north of I-94.
.DISCUSSION...(This evening through next Saturday)
Issued at 331 PM EDT Sat Sep 17 2022
-- Chance for showers/few storms this evening --
The increase in moisture from the southwest flow has boosted MUCAPE
values to 500-1000 J/KG. Highest values are across Central Lower
Michigan where surface dew points are 62f to 64F. A shower with
some decent low level reflectivity (50dbz) has recently developed
in Montcalm County. We expect more shower development this evening
as well as some isolated thunderstorms. This activity should fade
-- Better chances for precipitation late tonight/Sunday morning --
A better chance for showers and thunderstorms will come late
tonight and Sunday morning in a decaying mode. Showers and storms
should form on the low level jet axis in Iowa tonight and move
east into our area late. We should see precipitation increase
after 06z, with the best chances probably towards 12z. This
activity will likely be in a diminishing phase as it moves
through. The rain and clouds will likely temper our instability
-- Small chances for showers and storms again Sunday
The Sunday morning precipitation will likely curb what activity
develops in our area in the afternoon and evening. The HREF shows
this well with much of the redevelopment in the afternoon and
evening off to the south and east of our area. If the activity
comes in weaker tonight however our chances will increase for
precipitation on Sunday. At least some chances for precipitation
will continue into Sunday night as the front will be sliding
through the area at that time.
-- Work week forecast --
After a dry Monday, it appears we have the chance for some
nocturnal showers and storms Monday night into Tuesday morning
with a warm front in the area. A healthy 40 knot low level jet is
aimed in our direction Tuesday morning so this will be a time
frame to watch. A cold front will bring additional chances for
showers and storms Tuesday night.
Cooler and drier weather overall settles into the area for much of
the rest of the forecast. 850mb temperatures plunge from around
+20C Tuesday night near the front to around +3C on Thursday. Not
out of the realm of possibilities to see some lake effect rain
showers on Thursday with Delta Ts near 17 degrees C.
.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1200 AM EDT Sun Sep 18 2022
VFR conditions are expected at all the terminals overnight with
scattered rain showers. Potential for isolated storms overnight is
too low to warrant inclusion in any of the terminal forecasts at
this time but forecasts will be updated accordingly if
VFR conditions are forecast to continue at all the terminals
Sunday through Sunday evening. Showers will redevelop Sunday
evening. There is also potential for a few thunderstorms but it is
too early/potential is too low to mention them in the terminal
forecasts at this time. Thunderstorms may be added to some of the
terminal forecasts for Sunday evening later today.
Issued at 331 PM EDT Sat Sep 17 2022
Earlier today we updated marine headlines to push them through
tomorrow and expand in area to the south. Through this evening
the Beach Hazards Statement (BHS) and Small Craft Advisory (SCA)
are in effect for areas up towards Big and Little Sable Points.
After 06z tonight, that expands to include marine areas southward
Southwest winds will boost waves heights to 3-5 feet this evening
near the points. After dark tonight, southwest winds ramp up
further with a low level jet increasing to around 40 knots at
1,500 feet. Some of this wind will reach the water surface, more
on the order of 15-25 knots which should build a wave field to
3-5 feet in all areas north of Holland. It is not out of the realm
of possibilities that we may need headlines further south as well.
There is a chance from another increase in southwest flow Sunday
night, but only feel comfortable with headlines through the day on
Sunday at this point.
MI...Beach Hazards Statement through Sunday evening for MIZ037-043.
Beach Hazards Statement through Sunday evening for MIZ050-056.
LM...Small Craft Advisory until 8 PM EDT Sunday for LMZ846-847.
Small Craft Advisory until 8 PM EDT Sunday for LMZ848-849.
Area Forecast Discussion
National Weather Service Wilmington NC
1006 PM EDT Sat Sep 17 2022
High pressure continues to keep the area dry through mid week
Temperatures look to linger near seasonal norms through the
weekend, before a noticeable increase by the beginning of next
week. A cold front will cross the area late Thursday and well
off the coast on Friday.
Only minor tweaks made to previous forecast. Isolated light
showers across southern Georgetown county have diminished quite
a bit. Low level easterly flow expected to advect low clouds
across most of the area, particularly northeast SC, into middle
of the night before skies clear up before dawn. May see an
isolated, very light, shower or two move onshore coastal NE SC
overnight into early morning hours.
.NEAR TERM /THROUGH SUNDAY/...
The forecast has been quite a challenge along the coast today
where Gulf Stream moisture has increased rapidly beneath the
subsidence inversion between 3500-6000 feet AGL. An expansive
shield of low cumulus developed at the base of this inversion
and has advected onshore across the Cape Fear region and Grand
Strand. Initially hidden by thick cirrus aloft streaming
northward from convection off the GA/FL coast, this low cloud
deck has become the big weather story today, holding down temps
along the coast. Recently, radar even reveals showers and even a
thunderstorm near Bald Head Island. Looking at a NAM or GFS
forecast sounding and trying to explain how that thunderstorm
was able to punch through the inversion and grow to 33000 feet
is testament to how poorly those models are doing.
None of the synoptic models (GFS, NAM, ECMWF) really have a
clue what low level moisture fields are like currently. Their
dewpoints are much too low along the coast, especially near ILM
where our dewpoint has recently eclipsed 70. Among the high-res
guidance the RAP is doing the best job but still has the
dewpoint gradient way too washed out compared to observations.
Low clouds should be more expansive than any guidance shows
through the evening and possibly overnight hours along the
coast. Cirrus will likely become quite dense aloft again too
given recent upticks in convection over the SC/GA offshore
waters. I`m trending higher than guidance for low temps along
the coast tonight given the clouds and increased moisture, but
near the center of the guidance envelope inland. This gives
upper 60s along the coast and mainly lower 60s inland.
Low level onshore winds should continue into Sunday. The
inversion should continue aloft, but I have less confidence than
usual about low level moisture distribution and the potential
for shallow convection, especially along the coast. Forecast
highs Sunday are generally 83-87, coolest on the beaches.
.SHORT TERM /SUNDAY NIGHT/...
In the mid and upper levels, strong high pressure, 2 SD above
normal, over the Red River will slow shift to the Ark-La-Text by
12 UTC Tuesday. Over the Carolinas, there will be a break
between the Texas High and the Bermuda High, with an inverted
trough over the Florida Peninsula. There is a similar setup at
the surface with a break between the two high- pressure centers.
The Florida trough strengthens and pushes along the Carolina
coast early Monday before the ridge builds westward again
quickly Monday night.
With the easterly flow over the area, there is a minimal chance
of an isolated shower along the southern Georgetown coast. The
rest of the region will be dry.
Low temperatures Sunday and Monday nights will range from the
middle 60s inland to the low 70s along the beach strand. High
temperatures on Monday will run from the mid-80s at the coast to
the upper 80s inland. &&
.LONG TERM /MONDAY THROUGH SATURDAY/...
In the mid and upper levels, the strong high pressure, +2SD
above normal, will remain over the heart of Texas for much of
this week. The trough centered just offshore of the Carolinas
will provide a break to allow Fiona to stay well east of the
coast. The most significant impact will be the long period
swells beginning Tuesday and peaking on Friday. Of course, this
will be highly dependent on Fiona`s intensity and track. These
swells will provide a dangerous rip current setup but joy for
the surfing community.
During this forecast period, the models show the deep 2"
precipitable water staying off the coast. A cold front in the
upper plains is expected to approach the Carolinas on Thursday
and offshore Friday morning. At this time, the chances of
precipitation continue to be low, but ahead of the cold front,
the high temperatures will peak in the middle 90s inland on
Thursday. Humidities are expected to be lower than normal;
therefore, the heat indices will reach into the upper 90s
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
With high pressure to the north and a surface trough to the
south, low level easterly flow is advecting moisture into the
area particularly across NE SC. Easterly LLJ of 20 kt around
3kft continues bringing the low level moisture inland into early
overnight hours, but expect more FEW/SCT vs ceilings. At the
coast, high clouds will continue to move out of the area
overnight before returning tomorrow afternoon. Low chance for
brief MVFR visibilities across northern parts of the area,
including LBT, where winds will be weaker closer to center of
high. May see an isolated shower move onshore coastal SC during
pre-dawn hours. ENE winds tomorrow around 5 kts away from coast,
with more easterly sea breeze around 10 kts at coastal terminals
in the afternoon.
Extended Outlook...VFR. There is a low potential of early
morning fog/low stratus Monday through Wednesday. A cold front
may reach the area late Thursday.
1025 mb high pressure is moving off the Mid Atlantic coast.
This will finally allow days of breezy northeasterly winds to
come to an end, replaced by somewhat lighter easterly winds
tonight into Sunday.
Models do not have an especially good handle on the very near term
where we`re seeing significant cloud cover and even some showers
near Cape Fear currently. Easterly winds are bringing in a very
humid Gulf Stream unstable airmass more quickly than was expected.
I`m kept a 20-30 percent chance of showers in this evening`s
forecast south of Cape Fear. Easterly winds are expected to maintain
10-15 kt speeds overnight, decreasing to around 10 kt Sunday
afternoon. Additional isolated showers may develop Sunday. Seas
should maintain 2-3 foot heights through Sunday.
Sunday Night through Thursday:
An easterly to northeasterly flow of 10 knots will dominate the
waters Sunday night through Tuesday as an inverted trough of
low pressure moves northward into the coastal waters but recedes
just as quickly. Winds are expected to be light and variable
before becoming southeast at 10 knots on Wednesday. A cold front
approaches the waters from the west on Thursday. The winds are
expected to veer and increase to 10 to 15 knots on Thursday
ahead of the cold front.
Seas will run 2 to 3 feet Sunday night into Monday and increase
to 3 to 4 feet late Monday before settling out at 3 feet
Tuesday. On Tuesday evening, the long period swells from Fiona
will begin moving into the waters. An increase in swell heights
to 6 ft could be seen by Thursday. Of course, this highly
depends on Fiona`s track and intensity.
Area Forecast Discussion
National Weather Service Lincoln IL
804 PM CDT Sat Sep 17 2022
Issued at 241 PM CDT Sat Sep 17 2022
Warmer than normal temperatures stick around through early next
week. Shower and storm chances return to the area tonight into
Sunday, with the potential for strong to severe storms later Sunday
into Sunday night.
Issued at 802 PM CDT Sat Sep 17 2022
Thunderstorms are ongoing across portions of south central and
southeast Iowa this evening within a corridor of warm air
advection that stretches from eastern KS/NE into far western
Illinois, though the greatest focus of a developing low level jet
is near the mid Missouri Valley. Latest RAP indicates the eastern
most storms are occurring within a region of 1000-1500 J/kg
MUCAPE. The instability gradient drops off sharply west to east in
western Illinois with 500 J/kg or less along and east of the
Illinois River Valley, and, in the near term, instability is
progged to diminish as it lifts north slightly. Some of the precip
in eastern Iowa will ride the 850-300mb steering flow east into
the forecast area but will be in a decaying state as it moves into
a less unstable environment and becomes displaced from the better
forcing from WAA to our west. Additional rounds of storms forming
farther west closer to the nose of the low level jet are possible
overnight, but confidence in how this will evolve remains low
considering poor initialization and agreement of convective
allowing models. Locally, the best chance for precip is still late
tonight into Sunday morning as the low level jet veers into NE
MO/west central IL.
.SHORT TERM...(This evening through Sunday night)
ISSUED AT 241 PM CDT Sat Sep 17 2022
Southwest flow is setup aloft with broad upper ridging positioned
over a good portion of the eastern CONUS. A few upper shortwaves
paired with broad WAA will be the focus for precipitation chances
through the weekend, though the most notable timeframe looks to
be later Sunday into Sunday night when a stronger system sends a
cold front toward the area. Shower and storm chances increase
overnight tonight as 850mb moisture transport ramps up and spills
into our area. Activity during this time looks to remain mostly
confined along and west of I-57 and is not expected to be severe
due to limited instability available.
Isolated shower and storm activity may persist into the daytime
hours of Sunday which may limit temperatures from reaching their
full potential, though still will be warmer than normal. Breezy
south winds will pull in dewpoints in the upper 60s to low 70s
making the air feel more uncomfortable and allowing strong
instability to build. Guidance suggests CAPEs of 2500-3000 J/kg
build in by Sunday afternoon, with shear improving as we go into the
evening hours when a cold front approaches from the northwest and
the LLJ kicks in - bulk shear looks to be between 40-50 kts. A
limiting factor at play is noted in the forecast soundings which
depict a CAPing inversion present well into the evening hours. That
being said, instability may be strong enough to overcome that,
especially where CIN will be a tad bit lower west of I-55. CAMs
remain in disagreement on where and when activity will fire up, but
most of the storms should initiate over eastern IA/northeast MO
and move into our CWA by either late afternoon or evening.
Given the parameters at play (strong instability, favorable shear, a
cold front paired with an upper wave for lift) the chance for strong
to severe storms will be possible. Damaging winds and large hail are
the biggest threats, though a tornado threat does exist with the
focus being along and north of I-72 where isolated storms could tap
into the maximized 0-1 km shear values of 20-25 kts. HREF updraft
helicity is also focused in this area. A slight risk for severe
storms exists across the majority of the CWA for Sunday into Sunday
Climatologically high PWATs and warm cloud depths will be in place
Sunday into Sunday night. A nearly parallel orientation of the front
in respect to the flow aloft will likely support training of storms.
Recent drier conditions and fast storm motion should limit
widespread flash flooding, though localized pockets where storms
repeat over the same areas could lead to flash flooding concerns.
The 17.12Z SPC HREF pinpoints an area of mean rainfall amounts
between 1-2" from extreme northeast MO into west-central IL with the
LPMM product suggesting high end amounts of 2-4"+ in this same
corridor. At this time, the threat seems highest from roughly Macomb
southeastward toward Shelbyville.
.LONG TERM...(Monday through Saturday)
ISSUED AT 241 PM CDT Sat Sep 17 2022
Shower and storm chances may linger across eastern and southeast
parts of the area going into Monday. Once that moves out, things
look to get dry and hot for the start and middle of the new week. A
strong upper ridge will progressively build over much of the US,
bringing near-record temperatures to central IL. The hottest day of
the week looks to be Tuesday as 850 mb temperatures near the middle
20 degrees C mark. Surface temperatures look to be in the low to
middle 90s with heat indices near 100 in some spots. Records for
September 20 are a couple degrees warmer than our current forecast
highs, though something worth keeping our eyes peeled on.
The upper ridge starts to flatten out Wednesday into Thursday as a
mid-level trough dives southeast toward the Great Lakes Region from
Canada. A surface low will track across the southern Canadian
provinces, sending a cold front further south through the Midwest
sometime Wednesday into Thursday. Cooler temperatures will make a
comeback Thursday for most, but especially Friday for all.
Precipitation chances with the frontal passage appear pretty low
at this point, but are not zero. Cooler temperatures stick around
for the start of the weekend.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 625 PM CDT Sat Sep 17 2022
A cold front is in place from the Upper Midwest back into the
central Great Plains this evening and will slowly approach central
Illinois tonight and through the day Sunday. Breezy S/SSW winds
are expected ahead of the front with gusts to around 20 kt during
the daytime hours. There will be a couple possible rounds of
showers and storms that occur ahead of the front. A decaying line
of showers is expected to push into central Illinois mid to late
Sunday morning. A second round of stronger storms is expected late
afternoon and evening, though at this time there is a
considerable amount of uncertainty on timing and placement of
storms. Outside of precip, expect VFR conditions to prevail
through the period.
Area Forecast Discussion
National Weather Service Marquette MI
1159 PM EDT Sat Sep 17 2022
.SHORT TERM...(Through Tonight)
Issued at 241 PM EDT SAT SEP 17 2022
Upper air pattern consists of a broad 500 mb trough across the
western half of the U.S. with a shortwave over the northern plains.
The shortwave over the northern plains heads east to the upper Great
Lakes tonight. Confidence low in this forecast as unstable airmass
over the area could have convection go at any time or place and with
convection elevated, models tend to do a poor job predicting where
things set up. Best approach continues to be a broadbrush of pops
and have basically chance pops almost everywhere. Does look like
areas further west and north will have the best chance for pops
through tonight and that is where the highest pops are. There will
be some fog around as well.
.LONG TERM...(Sunday through Saturday)
Issued at 352 PM EDT SAT SEP 17 2022
The longterm period starts off Sunday morning with a deep trof off
the West Coast as a ridging begins to amplify across the central
CONUS. Across the Northern Plains, a shrtwv is shifting east along
the international border in ND and MN - this wave will bring a cold
front across the UP from west to east Sunday. Behind this wave and
front, the central CONUS ridge will amplify and build northward into
the Northern Plains on Monday. Another wave is progged to drop SE
from the Canadian Rockies into the Northern Plains Tuesday night
into Wednesday, as the West Coast closed low begins to shift into
the Pac NW with the central CONUS ridge weakening. This Canadian
Rocky wave will pass through the Upper Great Lakes on Wed evening
before an amplified shortwave ridge moves in behind it on Thursday
night. By next weekend, the closed low/trof off the West Coast will
begin to traverse across the Northern Plains. This pattern will
bring a chance for rain throughout the week as temperatures trend
above normal for the start of the week with ridging in place - by
the end of the week, temperatures will return towards normal, if not
slightly below normal behind a midweek cold front.
Clearing skies will be the trend on Sunday as a cold front moves
across the UP from W to E. Some showers and perhaps a thunderstorm
or two will remain possible along the frontal axis, but there is
some uncertainty on instability. Most CAMs actually hold pcpn off on
Sunday, but the HRRR has remained steady with bringing some
thunderstorms across the central and east with some diurnal heating -
especially across the east. Dry weather will then take over on
Monday with a weak sfc high pressure overhead.
WAA returns on Tuesday as ridging builds across the central CONUS -
this should bring temps into the upper 70s across the UP. A small
perturbation to the north of the UP could bring an isolated shower,
but for the most part it looks like the dynamics will split the UP -
so ongoing fcst could be a little too optimistic.
Wednesday will bring a stronger cold front across the UP as a strong
wave drops south from the Canadian Rockies into the Upper Great
Lakes. This will likely bring some gusty winds, lake-effect rain,
fall-like temperatures. The cold front will bring temps back down to
normal and evening blo normal into the weekend as high pressure
moves in Friday and brings an end to the lake-effect clouds.
.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1159 PM EDT SAT SEP 17 2022
Challenges remain in this TAF period, as discussed in the previous
TAF issuance. That said, there is increasing confidence of LL
stratus struggling to move out in a timely fashion on Sunday with
a copious deck building in and observed on satellite imagery
tonight. KCMX will be the most negatively impacted, but KIWD and
KSAW appears to at least go MVFR overnight into early Sun. As Wrly
winds move in behind the finally-departing frontal boundary, drier
air should assist in pushing out the stratus and lingering LL
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 352 PM EDT SAT SEP 17 2022
Thunderstorms, rain, and some patchy fog will remain possible
through tonight as a warm and humid airmass remains over the lake.
On Sunday, a cold front will move across the lake from west to east,
bringing clearing skies and the end to any remnant fog. This front
will bring winds around to the W with gusts btwn 20 to 25 knots
through Sunday evening. West winds remain seasonably light under 20
knots through Monday before becoming southerly on Tuesday, remaining
btwn 15 to 20 knots. A potent cold front will ample cold air
advection will cross the lake on Wednesday, bringing NW winds around
30 knots. At this point, gales can be expected Wednesday night into
Thursday morning as the cold air moves across the lake, but will
keep winds around 30 knots until more confidence in timing and
placement of strongest winds is obtained. Winds relax on Thursday
afternoon from the north, but will become southerly and remain light
as a high pressure system passing over the lake Friday.
Area Forecast Discussion
National Weather Service Pendleton OR
535 PM PDT Sat Sep 17 2022
Updated the aviation discussion
.SHORT TERM...Saturday through Monday...Current water vapor imagery
pins a low pressure system centered west of the northern California
coast. The outer band of cumulus is starting to push into central
OR, with some shower activity popping up around eastern Grant
County. Latest HRRR guidance shows main band of rain arriving around
5pm in central OR, spreading north-northeastward and lasting until
early Sunday morning.
Models continue to show convective development associated with this
system, however CAMs and deterministic NAM showing limited
instability and lower moisture compared to model runs over the last
several days. Overall trend, in fact, has been for a drier forecast
associated with this first round of rain, with QPFs ranging around
0.05 to 0.15 inches, locally higher closer to the OR Cascade crests
and southern Blues. PWATs around 0.6 to 0.8 across the forecast
area, around the 75th percentile for this time of year, but moisture
advection into the region appears to be not has enhanced as
previously seen. Still, some MUCAPE is present across the southern
half of the CWA, and CAMs seem to be consistent in depicting
convective cells this evening, so will leave mention of
thunderstorms in the forecast, but still think majority of shower
activity will be more stratiform in nature. That being said, a few
isolated convective cells could certainly throw a wrench in the
Trend across the models has also been to cut back on QPF across the
eastern mountains of OR, with the main shield of precip taking a
more north than northeast trajectory. Better chances for precip for
the eastern mountains looks to be more during the day Sunday, when
the area will fall under an elongated stretch of moisture from the
winds aloft stretching from the southern California coast up through
the northern Rockies. CAMs and NAM a bit more aggressive at
depicting convection during the day Sunday, possibly due to
favorable upslope enhancement, so feeling a bit more confident in
the thunderstorm forecast for Sunday afternoon across the eastern
mountains. Storms should be wet enough to offset any fire risks
associated with lightning strikes.
Forecast on Monday looks drier, with the exception of central OR as
the low pressure system will stall off the California coast and
remain in place for much of the week, continuing to pump moisture
into the far southern reaches of the forecast area. Any rain there
on Monday should be on the lighter end. Temps over the period will
be cool, in the 60s and 70s today and Sunday, before warming back up
on Monday as the low falls south enough to allow for skies to clear
and for more efficient daytime warming to take place. Evans/74
.LONG TERM...Guidance is in excellent agreement that the long-
term period will be dominated by the presence of a deep, cut-off
upper-level low. This low is currently tracking southward offshore
of southwest OR, and concensus among ensemble and deterministic
guidance is that it will stall just offshore of SW OR/NW CA
through Monday, tracking slowly southward. Weather models often
have difficulty resolving how cut-off lows will rejoin the jet
stream, and this case is no exception with ensemble clusters
revealing that between 50-67% of the variance among members` 500
mb height fields Tuesday through Thursday are driven by
timing/location differences of this upper low. Notably, the GEFS
is presenting a more progressive solution than the EPS and CMC,
one which is mirrored in 12Z deterministic runs. This solution
would see the low spin offshore Tuesday, then track onshore and
overhead into the Interior Northwest on Wednesday before rapidly
departing to the east on Thursday bringing seasonal temperatures
and widespread rain showers, especially for the central and
eastern mountains. The ECMWF and Canadian eject the low across the
region more slowly, having it linger through Thursday before
exiting Thursday night into Friday, again bringing seasonal
temperatures and rain showers. With either solution, thunderstorms
will be possible for the central and eastern mountains if
supported by daytime heating.
Prior to the low tracking onshore, pressure gradients are supportive
of some breezy northeast winds Tuesday for the Columbia and
Deschutes plateaus, and the ECMWF EFI is highlighting this. Thursday
into Friday, depending on the timing of the upper low`s passage,
will see breezy to windy west winds through the Cascade gaps and
into the Columbia Plateau.
Ensembles and all 12Z deterministic runs are then hinting at a
decaying shortwave tracking into northwest Washington or southern
British Columbia on Friday with the possibility of showers for the
Washington Cascades. Plunkett/86
.AVIATION...A weather system may bring showers to all taf sites
tonight. Isolated thunderstorms may also affect taf sites
krdm...kbdn...kpdt...kalw...kpsc...kdls until 06z that may approach
lcl mvfr conditions. Otherwise mainly vfr conditions can be expected
for the next 24 hours.
.PRELIMINARY POINT TEMPS/POPS...
PDT 48 68 46 78 / 40 40 20 0
ALW 50 71 49 80 / 40 40 20 0
PSC 56 73 52 82 / 50 30 10 0
YKM 48 75 48 82 / 60 20 0 0
HRI 52 71 49 83 / 40 40 10 0
ELN 48 78 48 83 / 50 20 0 0
RDM 42 68 40 75 / 70 40 10 10
LGD 47 69 45 78 / 40 60 30 10
GCD 46 73 44 81 / 50 40 20 10
DLS 55 77 53 85 / 70 20 0 0
For frequently asked questions about the Area Forecast Discussion