Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/27/23
Area Forecast Discussion
National Weather Service Columbia SC
1038 PM EDT Thu Oct 26 2023
.SYNOPSIS...
Strong high pressure will remain anchored over the forecast
area into this weekend generating above normal temperatures and
dry conditions. Expect scattered daytime clouds and light winds
through Monday before a frontal passage brings more Autumn-like
temperatures back to the region next week.
&&
.NEAR TERM /UNTIL 7 AM FRIDAY MORNING/...
Low level flow remains out of the southeast with the center of
the surface high to our northeast. This will set the stage for
increasing chances of fog and possible stratus developing along
the Coastal Plain and moving over the Midlands. The latest HRRR
shows stratus and strato-cu developing late and spreading into
mainly the east Midlands around sunrise. The higher dewpoints
today and overall higher atmospheric moisture with PWATs close
to an inch will support fog formation again tonight with near
calm winds. The increased moisture and potential cloud cover may
limit overnight lows, stunting the otherwise strong radiational
cooling during the predawn hours. However, expect temps to drop
early into the overnight hours before slowing and potentially
holding steady in areas where fog/clouds develop. Overnight lows
should range from the lower to mid 50s northwest to upper 50s
southeast.
&&
.SHORT TERM /7 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Really not a whole lot to say that hasn`t been said about this time
frame. Very quiet and warm weather is expected, as a ~591dm 500 hPa
ridge remains a stalwart across the southeastern US. This is easily
approaching or exceeding the 99th percentile for this time of year,
leading to above normal temperatures both days. Highs are expected
to be in the low and mid 80s across the area, with lows in the mid
50s. Surface high pressure will continue to sit across the area, as
well, providing dry and generally sunny weather. One complicating
factor with tomorrow`s forecast specifically is that we may have
morning fog and stratus, owing to low-level southeasterly flow on
the southern side of the surface high. Depending on how fast that
mixes out, highs may be a bit muted on Friday, but still expecting
temps in the 80s in the afternoon. We may have afternoon cumulus as
we have seen the past couple of days, but a subsidence inversion
underneath this ridge should keep these just clouds. PWs will be
near seasonal norms during this period, as well, adding confidence
to no precipitation chances.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Confidence is fairly high regarding the weather through Monday, with
some uncertainty arising thereafter. Despite this, confidence is
growing in the coldest airmass of the season pushing in by the
middle of next week.
The ridge will still be going solid on Sunday and Monday, with it
beginning to really feel the push of the deep trough shifting into
the eastern half of the CONUS. Heights will begin to slowly fall on
Sunday before starting to quickly fall in anticipation of that
trough on Monday. There are considerable differences with the
trough`s structure and speed at this point, but with southwesterly
flow on both Sunday and Monday, and a cold front approaching by
Monday, expecting both days to be very warm despite the lowering
heights. Look for sunny skies on Sunday, with some high clouds by
Monday evening. Expect highs in the mid 80s, with isolated values in
the upper 80s possible.
The tricky part of this forecast is in regards to the timing of next
week`s cold front. The pattern is expected to transition and
flip rapidly over the next week. Our ridging is being largely
driven by an intense Omega block at 500 hPa over the Gulf of
Alaska, which is driving a deep trough across the western CONUS.
This is aligned with strongly negative PNA values, indicative
of west coast troughing. However, ensemble guidance is unanimous
in flipping this over to positive PNA by Monday of next week,
indicative of a strong ridge redeveloping along the west coast.
When looking at GEFS and EPS guidance, this is supported by low
IQR values of member 500 hPa heights in the western US in the
Mon-Thur timeframe. However, there is considerable uncertainty
regarding the trough that pushes eastward into the eastern CONUS
during this time. It will be a longwave trough, with embedded
shortwaves rotating through it and digging it further. EPS and
ECMWF guidance indicates a much more amplified shortwave pushing
southward out of Canada on Monday, with the GFS less amplified.
This leads to an overall slower solution with the cold front
and associated surface high from the EPS whereas the GEFS is
much faster. However, over the past several runs, the GEFS has
been trending more amplified with the trough diving out of
Canada and reinforcing the overall longwave trough. For now,
this gives some credence to a slower arrival time with the
front early next week. It is still expected to pass through
sometime on Tuesday, with mid to late day looking more likely as
the EPS suite of guidance increases in probability.
Experimental Machine Learning models are trending in this
direction as well.
A slower and more amplified shortwave, causing the front to arrive
later in the day on Tuesday, is certainly and interesting trend and
would likely have sensible weather impacts to temperature and even
precipitation chances. Given the recency of this trend, will opt to
avoid changing the forecast too much on Tuesday and Tuesday night.
Wednesday and Thursday have much higher confidence. A 90th
percentile (per NAEFS, may be even stronger than that by middle of
next week) surface high is expected to push into the southern and
eastern US, ushering in the coldest airmass of this fall season so
far. Guidance is indicating a high, at the center, that could
be 1032mb+ in strength, which would indicate a cold and dry
airmass. As such, look for well below normal temps at the end of
this period, with a potential frost event by the middle of next
week.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Relatively little change in the overall weather situation today
compared to 24 hours ago. Surface high pressure centered over E
NC ridging SW into our region. Satellite indicates areas of
Atlantic Scu cloudiness, with bases above VFR level streaming NW
into the region. Within breaks in the cloud cover, will expect
potential for fog. Mixed results in guidance but general
appearance of similar conditions to last night, where fog was
more of an issue than stratus. So, will lean towards a
persistence forecast, with expectations of periods of LIFR VSBYs
at fog-prone AGS and OGB, with less potential for VSBY
restrictions at DNL/CUB contained within warmer urban centers.
CAE somewhere in between.
After any morning restrictions dissipate/lift, VFR expected
Friday with SCT to BKN diurnal Cu with bases above VFR level and
light winds.
EXTENDED AVIATION OUTLOOK...Chances of late night/early morning
VSBY/CIG restrictions.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
Area Forecast Discussion
National Weather Service Dodge City KS
639 PM CDT Thu Oct 26 2023
...updated aviation section...
.KEY MESSAGES...
Issued at 404 PM CDT Thu Oct 26 2023
- Intense cold front tonight will lead to strong north winds 25 to
35 mph, gusts over 45 mph at times.
- Temperature trends continue to be colder in the forecast,
leading to a growing concern of more prolonged precipitation
event as a wintry mix of sleet and/or freezing rain...
particularly late Saturday and Saturday Night.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 404 PM CDT Thu Oct 26 2023
The much advertised cold front that will be making a dramatic change
in our sensible weather going forward...had just reached I-70 from
Burlington CO to Colby KS mid afternoon with their temperatures
falling quickly down into the upper 40s to around 50.
Unsurprisingly, the front was nosing south faster than any of the
00Z or even 12Z runs indicated. The official frontal timing and wind
shift follows the latest HRRR runs which handles High Plains density
currents very well once the model picks up on them. Look for the
front to reach Dodge City by 9 or 10 PM this evening and the Red
Hills region of south central Kansas by Midnight to 2 AM. Following
the front will be low clouds and an abrupt increase in wind speed to
25 to 35 mph sustained. While the official forecast follows closely
the HRRR model, wind speeds and gusts have been increased north of
the front, to fit better what GFS hourly Bufr forecast model sounds
would suggest, as the cold advection mixed layer will reach to about
500m AGL. The GFS shows 45 to 50 mph gusts at the top of the mixed
layer in the most intense cold advection overnight. The NBM does
show a 75th percentile in peak wind gusts around 45 mph, so there is
certainly support for gusts in excess of 45 mph over a fairly large
area for a few hours overnight/early Friday morning.
As models continue to play catch up with the magnitude of the cold
air mass upstream, the official temperature forecast will be below
NBM deterministic, closer to 25th percentile numbers, which includes
49 at Dodge City, 45 at Hays, and 53 at Medicine Lodge. The initial
cold surge will wedge itself in across the High Plains Friday Night
and winds will become more easterly (and much weaker). Humidity will
be on the increase as south winds above the shallow cold layer will
bring in much greater moisture ahead of the developing longwave
positive-tilted trough. This will set the stage for Saturday and
Saturday Night`s storm which is discussed in the Long Term
Section.
.LONG TERM...(Saturday through Thursday)
Issued at 404 PM CDT Thu Oct 26 2023
As models and their respective ensemble systems continue to play
catch up with the magnitude of the cold air upstream, the forecast
becomes more and more pessimistic with more winter precipitation
likely in play. Saturday temperatures will likely stabilize
somewhere in the 30s as the initial rounds of rain develop. There
are still huge question marks on precipitation type, but for now,
much of the precipitation Saturday should be a cold rain with temps
34 to 38 degrees for most of the DDC CWA. However, once we approach
early evening Saturday, the probability of the 32F line at the
surface encompassing much of southwest Kansas increases. From late
Saturday afternoon through much of Saturday Night, southwestern
Kansas will be in a favored right-entrance region of a pronounced
upper level jet, and this will enhance 700mb frontogenesis across
western Kansas, supporting more widespread precipitation. The latest
NBM shows increasing freezing rain and sleet chances early Sunday
evening at Dodge City specifically, and in fact the favored
precipitation type is sleet/freezing rain on the NBM from about 1 AM
to 7 AM or so early Sunday morning with much of the event as just a
plain cold rain. Again, it should be noted that, since the NBM is a
product of many models, and since many models are still playing
catch up with the magnitude and precipitation timing, that
precipitation type of freezing rain/sleet may be longer than this
latest forecast. Longer period of mixed winter precipitation means a
longer period of potential accumulation and the worse the impacts.
As it stands now, today`s 18Z run of the NBM shows freezing rain
accumulation of 0.03" for this event and 0.07" 75th percentile, and
a 0.10" Probability of exceedance at around 20%. Our official
forecast this cycle follows closely the 75th percentile of around
0.08" freezing rain accumulation as our official temperature
forecast is slightly colder than the deterministic NBM. Keep
checking back for updates on this component of the forecast, as
there is some growing concern of further catching up of the models
on the magnitude of this potential winter event.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 627 PM CDT Thu Oct 26 2023
A cold front will sweep across the entire area over the next 6
hours. The southerly winds at 10-15 knots we are seeing the pre-
frontal time will be abruptly turned to a north wind with more
momentum. Expect stronger north wind component around 20 knots
sustained and gusts to around 30 knots or higher, for several
hours after frontal passage at each site. Wind shifts are most
probable to fall in the 04-06Z window. The post frontal
environment will also bring a stratus layer with some potential
impacts to flight categories. High resolution ensemble forecasts
for selected cloud layers give around a 50 percent chance for
ceilings at 1000ft or lower (IFR) at HYS-GCK as early as about
4z. These probabilities for IFR diminish for other sites as the
front moves southward through 6z.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 40 49 31 37 / 0 0 10 50
GCK 37 49 29 36 / 0 0 10 40
EHA 39 52 32 47 / 0 0 10 20
LBL 40 52 32 42 / 0 0 20 40
HYS 36 45 28 35 / 10 0 10 60
P28 46 52 35 42 / 0 0 20 70
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Umscheid
LONG TERM...Umscheid
AVIATION...Russell
Area Forecast Discussion
National Weather Service Duluth MN
629 PM CDT Thu Oct 26 2023
.DISCUSSION...(This evening through Wednesday)
Issued at 245 PM CDT Thu Oct 26 2023
1. First snow of the season for portions of the CWA
2. Much cooler temperatures over the weekend into next week
3. Another chance of snow early next week
A surface low pressure over southern MN with an inverted trough
north/northwestward is bringing widespread light rain/drizzle to the
Northland. As this low pressure moves northeastward to northern WI
by tomorrow morning an elongated upper level trough moves in
northwestern MN around 06Z. By Friday morning, expecting rain to
transition over to snow, but the timing of this is still in
question. The NAM/GFS/RAP tend to bring in a strong area of omega
associated with the DGZ between 06-12Z tomorrow with the HRRR being
the outlier which bring it in a little earlier around 03Z. The
question is, is this enough lift to create dynamic cooling which
will transition the rain over to snow a little sooner than
expected. Additionally will this help with snow totals. Given the
ground temperatures are still rather warm, the earlier snow start
time may not affect the overall snow totals.
By Friday afternoon, the surface low pressure will be over
southeastern Ontario with the upper trough retreating into
southwestern Ontario. This will transition the winds to become more
westerly/northwesterly which will help filter much cooler
temperatures into the Northland. Therefore any precipitation still
lingering around with the system may become snow for portions of NW
MN. Little accumulation is expected. This will also bring in
single digit wind chill temperature.
The cold air will hang around through the weekend into early next
week. Another upper level system will move into the region overnight
Monday into Tuesday morning. With the cold air already in place, it
is possible the area could see another round of snow. However,
models are not quite in agreement on timing and location of the
upper level low pressure therefore it is hard to say how this storm
will play out. Additionally, some models are showing signs of Lake
Effect Snow over NW WI.
As the low pressure moves eastward, surface high pressure will be
build in bringing back somewhat warmer temperatures with highs in
the upper 30s/lower 40s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 628 PM CDT Thu Oct 26 2023
Active weather across the region this evening with drizzle, fog, and
low ceilings widespread across the Northland. Flight categories will
remain IFR/LIFR through the night. Additionally, rain will spread in
tonight, with a rain snow mix across INL. Snow will eventually
become the dominate precip type for INL with an inch of snow
possible. However, the warm ground and surface temperatures will
make quick work of the snow that falls. As this system passes winds
will turn to out of the northwest and be gusting in excess of 25kts
for tomorrow.
&&
.MARINE...
Issued at 245 PM CDT Thu Oct 26 2023
Gale force winds have been experience by marine traffic therefore
issued a Gale Warning through this evening before transitioning
to a Small Craft Advisory through Saturday.
Generally the winds will be out if the northeast, however, winds
will switch around to the northwest by tomorrow morning as an
upper level system moves through. Additionally, this system will
bring light rain showers through tomorrow afternoon.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 38 45 24 35 / 100 20 0 10
INL 31 37 19 32 / 100 70 20 10
BRD 33 38 22 33 / 90 0 0 10
HYR 38 51 24 37 / 80 30 0 20
ASX 43 50 28 39 / 80 30 10 10
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 1 AM CDT Saturday for LSZ121-140-141-
148.
Gale Warning until 7 PM CDT this evening for LSZ142>147-150.
Small Craft Advisory until 1 AM CDT Saturday for LSZ142>147-150.
&&
$$
DISCUSSION...KSE
AVIATION...Britt
MARINE...KSE
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
730 PM CDT Thu Oct 26 2023
...Short Term and Aviation Update...
.UPDATE...
Issued at 730 PM CDT Thu Oct 26 2023
-- Various notes regarding the evening-overnight forecast (these
first 12 hours):
- Precipitation:
Have primarily made two adjustments to inherited forecast from
afternoon "forecast package":
1) While actual rain amounts will likely be rather light (ranging
from only a trace up to maybe around 0.10" in isolated spots),
boosted actual chances (PoPs) for seeing rain, with PoPs now as
high as 60-90% mainly north of I-80 and mainly pre-midnight.
Expect a fairly broad band of mainly light showers to increase in
coverage this evening mainly across our Neb zones, but possibly
down into KS too, as a quick-hit of decent forcing/lift will go
through as our coverage area (CWA) resides along the southern
fringes of lift associated with a moderately-strong shortwave
trough racing from WY/MT across the Dakotas overnight. Although
not in the official forecast due to expected very limited
coverage, there is a small chance for a few brief/weak
thunderstorms as well late this evening...particularly in our
northeast CWA, as elevated CAPE could top out as high as 200-400
J/KG per latest RAP progs. On one last note on this topic,
although it could be a close call (especially in a few far
northern counties) whether there might be a very brief period of
light freezing rain on the far back side of departing precip
overnight (as temps fall to freezing), we still think at least the
vast majority of precip will end/move out before temps get this
low, and thus not expecting any late-night travel impacts at this
time.
2) Added official mention of "patchy drizzle" to especially most
Nebraska zones mainly pre-midnight:
Along with the aforementioned chances for legitimate light rain
showers, went ahead and added "patchy drizzle" as well to all
areas where cloud bases (ceiling) are expected to be at-or-below
1K ft. While these lowest clouds will steadily sweep out from
northwest-to-southeast overnight as the cold front scours out low-
level moisture, prior to this, at least brief patchy drizzle is
certainly possible.
3) Temperatures and decision to refrain from a formal Freeze
Warning for some counties tonight-Fri AM:
Made very little change to inherited low temps so far this
evening, as they still appear on track to range from mid-upper 20s
far north/west-central (Valley/Dawson counties), to around 30
central (Tri Cities) to mid-upper 30s far southeast
(Thayer/Mitchell counties). Technically, we are forecasting at
least a "soft freeze" of 29-32 degrees for several counties within
the northwest 2/3rds of our CWA that are still considered
"eligible" for Freeze Warnings (we declared
Valley/Greeley/Dawson/Gosper/Furnas counties ineligible a few
weeks ago due to a legit hard freeze back on Oct. 7th). However,
given that all of these counties have already experienced at least
1-2 rounds of frost and/or "soft freeze" already this month, we
have decided to refrain from a formal Freeze Warning for tonight,
and will likely instead give greater consideration for a formal
Freeze Warning to FRIDAY NIGHT/SAT AM, which appears to carry a
greater chance of featuring a more widespread hard freeze in the
mid-upper 20s (this would likely be our FINAL Freeze Warning of
the season).
&&
.DISCUSSION...(This evening through Thursday)
Issued at 219 PM CDT Thu Oct 26 2023
Key Messages:
* Strong northerly winds and a small chance for showers are
expected overnight as another cold front in concert with an
upper level disturbance pushes across the region. Winds could
gust to 45 MPH late tonight through early Friday morning.
* Marginal Freezing temperatures are anticipated across a large
portion of the area Friday morning, but this is just a precursor
to much colder temperatures expected for the subsequent days.
The combination of strong winds and these cool temperatures will
however result in wind chills in the teens to start the day
Friday. Morning air temperatures in the teens are possible in
spots for several days thereafter.
* The first accumulating snowfall of the season (in spots) is
expected on Saturday (although most folks should at least see
some flakes). One to four inches of snowfall accumulation will
be possible, with the lower totals south of highway 6, and the
higher snowfall totals north of Highway 30.
* Dry weather with below normal temperatures are expected from
Sunday afternoon through the middle of next week, with a
potential return to near normal temperatures (mid-upper 50s) by
the end of next week.
A cold front pushed through Ord early this morning and as of this
afternoon can be seen on radar continuing to track southeast of
Blue Hill. Expect this front to continue to make slow progression
southeastward, with a reinforcing shot of cold air, strong winds,
and a small chance for some light rain showers anticipated
overnight.
This reinforcing shot of cold air overnight will result in a
prolonged stretch of very cold fall weather, with well below
normal temperatures expected through the middle of next week.
While skies will clear behind this secondary front Friday morning,
an upper level disturbance rounding the base of the trough across
the southwest will cross the local area on Saturday providing
sufficient lift for some light precip across the local area. Given
the very cold temperatures in place, think this will mostly fall
in the form of snow, especially across our Nebraska area, with
some light accumulations possible. That said, overall QPF amounts
are on the light side, 0.1-0.2 inches, and do not expect a major
event, but possibly more of a low end snow advisory event for a
few of our northern and possibly western counties. Still plenty of
uncertainty with this system, and the latest models have now
hinted at more sleet - especially south of I-80 with this event -
but should see a band of snow develop somewhere across our north
that will likely result in 2-4 inches of accumulation. GEFS snow
probs for 3 inches or more of snow remains in the 30-60% range for
areas generally along and northwest of Highway 30.
Behind this disturbance Saturday, northwesterly flow aloft will
continue for several days, with another upper level low and cold
front possibly impacting the area next Tuesday. This front looks
to be dry locally, with the better chances for precip well to our
northeast, but should bring another shot of cold air, resulting
in a dip in temperatures on Tuesday, before gradually warming
back up to near climo by next Thursday. This will be in response
to a potential shift in the upper level pattern which will bring
more zonal flow aloft (but continued dry) late in the period,
although the EC wants to continue with a more northwestelry and
cooler weather pattern...so will have to wait and see for those
very extended periods.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Saturday)
Issued at 730 PM CDT Thu Oct 26 2023
---UP FRONT NOTE REGARDING KEAR TAF/WEATHER OBSERVATIONS:
An "AMD NOT SKED" (amendment not scheduled) continues for the KEAR
TAF given a failure of the automated weather observations system
since Tuesday afternoon. A NOTAM is currently in effect regarding
this issue, and KEAR TAF will likely remain in an AMD NOT SKED
status until automated observations resume.
- General Overview:
This period will feature changing conditions in various weather
elements, including: 1) ceilings starting out LIFR/IFR/MVFR for
the first several hours but then going VFR thereafter...2) a
possibility of patchy drizzle and/or passing light rain showers
the first several hours (then dry thereafter)...3) Moderately-
breezy northerly winds through the majority of the period (peaking
the first 12-18 hours), before steadily diminishing late in the
period Friday afternoon. Going into a bit more detail...
- Ceiling/visibility trends:
By far the worst conditions of the period are right away these
first 3-6 hours, as ceilings will prevail anywhere from LIFR to
MVFR, before lifting/scattering out to VFR for good around or
slightly after 06Z. In fact, skies through the latter half of the
period (Friday daytime) should prevail mostly sunny. As for
visibility, cannot rule out brief MVFR these first 3-6 hours
(especially if a period of drizzle or steadier rain passes
through), but have kept TAFs low-end VFR at this time.
- Precipitation:
Have a mention of both light drizzle (-DZ) and vicinity shower
(VCSH) going through 06Z, as one or both of these rain types are
certainly possible. The potential for brief/passing showers could
actually extend out closer to 08-09Z, but will defer to later
issuances to address this possibility.
- Winds:
Winds are already starting to pick up out of the north this
evening, with the overall-strongest speeds expected to focus
between 03-18Z, during which time sustained speeds will commonly
be around 20KT/gusts 25-30+KT. A steady drop-off in speeds will
occur late in the period Friday afternoon, with sustained speeds
likely dropping to at-or-below 10KT by around 22Z.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&
$$
UPDATE...Pfannkuch
DISCUSSION...Rossi
AVIATION...Pfannkuch
Area Forecast Discussion...Updated
National Weather Service Lincoln IL
914 PM CDT Thu Oct 26 2023
.SYNOPSIS...
Issued at 914 PM CDT Thu Oct 26 2023
A cold front will slowly move across the region through the day
Friday. Ahead of the front, occasional showers, breezy south to
southwest winds and mild temperatures with highs in the 70s are
expected. Temperatures will cool down with highs only in the 40s
and 50s this weekend, but additional showers are expected, some of
which could be heavy south of I-72. Overnight lows in the 20s are
expected through the first half of next week.
&&
.UPDATE...
Issued at 914 PM CDT Thu Oct 26 2023
Updated PoPs this evening and overnight to reflect a couple of
areas of scattered to numerous showers. First, a shortwave feature
producing showers currently from Peoria vicinity to around
southern tip of Lake Michigan has had high coverage and updated to
categorical coverage, moving out of the central IL forecast area
to the northeast by midnight. A second feature is an area of
strong warm advection in southeast to east central IL late
tonight focused on by several CAMs solutions. Raised PoPs to
around 40-50 percent for this feature for now. Otherwise, lows in
the low to mid 60s and south winds around 10 mph look good for the
tonight period.
37
&&
.DISCUSSION...
Issued at 225 PM CDT Thu Oct 26 2023
************ ************ KEY MESSAGES ************ ************
* A slow moving cold front will bring daily chances for showers
through the weekend including potentially (50-70%) heavy rain
in excess of 2 inches south of I-72 this weekend.
* A growing-season ending hard freeze (<28 degrees) is likely
(>80%) Monday morning west of I-55 followed by two additional
nights of lows in the 20s area-wide (90% confidence).
************ ************ ************ ************ ************
This afternoon, a disorganized area of low pressure is over
southern MN with a trough stretching southwest into SE CO.
Southwesterly flow ahead of these features is in place. Warm air
advection is contributing to mild conditions across central
Illinois along with extensive cloud cover and precipitation. RAP
indicates that modest instability will be in place, mainly west of
I-55 through late this evening, then spreads across the remainder
of the area overnight. A few storms will be possible as a result.
HREF LPMM show a few swaths of around three quarters of an inch
of rain through tonight, mainly west of I-55, but most of the area
is expected to see less than a quarter inch of rain through
Friday morning.
Through the day Friday, the cold front will very gradually move
across central Illinois. Many areas will still top out in the 70s
ahead of the front with 80s possible south of I-70. With frontal
passage expect temps to drop sharply back through the 60s into the
50s. Overnight lows will be in the mid 30s near Galesburg to mid
50s near Lawrenceville. Rain will accompany the front and cannot
rule out a few thunderstorms as well. GFS indicates a narrow
ribbon of around 500 J/kg MLCAPE, but extensive cloud cover may
make this difficult to realize. DESI LREF probs indicate that
there is only a 30-40 percent chance for exceeding 500 J/kg. That
said, if we do end up having some pockets of stronger diabatic
heating, strong deep layer shear of 40-50 kt would be sufficient
for some stronger or severe storms. CSU machine learning does
paint a 5-15% swath across central Illinois for possible damaging
wind gusts.
The frontal boundary will sag south of the Ohio Valley Saturday
but strong isentropic ascent will begin to set up north of the
boundary Saturday afternoon and continue into the day Sunday. NBM
48-hour QPF probs indicate a 50-70 percent chance of areas along
and south of the I-70 corridor receiving over two inches of rain
this weekend with probs quickly dropping off further north. Mean
48-hour QPF amounts are roughly 1.0-1.5 inches north of I-72 and
1.25-2.5 south. Instability looks to be weak/negligible over the
weekend so will keep thunder probs in slight chance category
(<24%) where forcing is strongest in the southern forecast area.
By Monday morning, precip chances will begin to settle to our
south as high pressure spreads from the central Great Plains
into the mid Mississippi Valley. A much colder air mass will be in
place through the first half of next week. A hard freeze (<28F)
is possible as early as Monday morning with the highest
probabilities (60-80%) west of the I-55 corridor. These probs
further increase (70-90+%) across the entire forecast area for
Tuesday and Wednesday morning. This should effectively end the
growing season. A strong shortwave is progged to dig across the
region Tuesday or Tuesday night (ECMWF lags the GFS about 12 hours
on this wave). This will bring in a reinforcing shot of cold air,
and depending on the track, possibly some snow flakes.
Deubelbeiss
&&
.AVIATION... (For the 00z TAFs through 00z Friday Evening)
Issued at 636 PM CDT Thu Oct 26 2023
A disturbance embedded in southwesterly flow aloft will continue
to bring showers the the central IL terminals, especially KSPI,
KBMI, and KPIA until around 03Z-06Z then a relative lull in shower
activity should take place until a cold front nears the area
around 16Z-21Z. Conditions should be primarily VFR this evening,
with some occasional/isolated MVFR cigs and vsbys with heavier
showers. Cigs should slowly lower across the area, becoming
primarily MVFR by 06Z-11Z. Winds S-SE around 10 kts overnight,
shifting to W-NW by 18Z-21Z behind the approaching cold front.
37
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Norman OK
633 PM CDT Thu Oct 26 2023
...New AVIATION...
.SHORT TERM...
(This evening through Friday)
Issued at 306 PM CDT Thu Oct 26 2023
A pleasant afternoon will give way to an agreeable evening across
our area. Winds will remain out of the south ahead of tonight`s cold
front.
That cold front, of course, will be the primary focus of the short-
term forecast. Surface observations across the central Plains
clearly show the frontal boundary just south of the Kansas-Nebraska
border, where it has remained for most of the day so far. Sunshine
to the south of the boundary and thick stratus to the north of it
has contributed to diabatic frontogenesis today, which will keep the
temperature gradient sharp as the front begins to surge south
tonight.
The front will likely enter northern Oklahoma sometime around 3:00
am and will clear Bryan County sometime before sunset tomorrow
night. In its wake, a period of gusty northerly winds will occur
across northern Oklahoma tonight, but those winds should die down
with southward extent as the 850 mb cold front fails to keep up and
the mixing depth of the postfrontal layer becomes constricted. A few
gusts to nearly 40 mph are possible in Harper County.
Front-end high temperatures will occur across much of our area
tomorrow, with temperatures getting knocked down 10-20 degrees with
frontal passage. The question, then, will be whether or not
temperatures can recover any in the afternoon. This will largely
depend on the strength of cloud cover, with much of the guidance
envelope suggesting sunshine returning out west by late afternoon
and some recovery into the upper 50s or low 60s. Given the strength
of stratus across Nebraska today, am leaning toward the NAM
solution, which as always is to sock the shallow cold airmass in
under a deck of stratus. This would keep tomorrow much chillier area-
wide.
Meister
&&
.LONG TERM...
(Friday night through next Wednesday)
Issued at 306 PM CDT Thu Oct 26 2023
A cold surface airmass will continue to settle in tomorrow night
with lows dropping to around 50 across southern Oklahoma and western
north Texas, and the upper 30s across northern Oklahoma. Aloft,
however, west-southwest flow will continue to strengthen, and the
850-700 mb layer will actually begin to revert to a warm advection
pattern around daybreak on Saturday.
If you can read between the lines on that, then yes, we should start
to see a warm nose develop Saturday morning just as isentropic
ascent contributes to the development of precipitation. Of note: the
moist layer does not appear to be particularly deep, and we actually
have some dry air aloft. This may signal less of a steady, moderate
rain and more of a drizzle. There should be pockets of greater rain
rates involved, however, as short-range guidance suggested 300-500
J/kg of elevated instability atop the warm nose. Indeed, the HRRR
and NAM both depict a cellular mode with convective enhancements to
the rain rate. Some lightning and potentially small hail can be
expected during the day on Saturday, which will otherwise be breezy,
wet, and miserable.
The pressure gradient will sharpen Saturday night as the core of the
upper-level trough ejects into the northern Plains. This will bring
in another round of gusty northerly winds early Sunday morning as
well as a reinforcing shot of cold air at the surface. Here is where
moderate uncertainty gets introduced into the forecast. First of
all, NBM continues to maintain much colder lows than any available
deterministic guidance (and is sitting at the very bottom of
ensemble guidance as well). Given the bias-correction NBM employs
for shallow cold airmasses, this is understandable, and seems to
be backed up by a widespread zone of 20-25 temperatures across the
northern Plains this afternoon, well in advance of when global
models suggested it. Meanwhile, as this second shot of cold air
comes in, the cold front aloft will begin to race southward with
it. This will begin to choke off the spigot of warm
advection/isentropic ascent that is the source of the
precipitation. We may see rain reduce to a drizzle during this
timeframe. Any frozen precipitation that does occur will take the
form of freezing rain or freezing drizzle. Given how warm the
ground is, it seems unlikely that impactful freezing rain will
occur, but this bears monitoring. To give some confidence
analysis:
Confidence that lows get below freezing in northwest Oklahoma:
medium-high
Confidence in freezing rain occurring: medium
Confidence that freezing rain impacts are felt: low
Precipitation chances will linger across our southern zones Sunday
during the day where elevated instability remains. Small hail will
again be possible. After that, attention will turn to the potential
for a widespread freeze from Monday morning through Wednesday
morning.
Meister
&&
.AVIATION...
(00Z TAFS)
Issued at 630 PM CDT Thu Oct 26 2023
A cold front will move into OK tonight resulting in an abrupt wind
shift from the north, with gusts around 25 to 30 kt. MVFR to IFR
cigs will also return both ahead of it, and briefly behind it.
It`s unclear how widespread BR will be tonight, but indications
are it should remain fairly patchy so have only included it for
central OK TAFs were confidence is higher. Either way, any BR/DZ
should remain brief.
&&
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 57 62 45 54 / 10 10 50 80
Hobart OK 52 59 45 56 / 0 0 30 60
Wichita Falls TX 63 69 50 63 / 0 30 70 60
Gage OK 44 55 38 47 / 0 0 10 60
Ponca City OK 52 56 41 51 / 10 10 20 80
Durant OK 70 82 53 68 / 10 50 80 80
&&
.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&
$$
SHORT TERM...04
LONG TERM....04
AVIATION...03