Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/18/22
If you`ve made it this far into the forecast discussion and are
hoping for more engaging forecast details, you might be a tad
disappointed, as we`re in for a rather uneventful few days on the
heels of today`s snow.
That said, it`s certainly worth emphasizing the anomalously cold
air mass that will linger over Colorado as we enter the weekend.
Friday night will be very cold once again with clear skies and
remaining snow cover keeping lows in the single digits for the
lower elevations. Cold air pooling will likely be significant in
the high mountain valleys, particularly Middle and North Park
where snow cover will be more likely. Have lowered nighttime
temperatures there, where the thermometer could drop into the
negative teens.
We`ll begin a gradual transition to milder and more seasonal
conditions over the weekend and into Monday under weak ridging
building in from our west and mostly sunny skies. Temperatures
will steady early next week but we`ll remain dry at least through
Tuesday.
Details become fuzzy by the middle of next week. Deterministic
guidance varies in its solutions, ranging from a closed low over
Arizona to much more progressive, weak shortwave over Colorado.
Ensembles are not at all bullish on precipitation chances, which
would favor the mountains if anything. A handful of solutions
produce some measurable snow east of the Front Range but really
the signals are quite meager at this point. Just chance PoPs
currently for Wed-Thu period, primarily for the mountains.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 435 PM MST Thu Nov 17 2022
ILS and MVFR/IFR conditions will continue through the evening and
overnight. The early afternoon lull is now over, with snow quickly
developing and intensifying across the terminal sites over the
past hour or so. Ceilings and visibilities should fall a little
lower this evening as heavier snow moves in. There could be some
brief LIFR conditions depending on where the heavier bands develop
tonight. Snow will gradually wind down tomorrow morning. Ceilings
should rise through the morning hours with VFR conditions expected
a little before noon. Winds will remain fairly light out of the
northeast tonight and will become more variable tomorrow.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 AM MST Friday for COZ031-033>036-
040-041-043-045.
Winter Storm Warning until 9 AM MST Friday for COZ038-039.
&&
$$
UPDATE...Hiris
SHORT TERM...Danielson
LONG TERM...Rodriguez
AVIATION...Hiris
Area Forecast Discussion
National Weather Service Lincoln IL
712 PM CST Thu Nov 17 2022
.SYNOPSIS...
Issued at 212 PM CST Thu Nov 17 2022
A cold front will move across the region this afternoon through
tonight bringing a few widely scattered snow showers to central
Illinois. Temps are expected to fall to around 20 degrees tonight
behind the front, then will only warm into the mid to upper 20s
north of I-70 Friday. South of I-70 is expected to reach the lower
30s. Overnight lows are expected to dip into the teens and single
digits Friday night and Saturday night.
&&
.UPDATE...
Issued at 712 PM CST Thu Nov 17 2022
A cold front was pushing east of the I-55 corridor early this
evening. Water vapor imagery indicated a shortwave moving into
northwest IA. Lift ahead of the wave combined with steeper lapse
rates behind the front to produce scattered rain and snow showers
over the northern CWA. As temperatures cool below freezing a few
slick spots will be possible, especially where briefly heavier
snow showers put down a light accumulation, likely a half inch or
less. IR satellite data showed cloud cover extending northwest
through central and northern IA, thus mostly cloudy skies
persisting overnight will keep lows mainly in the 20s with upper
teens where any clear pockets develop. After a lull in the winds
along the frontal zone, brisk west-northwest winds are already
gusting 20-30 mph west of the IL River and these will spread east
over the remainder of the CWA tonight.
&&
.SHORT TERM...(This evening through Friday)
ISSUED AT 212 PM CST Thu Nov 17 2022
This afternoon, low pressure is in place across the Great Lakes
resulting in cyclonic flow and cloudiness over much of the
Midwest. A cold front is currently moving across the Illinois
River Valley and will continue to push across central Illinois
through the evening. In its wake, steepening low level lapse rates
will allow weak instability to develop which will support some
isolated to widely scattered snow showers. Overall forcing
remains weak which will help keep coverage low, but given the
depth of the steep lapse rates which result in equilibrium levels
near the top of the snow growth zone, an isolated moderate or
heavy snow shower couldn`t be ruled out. HREF ensemble max snow
totals do show the potential for a couple narrow, isolated swaths
of around an inch of snow which seems reasonable if instability is
realized. Most of the area should only see flurries or a dusting
of snow, but within these isolated stronger showers, visibility
will be greatly impacted and quickly go down to a quarter mile or
less within a short period of time. RAP snow squall parameter
values top out between 3-4 roughly along and north of a Havana to
Paris line further highlighting the potential for some heavier
bursts of snow.
By Friday morning, mid level height rises begin to overspread the
region while at the surface, high pressure spreads southeast from
the northern High Plains across the central Great Plains and to the
middle Mississippi Valley. This combination of factors will keep
central Illinois dry through the day Friday, albeit cold with highs
generally in the mid to upper 20s north of I-70 and lower 30s south.
.LONG TERM...(Friday night through Thursday)
ISSUED AT 212 PM CST Thu Nov 17 2022
Deep, closed upper low remains over Hudson Bay to start the day
Saturday but a strong shortwave rounding the base of the trough
over the Great Lakes will finally help nudge the system to our
east as it lifts to New England Sunday. Temperatures will start
off quite cold Saturday morning, in the teens across all of
central Illinois, and will only warm into the upper 20s north of
the Illinois River and 30s south. Meanwhile, surface high will
build over the mid Mississippi River Valley Saturday night into
Sunday morning allowing skies to clear as cyclonic flow finally
exits the region. Favorable radiational cooling conditions will be
in place and some locations could dip into the single digits
Sunday morning, with lows in the teens elsewhere. The surface
ridge axis will shift to the upper Ohio River Valley by late
Sunday with southwest flow overspreading portions of the Midwest
in its wake. This will allow temperatures to moderate through the
first half of next week. 40s return to the forecast Monday
followed by 50s Tuesday and Wednesday.
Attention turns back to the west Thursday as a strong shortwave
emanating from the Pacific Northwest digs across the Great Plains
to the mid Mississippi Valley. A surface low develops in
response and tracks across the region Thursday and Friday. At this
time there remain rather significant differences in timing and
placement of this system which leaves forecast details uncertain.
NBM P-type probs favors rain with this system, but do at times
show the potential for snow or a wintry mix. Meanwhile, the
ECMWF/EPS hints at more of an alberta Clipper like setup favoring
snow. This system will bear watching in the coming days as details
come into better focus.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 523 PM CST Thu Nov 17 2022
Scattered snow showers will affect the terminals this evening,
most concentrated at KPIA-KBMI where tempo MVFR ceilings and
visibilities are forecast. There is a low chance that IFR
visibility will be seen in the heavier showers, as has been noted
in a couple obs out of eastern IA. Outside of the showers VFR
ceilings will lower to MVFR from 05-07z at KPIA-KBMI-KCMI. There
is a low chance that these ceilings will affect KSPI-KDEC but are
not included in this set of TAFs. The MVFR ceilings are forecast
to persist through 17-18z, then go VFR through afternoon. Winds
will be persistent from the west at 10-20 kt.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...25
SYNOPSIS...Deubelbeiss
SHORT TERM...Deubelbeiss
LONG TERM...Deubelbeiss
AVIATION...25
Area Forecast Discussion
National Weather Service Louisville KY
944 PM EST Thu Nov 17 2022
.Forecast Update...
Issued at 925 PM EST Thu Nov 17 2022
Cold front approaching the I-70 corridor this evening, but its bark
on radar is worse than its bite in sfc obs as there is still a fair
amount of precip evaporating before it reaches the ground. Still
looking for this boundary to press southward through the night, and
push through southern Indiana and Kentucky on Friday morning.
Min temps are a little tricky overnight as we could still drop a
couple more degrees, but we should flatline by about midnight as
clouds increase and the boundary layer becomes more mixy. Temps
should level off in the mid/upper 20s for most.
Models have not had a good handle on snow coverage with any of the
systems this week, so the precip forecast is fairly low-confidence.
Will stick with a 20 POP for isolated snow showers, with the best
chances near the I-64 corridor from Louisville to east of Lexington,
and perhaps another max W/SW of Elizabethtown as the front lights up
over western Kentucky. No major changes to the previous forecast,
but any more focused areas of precip will bear watching overnight.
&&
.Short Term...(This evening through Friday)
Issued at 225 PM EST Thu Nov 17 2022
Low level clouds over southern Indiana and north central Kentucky
continue to erode late this afternoon. Expect skies to become only
partly cloudy by this evening before more clouds build in after
midnight ahead of an approaching cold front. Temperatures look to
drop into the lower 20s late tonight.
A cold front will begin approaching from the northwest late tonight
and likely push into the region during the early morning hours
tomorrow. Some models indicate we could see a narrow band of light
snow flurries or showers develop ahead of the front. The HRRR has
been most consistent with this light snow tomorrow morning while
other short range models keep us dry. In this type of environment,
can`t rule out some isolated snow showers dropping a quick dusting
of snow ahead of the front so did continue isolated light snow
shower mention for tomorrow morning.
Skies will become partly cloudy tomorrow afternoon with breezy
westerly winds behind the front. High temps look to stay in the 30s
to around 40.
.Long Term...(Friday night through Thursday)
Issued at 154 PM EST Thu Nov 17 2022
Very Cold Weekend...
The nose of a dome of Canadian high pressure will poke into the
Ohio and Tennessee Valleys Friday night and Saturday morning, taking
temperatures down into the teens for many with mostly clear skies
and nearly calm winds. This will be followed by a quick cold frontal
passage Saturday evening, but the boundary will be weakening and
will have very little moisture with it (PWAT 0.18"), so no
precipitation will accompany its passage. However, behind the front
a new, stronger dome of high pressure will move into the region and
supply us with temperatures Sunday morning a few degrees colder than
what we will have seen Saturday morning, with everyone dropping into
the 10-19 degree range (still above record lows).
Holiday Week...
Dry weather will continue at least through mid-week as that surface
high settles into the southeast United States and deflects an
approaching Monday cold front off to our north, passing through the
upper Great Lakes. By the holiday a cut-off 5H low will be in the
vicinity of the Gulf of California while a northern upper trough
tries to dive southeast from the Prairie Provinces. This is far out
in the forecast and the models will struggle with how these systems
interact. As of now, the deterministic runs have slowed down the
advancement of precipitation, though there are enough individual
ensemble members to support keeping low PoPs in the forecast for
Turkey Day. Temperatures will moderate as the week goes along, so by
the time Thanksgiving arrives we should have daytime temperatures in
the 50s, and for now we just have plain rain in the forecast.
Thunder chances will hold off well to our southwest.
&&
.Aviation...(00Z TAF Issuance)
Issued at 625 PM EST Thu Nov 17 2022
IMPACTS: Potential for snow showers early Fri morning at SDF and LEX
CONFIDENCE: Low to moderate
Expect mainly VFR conditions through the valid TAF period. Wind
direction will back to SW this evening ahead of a weak cold front.
There is some hint that we could squeeze out a few snow showers at
SDF and LEX, mainly from the pre-dawn hours through mid-morning.
Models have not handled this well all week, so will go cautiously
forward with a PROB30 to highlight the potential impact, mainly on
ground operations. Prevailing vis even in snow showers should be
MVFR, with cigs remaining VFR.
Winds will veer to due west with the fropa, with afternoon gusts
just either side of 20 kt. The low-end VFR strato-cu deck in the
morning should scatter out as the afternoon progresses.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...RAS
Short Term...AMS
Long Term...13
Aviation...RAS
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
842 PM CST Thu Nov 17 2022
.UPDATE...
Issued at 820 PM CST Thu Nov 17 2022
Current surface observations show that the cold front is just
south of the I-44 corridor in Missouri and I-70 corridor in
Illinois. As discussed earlier, the signal for low-level
frontogenesis was trending weaker, and that trend has so far been
verifying per recent RAP analysis. Additionally, soundings across
the area based on the RAP analysis show only shallow layers of
saturation in the lower atmosphere primarily outside of the
dendritic growth zone, leading to a lack of ice crystals aloft.
Therefore, our confidence in snowfall continues to decrease. I
still have a low chance of snow across portions of southeastern
Missouri and southwestern Illinois over the next couple of hours
to account for the weak low-level frontogenesis there, but I feel
the worst case scenario is a dusting on grassy and elevated
surfaces in those parts of the CWA. Spotty sprinkles/flurries are
more likely this evening into the early overnight hours before
drier, post-frontal air moves in and drys out the lower
atmosphere.
Elmore
&&
.SHORT TERM... (Through Late Friday Night)
Issued at 228 PM CST Thu Nov 17 2022
Deep, cyclonic flow will persist across the Midwest through Friday
and beyond as time-mean upper-level longwave troughing remains over
the Great Lakes. In a continued parade of mid-level shortwave
troughs navigating the cyclonic flow, two shortwave troughs will
traverse the Midwest this afternoon and overnight. The first
shortwave trough has forced a cold front southeastward into the CWA
that has reached northeastern MO and west-central IL this afternoon
and will continue through the rest of the CWA through the evening.
Passage with the onset of strong low-level CAA and some stratocumulus
with scattered flurries, or initially sprinkles. Beside flurries, a
frontogenetical band of light snow still appears possible from south-
central MO to southwestern IL behind the front as well. But latest
short-range model guidance has trended toward weaker and less
organized low-level frontogenesis translating to lighter associated
QPF, generally 0.01" or less. The latest HREF LPMM still has a swath
of just over 0.01" across portions of southeastern MO and
southwestern IL but is attributed nearly entirely to its time-lagged
members. Therefore, the current expectation is for even the highest
snowfall rates to be too light for anything more than a dusting
accumulating on grassy and untreated surfaces.
Any flurries should exit the CWA by Friday morning, along with a
potential brief break in stratocumulus for mainly the southern two
thirds of the CWA; however, some expansion back southward appears
possible through the morning. Strong low-level CAA from overnight is
anticipated to place an anomalously cold airmass across the Midwest
with 850-hPa temps settling in the low-negative teens to mid-
negative teens C. These remarkable 850-hPa temps are between the
minimum and 1st climatological percentile. As a result, Friday`s
high temps should only warm into the mid-20s to mid-30s F and near
KUIN and KCOU`s daily record minimum high temps, especially if
stratocumulus is more prevalent. Low-level WAA initiating Friday
night should begin releasing the CWA from the clutches of this cold
airmass. In fact, low temps Friday night in the mid-teens to low-20s
F may occur during the first half of the night as the WAA strengthen
and surface pressure gradient tightens beneath mostly clear skies.
Pfahler
.LONG TERM... (Saturday through Next Thursday)
Issued at 228 PM CST Thu Nov 17 2022
Deep, cyclonic flow will continue through Saturday with the passage
of another mid-level shortwave trough and southeastward-advancing
cold front. Timing of this cold front will be crucial in determining
Saturday`s high temps, marking the quick transition from low-level
WAA to another shot of CAA. Most model guidance has the front bi-
secting the CWA around midday, leading to a large areal spread in
high temps from the upper 20s F in northeastern MO to the mid-40s in
southeastern MO. Moisture is forecast to be more limited with this
cold front than its predecessor, precluding precip but a few
flurries cannot be ruled out. The CWA should be spared the core of
this post-frontal cold airmass, but conditions favorable for
efficient radiational cooling (i.e., mostly clear skies and
light/calm winds from a nearby surface anticyclone) could still
allow low temps Saturday night to fall into the teens F CWA-wide.
These temps will likely come short to daily records, though.
Sunday into Monday, global model guidance advertise the time-mean
upper-level longwave troughing becoming more progressive and finally
departing the Great Lakes, leading to more zonal flow across much of
the central CONUS. Large-scale subsidence from height rises behind
this longwave troughing is anticipated to quickly translate Saturday
night`s surface anticyclone eastward into the eastern CONUS. The
resulting flow pattern will favor low-level southwesterly or
southerly flow and WAA, with temps moderating to near average on
Monday. There is consensus that the first half of the week will also
remain dry with only a compact mid-level shortwave trough passing
south of the CWA late Monday into Tuesday.
The next opportunity for precip across the CWA will be around
Thanksgiving Day, but global model guidance continue to depict
vastly different evolutions between upper-level troughs in the
northern stream and those in the southern stream with little run-to-
run consistency. The leading WPC Cluster Analysis clusters (75%)
both contain dominant northern stream troughing over the central
CONUS. The other cluster has more dominant southern stream troughing
hanging back across the Four Corners Region. The nature and track of
any trough or troughs will have large implications for the exact
sensible weather across the CWA during this timeframe, which is
highly uncertain.
Pfahler
&&
.AVIATION... (For the 00z TAFs through 00z Friday Evening)
Issued at 527 PM CST Thu Nov 17 2022
A cold front is currently moving southward through the region,
having already passed over KUIN, KCOU, and KJEF and currently in
the vicinity of KSUS, KSTL, and KCPS. The front is expected to be
moving through the latter three terminals at the start of the
period, with winds quickly shifting to out of the northwest with
its passage. Additionally with the passage of the front is the
chance for a quick hit of light rain or snow. Confidence is high
that this precipitation will be light enough to not impact
visibilities, and snow that falls will at worse provide a dusting
on grassy and elevated surfaces near these terminals given above
freezing near-surface and ground temperatures. Flurries can be
expected around KUIN through this evening given deeper moisture
residing near that terminal. Drier air will move into the region
behind the front through tonight, eroding much of the lower cloud
cover from over the terminals. The exception to this is KUIN,
where confidence remains high that a brief period of MVFR ceilings
will occur Friday morning. These lower ceilings will remain well
to the north of the other local terminals, including KSTL.
Elmore
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX
Area Forecast Discussion
National Weather Service Phoenix AZ
456 PM MST Thu Nov 17 2022
.SYNOPSIS...
Cool and dry conditions will prevail through at least the first
half of next week with only occasional periods of high clouds
tonight through Friday afternoon and again early next week. A weak
and dry weather system passing through the region on Saturday
will bring another round of breezy winds, particularly across
portions of southeastern California. Temperatures will continue to
run 5 to 10 degrees below normal with lower desert highs mostly
in the upper 60s and lower 70s. A warming trend is then
anticipated by late next week as high pressure builds across the
intermountain West.
&&
.DISCUSSION...
Latest water vapor imagery and RAP streamline analysis reveal a
dry northwesterly flow predominating across the Desert Southwest.
This is again resulting in sunny skies along with below normal
temperatures and dewpoints in the teens and twenties.
Model clusters show little difference through the weekend and
indicate another shortwave trough will drop southward out of the
Rockies and towards Arizona Friday and Friday night. PWATs remain
well below normal and there is no chance of rain associated with
the trough. Instead the main impact will be another period of
breezy/windy conditions, particularly Saturday across southeastern
California and further east across the foothills of Pinal County
Sunday morning. However, while ECMWF EFI values suggest gusty
conditions are likely, peak gusts will likely remain well below
Wind Advisory criteria.
&&
.PREVIOUS DISCUSSION...
The weather pattern will begin to change by early next week as the
ridge over the Western U.S. weakens enough to start to allow for
more progressive and stronger weather systems to move across the
Northern Pacific, eventually reaching the Pacific Northwest. This
will likely bring decent precip across the Pacific Northwest, but
model ensembles show dry westerly flow persisting across our
region through the first half of next week. NBM temperature
guidance for the first half of next week does show a very slight
uptrend in temperatures, but highs will still mostly stay in the
lower 70s. For the latter half of next week, a stronger ridge is
favored to move out of the Central Pacific, potentially reaching
our region around next Friday. If this were to happen, we could
see highs approaching 80 degrees over the western deserts to the
mid to upper 70s in the Phoenix area.
&&
.AVIATION...Updated 2356Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Very light winds will prevail through the TAF period, with speeds
generally aob 7 kts. Periods of variability are likely with these
light winds. Otherwise, directions will favor typical diurnal
trends. A late and brief W to WNW shift is anticipate this
evening before returning to E tonight. High clouds will increase
heading through the overnight hours with perhaps some isolated
light virga developing above 15-20 kft across the area. Skies then
clear up by midday Friday followed by another round of high clouds
Friday evening.
Southeast California/Southwest Arizona including KIPL and KBLH:
Winds through the next 24 hours will mostly remain on the light
side (aob 8 kts) with periods of light and variable winds at
times. Otherwise, high clouds will increase through this evening
with perhaps some light virga developing above 15-20 kft across
the area. Skies clear after sunrise Friday.
&&
.FIRE WEATHER...
The weather pattern through the first half of next week will
heavily favor cooler than normal and dry conditions over the
region. Winds through the weekend will at times be breezy with
gusts of 20-25 mph likely, favoring southeast California and the
Arizona high terrain. The strongest winds are likely to be across
southeast California Friday night through Saturday afternoon when
localized gusts to 30-35 mph may be possible. Moisture levels will
remain quite low through the period with daily MinRHs in the
teens across the western districts to 15-25% across the eastern
districts.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Kuhlman
AVIATION...Benedict
FIRE WEATHER...Kuhlman