Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/20/23
Area Forecast Discussion
National Weather Service Columbia SC
718 PM EST Tue Dec 19 2023
.SYNOPSIS...
Below average temps and dry air will dominate much of the week
before steadily warming up and moistening by the weekend. The
next rain chances will hold off until early next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
Surface high pressure based on surface analysis appears to be
centered just northwest of the area. Latest ACARS sounding out
of CAE shows limited wind in the boundary layer which should
decrease further as the high shifts closer to the area.
Radiational cooling has already been strong since sunset with
temperatures near freezing as of 7pm this evening. As a result,
low temperature forecast remains on track with lows likely in
the low 20s to upper teens in sheltered locations.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Deep ridging will build across the central-eastern CONUS
throughout the middle part of the week with the associated
confluent flow aloft forcing a strong surface high into the Mid-
Atlantic. Dry air will remain in place as weak northerly low
level flow continues in conjunction with west-northwesterly flow
aloft, keeping PWAT`s well below average (near 0.25" or lower).
A few good radiational cooling nights are expected Wednesday
and Thursday mornings as clear skies and light winds develop as
the high slides just to our north. High and low temps are
therefore expected to run a few degrees below average until late
week, mid 50`s for highs and low 30`s and upper 20`s for lows.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
There is good agreement across the GEFS and EC ensembles heading
into late week. 500mb heights are expected to build above
average by Friday as the ridge axis will likely move down the
eastern seaboard. The associated surface high pressure is then
expected to consequently shift offshore. So overall, little in
the way of advection is expected in both temps and moisture
until later in the weekend, so the airmass will steadily
moderate a little each day. By late weekend, GEFS and EC members
favor some sort of developing low pressure system in the
south-central CONUS and therefore help drive a warm advection
regime into our area. There is a high guidance variance in how
the low pressure system will progress eastward, but the general
trend in the ensembles suggest increasing rain chances by late
Sunday and Monday.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
VFR through the period.
Very dry high pressure settling over the region will keep winds
light and variable, and conditions vfr the next 24 hours.
EXTENDED AVIATION OUTLOOK...Gradual air mass modification may
provide some opportunities patchy ground fog at the usual fog
prone AGS and OGB by late week. Otherwise, no significant
impacts to aviation expected through Sunday.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
Area Forecast Discussion
National Weather Service Indianapolis IN
1020 PM EST Tue Dec 19 2023
.Key Messages...
- Low RH values down to 25-30 percent possible Wednesday afternoon
- Warming trend with rain chances returning late week into the
holiday weekend
&&
.Forecast Update...
Issued at 1018 PM EST Tue Dec 19 2023
No major changes needed to the forecast this evening. ACARS
soundings out of IND depict a developing low-level jet of 20-30
knots centered around 1-2km agl. Blended guidance is quite
aggressive with mixing some of this momentum to the surface, which
seems overdone. Will maintain lower wind speeds/gusts compared to
guidance. Observations across central Indiana support this, as no
stations have sustained winds over 10kt and no notable gusts have
been reported. Further north and west into Illinois winds do
increase a bit (13G20KT near Decatur IL), but this coincides with
a tighter MSLP gradient. Said gradient relaxes quite a bit into
Indiana, but is enough to prevent winds from going completely calm
overnight except in sheltered / low-lying areas across the
southern portions of our CWA. Low temperatures will likely be
dependent on wind to some extent, as cloud cover looks to
gradually dissipate towards daybreak.
&&
.Short Term...(This evening through Wednesday)
Issued at 254 PM EST Tue Dec 19 2023
.This Evening and Tonight...
Cold and dry conditions persist one more evening across Central
Indiana as an arctic airmass slowly shifts eastward. Current
satellite imagery and surface analysis show temperatures in the low
to mid 30s with light southerly winds. Surface high pressure and low
level ridge axis push east this evening and tonight setting the
stage for rapid warm air advection in the lower levels into
tomorrow. Temperatures at 850mb warm from nearly -10C this morning
to +5C by Wednesday morning as strong southwesterly flow advects a
much more mild airmass northward. While temperatures this afternoon
and evening are stuck in the 30s, a warming trend is on the way.
With elevated southerly winds expected to persist tonight and upper
level clouds streaming in over the ridge, lows may only fall into
the mid and upper 20s across the region. Increased lows towards the
NBM 75th percentile to account for less than optimal conditions for
radiational cooling and quick warm air advection aloft.
.Wednesday...
Seasonably mild and dry air arrive tomorrow as ridging builds
overhead and southwesterly warm air advection aloft increases. While
subsidence under the surface high will keep the lower levels dry,
upper level moist air advection, seen on BUFKIT profiles, will likely
lead to upper level cloud cover passing through at times tomorrow
afternoon and evening. However, this should have minimal effects on
boundary layer heating. Expect highs to reach the mid to upper 40s
across the region, with the potential for areas across South Central
Indiana to reach 50. ACARS soundings around Indiana today show very
dry air through the column, which will be difficult to quickly
moisten. A potential weather concern tomorrow and over the next few
days will be very dry low level air mixing down to the surface
leading to RH values reaching critical thresholds for fire weather
concerns. Short term model soundings do show mixing into the shallow
dry layer just above the surface during the afternoon hours
Wednesday. Went well below most guidance for dew points and RH
values from 15z-22z Wednesday afternoon with RH values potentially
dropping into the 20-25 percent range for South Central Indiana. If
afternoon mixing is stronger than expected tomorrow, high
temperatures will likely be a few degrees warmer than what
forecasted highs currently area. Winds should stay below critical
thresholds, however sporadic gusts to 15-20 kts are possible as well
tomorrow afternoon. Overall, expect a mild, dry December day. Will
keep an eye on any potential fire weather concerns tomorrow
afternoon.
&&
.Long Term...(Wednesday night through Tuesday)
Issued at 254 PM EST Tue Dec 19 2023
Thursday through Saturday
The forecast continues to showcase a warming trend throughout the
beginning of the long term, with highs in the mid to upper 40s
Friday through Monday. Height rises within WAA will promote further
surface high pressure increases just east of Indiana, with
subsidence over the region on Thursday. Once again, this should
lead to some near PBL dry air, and low surface dew points as
mixing increases in the afternoon.
Ensemble members start to deviate in agreement towards the end of
the week as a modest upper level low pushes in from the west.
Prolonged subsidence Wednesday through Thursday, will dry out the
surface layer substantially out in front of the low, of which should
delay any precipitation from reaching the ground late on Friday.
Still, by Friday evening into Friday night, continued downward
moisture flux will eventually saturate the lower levels leading to
light rain and minor QPF. Low passage should occur overnight Friday,
with rain chances waning throughout the day on Saturday.
Sunday through Tuesday...
A deep trough over the Western CONUS late week will lead to lee
cyclogenesis, with most ensemble members realizing a deep surface
cyclone over various portions of the Plains this Weekend. There is
still a lot of uncertainty on low track and corresponding impacts;
regardless, there looks to be a greater than 50 percent chance of
precipitation sometime early next week. As the trough is sampled
later this week, model initialization will improve and confidence in
potential Christmas Eve/Day impact should increase.
With the parent trough slow to progress, some ensembles have been
trending towards a greater chance that the low occludes quickly and
detracts from the upper jet. The result would be a slower
progression eastwards, and much more disorganized low over the
Midwest. For this reason, Sunday and Monday PoPs have been decreased
slightly to showcase the uncertainty.
Either way, all ensemble members have the low passing to the west
leaving the warm sector over the Ohio Valley through Monday. Cooler
conditions are possible following low passage, but low passage
could be anytime from late Monday through Wednesday.
&&
.Aviation...(00Z TAF Issuance)
Issued at 640 PM EST Tue Dec 19 2023
Impacts:
- None
Discussion:
VFR conditions are expected through the TAF period. The development
of a low-level jet is expected tonight, centered around 925mb.
Speeds should be low enough to keep low-level wind shear under 30kt.
At the surface, generally southerly winds under 10kt are expected.
However, some gusts 15 to 20 knots are possible after sunrise.
Aloft, clouds should mainly be in the mid to upper-levels. Some low-
level clouds, around 5-6kft agl, are possible after 15z Wednesday.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...Eckhoff
Short Term...CM
Long Term...Updike
Aviation...Eckhoff
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
828 PM CST Tue Dec 19 2023
.UPDATE...
Issued at 828 PM CST Tue Dec 19 2023
Forecast is in good shape this evening, with no significant
updates necessary.
Evening RAOB analysis shows a minor-amplitude mid-level short
wave tracking east across MN/IA. Ahead of this feature, KLOT and
KDVN VAD wind profiles indicating a 35 kt south-southwesterly low
level jet at around 2 kft. Recent (~02Z) aircraft AMDAR soundings
from KORD shows a fairly stout inversion around 950 mb, though
even so we`re still seeing sporadic gusts in the 20-25 mph range
in surface obs across the area. These breezy south-southwest
winds, combined with associated low level warm advection and
patchy mid/high level cloud cover, were helping to hold temps
fairly steady around the 30 degree mark at mid-evening. Model
forecast soundings do indicate the low level jet will gradually
weaken after midnight as well as a decrease in the more opaque
cloud-cover, suggesting our forecast overnight lows in the mid-
upper 20s are reasonable. Did make some minor tweaks to sky cover
and raised dew points a bit overnight per obs trends, but
otherwise forecast appears to be in good shape.
Ratzer
&&
.SHORT TERM...
Issued at 248 PM CST Tue Dec 19 2023
Through Wednesday night...
Key messages:
* No impactful weather is expected during the short-term period
Discussion:
Overall quiet weather is expected in the short term before a more
active pattern ramps up Thursday into the pre-Christmas weekend.
High pressure to our southeast is currently sliding into the central
Appalachians, supporting another quiet day tomorrow with highs a bit
warmer in the low 40s. A low amplitude shortwave approaches the
Mississippi Valley late tomorrow night, introducing increasing low
level moisture (~850mb) that could spit out a few sprinkles
overnight, however the better forcing and necessary moisture does
not arrive until Thursday afternoon, thus have maintained a dry
forecast through the period.
BW
&&
.LONG TERM...
Issued at 248 PM CST Tue Dec 19 2023
Thursday through Tuesday...
Key Message:
- Periods of rain chances late this week through the Christmas
holiday, with temperatures well above normal for late December
Broad mid-level ridging drifting eastward across the region on
Thursday will promote continued dry conditions into at least
Thursday morning as an elongated surface ridge remains in place
across the eastern third of the CONUS. A pair of weak troughs
entering the Baja of California and the northern Rockies on
Wednesday will phase across the mid to upper Mississippi River
Valley by late Thursday night before crossing the CWA Friday
evening. While antecedent dry conditions will limit precip
potential through Thursday morning, increasing low-level
isentropic ascent within a narrow ribbon of low-level moisture
advecting NE from the southern Great Plains will support at least
some patchy drizzle or light rain late Thursday afternoon and
especially Thursday night. Coverage of light rain will expand
Friday as deeper synoptic ascent with the phased wave moves across
the area.
Precip will likely end by late Friday night, with a lull in
precip potential Saturday as a quickly strengthening upper ridge
builds across the Great Lakes region. The area may remain mostly
shrouded in stratus through the day Saturday within a broad area
of low-level isentropic ascent and moisture advection, but modest
low-level stability under a weak subsidence inversion may allow
some scattering of cloud cover. In the absence of more widespread
cloud cover potential, temps could push well above the 50F mark on
Saturday.
A conglomerate of two large troughs across the western CONUS and
Canada will phase in some form across the central CONUS on Sunday
before drifting and phasing or rotating around additional upper
troughs/lows through the middle of next week. While the inherent
uncertainty in specifics can be expected several days out given
the evolution of phasing waves, the broader consensus of guidance
supports multiple periods of rain Christmas Eve and beyond for
several days. We will remain safely on the warm side of the system
through Christmas, so no snow concerns are expected for the local
area. Temperatures will remain well above normal with temps
potentially 50+ both Christmas Eve and Christmas.
Kluber
&&
.AVIATION...
For the 00Z TAFs...
There are no major aviation weather concerns through the 00Z TAF
period.
Near-southerly winds should continue to favor west of south tonight,
especially prior to 06Z. Occasional flips to SSE are more likely
overnight and during the morning tomorrow, though winds will be
moving at under 10 kt. Also up until around 06Z, sporadic gusts to
around 20 are expected to persist. There is some, albeit low,
confidence in a LLWS set up this evening. Best guess is that winds
will make it up to about 35 kt at FL015, although some model
guidance brings that number closer to 40 kt. Timing on this would be
roughly 02-07Z. The lack of confidence in a true LLWS environment
kept a mention out of the TAF. Winds will flop to easterly around
mid-afternoon tomorrow. VFR can be expected throughout the period.
Doom
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...IL and IN nearshore waters until 3 AM
Wednesday.
&&
$$
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