Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/13/23
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
532 PM CST Thu Jan 12 2023
.SHORT TERM...
Issued at 219 PM CST Thu Jan 12 2023
Through Friday night...
The main weather highlights in the short term include:
* Pockets of drizzle (and some snow) gradually expanding across
the region this afternoon, eventually transitioning to snow
showers.
* Temperatures fall below freezing after midnight; patchy slick
spots possible.
* Lake effect snow focusing into NW Indiana overnight and Friday
morning.
We`re currently in between disturbances, although starting to see
signs of increasing low-level moisture as some light radar returns
are pushing towards the Wisconsin state line and also off the
lake. Recent AMDAR vapor soundings indicate a roughly 2 kft thick
saturated layer down low, and several icing PIREPs suggest there
is very little, if any, cloud ice present with cloud top temps
warmer than about -6 C. Way too much dry air in the intervening
mid-levels to allow for any seeder-feeder mechanisms this
afternoon. As a result, in the absence of steeper low-level lapse
rates and instability, seems like most precipitation will favor
drizzle/light rain, although pockets of snow will be possible
within any developing convective elements near the lake.
Temperatures will be above freezing.
Through this evening as the column slowly cools and the saturated
layer deepens, drizzle/rain should turn to mainly snow showers.
An incoming subsidence inversion means the time period of
saturation reaching more into the base of the DGZ will be
somewhat brief, and maximized from late-evening through the early
overnight. Temperatures are expected to only slowly meander their
way below freezing, so not expecting much more than patchy
coatings of snow on grassy surfaces for the most part. Any
remaining wet roads into early Friday morning could turn slippery,
however, as temperatures fall.
In the vicinity of the lake, lake effect snow showers are expected
to develop through the night as colder 850 mb temperatures arrive
and localized convergence increases. LES parameters are altogether
fairly marginal as things will be capped off by the aforementioned
building inversion. Lake-induced ELs are only forecast to peak
near 5-7 kft, and with saturation only ephemerally reaching into
the DGZ, not looking at an overly high-quality snow. Certainly the
availability of the near full fetch of the lake and limited shear
would support more of a concern, but as they stand right now,
the thermodynamic profiles are a significant limiting factor.
Multi-model consensus suggests a 1-2 inch type event through
Friday morning across NW Indiana, with spotty amounts perhaps
pushing north of 2 inches away from the 36-38 degree lake
influence. Can`t rule out the LES band flopping westward through
Friday morning which could deliver a last burst of snow to Chicago
before winds shift out of the NW and guide lingering LES
eastward.
Inversion really builds down through Friday afternoon, so any
lingering LES will become increasingly spotty and could even end
as a little drizzle as deeper saturation is lost. Given the thin
nature of the stratus deck, think we should be able to readily
punch some holes in it through the afternoon as the inversion
falls. If we manage to clear out across Illinois through the
evening, overnight temperatures into Saturday morning may fall
into the teens.
Carlaw
&&
.LONG TERM...
Issued at 253 PM CST Thu Jan 12 2023
Saturday through Thursday...
Main Forecast Messages and Concerns:
* Continued above/well above normal temperatures
* Breezy/windy on Sunday depending on mixing depths
* Chance for isolated thunderstorms on Monday PM
Aside from the localized lake effect accumulations Friday, the
decided lack of snow cover across the region will allow for a
rapid recovery to above normal temperatures on Saturday following
a seasonably chilly start to the day. Highs will reach the upper
30s to lower 40s under plenty of sunshine and modest southwest
winds. A southerly low level jet will develop overnight Saturday
night, yielding steady to occasionally breezy southerly winds and
temperatures unlikely to fall much as high clouds increase.
On Sunday, persistent pressure falls will help tap into the
strengthening low level jet, the extent of this depending on exact
mixing depths. The NAM is likely underdone given the lack of snow
cover and cloud cover signal being primarily mid and high level.
During the afternoon, gusts up to 30-35 mph, with some upside
potential in the western and southwestern CWA. Climatology of the
warmest 1/3 of progged 925 mb temps (given mild start, dry air
mass, and 0 snow cover) supports highs in the mid to upper 40s.
Sunday night will be unseasonably mild for our coldest time of
year (solidly above normal highs) with gusty southerly winds into
or through the evening.
Later Sunday night through Monday, a neutrally tilted 500 mb
short-wave trough and associated surface low will eject northeast
from the southern/central High Plains to near the MS River
(uncertainty on exact track just to our northwest or overhead).
Increasing warm and moist advection and large scale ascent will
foster increasing shower coverage pre-dawn Monday through the day,
peaking mid day through early evening ahead of the dry slot. Cold
500 mb temps with the trough will steepen mid-level lapse rates
enough for minor MUCAPE and a threat for a few embedded
thunderstorms. Continued slight chance thunder mention roughly
along and south of I-80. Current thinking is that MUCAPE is likely
to be too meager for any stronger thunderstorm risk.
Muted cold advection in the wake of the system could keep a few
spotty showers or sprinkles going into Tuesday (no explicit
precip mention yet). It will otherwise be a cloudy and mild day
in the offing as highs reach the 40s once again, following highs
well into the 40s to lower 50s on Monday. The next notable trough
ejection from the southwest will occur on Wednesday with broad low
pressure gradually consolidating and this low pressure then
tracking north-northeastward through Thursday. A dry column with
high pressure influence to start Wednesday and early closing off
of the 500 mb low suggest at this vantage point a slowed arrival
of precip with this system. Certainly too early to make a firm
call, but prefer the ECMWF/EPS and CMC to the faster GFS/GEFS
suite, which would entail much of if not all daylight hours on
Wednesday being primarily dry, with lower end PoPs perhaps
overdone and an evening precip. arrival more likely.
Evaporative cooling of a marginally cold air mass on the northern
periphery of the system could bring some very wet snow to portions
of interior northern Illinois Wednesday night. Have indicated a
chance for snow northwest 1/3 with otherwise enough confidence for
likely PoPs area wide Wednesday night-early Thursday. It`s too
early to tell on any threat of localized slushy accumulations far
north/northwest, though the generally above freezing temps would
likely mitigate impacts. A healthy slug of moisture with the
system could result in decent QPF amounts for a January system.
Precipitation may transition to snow showers Thursday night in the
cold advection regime behind the system. Looking beyond day 7,
the ensemble guidance has been consistently pointing toward there
finally being a shake-up in the remarkably mild pattern we`ve been
in to a more seasonable and probably still active look, so
*maybe* some more appreciable snow threats into late January.
Castro
&&
.AVIATION...
For the 00Z TAFs...
CIGS: While primarily MVFR, some variability is likely through
the TAF cycle, with some periodic improvement to VFR probable.
Anticipate MVFR CIGS to persist through Friday and likely into
Friday evening with perhaps some tendency for CIGS to drop to
lower end MVFR Friday.
WINDS: NNW winds expected through the TAF cycle. There will be
sporadic/intermittent gustiness tonight into Friday.
PRECIP: While not explicitly in the TAFs, there will likely be
intermittent flurries tonight into Friday morning. There is a
threat for some snow showers to occasionally knock VIS down to
MVFR briefly. Mostly likely timing for SHSN potential looks to be
mid- late evening into the overnight hours, so no changes made to
03-07Z tempo. SHSN threat may persist beyond 07Z, will address
that in later TAF updates if confidence increases.
- Izzi
&&
.MARINE...
Issued at 253 PM CST Thu Jan 12 2023
Northerly gales will continue along the Indiana nearshore through
mid to late Friday morning, with a few gale gusts at times on the
Illinois side. Hazardous waves will gradually subside Friday night.
Castro
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Warning...IN nearshore waters until 10 AM Friday.
Small Craft Advisory...IL nearshore waters until 10 PM Friday.
&&
$$
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