IWX issues Area Forecast Discussion (AFD) at Dec 30, 11:38 AM EST655
FXUS63 KIWX 301638
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
1138 AM EST Mon Dec 30 2024
.KEY MESSAGES...
- Tranquil weather returns today with highs in the low/mid 40s.
- Another system will bring roughly 0.5" of rain on Tuesday.
Rain may mix with snow at times, particularly in Michigan and
far northeast Indiana later in the day.
- Brief, light lake effect snow is possible Wednesday morning
but any accumulation will be less than an inch.
- Cold weather returns for the end of the week with some very
light snow possible late Thursday.
&&
.DISCUSSION...
Issued at 335 AM EST Mon Dec 30 2024
988mb surface low lifting NE into Canada this morning with rain and
wind slowly winding down across our area. Relatively tranquil
weather expected today with shortwave ridging overhead in between
pair of troughs impacting our weather this week. Some fog/BR may be
possible through the morning in the wake of this system but strong
gradient wind will likely prevent any widespread/lasting vis
reductions. Widespread low stratus upstream will likely be difficult
to erode though and prospects for sun today are looking low.
Therefore, highs today will likely only climb a few degrees warmer
than current values with neutral thermal advection through the
day.
Attention then turns to next Pacific jet streak and attendant PV
anomaly currently slicing through the southern Rockies. Slow but
steady strengthening of this system is expected later today and into
tonight as it moves through the Ohio Valley. Favorable left exit
upper jet placement and another negatively tilted trough axis will
support a roughly 995mb surface low tracking just south of our CWA
with a strong 925-600mb fgen signal swiping right across our area
late tonight into Tuesday. There will be plenty of moisture available
as 50 kt LLJ pushes PW values to around 0.75 inches in our area.
Modest trowal signature develops over our area and forecast
soundings/cross-sections indicate significantly reduced
stability in a deep layer above the frontal slope. Not as
impressive as the system now exiting but still respectable.
Aside from weaker dynamics this system will also move through
much faster than the previous and will cap QPF around a half
inch or so. The big question remains precip types. A thorough
review of forecast soundings (including from recent hi-res runs)
suggest a bit more snow than previously anticipated. Decent low
level cyclone will likely pull in just enough cool/dry air in
strong easterly flow to our north to support a rain/snow mix
with snow likely during the heaviest rates. In our far NE
(Hillsdale) this could hold true for the entirety of the event
and some light (1-2") accumulations are possible. Further S/SW
still expect primarily rain during the day (especially south of
US-24) but snow will likely mix in at times and have adjusted
wx grids accordingly. Don't expect any accumulation during the
day (when most precip falls) outside of extreme NE zones though
given highly marginal boundary layer temps and still warm soils.
Cooler air advects south Tue night with a changeover to snow
expected everywhere. However, deeper moisture and forcing will
be gone by then with only a few hundredths of precip and
little/no additional snow accums.
Brief shot of LES arrives early Wed morning as 850mb temps drop to
around -12C. Significant dry air entrainment, limited instability,
and poor fetch all point to a muted lake response. However, some
isolated light accums (<1") are possible in our SW MI zones 06-18Z
Wed. Another (much weaker and moisture-starved) shortwave arrives
late Thu which could bring a quick dusting of light snow. Additional
LES is also possible behind this feature but chances are very low
given dry/stable NW flow. It will turn cold though with highs in the
low 20s and lows in the low teens. Models suggest potential for a
more significant system early next week but there is still plenty of
time for drastic changes 180 hours out.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1138 AM EST Mon Dec 30 2024
Stubborn IFR to low MVFR stratus trapped under a strong
subsidence inversion remains the primary challenge into this
afternoon. Guidance/soundings overall favor some gradual
improvement with time, especially at KFWA where a full mixout
to VFR is on the table. Opted to hold with a more pessimistic
MVFR cig forecast however given trends and time of year.
The next low pressure system and strong WAA/fgen generated
precip then expands over northern IN later tonight into Tuesday
morning with a trend toward IFR conditions and increasing
northeast winds. Ptype likely begins as all rain, but could mix
with snow after 13-14z.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory from 7 AM Tuesday to 5 AM EST Thursday
for LMZ043-046.
&&
$$
DISCUSSION...AGD
AVIATION...Steinwedel
Source:
IWX issues Area Forecast Discussion (AFD) at Dec 30, 11:38 AM EST---------------
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