IWX issues Area Forecast Discussion (AFD) at Jan 18, 6:30 PM EST422
FXUS63 KIWX 182330
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
630 PM EST Sat Jan 18 2025
.KEY MESSAGES...
- Rain continues early this morning with perhaps a brief
changeover to snow. Accumulations will be minimal, if any.
There may be some slick spots on roads, bridges, and
overpasses.
- Lake effect snow gets going in southwest Lower Michigan and
northwest Indiana today and especially on Sunday. A Winter
Weather Advisory has been issued for Berrien County, MI
tonight through Sunday.
- An Extreme Cold Watch has been issued from Sunday night
through midday Wednesday. Dangerous cold begins filtering into
the area Sunday and lasts into the middle of next week.
Several nights with lows below zero are anticipated. Wind
chills as low as 20 to 25 below zero are expected at times.
- Gusty winds of 20 to 30 mph may cause some blowing and
drifting snow early in the week, especially closer to Lake
Michigan. Lake effect snow early in the week will be limited
by the dry, Arctic airmass.
&&
.DISCUSSION...
Issued at 301 PM EST Sat Jan 18 2025
The main analyzed cold front moved through this morning, but the
cold air won't be coming all at once. Temperatures will continue to
drop today with today's high really occurring this morning as
opposed to the usual afternoon time frame. Temps in the low to mid
30s will become lows in the teens tonight as 850 mb temps around
negative 10C become negative 18C or so. 850 mb temps drop to
the low to mid 20s Sunday night and Monday morning and then drop
again on Tuesday into Tuesday night to their lowest during this
period to negative 28C or so. Temperatures quickly moderate on
Wednesday on the back of a surface high. Still noting some warm
advection taking place Monday evening that may impact how cold
things get Tuesday morning, especially if winds become a little
weaker Tuesday morning as models indicate. With the two gustiest
days being Monday and Wednesday and the coldest temperatures
arriving Tuesday night into early Wednesday. As long as
Wednesday stays cold enough and that we don't warm up too
quickly in the morning, winds are expected to be high enough
that warnings are possible. Tuesday will need the temperatures
to do the most work to keep us around warning criteria of
negative 25F wind chills with gusts slackening off some. Monday
will need the winds to do a lot of work to get us down to
warning criteria of negative 25F, but previous times that we've
experienced these cold temps say that a knot of a wind gust
change can change wind chills by a couple of degrees that may be
enough to nudge us towards warning criteria then as well. Given
all of these issues with each day, am in agreement with keeping
the watch going given the extended period securely in advisory
threshold (aside from that 12 to 18 hr Monday evening period)
given opportunities for warning criteria to be met each morning
Monday to Wednesday. The other issue will be the cloud cover
from lake effect snow that pivots from a northwest orientation
to a more westerly orientation. This may provide a blanket for
temperatures to keep them a little warmer and potentially warmer
than the advisory as well.
Given the arrival of cold air and the mostly ice free and warm
leaning Lake MI, the brain flips to check for lake effect snow. Lake
induced inversions increase to just under 7000 ft at just above 800
mb Sunday morning with delta T values around 25C and that increases
to around 7000 ft and 30C delta T values Sunday afternoon. Low level
moisture begins to get into the area early Sunday morning and then
drops off during the later afternoon into the evening some as the
trajectories gain a little bit more westerly component to them.
Inversion heights collapse back to 6000 ft Monday, but Delta Ts stay
around 30C. So while, the coverage of area into our forecast area
lessens, we'll likely see lake effect snow continue in Berrien
county and possible Cass and St Joseph counties. The southwest winds
due to the WAA period Monday evening may shut off lake effect snow
for a portion of the area though too. The shortwave trough that
moves through Tuesday may help to allow for a brief return of lake
effect snow before it moves out.
Behind the aforementioned trough, by Wednesday, the orientation of a
passing surface high should allow for more of southerly trajectory
to bring an end to lake effect snow and allow for increased warming.
After being in the single digits above and below zero on Tuesday,
temperatures rise to the teens and low 20s for highs on Wednesday.
As we slowly warm towards, but still staying below, freezing during
the latter half of next week, a progressive trough with shearing
vorticity swings through the area. The wetter GFS has some light
precipitation forming from this whereas the drier ECMWF has the area
dry as a result of differing trough orientations. Will maintain the
NBM PoPs which appear to be lake effect snow-caused, but could see
them trend lower. Otherwise, the lack of surface lows moving through
the area should keep us on the drier side for the latter part of
next week.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 630 PM EST Sat Jan 18 2025
Conditions will continue to hover between VFR and MVFR through
much of the night as CAA ramps up. This CAA will support a
chance of LES at KSBN in the 06-12Z period but much better
chances will arrive after 12Z when a weak trough swings through
the area. Solid MVFR ceilings and steady snow are expected at
KSBN roughly 15-21Z with a brief period of snow possible at KFWA
17-20Z. Conditions look to improve at both sites at the very end
of this forecast window.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Extreme Cold Watch from late Sunday night through Wednesday
morning for INZ005>009-012>015-017-018-020-022>027-
032>034-103-104-116-203-204-216.
OH...Extreme Cold Watch from late Sunday night through Wednesday
morning for OHZ001-002-004-005-015-016-024-025.
MI...Extreme Cold Watch from late Sunday night through Wednesday
morning for MIZ078>081-177-277.
Winter Weather Advisory until 1 AM EST Monday for MIZ078-177-
277.
MARINE...Small Craft Advisory until 5 AM EST Tuesday for LMZ043-046.
Heavy Freezing Spray Warning from 1 PM Sunday to 4 PM EST
Tuesday for LMZ043-046.
&&
$$
DISCUSSION...Roller
AVIATION...AGD
Source:
IWX issues Area Forecast Discussion (AFD) at Jan 18, 6:30 PM EST---------------
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