IWX issues Area Forecast Discussion (AFD) at Jan 19, 1:15 AM EST566
FXUS63 KIWX 190615
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
115 AM EST Sun Jan 19 2025
.KEY MESSAGES...
- Lake effect snow gets going in southwest Lower Michigan and
northwest Indiana tonight and especially on Sunday.
- An Extreme Cold Watch has been issued from Sunday night
through midday Wednesday. 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.
&&
.UPDATE...
Issued at 922 PM EST Sat Jan 18 2025
Lake effect snow is slow to begin this evening given overall
very dry and stable airmass. Still expect lake effect to ramp up
by Sunday morning though as midlevel trough approaches raising
inversion heights and enhancing mid/upper level lift and
moisture. Hi-res models suggest a more organized single band for
a time Sun AM that will likely produce a quick 2-4" near the
Berrien/Cass border. Despite a delayed start to the accumulating
snow...no change to headlines at this time.
&&
.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 /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 115 AM EST Sun Jan 19 2025
A surge of arctic air across the Upper Midwest into the Northern
Plains will continue to shift southeast into the western Great
Lakes region later this morning. Lake aggregate troughing will
continue to sharpen overnight along eastern shore of Lake
Michigan and already seeing a southward extension of this
troughing taking shape across northwest Indiana. A dry subcloud
layer should keep snow more in the form of flurries, with better
potential of stronger lake effect snow showers after 09Z and
especially toward 12Z. By this time, some synoptic contribution
to the lake effect snow is possible as an upper level trough
approaches from the west. Rising inversion heights and increased
lake induced instability will allow for numerous lake effect
snow showers Sunday, with focus eventually becoming confined by
southern Lower Michigan by Monday. Some periods of IFR vsbys
will be likely at KSBN in this pattern, but with low confidence
at this forecast distance, will maintain extended period of MVFR
vsbys with the lake effect snow showers. Steep low level lapse
rates will result in gusty northwest winds to 20 to 25 knots
today.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Extreme Cold Watch from late tonight 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 tonight through Wednesday morning
for OHZ001-002-004-005-015-016-024-025.
MI...Extreme Cold Watch from late tonight 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 this afternoon to 4 PM
EST Tuesday for LMZ043-046.
&&
$$
UPDATE...AGD
DISCUSSION...Roller
AVIATION...Marsili
Source:
IWX issues Area Forecast Discussion (AFD) at Jan 19, 1:15 AM EST---------------
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