IWX issues Area Forecast Discussion (AFD) at Jan 19, 6:15 PM EST826
FXUS63 KIWX 192315
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
615 PM EST Sun Jan 19 2025
.KEY MESSAGES...
- A Winter Weather Advisory is in effect from now to 7 PM EST
Monday for Berrien and Cass counties. Additional snow
accumulations of 2 to 6 inches expected, with locally higher
amounts possible. Gusty winds of 20 to 30 mph may cause some
blowing and drifting snow early in the week.
- Dangerous cold continues filtering into the area into tonight
and lasts into the middle of the week. A Cold Weather
Advisory will be in effect from tonight through Wednesday
morning. Wind chills as low as 25 below zero are expected
during the early work week.
- Temperatures return to near normal by the end of the week.
&&
.DISCUSSION...
Issued at 215 PM EST Sun Jan 19 2025
A slightly eastward shifted lake effect snow trajectory this morning
compared to forecast has allowed for slightly eastward shifted snow
amounts. One area of moisture pivoted eastward away from the region
this morning and another small area of better columnar moisture
traverses the southern portion of Lake MI this evening. Overnight
tonight, better columnar moisture sets up along and just north of
the Berrien and Cass county MI areas and the northerly wind
component becomes much weaker allow more of a west wind. Lake
induced inversion heights start around 7000 ft this evening, fall
off Monday morning, and then rise again Monday evening before
leveling off around 7000 ft Tuesday morning. This lake effect snow
is expected to continue into Wednesday before wind trajectories
swivel around to more southwesterly, negative theta-e lapse rates
slow up, and the low level convergence of winds dissipates. Given
residence time of lake effect snow in the Michigan counties, will
continue winter weather advisory through its current expiration time
of Monday evening. That's the point that lake effect QPF begins
dropping off so hazardous impacts from more moderate snow rates also
wanes.
850 mb temperatures bottom out in the low to mid 20s below zero this
evening. Those temperatures last through Monday night before the
coldest 850 mb temperatures between 25 and 30 below zero pass
through during the day Tuesday. The period of warm advection is
still depicted on models as moving through between Monday and Monday
night before cold advection help us to reach those colder low level
temperatures. Perhaps some help from any lingering snow pack would
have helped us approach negative 25 degree wind chills with more
confidence as the snow would be more reflective than dirt or wet
ground where the rain from the other day remains. Skycover clears
out tonight south of the lake effect snow as trajectories become
more westerly and this would help those areas have good radiational
cooling. However, am also noting on NAM bufkit soundings that
decoupling may not be accomplished tonight given a mixed layer
between 925 and 850 mb allowing for a bit of a breeze overnight.
Temperatures tonight falling through the single digits and settling
either side of 0 degrees with times of gusty winds between 15 and 25
mph allows for wind chill values securely in the negative
teens, which is conducive for cold weather advisory wind chills.
The lake effect clouds will act as a blanket and keep those
areas on the warmer side of the advisory threshold of cold air
for areas north of US-6. The well mixed layer not allowing for
good radiational cooling and the lack of a fresh snow pack,
provides some confidence in wind chills staying above extreme
cold warning threshold of -25F. The one area that models have
been showing in on is in the St Joseph county IN area where a
few outlying areas have the potential to see those negative 25F
wind chill readings. Low temperatures Tuesday morning are
expected to reach, if not fall below Monday morning lows by a
few degrees. However, weaker winds will allow for similar cold
advisory threshold wind chills for Tuesday morning to Monday
morning. 850 mb temperatures begin to warm Tuesday night back
into the negative teens Celsius. While NAM bufkit soundings
indicate some decoupling may occur for a few hours Tuesday night
which often allows for colder surface temperatures, mid to high
level cloudiness pushing into the area as a system passes by to
our northwest could keep the area warmer still. Southwest
surface winds come in Wednesday and temperatures are able to
climb back into the teens above zero during the day Wednesday
which is just around 5 degrees cooler than our highs today.
That area of warm advection and lift coming through later Monday
into Monday night may be able to produce some flurries or light snow
as it adds moisture to the already conducive thermal column.
Next, it appears models have the trough that is scheduled to swing
through Thursday morning into the evening with better moisture so
will continue the PoP chances for that period as a cold front moves
through. Once the trough is finally through the area Friday and a
high pressure system sets up to the east this weekend, look for
temperatures to finally be able to rise above freezing in most
locations.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 615 PM EST Sun Jan 19 2025
Lake effect snow showers will continue at KSBN through much of
the night given a westerly fetch and decent convective depths.
Visibilities will likely vary substantially as snow bands move
in and out of the airfield. LES slowly shifts northward by early
Mon morning as winds back slightly. VFR is expected through most
of the day Mon. At KFWA...last push of MVFR stratus/snow is
moving through the area now and anticipate VFR conditions
shortly after 00Z that will persist through the period.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Cold Weather Advisory until 10 AM EST /9 AM CST/ Wednesday for
INZ005>009-012>015-017-018-020-022>027-032>034-103-104-
116-203-204-216.
OH...Cold Weather Advisory until 10 AM EST Wednesday for OHZ001-002-
004-005-015-016-024-025.
MI...Cold Weather Advisory until 10 AM EST Wednesday for MIZ078>081-
177-277.
Winter Weather Advisory until 7 PM EST Monday for MIZ078-177-
277.
MARINE...Small Craft Advisory until 5 PM EST Tuesday for LMZ043-046.
Heavy Freezing Spray Warning until 5 PM EST Tuesday for LMZ043-
046.
&&
$$
DISCUSSION...Roller
AVIATION...AGD
Source:
IWX issues Area Forecast Discussion (AFD) at Jan 19, 6:15 PM EST---------------
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