IWX issues Area Forecast Discussion (AFD) at Dec 20, 6:42 PM EST970
FXUS63 KIWX 202342
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
642 PM EST Fri Dec 20 2024
.KEY MESSAGES...
- 1 to 4 inches of lake effect snow tonight for La Porte county
and extreme southwest Berrien county. Snow covered roads and
reduced visibility are anticipated.
- Cold this weekend followed by a gradual warming trend.
- There are multiple chances for rain next week with
temperatures well into the 40s by Wednesday.
&&
.DISCUSSION...
Issued at 243 PM EST Fri Dec 20 2024
Lake effect snow is ongoing over western Lake Michigan amid
excellent convergence and a 12C temperature differential 850-mb to
the surface. Low pressure over southern Ohio continues to drop
southeast, so will the lake effect snow band. This will weaken the
band through time. This is because what was outstanding fetch
reaching all the way to Beaver Island late this morning, is now
breaking down as flow remains northeasterly but the fetch is reduced
as the band tracks south.
Lake effect snow will survive into the overnight hours, primarily
impacting Lake and Porter Counties, but the band will tumble into
LaPorte and even Berrien Counties about about a 6 to maybe 9 hour
period from about midnight to dawn Saturday. Flurries may linger
well beyond this amid northwest flow but an even more shallow DGZ
and equilibrium level. Forecast sounding depict generally modest
lake effect parameters. Primary weak points are an elevated DGZ, a
portion of which resides above the equilibrium level of about 11,000
ft. However, this morning, a shallow DGZ was enough to produce large
snowflakes for a time at a synoptic-scale. Therefore, while only 1
to 4 inches of lake effect snow is expected over a narrow area, the
primary travel corridors of northwest Indiana will be negatively
impacted by poor visibility and snow-covered roadways tonight
through Saturday morning.
Overcast skies are gradually breaking this afternoon across Michigan
which boosts confidence in skies clearing tonight outside of the
lake effect band. Given the fresh snowpack, some locations should
fall into the teens tonight. Otherwise, lows right near 20 are
expected.
After a crisp Sunday morning, a gradual warm up begins. Heights rise
and return flow off high pressure now to our east permit Sunday
highs to break freezing south of US 24. A weak area of low pressure
streaks across Michigan on Monday. Guidance continues to show
varying solutions here, with uncertainty revolving around poleward
moisture transport. There could be precipitation-type issue Monday
morning with lows in the 20s, preceding afternoon highs well into
the 30s. Confidence is low overall.
Tuesday night through Wednesday still features a chance of rain as a
trough lifts out of the Southern Plains. Its poleward extend may be
thwarted by lingering high pressure over Ontario, in which case dry
but mild conditions may prevail (highs near 40). To round out the
week, a deep trough through the Great Basin points a mild storm
track into the Midwest bringing more rain chances for the final
weekend of December.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 632 PM EST Fri Dec 20 2024
Unorganized bands of light snow showers is currently moving
southward through the area from disjointed moisture from the
northern Great Lakes and will have low impact for TAF sites
through around 06z Saturday. A reduction in clouds as the low
continues to move eastward out of the region and a more
northwesterly flow takes over. Confidence on total clearing is
low due to the prospect of lake effect clouds keeping cigs
around 5000 to 8000 feet through the remainder of the TAF
period.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 10 AM EST Saturday for LMZ043-046.
&&
$$
DISCUSSION...Brown
AVIATION...Andersen
Source:
IWX issues Area Forecast Discussion (AFD) at Dec 20, 6:42 PM EST---------------
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