771
FXUS63 KIWX 220003
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
703 PM EST Thu Nov 21 2024

.KEY MESSAGES...

- Snow tapers from north to south through early evening, with a
  change over to liquid across the west-northwest. Some minor
  impacts to the evening commute are expected mainly south of US
  30 across northern Indiana.

- Lake effect rain showers for later tonight through Friday evening.

- Some moderation in temperatures Sunday and Monday with next
  chance of rain Sunday night into Monday.

&&

.DISCUSSION...
Issued at 339 PM EST Thu Nov 21 2024

Snow will diminish from north to south this evening as stronger
upper vort max drops south across southern Indiana. Deformation
flow and pocket of low level moisture convergence associated
with strong low level jet provided some enhancement to the snow
across east central Wisconsin into far northeast Illinois and
extreme northwest Indiana. Snowfall accumulation efficiency has
been limited locally by warm ground conditions, strong low level
flow, and a very high based mid level dendritic growth zone.
Some drier mid level air is beginning to push southward across
the western Great Lakes and this should continue to minimize
snowfall efficiency over the next several hours. Warmer and more
moist air is also wrapping around this system which has
effectively pushed near sfc wet bulbs warm enough for a
transition to liquid precip type across northern suburbs of
Chicago and SW Lower Michigan as of 19Z. This rain/snow line
should continue to push southeastward over the next few hours
with focus for additional light snow accumulations shifting
south of the US Route 30 corridor in northern Indiana for the
evening commute. Pavements should primarily remain wet, but a
few slick spots are still possible over the next few hours.

Actual sfc reflection of this system is still over southern
Lake Michigan and will need to watch the evolution of Lake MI
enhanced mesolow as it tracks into northwest Indiana/north
central Indiana this evening. This sfc reflection has been
enhanced by high early season fluxes off Lake Michigan along
with tightening of the circulation from a 12 to 18 hour period
of latent heating. Precip types may be marginal with any
enhanced banding with this feature as low level wet bulb temps
creep upward. This evolution could produce a narrow band of
impacts if mesoband is able to materialize. Also cannot rule out
a few reports of graupel with mesolow feature as it pushes
inland. Outside of this mesolow feature, deep moisture profiles
will become progressively less favorable for accumulating snow
this evening.

Some brief stronger deep layer subsidence will push into southern
Lower Michigan and north central Indiana later this evening
with some breaks in low clouds possible. Lake effect rain
showers should eventually shift back eastward into the area as
axis of mid level moisture recovery approaches. Negative upper
height anomaly persists across eastern CONUS for Friday
maintaining a favorable northerly fetch for continued lake
effect rain showers. Moisture depths will be more limited on
Friday which will limit overall precip amounts. Moderation of
low level airmass on Friday should support highs in the mid-
upper 40s.

Lake effect rain showers should come to an end later Friday night
as better mid level height recovery commences across the Mid MS
Valley/western Great Lakes. A period of mainly dry conditions
is then in store through the day Sunday as temperatures warm
back to slightly above normal. A brief but respectable period of
low level moisture transport will be possible Sunday evening
ahead of associated cold front. Will maintain high chance PoPs
this period with main question centering on duration and
northward extent of better low level moisture transport. Colder
conditions build in behind this cold front early week. Looking
ahead, medium range guidance does indicate another system for
middle-late week, but still some question as to extent of
suppression of low level reflection. Given uncertainty at this
forecast distance will maintain just chance rain/snow PoPs
heading into Wed night/Thu.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 643 PM EST Thu Nov 21 2024

Predominantly MVFR to IFR conditions at the TAF sites, with a
brief period of LIFR ceilings possible this evening at KSBN. A
surface low centered over southern Lake Michigan and NW Indiana
will continue to sink SSE into Indy by 6z, then it will exit the
area. Upstream of KSBN we have 400-600 ft ceilings sinking
southward-it is unclear if it will drop as low as 400 ft at
KSBN, but if it does it will likely be before 2-3z. It`s
possible we have brief bumps to high end MVFR/VFR as subsidence
behind the wave takes hold. KFWA should remain IFR (ceilings
hovering around 1000 ft atm). Rain/snow showers will persist for
the next couple hours, with snow being reported right now at
KFWA beneath a band that formed along the main trough (extends
north into the Angola area).

We`ll have a period of subsidence around 6z where ceilings/vis
improve to either high end MVFR/VFR before another trough
pinwheeling around the low swings through again later tonight
into early Friday morning. Winds shift north-northwest at KSBN,
and we expect some lake effect rain showers to develop
around 10-13z. Some guidance keeps this going all day, but
think we`ll see an end to the most impactful conditions between
13-17z. At KFWA, less lake influence so we may remain dry with
higher ceilings until that second trough comes in, so once it
does (12-21z) we`ll see MVFR conditions most likely-and if rain
does develop we may see showers between 16-21z (with IFR
possible, have in a prob30 group for now given lower
confidence).


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Gale Warning until 1 AM EST Friday for LMZ043-046.

&&

$$

DISCUSSION...Marsili
AVIATION...MCD