IWX issues Area Forecast Discussion (AFD) at Nov 21, 12:51 AM EST646
FXUS63 KIWX 210551
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
1251 AM EST Thu Nov 21 2024
.KEY MESSAGES...
* Colder air pushes into the region tonight into Thursday morning.
* Scattered snow showers expected to develop tonight, greatest
coverage associated with lake effect snow showers overnight
with light snow accumulations of an inch or less possible
(mainly across grassy areas).
* Widespread snow develops for Thursday, mixing with rain at
times. Precip types should change to mainly rain late in the
afternoon across far northwest Indiana into southwest Lower
Michigan. Slushy snow accumulations of 1 to 3 inches are
possible. Lesser snow accumulations expected across far
northeast Indiana, northwest Ohio, and south central Lower
Michigan.
* Confidence in the extent of travel impacts remain on the low
side due to warmer ground temps and expectation of melting on
roadways. However, visibility reductions and some slick spots
on roads are possible in association with heavier snowfall
rates Thursday afternoon.
&&
.DISCUSSION...
Issued at 330 PM EST Wed Nov 20 2024
The active weather pattern will continue through Friday, with main
period of potential impacts concern centering on Thursday into
early Thursday evening.
A band of rain showers associated with strong mid level fgen
forcing has remained quite progressive as it exits northwest
Ohio this afternoon. A strong upper speed max progressing
through base of the associated upper level wave tracking across
the area will eventually allow low/mid level height reflection
to retrograde back to the west as this upper trough wraps up
across the Great Lakes region. To the south of this feature,
much colder low level air will continue to advect southeast. An
upper height minimum across the Upper Midwest will become a bit
more sheared in nature this evening as its influence reaches the
southern Great Lakes. The combination of this forcing and the
much colder low level air should give rise to lake effect snow
showers tonight, with scattered synoptic snow showers also
possible. Fetch will remain primarily westerly for this portion
of the lake effect event which should provide a multiband setup
tonight into early Thursday. Moisture depths should increase
tonight accompanying the increase in synoptic forcing which
could allow for some band organization. Would expect any
accumulations tonight to be minor given fetch limitations, which
is already captured nicely in previous forecast (less than an
inch and mainly across grassy areas).
Attention then turns to evolution of low level height minimum
as it drifts back across the western Great Lakes on Thursday
with an accompanying widespread precip shield dropping south
across the region. Preceding 24 hours of strong cold advection
should support mainly snow precip types Thursday morning into
Thursday afternoon, but confidence in precip types diminishes
after 20Z tomorrow closer to Lake Michigan as theta-e maximum
begins to wrap cyclonically back into the area. Previous
limitations to more efficient snowfall accumulation are still in
place including marginal wet bulb temps, potential of initial
snow melting, and low level riming. However, still expecting a
period of more robust snowfall rates late morning Thursday into
early evening that could result in a quick couple inches of
slushy snow accumulation. Confidence remains somewhat on the
lower side on the extent of impacts given marginal temps and
warm ground possibly limiting pavement accums, but precip rates
may overcome this limitation for some slick spots on roads
during the afternoon. HREF means do suggest potential for a
period of snowfall rates of 1" per hour possible some time in
the 16-20Z timeframe from NW Indiana to SW Lower Michigan. Some
concern also persists for brief but significant vsby reductions
with heavier snow bursts also. One of the least confident items
for this forecast is duration of ptypes into the mid/late
afternoon supporting snow closer to Lake Michigan where low
level wet bulbs will be right at the margins. This is also where
some of the heavier precip rates should be realized which could
cause a concern for locally higher snow accumulations if
changeover back to rain is delayed.
Low level reflection should drift southeast across the area into
Thursday evening but low level circulation/convergence should
tend to weaken as thermal convergence contribution from Lake MI
wanes. By the evening commute, potential of minor impacts should
tend to progress southward across southwest/southern portions
of the area, as locations across the northwest transition back
to liquid ptypes. One thing which may need some watching late
Thursday is the potential for mesovortices to track inland from
Lake Michigan. Lake induced convergence and circulation from
large scale diabatic PV anomaly could create a strong west-east
oriented shear zone across Lake MI that would be favorable for
mesovortex development. However, by the time this environment
reaches inland areas, ptypes should be more in the favor of
liquid. Some graupel also cannot be completely ruled out late
afternoon/early evening as convective element portion of this
event may maximize. Have maintained lower snow accumulations
east of I-69 into NW Ohio which will be bypassed by stronger
forcing mechanisms.
For late Thursday night into Friday night, lingering effects from
departing mid level cold pool and favorable lake effect fetch
should prolong rain chances, but additional precip amounts
should be on the light side. Some short wave ridging tries to
build into the area this weekend, but active northern latitude
short wave pattern will suppress any significant moderation.
Some indications in medium range guidance of another fropa late
weekend/early next week that may bring some additional lake
effect snow showers and a transition back to below normal
temperatures for much of next week.
&&
.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1250 AM EST Thu Nov 21 2024
Upper low almost directly overhead will continue to support SCT
snow showers and MVFR ceilings through the morning. A gradual
lowering of ceilings is expected through the morning as colder
air settles into the area. Still expect the heaviest snow to
occur roughly 17-23Z this afternoon as primary vort max and
surface low dive through the area. Far better chances for
accumulating snow and visibilities dropping to around 1/2SM will
be at KSBN but do still expect some brief, lighter snow at
KFWA. Conditions improve at KFWA Thursday night but lake effect
rain bands and low MVFR ceilings will likely persist at KSBN
well into Friday.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 7 AM EST this morning for LMZ043-
046.
Gale Warning from 7 AM this morning to 1 AM EST Friday for
LMZ043-046.
&&
$$
DISCUSSION...Marsili
AVIATION...AGD
Source:
IWX issues Area Forecast Discussion (AFD) at Nov 21, 12:51 AM EST---------------
If I'm using your data in a way that is against your terms please email the team at "threatweb@pupswoof117.com"! I am a bot who will not respond in the comments at all and is only designed to post RSS feeds!
