IWX issues Area Forecast Discussion (AFD) at Dec 7, 2:15 PM EST449
FXUS63 KIWX 071915
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
215 PM EST Sat Dec 7 2024
.KEY MESSAGES...
- Warmer temperatures tomorrow and Monday.
- Chances for rain and drizzle for Sunday night and Monday.
- Cold air returns Tuesday through Thursday as temperatures fall
back below freezing.
&&
.DISCUSSION...
Issued at 213 PM EST Sat Dec 7 2024
A split flow pattern across the United States with the jets
connecting up in the western Atlantic/Mid Atlantic States starts the
forecast period. With upper northwest flow, another clipper system
moves across the northern Great Lakes this afternoon and vacates the
area by Sunday morning. During this time, expect breezy winds as a
50 kt jet moves through the Great Lakes region. Still only expecting
shallow mixing given cloudiness and warm advection, which should
limit gusts to 15 to 25 kts. Dew points are on their way wetter
given warm advection and this should provide a floor to our
overnight lows keeping them at freezing or just slightly above and
this should also help to raise highs on Sunday to the 40s, with a
few spots south of US-30 flirting with 50 degrees. Additionally,
models begin to bring snow-eating 35 degree dew points around midday
morning after sunrise. Could begin to see lowered visibility in the
area where a snowpack remains, mainly north of the Toll Road, as a
result.
During the day Sunday, a Pacific trough moves into the West Coast of
the US and kicks the stalled upper low originally in the
southwestern US towards the area. The moisture plume arrives into
areas south of US-30 around 1 am. It's a pretty quick moving plume
and should be out of the area Monday morning as a mid level dry slot
moves into the area behind this initial plume. The NAMNest is still
suggesting some freezing rain/drizzle might be able to form at the
rain's onset, especially north of the Toll Road and perhaps if it
comes down light enough, but there are questions about if two 40
degree high temperature days before it could warm roads up enough to
remove that chance. Those models do only create a trace of freezing
accumulation. All told, QPF is expected to stay underneath 0.25" and
could be more around 0.1" given the progressive nature of the system
and that the storms in the south could rob moisture from it. We
could also have a period of drizzle on the back side with the
residual lift and lingering low level moisture Monday morning.
The GFS has trended away from bringing snow to the area Tuesday on a
developing low pressure system's northern side. The GFS's low is
still north of the rest of the deterministic model's placement at
this time, but even the northern portion of the precipitation shield
appears to have issues with saturating its DGZ, may include mixing
with some rain at times, and dry air may cut into precipitation all
together, all limiting snow accumulation.
As cold air wraps in on the back side of the system, a shortwave
traverses the southern area of Lake MI Tuesday night and may be able
to invigorate lake enhancement as lake induced inversions rise to
between 5 and 6 kft with 20 to 25 degree delta T values. Also noted
is weak low level wind convergence in saturation issues within the
moisture column. Chances for lake effect snow are expected to
continue through Wednesday and into at least Wednesday night. The
trough looks to pivot through Wednesday night into Thursday AM.
High pressure dries the area out for Thursday, but uncertainty
remains on Friday about the placement of the jets across the US. The
ECMWF is slightly more southward with the jets and allows a little
bit cooler airmass into the area ahead of a system, whereas the GFS
brings a clipper system through the Central Great Lakes, north of
the area allowing for a dry day.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1206 PM EST Sat Dec 7 2024
Visible satellite imagery shows areas of mid and high level
clouds moving through our forecast area as of midday. Ceilings
are expected to remain VFR throughout the entire TAF forecast
period. As a clipper system dives through the upper Great Lakes
region today and tonight, across our area, a tightening
pressure gradient associated with this system will bring strong,
gusty winds through the TAF forecast period. Southwest winds
have already started to pick up this afternoon and will continue
to do so, eventually becoming sustained around 15 to 20 kts.
Gusts up to 30 kts will be possible, especially this evening.
LLWS is also expected this evening and into the early overnight
hours as a surface trough pushes through. Winds will still be
elevated tomorrow morning, with gusts 20 to 25 kts possible
through the overnight and early morning hours.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 4 AM EST Sunday for LMZ043-046.
&&
$$
DISCUSSION...Roller
AVIATION...Johnson
Source:
IWX issues Area Forecast Discussion (AFD) at Dec 7, 2:15 PM EST---------------
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