IWX issues Area Forecast Discussion (AFD) at Dec 14, 12:57 AM EST
915
FXUS63 KIWX 140557
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
1257 AM EST Sat Dec 14 2024
.KEY MESSAGES...
- Another cold night is in store with mid teens to low 20s for
lows expected.
- Rain moves in from southwest to northeast Saturday evening
with the chance for freezing rain/wintry mix at the onset.
Some slick spots may be observed in our northeast as a result.
Rain/drizzle lingers into Sunday.
- Another rain chance can be expected Sunday night into Monday.
Temperatures are expected to be much warmer, as well, reaching
into the 50s.
- Temperatures cool again for midweek with more seasonable high
(mid 30s) and low (low to mid 20s) temperatures expected.
&&
.DISCUSSION...
Issued at 309 PM EST Fri Dec 13 2024
Winds were able to veer this from light northwest winds to more
east winds by around midday. The light northwest winds allowed
for some flurries or light snow showers in extreme southern
Lower Michigan for a time. As the surface high pressure center
moves into the eastern Great Lakes region, those east winds will
be more prevalent and dry air will be able to take over. On the
back side of this surface high, warm advection will be able to
take over. As such, expect a 5 to 10 degree increase in low
temperatures tonight, bottoming out in the mid teens to low 20s.
Highs on Saturday look to rise back into the mid 30s to low 40s
as well. This will be important because another trough
approaches with a cutoff system Saturday evening. With how dry
it's been there is some question about how quickly saturation
will occur with this system. If it occurs quick enough, models
indicate that perhaps roads would cool off enough along and east
of I-69 and along and north of US-6 to potentially see some
freezing rain. A problem with this is that perhaps the cold
layer near the surface is not thick enough to allow refreezing
of rain on surfaces. The HREF has 0.05 inch of freezing rain
during that Saturday evening time frame, which is probably
enough for a winter weather advisory. Otherwise, after this
onset freezing chance, a changeover to rain is expected as low
level temperatures warm. All told, it looks like 0.5 to 0.75
inch can be expected for this system. This system looks to have
a decent moisture column, but most of the lift is to the area's
southeast and there's no convective component. Additionally, we
may see a transition to drizzle or just dry out completely later
Saturday night as the mid levels dry out.
Then, as quickly as the rain system is out of here on Sunday, a
brief dry period Sunday afternoon and Sunday night gives way to
another rain system Monday. The trough associated with the system
gradually swings toward a neutral to negative tilt, but it may be a
little too late to impact our area with its increased moisture
advection. Although you can see the increased moisture pull in the
advection parameters when compared to the previous system. A similar
QPF range of 0.5 to 0.75 is expected for most areas. However, totals
up to 1 inch cannot be dismissed in areas south of US-24 due to the
increased moisture pull. There is even some very weak convective
instability on Tuesday that may help to increase totals slightly.
Temperatures on Monday look to be warmer with 50 degrees securely
across the area.
Uncertainty resides in the models after Tuesday as the placement of
the jets across the Central US comes into question. The ECMWF takes
the trough farther south across the Gulf States and cuts it
off whereas the GFS is much more progressive with a trough for
the Wednesday/Thursday time period and with more of a baroclinic
setup and therefore has a strong cold push and lake effect signal
for that time period. It looks like the top cluster, which appears
to be more GFS-aligned although some ECMWF members do reside in that
camp, with not quite as deep of a trough across the US has slightly
lower QPF than the grand NBM ensemble. As a result, PoPs have been
retained at slight chance during this period.
&&
.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1247 AM EST Sat Dec 14 2024
An expansive low level anticyclone will finally shift off to the
east today with southeast low level flow ramping up in response
to a compact sfc low pressure tracking east out of the Plains.
As low level moisture begins to ramp up through daybreak, cannot
completely rule out a few patches of MVFR low cloud developing,
but confidence in this scenario is low and will maintain VFR
conditions overnight with just some high cloudiness. Winds
expected to become more gusty during the day, with gusts to 20
to 25 knots possible at KSBN, and in the 15 to 20 knot range at
KFWA where gradient will be a bit weaker. Attention late
afternoon into tonight will turn to the upper level low that
will bring widespread rain to the area for Saturday evening into
Sunday morning. While cannot completely rule out some very
brief mixed precip at terminals, magnitude of moisture advection
and top-down saturation process should yield mainly rain at the
terminals. Flight conditions should deteriorate steadily this
evening to MVFR, and likely to IFR outside of this forecast
valid period Sunday morning. Strength of low level jet ahead of
this system also warrants a mention of LLWS at both terminals
tonight with 2000 foot winds around 40 knots anticipated.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Roller
AVIATION...Marsili
Source: IWX issues Area Forecast Discussion (AFD) at Dec 14, 12:57 AM EST (https://mesonet.agron.iastate.edu/p.php?pid=202412140557-KIWX-FXUS63-AFDIWX)
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