IWX issues Area Forecast Discussion (AFD) at Nov 18, 7:01 PM EST578
FXUS63 KIWX 190001
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
701 PM EST Mon Nov 18 2024
.KEY MESSAGES...
- Rain chances persist through late Tuesday morning.
- Highs in the 60s Tuesday will be quickly replaced by much
cooler temperatures in the 30s and 40s by Thursday.
- While some snow may occur between Wednesday night and Thursday
night, accumulations on pavement are not expected.
&&
.DISCUSSION...
Issued at 223 PM EST Mon Nov 18 2024
An upper low pressure departs, clearing a spot for another upper low
near Mexico to start moving northeastward as helped along by a
trough entering the Western US. From this afternoon to Tuesday
morning, the area will be under the influence of this low pressure
system and will provide chances for rain. First from the warm
advection wing moving through midday through the afternoon. This may
provide up to around a tenth of rain to the area west of US-31,
tapering off as you go east. After a brief break from dry air
advection this evening, rain looks to move back into the area again
after midnight and continue into Tuesday morning as a cold front
moves eastward through the area. There is around 500 J/kg of MUCAPE
to work with so there may be some rumbles of thunder west of IN-15,
but that chance looks to dissipate as you move eastward with the
CAPE diminishing. This may provide an additional 1/4 inch or so of
QPF ending by around midday. Expect a breezy day Tuesday with 20 to
30 mph gusts likely.
Then, as the arriving western US trough interacts with the
aforementioned upper low, the two actually combine into a strong
upper low across the Northern Plains. A strong shortwave is then
able to move eastward toward the area early Wednesday morning. The
NAM and GFS create a development out in front this shortwave so
will create some PoPs to handle that period. Initial
precipitation type is rain since the low is not able to wrap in
cold air yet. The handling of this surface low still is bouncing
back in forth between model runs on whether to have it or not.
The first opportunity to introduce cold air into the forecast is
Wednesday night. This is as the strong shortwave discussed for
Wednesday AM departs eastward, a second vort max drops southward
from the Northern Plains and a spoke of vorticity within the upper
low takes a trajectory close to Lake MI. 20 degree delta T values
between the low 50s lake temperatures and the arriving air mass and
inversion heights up to 700 mb along with low level wind
convergence, negative low level theta-e instability, and times of
low level moisture may make it conducive to creating lake enhanced
precipitation. Although that level low level dryness likely cuts
into how much of it reaches the ground. Thermal profiles do appear
to be conducive to snow mixing in or even being predominant at times
later Wednesday night. Snow showers do look to continue at times
during the day Thursday and high temperatures will struggle to
exceed the mid 30s as a result. At current, think the rates are weak
enough that the warm pavement will not be overcome so any resultant
accums will be less than 1 inch and mainly relegated to grassy
areas.
With the upper low now in the vicinity of PA later Thursday, an
instability trough moves southward across Michigan and this may
introduce some additional showers across the area later Thursday. It
appears this would be wrapping warmer air around, but the initial
surge of the boundary may come through in time to have snow if a
surface low forms along the boundary or graupel if just an
instability trough itself moves southward. Some uncertainty exists
with the strength of this trough as this is the first run that
models have converged on forming a surface low on it. Disagreement
in previous runs existed with this type of solution. Perhaps the
warm lakes are influencing this type of solution.
The coldest of the air departs Thursday night into Friday taking
with it the cooler, more snow-conducive airmass. Low clouds and lake
enhanced precipitation may continue through Friday into early
Saturday before the above-zero 850 mb temperatures begin shifting
northward into the area.
Beyond Saturday, blocking begins to formulate across the
northeastern US and eastern Canada creating almost zonal flow across
the CONUS, which may act to suppress any systems. There is model
support for another system between Sunday night and Monday.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 654 PM EST Mon Nov 18 2024
Expect LIFR conditions at KSBN/IFR at KFWA to improve within the
hour as we get into the warm sector. The stationary front
extends from KPPO through North Webster (KIWX) and KOWX in
Ohio. As warm air advects northward, expect a temporary
improvement in visibility/ceilings with gustier ESE winds
becoming more SSW through the period. The warm front lifts into
Michigan, and then we have the cold front arriving that will
bring yet another band of precipitation through late tonight
into Tuesday morning-this time moving roughly west to east. This
brings us potential for more MVFR/IFR conditions until the rain
ends around 15-18z. Expect both sites will be VFR or close to it
sometime in the 21-00z time frame.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory from 10 PM this evening to noon EST
Tuesday for LMZ043-046.
&&
$$
DISCUSSION...Roller
AVIATION...MCD
Source:
IWX issues Area Forecast Discussion (AFD) at Nov 18, 7:01 PM EST---------------
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