IWX issues Area Forecast Discussion (AFD) at Nov 19, 3:54 PM EST462
FXUS63 KIWX 192054
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
354 PM EST Tue Nov 19 2024
.KEY MESSAGES...
- Next rain chances arrive Wednesday morning, with rain chances
diminishing from west to east during the afternoon.
- Much colder air builds into the region late Wednesday afternoon
into Thursday morning.
- Scattered to numerous snow showers develop Wednesday morning,
with rain and snow becoming widespread during the afternoon.
Slushy snow accumulations of an inch or two possible across
grassy areas, especially across northwest and north central
Indiana along with portions of southwest Lower Michigan.
- Some minor travel impacts possible if heavier snowfall rates
materialize Thursday, but current forecast thinking is for
snow to mainly melt on roadways.
- Windy conditions are expected for much of the Wednesday night
through Friday period.
&&
.DISCUSSION...
Issued at 337 PM EST Tue Nov 19 2024
A mix of rain and snow with some possible slushy snow accumulation
on Thursday is still the main weather story this forecast
cycle.
In the meantime, a cold front tracking across northern Illinois this
afternoon will make its way across the southern Great Lakes late
tonight into early Wednesday. Some increase in moisture depth
is expected late tonight as a strong upper vort max across
Colorado and accompanying 120+ knot upper jet streak begin to
shift east-northeast into the Mid MS Valley. Strengthening mid
level fgen ahead of this short wave and good upper dynamics
should support blossoming area of rain showers with this
disturbance in the 12Z-18Z timeframe Wed. A mid level dry slot
will briefly punch into the area Wednesday afternoon bringing an
end to the rain chances. Moisture quality is limited, but given
strength of mid and upper level forcing and fgen fields,
likely/categorical PoPs still seem reasonable. Progressive
nature and moisture considerations still suggest light amounts
of rain of a tenth of an inch or less. Any decrease in cloud
cover should be short-lived in wake of these rain showers
Wednesday as another stronger cold front drops into the region
for Wednesday evening. Stratocu should overspread the area as
this cold advection strengthens, with some possibility of
scattered snow shower development Wed night, especially
downwind of Lake Michigan. Lake effect snow showers may struggle
initially however, with mid level profiles still somewhat on
the dry side. By late Wednesday night into Thursday morning,
moisture depths should increase as better mid level moisture
wraps cyclonically around the initial vort max passing across
the area area earlier in the day.
The active weather continues on Thursday as ball of upper level
vorticity drops south across the southern Great Lakes. The low level
reflection with this system will likely be enhanced by a large
amount of flux from warmer Lake Michigan waters and an enhanced
low level PV anomaly from widespread precip across the Great
Lakes. Timing of the upper level DPVA and low level reflection
still suggest the 15-02Z timeframe for most widespread precip
from north to south. Occluding nature of this system will allow
broad warm/moist advection to wrap across western Great Lakes
during the afternoon Thursday, and thus it still appears as
though best chance of accumulating snow will be at leading edge
of this precip shield Thursday, and possibly in the evening
during a more diurnally favored period.
Several factors to consider for snow to liquid ratios that could
limit snow accumulations including strong flow leading to dendrite
fracturing, initial warmer ground temperatures causing some melting,
and fairly deep riming layer in the low levels. Still expecting
accumulations to be mainly for grassy areas, but if brief spurts of
higher precip rates can be realized for a time, some minor travel
impacts are possible. In addition, it will be quite windy
Thursday/Thursday night, and some visibility restrictions are
possible with any heavier snow showers.
Guidance has been hinting at perhaps a slight westward trend in
track of the above forcing mechanisms over the past few cycles, and
tried to incorporate some hint of that with latest package with
slightly lower snow accums in NW Ohio. Have gone with 1-2" type snow
accumulations across the west, but cannot rule out some localized
higher accumulations depending on how ingredients come together.
Given some dependence on diabatic PV anomaly, the track of low level
reflection will certainly wobble over next few year guidance runs
and additional forecast adjustments will be needed. Confidence
remains on the high side in eventual transition back to rain from
north to south later Thursday afternoon into Thursday evening as
higher theta-e air wraps into the area.
Broad upper level height minimum will be slow to depart into Friday
with mid level cold pool still residing across the southeast
portions of the area. In addition to some lingering shallow
instability rain showers, some lake effect rain showers are also
expected.
For the weekend, low level flow will become more backed as mid/upper
level heights recover upstream. This will allow moderation of temps
back to seasonable levels. Guidance consensus does hint at next more
substantial eastern Pacific wave possibly impacting the area early
next week with next notable chance of rain showers and temperatures
briefly warming to slightly above normal.
&&
.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1152 AM EST Tue Nov 19 2024
Post-frontal mixing and drying will allow stratocu near 3 kft to
scatter/mix out this afternoon. Southwest winds will also gust to
near 25 knots at times in this regime. A brief lull in winds then
into tonight gives way to a period of MVFR cigs, gusty west winds
and rain chances mid-late Wed morning as a robust shortwave and
associated secondary cold front moves through.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory from 10 AM Wednesday to 7 AM EST Thursday
for LMZ043-046.
&&
$$
DISCUSSION...Marsili
AVIATION...Steinwedel
Source:
IWX issues Area Forecast Discussion (AFD) at Nov 19, 3:54 PM EST---------------
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