IWX issues Area Forecast Discussion (AFD) at Jan 3, 4:21 AM EST553
FXUS63 KIWX 030921
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
421 AM EST Fri Jan 3 2025
.KEY MESSAGES...
- Lake effect snow today tapering off tonight will spread well
inland at times resulting in variable travel conditions along
the Michigan state line.
- Snow is expected Sunday afternoon and evening through Monday.
A tight gradient in snow amounts will occur from north to
south across Indiana and Ohio.
- Very cold next week with periods of lake effect snow.
&&
.DISCUSSION...
Issued at 418 AM EST Fri Jan 3 2025
An upper-level vort max drops south across Lake Michigan early this
morning, sparking lake effect snow in its wake as cold air advection
builds in. Multiple bands are expected, with high resolution keying
in on a strong band impacting the Kalamazoo area. This band could
reach will inland impacting St. Joseph (MI) and Branch counties. As
mentioned by the previous forecaster in this space, many favorable
ingredients exist for about 1 to maybe 3 inches accumulation in far
southern Michigan, but dry air entrainment and a fairly stiff west
wind through the low-levels will keep amounts in check, as will a
relatively brief residence time. I entertained the idea of a winter
weather advisory, but for the above reasons have remained headline-
free for lake effect. Equilibrium levels fall toward 6k feet soon
after midnight early Saturday morning, thus any lake effect snow
would taper off toward flurries.
Inland today, the upper-level vort max already has an area of light
snow associated with it moving across Chicagoland early this
morning. This will bring a brief period light snow to most of the
forecast area this morning before departing. Little to no
accumulation is expected (upstream visibility is generally 5+
miles). In the wake of this disturbance, lake effect snow should
spill well inland at times due to favorable northwest flow. Narrow
corridors of 1" snowfall are plausible, but the bigger concern is
highly variable visibility across the Toll Road, I-94, US-6 and other
thoroughfares along the Michigan state line. Increasing wind gusts
later this morning will also pose the risk of blowing snow from this
morning's clipper system.
After careful examination and consideration, a winter storm watch
was issued for the US 24 corridor. I have high confidence in at
least advisory-level snow in the impacted counties, with a
reasonable shot at warning-level impacts (snow and wind) for at
least the far southeast portion of the watch. Cluster analysis
reveals differences in the strength and placement of the 500-mb low
which results in varying snowfall forecasts. In fact, it is now
appearing that the ECMWF (and ensemble) is a bit of an outlier with
its slower, less-amplified solution.
The talk of the town is the northward leaning GFS/GEFS. This
northern solution has impacted the in-house blend significantly this
morning. Neighboring offices and I wrestled (significantly) this
beast out of the forecast somewhat by reducing QPF and adjusting
inherited snow ratios downward. Some truly eye-popping totals are
advertised in the guidance and these cannot be blindly followed at
this distance. Thus, some weight to the ECMWF is still warranted.
Our winter storm watch of 4-6 inches is a safe middle ground at this
time, allowing us to pivot up or down as needed. Breezy northeast
wind (eventually becoming north) will pose problems as well. The
track of storm is still in some state of flux and messaging will be
adjusted as needed in the coming days. A very tight gradient of
snowfall will occur across northern Indiana and northwest Ohio.
In the wake of this storm, very cold with highs in the 20s and lows
in the single-digits at times. Lake effect snow pivots from western
Lake Michigan to the eastern shore as the low departs Monday. This
is followed by more lake effect snow Wednesday through Thursday as
an upper-level disturbance ripples through the Great Lakes.
&&
.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1209 AM EST Fri Jan 3 2025
A clipper system is currently moving through the area, bringing
snow showers and reduced visibilities across (primarily along
and south of US 30). KFWA has seen visibilities as low as 1 mile
and visibilities will remain between 1 to 3 miles in areas where
light to moderate snow is falling early this morning. Snow
should be done around 09Z, with a few hours of quiet weather
this morning before lake effect snow showers ramp up during the
afternoon. Winds will increase as well this afternoon, with
gusts to 20 to 25 kts. In any lake effect snow showers, expect
MVFR visibilities. There may also be some patchy blowing snow
this afternoon with those gusty winds that could also help
reduce visibilities.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Storm Watch from Sunday afternoon through Monday
evening for INZ020-022>027-032>034.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 10 PM EST Saturday for LMZ043-046.
&&
$$
DISCUSSION...Brown
AVIATION...Johnson
Source:
IWX issues Area Forecast Discussion (AFD) at Jan 3, 4:21 AM EST---------------
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