Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 232339
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
539 PM CST Sun Feb 23 2020

.UPDATE...

The current forecast is on track and no changes are needed at this
time.

&&

.AVIATION(00Z TAFS)...

VFR conditions are forecast through Monday afternoon and evening
but clouds will be gradually lowering through the day Monday.
Winds have shifted to the west and will turn more northwesterly
overnight. A system over the south-central US moves towards the OH
Valley on Monday and will switch winds to the E/NE this is when
cigs begin to lower. Just beyond the current TAF period closer to
06z Tuesday cigs fall to MVFR as light snow approaches from the
south.

&&

.PREV DISCUSSION... (Issued 338 PM CST Sun Feb 23 2020)

SHORT TERM...

Today and Tonight...Forecast Confidence is High.

A surface trough crossing southern WI this evening will bring a
wind shift to the northwest, along with cooler temperatures.
There are no clouds or precip associated with this front. Winds
will shift to the northeast Tuesday morning as low pressure
develops on the southern Plains. Mid level clouds will begin to
spread into southern Wisconsin Tuesday morning and then low clouds
may develop near the lakeshore Tuesday afternoon as we get a
longer fetch of northeast winds off of Lake Michigan.

Low temperatures tonight will be in the 20s, coolest toward
central WI. The high temps on Monday will be in the upper 30s.

LONG TERM...

Monday Night Through Wednesday...Forecast Confidence Low to Medium...

Overall, our next next system continues to remain complex
especially as models continue to vary on the finer details from
run to run. Thus, there still remains some questions about the
exact snowfall amounts at this time. Nonetheless, there has been a
persistent signal showing several inches of accumulating snow
across portions of southern WI Tuesday and Wednesday with amounts
possibly exceeding 8 inches, especially for areas south of I-94
and counties near the Lake. These higher snow amounts will likely
result in travel impacts for Tuesday evening and Wednesday
morning commutes. Additionally, the snow is expected to initially
be heavy and wet, which will can shoveling difficult. This
combined with stronger winds may also lead to power outages as
well. Hence, a Winter Storm Watch has been issued for portions of
the CWA Tuesday into Wednesday.

Monday night, a mid-level trough and its associated surface low
will work northeastward from the southern Central Plains into
IL/IN. This is expected to bring the initial push of moisture
into southeast WI overnight Monday, but the NAM/GFS progs a dry
layer between 900mb-700mb to hold on at least through 06z.
However, given the northeast flow off the lake, areas closer to
lake, especially in the southeast, will saturate faster and be
subjected to earlier onset of snow. While saturation in areas to
the west will lag behind by a couple of hours. Around sunrise/12z,
snow is expected to spread into most of southern WI.

Then as this mid-level trough weakens as it lifts to the northeast,
a strengthening mid-level low will dig across the Central Plains and
push in shortly behind it Tuesday late morning/afternoon. As this
mid-level low works its way into IL it will catch up with the
previous surface low and reinvigorate cyclogenesis later on
Tuesday. One of the complicating factors of this event is where
will the cyclogenesis occur. The latest GFS and GEFS progs a bit
more of a north and western track than the ECMWF, which is further
south and a bit drier.

Regardless of which model setup materializes, the overall
synoptic pattern with upper-level diffluence combined with dCVA
from the progressive mid-level low and low-level
frontogenesis/TROWAL setup as the surface low occludes remains
favorable for a prolonged, impactful snow event over southern WI.
Snow can begin as early as overnight Monday, but the bulk of the
snow looks to be on Tuesday continuing into Wednesday. The initial
snow ratios are expected to be around 8:1-10:1, thus snow will
likely be a wet snow Tuesday, but as cold air filters in on
Wednesday, snow ratios are expected to increase closer to 13:1,
which will become more of the lighter variety. Additionally,
persistent strong northeasterly winds off the lake could provide
lake enhancement for our lakeshore and neighboring counties, which
could increase snow amounts through Wednesday. Given these snow
ratios combined with qpf values around 0.3-0.6 inches across
central WI and 0.6 to +1.0 inches across south and southeast WI,
confidence is increasing in seeing higher/impactful snowfall
amounts greater than 6-8 inches.

Thursday and Saturday...Forecast Confidence Medium...

Snow is progged to taper off later in the day Wednesday. Drier and
colder conditions are expected for the later half this week as winds
shift to the north-northwest and high pressure builds behind this
early week system.

AVIATION(21Z TAFS)...

Gusty southwest winds are occurring near Lake Michigan this
afternoon with lighter winds inland. Winds will become lighter
tonight as they veer west to northwest/north. Low clouds may
develop Monday afternoon in southeast WI due to northeast winds
drawing low level moisture from Lake Michigan. Snow may begin
there by late afternoon.

MARINE...

A surface trough will cross the lake this evening, shifting winds
to the northwest to north later tonight, and weakening them into
Monday morning. Low pressure tracking from the southern Plains
into central Indiana tonight into Tuesday will bring a period of
gusty northeast winds and building waves Monday afternoon through
Wednesday morning. Winds should gradually shift north to
northwest Wednesday afternoon.

Gales are expected at times Tuesday afternoon through Wednesday
evening and possibly longer, with highest confidence for the
south half. A Gale Watch is in effect for the south half and
nearshore waters. A Gale Watch may be needed for the north half,
but perhaps not until Wednesday. Some freezing spray may occur
later in the week.

BEACHES...

Persistent northeast winds and waves of 7 to 10 feet, along with
high Lake Michigan water levels, will give us a threat for
lakeshore flooding. Main timeframe for this is Tuesday afternoon
through Tuesday night.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from Tuesday morning through Wednesday
     afternoon for WIZ062>072.

     Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for WIZ051-052-057>060.

LM...Gale Watch from Tuesday afternoon through Wednesday evening for
     LMZ080-643>646-669-671-673-675-777-779-870-872-874-876-878.

&&

$$

Update...Stumpf
Tonight/Monday and Aviation/Marine...Cronce
Monday Night through Sunday...Wagner



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