Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 231930

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
230 PM CDT Fri Oct 23 2020

(Issued 230 PM CDT Fri Oct 23 2020)

Tonight through Saturday:

Moisture being pulled northeast in response to a shortwave lifting
across the Upper Mississippi Valley brought additional light rain
showers to the area today. Along the southern edge of the vort
max pivoting across northern Wisconsin, an area of light rain and
snow developed across central Minnesota and western Wisconsin.

Outside of some light lingering rain across east-central
Wisconsin, the bulk of the rain showers have exited over Lake
Michigan and Illinois this afternoon. While the rain has come to
an end for the most part, expect cloud cover to hang on a bit
longer into this evening. As the pressure gradient remains
enhanced between the departing surface low to our northeast and
high pressure moving into the northern Plains, northwest winds
will remain breezy this evening. Skies will eventually scatter out
overnight as drier low-level air arrives. The decrease in cloud
cover overnight and winds relaxing will lead to a cold night,
with lows in the upper 20s to around 30.

Saturday we will find ourselves on the eastern extent of the
surface ridge, which will keep winds out of the northwest to
north. With colder air aloft, expect diurnal cumulus to develop
mid/late morning. Cumulus look to thin in the afternoon, with
passing upper-level cloud cover increase in coverage from the
west. The combo of cold air aloft and cloud cover should help
keep temperatures down, with highs in the upper 30s and lower 40s.



(Issued 230 PM CDT Fri Oct 23 2020)

Saturday night:

Low level ridging will prevail with high pressure extending eastward
eastward from the northern Rockies. Precipitation associated with
the next wx maker will likely remain to our west.

Sunday through Monday:

Strong H-2 H-3 jet stream will be across the area. Seeing some
potential for a couple different maxes within this flow regime
leading to some coupling at times and then more of a right rear
scenario. Little in the way of cyclogenesis noted with primary low
in the southern states. However a weak low does appear to take
shape with some weak isentropic ascent noted as well. Moisture
looks meager at the outset Sunday morning with better saturation
taking shape moving forward. The far southeast looks like the
last to fully saturate. Thermal profile initially will be warmer
in the southeast/cooler in the northwest. Correspondingly the
profile looks a little more rain/mixy in the southeast. Cold
advection begins Sunday night into Monday with any mix likely
changing over to pure snow. The models have been a bit out of sync
with precip coverage. The GFS has trended drier in the 23.12z
run. Again this is more of a jet driven system and doesn`t have
that feel of a classic def zone with no organized vort max or
lower level well defined cyclone. So weaker isentropic lift and
upper jet action will largely drive this. Overall, not a big
system for our area but the first snowfall nonetheless. Overall
consensus at the moment is a few tenths in parts of the southeast
to an inch or two in the far northwest cwa.

Tuesday through Friday:

We will see an overall benign northwest flow regime in place with
a southern stream upper low meandering from the desert southwest
through the central Plains into the Ohio Valley this period.
Overall, at this time see no reason to have any precip in the
forecast this period.



(Issued 230 PM CDT Fri Oct 23 2020)

Rain showers continue to wind down this afternoon, with a few
terminal seeing some lingering IFR ceilings. Ceilings will begin
to lift into the MVFR range later this afternoon and evening.
Breezy winds will remain in place from the northwest into this
evening, before gradually relaxing overnight into Saturday
morning. MVFR ceilings will also scatter out overnight, but return
as diurnal heating picks up mid-morning Saturday.



(Issued 230 PM CDT Fri Oct 23 2020)

North to northwest winds are expected to prevail tonight over Lake
Michigan behind the departing surface low and trailing cold front
moving across Lake Huron and lower Michigan this afternoon.
Occasional gale force gusts to 35 knots continue to look possible
under this north to northwest flow, thus the gale warning remains
in effect. The only change was to run the warning down further by
two zones (LM669 and LM870). Across the south half of the lake, it
is not out of the question that a gale force gust or two may
occur this evening, but confidence wasn`t high enough to extend
the warning further south. A small craft advisory remains in
effect as well for the nearshore areas given the gusty northwest
winds expected into this evening.

This weekend into early next week, the eastern extend of high
pressure dropping south along the northern and central Rockies
will impact the region, bring winds between 10 and 20 knot from
the west and north at times. The next chance for enhanced flow
over Lake Michigan appears to arrive Tue/Wed as southwest winds
pick up to 20 to 30 knots ahead of the next system tracking north
of the border in Canada.



LM...Gale Warning...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ868-LMZ870 until 10 PM Friday.

     Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 1 AM



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