Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 190346
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1046 PM CDT Wed Apr 18 2018

.UPDATE...
The snow is diminishing quickly across southern Wisconsin. It
should exit south of the state by 1 am. Drier air is working in
and will help to scatter out the lower clouds by 3 to 4 am. We`ll
cancel the headlines as the snow exits. Many roads will remain
snow covered and slippery overnight.

&&

.AVIATION(06Z TAFS)...
Look for VFR conditions to quickly spread across the area over the
next few hours. All of southern Wisconsin should be VFR by 06-07z
Thursday with VFR conditions expected through the rest of the TAF
period. Look for winds to very gradually back to the north then
northwest during the TAF period.

&&

.PREV DISCUSSION... (Issued 830 PM CDT Wed Apr 18 2018)

UPDATE...
The potent mid level circulation is tracking very quickly to the
southeast this evening. Its currently near Rockford and will be
moving into northern Indiana around midnight. The deep forcing is
beginning to break down with the departing system. Radar shows the
main snow area beginning to shrink/contract and it should begin a
quick southerly movement in response to the departing system.
We`re still looking at the snow exiting the southeast right around
midnight. Skies will clear overnight with sunshine for everyone by
sunrise. The sun combined with mild temps will do some quick work
on area roads covered in snow and ice.

The forecast update this evening will be consistent with the
precip ending.

MARINE...
A Small Craft Advisory is in effect until 7 PM Thursday. Brisk
northeast winds will become northerly tonight. Waves to 4 to 6
feet will continue through Thursday morning. The winds and waves
will gradually subside through Thursday afternoon.

PREV DISCUSSION... (Issued 551 PM CDT Wed Apr 18 2018)

UPDATE...

Things are progressing very well and mostly as expected. The main
band of snow lifted north of our southern tier of counties, but
more snow will spread in there over the next hour or so as the
upper circulation begins to push southeast this evening. That
upper circulation will race southeast as it gets picked up by a
trough pivoting northeast of it. That circulation is near Dubuque
at 6 pm and will be in northern Indiana by around midnight. That`s
quick. We should begin to see the snow intensity diminish by 8-9
pm as the main forcing breaks down. The snow will then exit from
northwest to southeast, exiting Kenosha county by midnight. No
adjustments to the forecast at this time.

AVIATION(00Z TAFS)...
Look for IFR conditions going into the evening, then improving
quickly to MVFR then VFR overnight as dry air arrives quickly from
the north. Skies will clear quickly between 08-10z Thursday across
all the TAF sites. Look for the snow to end at KMSN by 10-11 PM
and KMKE/KUES/KENW by about 05z. Look for winds to be northeast,
then very gradually back to the northwest on Thursday.

PREV DISCUSSION... (Issued 258 PM CDT Wed Apr 18 2018)

SHORT TERM...

This afternoon through Thursday...Forecast Confidence is high.

The heavy snow band along the MN/IA border is continuing to
extend ewd into the warned area of Sauk, Iowa, Dane, and Columbia
Counties. The catalyst for this band is 850-700 mb isentropic
lift supported by strong PVA and warm advection at the jet level.
The band will continue to extend farther east and north through
the afternoon, but the heaviest amounts of 5-7 inches will be
found in the warned counties, with high end advisory amounts to
the east. Much less snow is expected toward the IL border via the
dry slot, and toward central WI, which is on the nrn periphery of
the storm. The snow will continue into the evening ending from
north to south from 02z to 05z as the upper low and isentropic
lift moves east. Skies will then clear late tnt through Thu.
Temps rebounding into the 40s on Thu.

LONG TERM...

Thursday night through Tuesday...Forecast Confidence is high

This will be a very quiet period with a split upper level flow.
In the northern stream through the end of the week, a trough will
be moving off the East Coast with another trough1 coming onshore
in the Pacific NW and a ridge between these two features across
the central CONUS and southern Canada. The southern stream has a
closed low slowly moving from the desert SW at the beginning of
the period to the lower MS River Valley by the end of the weekend
and then on into the SE US early next week. All the precipitation
with this system is expected to remain well south of the CWA. This
scenario puts the local CWA in weak NW flow with slowly rising
heights through the weekend. At the surface, a 1030+mb high will
dominate the conditions across all the the Midwest. The center of
the high is forecast to drift east from IA Thursday night to New
England by early next week.

What all this means for our sensible weather across southern
Wisconsin is that there should be a slow warming trend of approx
2-5 degrees per day into early next week. Locations that get the
most snow today will likely have reduced highs from the
surrounding area after the snow melts across the rest of the area
late this week and potentially into the weekend, but it is too
early to attempt that level of detail this many days out.
Regardless, we should be in the lower 60s by early next
week...well away from the Lake. Light winds due to proximity of
the surface ridge means a good set-up for lake breezes each day
through the weekend. There is some model discrepancy as to exactly
where the center of the high tracks and whether S WI remains in
the light wind regime of the ridge axis or just south of the ridge
axis resulting in synoptic easterly flow which would only act to
enhance the lake breeze. Due to the persistent cold spring, Lake
Michigan water temperatures are still running in the middle 30s
which will mean strong cooling potential associated with the lake
breeze. Even though areas away from the lake will be getting into
the 50s and 60s, lakeshore areas will likely remain in the 40s.
Current guidance may be underdoing the cooing potential of the
lake breeze over the weekend and into early next week.

Upper flow begins to change by early next week as a short wave
approaches the region in association with the trough that moved
onshore along the west coast over the weekend and then lifting
into central Canada. As is usually the case at these ranges, there
are differences with respect to strength, timing and placement, but
the overall scenario is a chance for precipitation along a cold
front Tuesday into Tuesday night. Temperatures should remain warm
enough for all liquid precipitation this time...thankfully.

AVIATION(18Z TAFS)...

A mixture of rain and snow will occur near the IL and IA border
this afternoon into the early evening before becoming all light
snow. Farther north, mostly snow is expected including moderate to
heavy snow at times. Vsbys will fall to 1/4-3/4 miles at times
with the snow while Cigs will range from 600-1900 feet. Much
lesser impacts toward central WI with this storm system. Skies
will clear from north to south during the late evening and early
morning hours. VFR conditions will continue through Thu.

MARINE...

A Small Craft Advisory is in effect from this afternoon until 7
PM Thursday. Brisk nely winds will become nly tonight. Waves will
build to 3 to 6 feet through the afternoon and continue through
Thursday morning. The winds and waves will gradually subside
through Thursday afternoon.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 1 AM CDT Thursday for WIZ058>060-
     064>072.

     Winter Storm Warning until 1 AM CDT Thursday for WIZ056-057-062-
     063.

LM...Small Craft Advisory until 7 PM CDT Thursday for LMZ643>646.

&&

$$

Update...Davis
Tonight/Thursday and Aviation/Marine...Gehring
Thursday Night through Wednesday...BM


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