Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 131540

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1040 AM CDT Thu Aug 13 2020

(Issued 1035 AM CDT Thu Aug 13 2020)

Shortwave trough that was producing showers and storms across
central WI this morning is working its way out of the region and
drier air is overtaking what is left from this morning activity.
May see some light showers/sprinkles creep into our northern
counties within the next hour or so, but a diminishing trend
continues. However, will likely see some of the higher clouds
push into these areas later this morning into the afternoon.

Otherwise, the forecast remains on track with dry conditions as
high pressure and mid-level ridging dominates. Light east-
southeasterly winds will continue increasing slightly into the
afternoon to around 5-10 mph before becoming calm again overnight.
These dry conditions look to persist into Friday with a bit
warmer temps in the mid to upper 80s before a cold front pushes
across the region on Saturday bringing increased shower and
thunderstorm activity.



(Issued 300 AM CDT Thu Aug 13 2020)

Today through Friday:

The influence of a sfc high pressure will continue through today
and into Friday. Winds will be modest out of the east-southeast
with passing high clouds at times and highs in the 80s on both



(Issued 300 AM CDT Thu Aug 13 2020)

Friday night through Saturday night:

Short and long term guidance are in better agreement on weakening
short wave trof moving through the Upper Midwest and western
Great Lakes Friday night and Saturday. The short wave will be
rotating around parent low pressure located well to the north in
northern Canada. The short wave will be running up against a
nearly stationary high pressure ridge which will be lingering over
the eastern Great Lakes. This ridge will be slowly pinched off
and weaken over the weekend as slow moving low pressure over the
eastern CONUS moves towards New England.

The short wave will pull a weakening cold front across southern
Wisconsin on Saturday into Saturday evening. The stronger synoptic
lift associated with the mid-level wave and low level warm air and
moisture advection will remain to the north and west on Saturday.
Although the stronger low level winds will be focused elsewhere,
weaker moisture advection will result in precipitable water
increasing to around 1.5" on Saturday as surface dewpoints inch
upwards into the mid to upper 60s. Surface based Cape is expected
to be in the 1-2K joule range as the front moves through, however
low level shear will be on the lower end. At this point, can not
rule out one or two storms becoming stronger to isolated severe in
the vicinity of the low level front. However there remains
uncertainty as to the exact timing of the frontal passage on
Saturday. Some guidance has it moving through southern WI earlier
in the day and would be to the east and south during peak
afternoon heating. For now, wl continue chance pops for convection
into Saturday evening, with the afternoon and evening hours
remaining the favored time period for showers and storms due to
the nearness of the sfc and low level front and potential
frontogenetical forcing.

Sunday through Wednesday:

Increasing long wave troffing in the eastern Pacific and eastern
Canada into the northeast CONUS will result in northwest steering
flow setting up over Upper Midwest and western Great Lakes Sunday
into next week. This will usher a second reinforcing push of
cooler air across the region on Sunday. Low level convergence will
be weak along this second cold front moving through on Sunday.
Also, soundings look pretty dry in the low to mid levels, so will
hold off on introducing any shower chance. Otherwise, a cooler
and dry period of weather is expected through at least Monday and
Tuesday with lighter winds and daytime temps in the 70s, and
comfortable night time temps in the 50s and a few 40s. The
northwest steering flow may carry a a weak disturbance through the
western Great Lakes on Wednesday resulting in shower chances
returning. However wl continue the dry forecast for now due to
uncertainty with regard to this disturbance as well as the amount
of the available moisture.



(Issued 1035 AM CDT Thu Aug 13 2020)

Some high clouds will persist across parts of southern WI today
with winds around 5-10 mph. Quiet and dry VFR conditions will
continue this evening with winds becoming light and variable
overnight into Friday morning before picking back up by mid



(Issued 300 AM CDT Thu Aug 13 2020)

High pressure will continue to support modest E-SE winds, low
waves, and dry conditions through Friday. This weekend a cold
front is expected to pass Saturday night into Sunday morning,
bringing a period of showers and storms across the lake. As high
pressure builds in behind the front on Monday, a period of gusty
NW winds will be possible.




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