Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 211657

Area Forecast Discussion
National Weather Service Green Bay WI
1157 AM CDT THU JUL 21 2016

Updated aviation portion for 18Z TAF issuance

Issued at 345 AM CDT Thu Jul 21 2016

A round of thunderstorms this morning...otherwise very warm and
humid the next several days. a little cooler and not as humid next

The main band of westerlies will sag south a bit and deamplify
during the period. The warm and very humid air across the area
will gradually get displaced to the south by a series of frontal
systems and thunderstorm outflows. That will allow temperatures to
settle back closer to, but still above, normal levels by early
next week. Given the available moisture and numerous opportunities
for convection, precipitation amounts for the next week are likely
to be above normal.

.SHORT TERM...Today...Tonight...and Friday
Issued at 345 AM CDT Thu Jul 21 2016

Large, mature MCS is barreling southeast toward the area from
northwest Wisconsin. It is likely to affect the entire forecast
area this morning. Morning PoPs were based on radar trends. Severe
potential is a little less clear. System may tend to weaken as it
arrives. But any upticks in intensity could certainly result in a
threat for damaging winds.

The forecast becomes much less certain after the MCS moves
through. The models that were handling it (and it was certainly a
minority of them) suggest it will be the main show and the
potential for redevelopment this afternoon and evening is
minimal. Hard to completely go with that, so PoPs were trimmed
back in the wake of the MCS, but left some 20-30 PoPs in for the
afternoon and evening in case there is redevelopment.

After the arrival of rain-cooled air with the MCS outflow and
having considerable debris clouds to break through, max temps
needed to be trimmed. Updated apparent temperatures for the
afternoon were marginal at best for a Heat Advisory. After talking
things over with the forecaster at MKX, decided to drop the

Friday looks to be a lull in the thunderstorm potential as the
boundary sags a little farther south of us with upper flow tilting
a little more WNW in advance of shortwave ridging approaching from
the west.

.LONG TERM...Friday Night Through Wednesday
Issued at 345 AM CDT Thu Jul 21 2016

Zonal upper level flow across southern Canada and the northern
CONUS is expected during this part of the forecast. Though the
models continued to show some differences in the timing of a mid
level trough and surface system moving through the area, Saturday
night appears to be the most likely time for thunderstorms over the
weekend. There should be plenty of time for the atmosphere to
destabilize Saturday afternoon ahead of the approaching cold front
so it looks like some of the storms will be strong, possibly
severe. Highs on Saturday and Sunday will be above normal, but
temperatures should be closer to normal for the early part of next
week, in the wake of the cold front.

The best bet for showers and storms during the rest of the long
term forecast looks to be on Wednesday with the approach of the
next significant mid level short wave.

.AVIATION...for 18Z TAF Issuance
Issued at 1157 AM CDT Thu Jul 21 2016

A large thunderstorm complex has exited the taf sites at midday, but
additional storms are developing over central Minnesota and western
Wisconsin.  Some of these storms may push across central and east-
central WI later this afternoon or early this evening, if they
survive the trip.  The airmass will be more stable to the east after
this mornings storms, so confidence is low enough on timing and
coverage to leave out of the taf forecast for now.

Then a cold front will drop through the region this evening into
early overnight.  This may be a tad sooner than what was expected
earlier.  Dewpoints will be dropping behind the front, which will
limit fog potential despite the rainfall and muggy airmass in place.
Based on these facts and the recent statistical guidance, have
backed off fog formation over central and north-central WI.  East-
central will still have potential for lower vsbys/cigs in fog late
tonight, since the passage will be later in the night that other taf
sites. Once any fog burns off, vfr conditions to resume on Friday



SHORT TERM.....Skowronski
AVIATION.......MPC is the U.S. government's official web portal to all federal, state and local government web resources and services.