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FXUS63 KGRB 221728
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1228 PM CDT Thu Jun 22 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 353 AM CDT Thu Jun 22 2017

Scattered thunderstorms across the southeastern half of the
forecast area should dissipate around daybreak, as the low level
jet diminishes a bit and cloud tops warm.

Additional thunderstorms are likely by late morning or early
afternoon as a surface low and warm front move northeast towards
the area. There is some uncertainty as to how far north the warm
front gets.It may stay just to our south, which would keep the
best instability and warmest temperatures down there. The
instability this afternoon also hinges on if we get some breaks in
the clouds.

Think there is a slight chance of severe thunderstorms where SPC
slight risk is forecast. Strong winds and some hail is possible.
Another possible hazard is heavy rain, as precipitable water
values of 1.5" to 2.0" are forecast this afternoon and evening
with showers and thunderstorms along the slow moving front. The
heavy rain could cause some rivers and streams to rise above
bankfull again. Showers and thunderstorms will end from northwest
to southeast tonight, with cooler and drier air filtering into
the region Friday.

.LONG TERM...Friday Night Through Wednesday
Issued at 353 AM CDT Thu Jun 22 2017

Models continue to show an upper ridge setting up over the western
CONUS, while an upper trough settles over the eastern half of the
CONUS into early next week. This amplified pattern is forecast to
break down toward the middle of next week with a somewhat zonal
flow the end result. Unsettled weather/cool conditions to prevail
over northeast WI through Monday, as long as the upper trough
remains nearby. As the flow de-amplifies, new questions emerge as
to the timing of WAA-induced precipitation into WI by next
Wednesday. Temperatures should return closer to normal values by
next Tuesday/Wednesday.

The loss of daytime heating plus the exit of the shortwave trough
equates to a quick demise of any precipitation early Friday
evening. This will leave sky conditions generally partly cloudy
south, mostly cloudy north through the overnight hours. Min
temperatures to range from the upper 40s to around 50 degrees
north-central, middle 50s east-central WI. The next shortwave
trough is expected to move southeast into the western Great Lakes
on Saturday and with daytime heating adding some instability/
steepening low-level lapse rates, anticipate showers/afternoon
thunderstorms to develop in scattered fashion. Cool air aloft,
increasing clouds and precipitation will hamper diurnal heating
with max temperatures only reaching the lower to middle 60s
north-central, around 70 degrees eastern WI.

Much like Friday night, this latest round of showers/storms will
dissipate Saturday evening after sunset leaving another night with
partly to mostly cloudy skies. Temperatures are forecast to be a
couple of degrees cooler with readings down into the middle to
upper 40s north, lower to middle 50s south. Toward the latter half
of the weekend, northeast WI is expected to be on the cyclonic
side of the broad upper trough with several embedded shortwaves
moving through the now-northwest flow aloft. This should lead to
additional shower chances on Sunday and cannot rule out a few
afternoon thunderstorms if enough instability can develop. Another
cool day across the region with max temperatures again in the
lower to middle 60s north-central, around 70 degrees eastern WI.

Most of this latest batch of showers will dissipate Sunday
evening, although with more shortwave activity to move through WI
overnight, a few showers could linger through Sunday night. It
appears that the last of these shortwave troughs will sweep
through the western Great Lakes on Monday, thus will need to carry
another chance of showers/afternoon thunderstorms in the forecast.
Since the coolest air aloft to have shifted east on Monday, max
temperatures are expected to edge upward into the upper 60s
north-central/lakeshore, around 70 to the lower 70s elsewhere.

High pressure is progged to build into WI Monday night and slide
to the east on Tuesday. This should finally allow for nil pops
across the forecast area with plenty of sunshine for Tuesday and
temperatures recover at least closer to normal. Look for readings
to reach the lower 70s north-central/lakeshore, middle 70s
elsewhere.

As the mean flow becomes more zonal toward the middle of next
week, models begin to have timing issues with both the onset of
stronger WAA and the next chance of showers/thunderstorms. The GFS
is faster, with a strengthening low-level jet transporting
warmer/ more moist air into WI by late Tuesday night. This
scenario would bring precipitation back to northeast WI late
Tuesday night and continue into Wednesday. The ECMWF is slower,
and essentially holds the bulk of the precipitation away from
northeast WI until Wednesday night. Have followed the consensus
solution which does bring in low pops for both Tuesday night and
Wednesday. Max temperatures on Wednesday will continue to inch up
with lower to middle 70s north-central/lakeshore, middle to upper
70s elsewhere. &&

.AVIATION...for 18Z TAF Issuance
Issued at 1215 PM CDT Thu Jun 22 2017

Clusters of showers and thunderstorms will continue to move across
the area this afternoon into this evening. An isolated severe
storm is still possible south of a Marshfield to Green Bay to
Algoma line, although it appears less likely than earlier today.
The showers and storms should exit from northwest to southeast
tonight, exiting east-central Wisconsin after midnight.
Weak high pressure builds into the region tonight into Friday
morning. Fair weather cumulus clouds will develop Friday
morning with a few showers possible Friday afternoon, especially
across the north.

&&

.HYDROLOGY...
Issued at 353 AM CDT Thu Jun 22 2017

Another round of heavy rain expected this afternoon and evening,
especially across central and east central Wisconsin. Rainfall
totals of 1 to 2 inches are possible in some places south of a
Merrill to Sturgeon Bay line. This could keep some streams and
rivers above bankfull for a few days.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....RDM
LONG TERM......Kallas
AVIATION.......Eckberg
HYDROLOGY......RDM