Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 251116
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
616 AM CDT Tue Jul 25 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 339 AM CDT Tue Jul 25 2017

Despite high pressure over the Great Lakes region, an area of
showers continues to steadily track east through the upper
Mississippi Valley early this morning. The main question is how
far east these showers will make it as the atmosphere is quite dry
downstream. Therefore will introduce POPs across the western part
of the cwa this morning and keep the east dry, however this could
be updated with future forecasts if this activity holds together.

An approaching frontal boundary will bring an increased chance for
showers and thunderstorms tonight into Wednesday. This frontal
boundary will be slow moving, bringing the chance for multiple
rounds of convection as it tracks through the western Great Lakes
region. In addition, there will be a risk for severe weather
during this period as MUCAPEs increase to 1000 to 2000 J/kg with
bulk shear values of 30 to 50 knots. The main question regarding
severe potential will be timing, as lift doesn`t always coincide
with the best instability or shear values. Also of concern
Wednesday is cloud cover keeping instability limited as the
frontal boundary moves through. Overall confidence in severe
potential is fairly low given the substantial capping in place and
the uncertainty regarding the timing of the dynamics with the
instability and shear.

What appears to be a bit more certain is the potential for heavy
rain as PWATs increase to around 2 inches tonight and Wednesday.
Given the potential for several rounds of heavy rain localized
flooding is certainly a concern, particularly over areas that have
recently received heavy rainfall such as northeast and east-
central Wisconsin.

.LONG TERM...Wednesday Night Through Monday
Issued at 339 AM CDT Tue Jul 25 2017

Typical summertime pattern expected to continue through the period
with chances of thunderstorms at times with the core of the hot
weather expected to stay across the western United States. So far
this summer, Green Bay has not hit 90 degrees despite temperatures
running at least a few degrees above normal so far this summer.
With the expected pattern, it does not look likely Green Bay will
hit 90 degrees during the next week.

For Wednesday night, a cold front will continue to sag southward
and move south of the area by late evening. Ongoing convection
is expected with the front. Some of the storms could be strong or
severe with damaging winds and large hail. Clouds will be on the
decrease after midnight from north to south. On Thursday, models
indicating an upper level disturbance and compact 500mb trough
moving across the western Great Lakes. Models do not do much with
this feature, but it was worthy of adding a small chance of
showers and storms. Since there was uncertainty in the forecast
with the extent of the rain, only added a chance of rain during
the daytime. Later shifts may need to add rain into the forecast
for early Thursday evening as well across northeast Wisconsin if
this feature slows down by a few hours. A fairly cool night is in
store Thursday night with lows dropping into the middle to upper
40s in the typical cold spots across the north with 50s elsewhere.
Daytime highs on Friday should rebound nicely with highs around
80. Similar conditions are expected again Friday night and
Saturday, although lows Friday night are expected to be a few
degrees warmer. There are small chances of showers and storms
Sunday into Monday, but confidence is low if rain would occur.
Latest numerical guidance indicating cooler than normal conditions
are possible across northern Wisconsin early next week.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 616 AM CDT Tue Jul 25 2017

Some light showers are possible across the western TAF sites this
morning. Otherwise increasing southerly winds will draw
moisture today, resulting in scattered cu formation by late
morning to early afternoon. Then lower cigs, possibly mvfr, will
arrive this evening ahead of a cold front over north-central WI as
a thunderstorm complex arrives from the west. The best chances
will be across the western TAF sites later tonight, with lesser
chances further east.
&&

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

$$

SHORT TERM.....Kurimski
LONG TERM......Eckberg
AVIATION.......Kurimski



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