Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 200337

Area Forecast Discussion
National Weather Service Green Bay WI
1037 PM CDT Mon Jun 19 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Tuesday
Issued at 226 PM CDT Mon Jun 19 2017

The latest rap analysis and satellite/radar imagery show deep layer
cyclonic flow across the western Great Lakes region.  Several
shortwaves within this cyclonic flow are interacting with daytime
instability (sb capes > 1000 j/kg over eastern WI) to produce
numerous showers and scattered thunderstorms.  Highest coverage of
showers and storms should occur over eastern WI for the rest of the
afternoon.  Not out of the question any storms could produce small
hail, brief gusty winds, and even funnel cloud given high non-
supercell tornado parameter. The next shortwave is located over
Saskatchewan and poised to arrive early tomorrow morning. Precip
trends are the main forecast concern in the short term.

Tonight...Upper troughing will remain firmly in place over the
region.  Scattered showers will likely persist into the evening but
coverage/intensity should gradually diminish with loss of heating.
Still though, coverage should be highest over eastern WI this
evening, where a few thunderstorms will likely persist.  Once the
showers have ended, should see quiet conditions for a several hour
period under scattered to broken clouds.  Then clouds will be on the
increase late tonight as a potent shortwave over Saskatchewan moves
towards the region.  This shortwave will generate a chance of
showers by 7am over central and north-central WI.  Low temps ranging
from the upper 40s north to mid 50s south.

Tuesday...The shortwave will track across the region during the
morning before exiting in the afternoon.  The higher resolution
models place the highest qpf over central and east-central WI, where
the best forcing via mid-level fgen/upper divergence and also
instability will reside.  With capes of 200-400 j/kg, a few
thunderstorms could also accompany the shortwave.  As the shortwave
and associated precip exits, isolated to scattered showers could
persist through the end of the afternoon.  Highs ranging from the
mid 60s north to low 70s south.

.LONG TERM...Tuesday Night Through Monday
Issued at 226 PM CDT Mon Jun 19 2017

The next chance of rain and the focus of this part of the
forecast will be toward Wednesday evening into Thursday.

A few stray showers may linger Tuesday evening over eastern
Wisconsin as a short wave trough departs the area. Otherwise a
surface high pressure ridge will drift over the western Great
Lakes late Tuesday into Wednesday as upper heights increase and
the flow aloft goes from a northwest flow regime to a zonal flow.
A brief quiet stretch of weather is the result.

The the next frontal system will approach from the northern
plains Wednesday afternoon or Wednesday evening, followed with a
cold frontal passage toward Thursday morning. Progs have slowed
down the timing of arrival starting Wednesday evening. A period of
PWATS climbing to 1.75 inches along and ahead of the cold front
will potentially produce up to an inch of widespread rain in the
24 hour period.

The slow down of the frontal system may delay the departure of
the precipitation from northwest to southeast on Thursday. Progs
are consistent with dropping the cold front south of the area by
noon Thursday for brief trend toward drier conditions for at least
northern wisconsin. A few showers may linger over parts of
central and east central Wisconsin Thursday into Thursday night
closer to the cold front, or mainly south of highway 10. Will keep
a dry forecast going friday as drier air continues to settle

Consensus of the medium range progs transition to a broad upper
trough dropping into the Northern and Central Plains this
weekend. A southwest flow aloft over the Great Lakes will allow
a moist air mass to settle into the area with a return of more
precipitation. Max temperatures will depend on amount of clouds,
but appears cooler than normal this weekend.

.AVIATION...for 06Z TAF Issuance
Issued at 1036 PM CDT Mon Jun 19 2017

Showers have diminished with the loss of heating. A strong
shortwave dropping southeast into the region will bring another
round of showers to the area late tonight into Tuesday. The
strongest forcing is likely to pass southwest of the area, but
there should still be enough forcing for another round of at least
scattered showers.



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