Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 182341
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
641 PM CDT Wed Apr 18 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Thursday
Issued at 239 PM CDT Wed Apr 18 2018

WV imagery showed a potent upper low tracking east through
northern IA this afternoon. The associated deformation zone was
pivoting north, and appeared poised to just clip our far southern
counties during the late afternoon and early evening before
dropping south again. Weak lake-effect rain/snow showers near MTW
should taper off as winds turn northerly this evening, but that
region will also be briefly impacted by the deformation band.
Overall, expect the far south to receive around an inch of snow,
with spotty rain/snow showers occurring just north of the main
band.

Partial clearing has already occurred over far northern WI, and
should progress southward during the evening hours. Blustery
conditions will ease overnight, except in the Fox Valley and
lakeshore areas. Sunny skies are anticipated on Thursday, as
a Pacific high pressure system builds in from the west.

Lows tonight should drop into the lower to middle 20s, except
upper 20s east. Highs on Thursday are tricky due to the deep snow
cover. Continued to go below guidance, with highs in the middle to
upper 40s, cooler lakeside.

.LONG TERM...Thursday Night Through Wednesday
Issued at 239 PM CDT Wed Apr 18 2018

The latest GFS ensemble mean indicates that a change in the upper
air pattern to split flow will result in warmer air invading the
region through early next week.  Though split flow supports quiet
and mild weather typically, the arrival of warmer temperatures will
lead to melting of the deep snow pack and rise of area rivers.
Forecast concerns mainly revolve around temperatures during this
period.

Thursday night through Saturday...A sprawling high pressure system
will be slowly moving east across the region during this period.
Thursday night into Friday morning will likely remain mostly clear
and nearly calm.  A shortwave will then push scattered to broken
high clouds overhead and across the region on Friday afternoon into
Friday night.  Progged soundings indicate that saturation is
projected to remain above 550 mb while mid-level RH generally
remains below 30%.  Therefore no precipitation is anticipated at
this time.  High clouds then should depart on Saturday, which should
lead to the return of mostly clear skies.  Low level temps will be
warming over the period, with 925mb temps suggesting highs near 60F
on Saturday.  Will warm highs a couple degrees for Friday and
Saturday, but the melting snow pack will likely hold back temps
some.

Rest of the forecast...The large high pressure system will linger
across the region on Sunday before exiting to the east on Monday. As
winds shift to the south on Monday, should see the warmest day of
the period, with highs in the 60s possible.  The next front looks to
arrive on Monday night into Tuesday.  Moisture should be very
limited, so precip potential looks relatively low.  A brief cool
down should occur behind the front through midweek.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 641 PM CDT Wed Apr 18 2018

Light snow and IFR conditions south of Y50 and OSH
will end by 02. The rest of the region will have VFR ceilings this
evening. Clouds will exit the area from north to south overnight,
with mostly clear skies forecast Thursday.

Marginal low level winds shear is possible across most of the area
tonight from 03z to 12z with light north winds at the surface and
northeast winds around 35 knots at 1000` agl.
&&

.HYDROLOGY...
Issued at 239 PM CDT Wed Apr 18 2018

Warming temperatures are expected to produce significant melting
of the current snowpack over northeast WI. This will lead to
runoff into area rivers and streams. Most of the rivers in
northeast WI were low before the historic snowstorm hit, thus only
minor flooding is expected from the runoff. River levels will be
on the rise starting this weekend. People living near rivers and
streams should keep a close eye on river levels and keep up to
date on the latest river forecasts.
&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......MPC
AVIATION.......RDM
HYDROLOGY......MPC



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