Area Forecast Discussion
Issued by NWS Green Bay, WI

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837
FXUS63 KGRB 252358
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
658 PM CDT Tue Apr 25 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Wednesday
Issued at 251 PM CDT Tue Apr 25 2017

Primary issue is a switch from a dry pattern to a wetter pattern
this week. Developing upper trough over the Plains will produce a
southwest flow aloft. A series of surface waves with shortwaves
will track northeastward into the state while as a frontal
boundary slides in from the west. At 200 pm the surface front
extended roughly from DLH, along the wisconsin/minnesota border to
central Iowa. Challenge with this forecast will be precipitation
trends due to the dry air mass at the start.

The air mass this morning as per morning sounding was dry, which
explains the mid level clouds and sprinkles across northwest
wisconsin early this morning with the first short wave.

Radars to the west show the leading edge of the next wave over
southern Minnesota and northeast Iowa moving northeastward.
Will time the spiral band lifting north during the afternoon and
early evening hours, otherwise focus of precipitation appears
mainly post frontal as upper height falls nudge into the state
west overnight. Will confine higher pops near or west of the
front tonight into Wednesday. As far as thunder, no lightning
strikes noted so far with the spiral band lifting northward this
afternoon, so will keep thunder mention out. Lower level lapse
rates were becoming more steep this afternoon, but the dry mid
levels were narrowing the initial band of showers. Will keep a
mention of thunder for Wednesday afternoon over eastern Wisconsin
near the frontal boundary and very marginal instability.

Quite a range in max temps for Wednesday ranging form the lower
70s over the east, to mid 50s across the northwest where cooler
air is filtering into the area along with the more widespread
rains.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 251 PM CDT Tue Apr 25 2017

The low pressure systems should be slowly exiting
late Wednesday night and Thursday, with rain diminishing from west
to east. Freezing rain is possible across northcentral Wisconsin
late Wednesday night and early Thursday as cold air arrives in low
levels while temperatures remain above freezing aloft.

Generally cool and dry weather is expected Thursday afternoon
through Saturday with temperatures 5 to 10 degrees below usual.

A classic spring storm is forecast by the models Sunday and Monday
that would produce possible heavy snow to it`s northwest and
severe weather to it`s southeast. Minneapolis and Duluth look to
be on the cold side.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 641 PM CDT Tue Apr 25 2017

A cold front will move slowly from western WI this evening to
eastern WI Wednesday afternoon. A low pressure system will lift
northeast along this boundary, and produce periods of showers,
heavy at times. The rain should be focused over central, north
central and far northeast WI for most of tonight, then overspread
the Fox Valley and lakeshore areas overnight into Wednesday
morning. Additional showers and possibly a few thunderstorms may
form along the cold front over eastern WI Wednesday afternoon.
However, confidence is not high enough to include thunder in this
set of TAFs.

Expect flight conditions to deteriorate to MVFR as the heavier
rains develop, and to IFR n the cool side of the cold front. A
dry slot may bring a decrease in the rain over central and north
central WI Wednesday afternoon, and allow for improving
visibilities later in the day.

Have pulled back a bit on LLWS in this set of TAFs, and only
included it in the MTW TAF, where it seemed most likely
overnight.

&&

.HYDROLOGY...
Issued at 251 PM CDT Tue Apr 25 2017

A series of low pressure systems progged to track over the region
for the next several days will serve to keep rivers at current or
slight increases for the remainder of April. Next system to
impact the region will slowly track over the area tonight into
Wednesday before lifting north of the wednesday evening. Up to an
inch total of a widespread rain possible over north central and
parts of central Wisconsin through Wednesday evening, lesser
amounts eastward. Another system appears to be mainly south of the
area on Friday, but return flow setting up late in the weekend
and into early next week may again produce a widespread inch of
rain, with the potential of 1.50 to 2.00 inches total. Fortunately
we are getting a few days spacing between these systems.
&&

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

$$

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



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