Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 261906

Area Forecast Discussion
National Weather Service Green Bay WI
206 PM CDT THU MAY 26 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Friday
Issued at 205 PM CDT Thu May 26 2016

The latest rap analysis and satellite/radar imagery show a shortwave
trough lifting northeast into the Upper Peninsula early this
afternoon.  Showers and a few thunderstorms are in the process of
exiting northeast Wisconsin, and do not pose a threat of severe
weather.  With the showers moving through, its rather difficult
finding a stationary boundary, which looks roughly draped from far
northern Wisconsin to the central Upper Peninsula. If the atmosphere
can recover later this afternoon, and its a big if, then not out of
the question that additional showers and storms can fire along the
boundary.  Will keep only a slight chance in the forecast.  Then the
attention turns to they next system moving northeast over the
central Great Plains.  Thunderstorm and severe weather potential
from this system are the main forecast concerns in the short term.

Tonight...The stationary front positioned over far northern
Wisconsin and the Upper Peninsula is not expected to move much.
Assuming the atmosphere can recover this afternoon, an isolated
shower or storm remains possible along the boundary for the first
few hours into the evening.  Otherwise, will be waiting for the
next shortwave originating out of Oklahoma to move into the region
and provide the next shower and storm threat.  Most guidance does
not have this next round of precip arriving until Friday
morning, but will leave small chances across the area late tonight.
Some elevated instability will be present, which varies wildly among
the guidance.  But since the forcing looks relatively weak, think
any severe chance is isolated at best.  The other issue is fog late
tonight.  With a more humid airmass in place and the recent
rains, patchy dense fog is again possible after midnight.

Friday...Better chances for precipitation will arrive during the
morning as shortwave energy and accompanying mid-level moisture
advection pushes into the region from the southwest.  Areas over
central and north-central WI look to be the first impacted, before
precip chances spread east.  Evaluating potential instability is
awfully difficult, not only due to the wide range depicted between
the nam and gfs, but also the possible presence of widespread low
clouds and fog, and also southeast winds off Lake Michigan slowing
down diurnal heating.  Since precip is anticipated to arrive during
the morning, think the heating curve could be significantly
impacted, which would keep a severe threat as no more than isolated.
This thinking would also maintain continuity from previous
forecasts. Highs in the mid 70s to low 80s, though some potential
for cooler highs depending on precip coverage.

.LONG TERM...Friday Night Through Thursday
Issued at 205 PM CDT Thu May 26 2016

South to southwest flow aloft will continue to lift a warm moist
air mass into the area through at least the first half of the
weekend. Challenge will be focusing best precipitation chances
with primary triggers for convection.

Progs in good agreement with a southern stream short wave over
southern and central states lifting northward into the Northern
Plains and western Great Lakes region through Saturday night
before shifting eastward during Sunday. This short wave trough
will also lift a surface to h850 low into Northern Plains region
through the same period. Progs suggests the best forcing with
upper jet couplet region along with best instability to be west
of the area. But pwats do climb into the 1.50 to 1.75 range with
the persistent south flow. Isolated storms will have the potential
of producing locally heavy rainfall Friday night through Saturday
night...but difficult to locate where heavy rainfall will occur
due to boundary locations. Height 700 mb level of 30 kts may
provide enough movement to the storms.

Upper ridge slides into the area Sunday night into Monday night
for a possible low pop or dry period. Gfs keeps some pcpn going
on monday but could be having some issues with instability
parameters. This upper ridge was developing ahead of a Northern
Rockies deep trough working into the Northern Plains. Convection
chances and a return to a southwest flow aloft likely to increase
pops again by mid week next week. Source of moisture will be from
the Central Plains region so pwats will likely not be as high
compared to early this weekend.

.AVIATION...for 18Z TAF Issuance
Issued at 1207 PM CDT Thu May 26 2016

An area of showers and storms will exit northern
Wisconsin early this afternoon.  Will still have a warm front
positioned over far northern Wisconsin or the southern Upper
Peninsula though...which could fire off a storm or two late this
afternoon into early this evening.  The probability that a storm
will impact RHI is too low to mention.  A muggy airmass will be in
place tonight...which should lead to fog formation late in the
evening and overnight.  Fog could become dense in along
the Lake Michigan shoreline and also north-central Wisconsin.  In
addition...expectations are for another round of showers and storms
to move northeast across the region late tonight and Friday
morning...which could lead to ifr/mvfr conditions continuing at some
locations through midday.  Timing is some adjustments
are likely.



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