Area Forecast Discussion
Issued by NWS Green Bay, WI

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481
FXUS63 KGRB 221745
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1245 PM CDT Tue May 22 2018

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 632 AM CDT Tue May 22 2018

Main forecast concerns center around possible low afternoon
relative humidities over the next couple of days and extent of fog
early today and again for tonight.

The 07Z MSAS surface analysis showed a broad area of weak high
pressure that stretched from the eastern Dakotas eastward into the
Great Lakes. The IR satellite imagery indicated plenty of low
clouds shrouded WI early this morning, especially over central and
southern sections of the state. Radar mosaic also picked up on a
few areas of very light rain or drizzle over the southern half of
WI.

Low clouds, patchy fog and patchy drizzle to start today as a
shortwave trough begins to exit the western Great Lakes region.
The patchy fog/drizzle should dissipate by mid-morning, but it may
take until later in the afternoon for the drier air to eat away at
the low-level moisture, especially over central WI. Have slowed
the clearing trend from the previous forecast. More clouds holding
on will mean lowering max temperatures a bit with readings now
expected to range from the lower to middle 60s near Lake MI, to
the upper 70s over far northeast WI where clearing skies to occur
first. Relative humidity levels should not be as low as Monday,
however dry conditions persist over northern WI and with green-up
only partially complete, an elevated fire weather risk continues
over the north.

The weak area of high pressure to remain situated over the Great
Lakes tonight and this should bring mostly clear to partly cloudy
skies with light winds to northeast WI. Low-level moisture to
linger over the region tonight with dew points holding in the 50s.
Anticipate at least some patchy fog to develop over most of the
forecast area later tonight. Min temperatures to be in the upper
40s near Lake MI, upper 40s to around 50 degrees north and lower
to middle 50s south.

This high pressure shifts into the eastern Great Lakes on
Wednesday and allows winds to become south-southwest by the
afternoon hours with weak WAA moving into WI. Meanwhile, an upper
ridge axis is forecast to be located over the Upper Midwest.
Stronger WAA to remain to our west, but a concern could be the
movement of a shortwave topping the ridge and perhaps sparking a
few showers/thunderstorms toward central WI late in the day. For
now, have kept everyone dry on Wednesday with max temperatures
warming to around 70 degrees along Lake MI, upper 70s to lower 80s
for most locations farther inland.

.LONG TERM...Wednesday Night Through Monday
Issued at 632 AM CDT Tue May 22 2018

The latest medium range models indicate that summer-like weather
will arrive for much of this period. Will use a blend of the
gfs/ecmwf.

Wednesday night through Thursday night...As mid-level ridging moves
into the western Great Lakes, warmer and more moist air will surge
into the region from the southwest on late Wednesday night into
Thursday.  Though elevated instability will be increasing with the
influx of moisture, MU capes of only 200-400 j/kg will spread into
central WI on late Wed night into Thu morning.  Deep layer shear is
relatively light, so although a small chance of thunderstorms will
arrive, there is not much of a threat of severe storms.  Will see
higher instability upwards of 1000 j/kg develop on Thu afternoon,
but without a trigger for convection.  Therefore cannot see much
more than an isolated storm developing.  Most convection should
remain off to our west through the period in closer proximity to
shortwave forcing over the Dakotas and Minnesota.  Highs ranging
from the upper 70s to mid 80s away from Lake Michigan on Thu.  Lows
warming into the mid 60s by Thu night.

Rest of the forecast...The best chance of showers and storms will
seem to occur on Friday.  Shortwave energy from Minnesota will
finally push into the region, and interact with diurnal instability
with BL capes upwards of 1000-2000 j/kg.  Appears up to 30 kts of
deep layer shear will be present, so its possible that an isolated
severe threat could develop on Fri afternoon if there is sufficient
shear. Additional storms also look possible on Saturday afternoon as
a secondary trough moves in from the northwest and ahead of a weak
cold front. Outside of a few showers across far northern WI on
Sunday, more quiet conditions are projected to arrive early next
week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1237 PM CDT Tue May 22 2018

Low clouds were eroding and shifting south at TAF issuance,
though MVFR ceilings are expected to persist for another hour
or two in parts of central and east central WI. Where skies had
cleared earlier, SCT-BKN cumulus clouds were redeveloping, but
ceilings were generally in the VFR category.

Patchy/areas of fog should redevelop later tonight into early
Wednesday, and send vsbys down to MVFR/IFR at most locations.

Winds are expected to remain light and variable through
tonight, then become southwest 5 to 10 knots on Wednesday.
&&

.FIRE WEATHER...
Issued at 632 AM CDT Tue May 22 2018

Dry conditions are expected across the north both today and
Wednesday. Even though dew points are forecast to be higher than
previous days, afternoon relative humidities will drop into the
lower to middle 30s over far northeast Wisconsin this afternoon
and into the upper 20s to middle 30s over northern Wisconsin
Wednesday afternoon. An increase in shower and thunderstorm
chances are forecast for the end of the week which could provide
much needed relief and ease the fire weather threat.
&&

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

$$

SHORT TERM.....AK
LONG TERM......MPC
AVIATION.......Kieckbusch
FIRE WEATHER...AK



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