Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 161755

Area Forecast Discussion
National Weather Service Green Bay WI
1155 AM CST Thu Feb 16 2017

Updated aviation portion for 18Z TAF issuance

Issued at 306 AM CST Thu Feb 16 2017

Quiet mid-winter weather expected. Seasonable temperatures today,
then much above normal through at least the middle of next week.

A positive upper height anomaly will shift east to the 80W-90W
the next couple days, then remain in place for the remainder of
the forecast period. That will result in split upper flow across
central and eastern North America. The forecast area will be
dominated by the northern branch of the split. No precipitation is
expected through the weekend. The only opportunity for
precipitation appears to be early next week when some moisture
from the southern stream may get pulled into the region ahead of
an approaching northern stream shortwave. A lingering polar air
mass will result in seasonable temperatures today. After that, the
forecast area will be dominated by mild air masses from the
Pacific that have downsloped the Rockies to get here. The result
will be a prolonged period of much above normal temperatures.

.SHORT TERM...Today...Tonight...and Friday
Issued at 306 AM CST Thu Feb 16 2017

Very quiet for the middle of February. Cloud trends are a little
tricky as cloud decks at various levels will continue to stream
across the area as a strong baroclinic zone slowly shifts east
through the region. A strengthening inversion could also result in
some stratus formation overnight, especially across the north.

Verification stats continue to show guidance running well on the
low side for temperatures. The ECMWF and its derivative guidance
products have been the warmest and generally been verifying best,
so adjusted temperatures toward a blend of those products. One
thing that could mess up the warmer temperatures on Friday is a
stratus deck. A strengthening inversion will be developing across
the area, which is favorable for stratus formation. On the other
hand, low-levels look rather dry and there isn`t much snowpack to
melt to the south of us anymore. Best guess now is that widespread
stratus won`t form. But forecasting stratus is tricky and this
will need to be watched closely.

.LONG TERM...Friday Night Through Wednesday
Issued at 306 AM CST Thu Feb 16 2017

No significant changes to the expected upper air pattern over the
next week.  Still primarily looking at split flow with above normal
mid-level heights continuing through the middle of next week before
a piece of the western conus trough arrives.  Have a slight
preference for the ecmwf.

Friday night through Sunday night...Quiet and mild during this
period thanks to a Pacific airmass in control.  Will see a moisture
starved trough work east across the area on Friday night, shifting
winds from the south to the west.  Winds should be a bit more breezy
behind this trough on Saturday.  Otherwise, should see mostly clear
to partly cloudy conditions on Saturday and Sunday with areas of mid
and high clouds overhead.  Clouds should thicken on Sunday night,
thanks to southerly winds bringing gulf moisture northward.  Precip
looks to hold off until Monday.

Rest of the forecast...A shortwave trough will push a cold front
across the region late Monday afternoon through early Tuesday,
bringing the next chance for widespread precip.  Temps look too warm
for any frozen precip along the front and should remain mild behind
the front since there wont be any real push of cold air. Still
looking at the possibility of colder air arriving behind a more
potent front Wednesday night into Thursday without much in the way
of upper support for precip.  There is potential for a large cyclone
to move into the center of the country by the end of next week.

.AVIATION...for 18Z TAF Issuance
Issued at 1155 AM CST Thu Feb 16 2017

VFR conditions will continue into the early evening hours as mid
clouds continue to push across the area. Then, some uncertainty
enters the forecast tonight as a strengthening inversion limits
mixing, snow on the ground (mainly over central and northern WI),
and a weak SE upslope wind coming off of Lake Michigan should
lead to the development of a low stratus cloud deck (low IFR or
LIFR). Negatives will be the dry weather over the past several
days and dewpoints only in the lower 20s. The MET shows the
stratus forming for AUW/CWA/RHI and the MAV now shows some in RHI.
So confidence is increasing there will be stratus tonight. In
these cases, it is usually all or nothing with the stratus. So it
would either be overcast or clear (with possibly some fog). That
will likely be the case tonight, although there will be some high
clouds still over the region, especially over eastern WI.
Confidence is high enough at this point to add a broken deck of
low clouds to AUW/CWA and RHI late tonight into Friday morning,
but will keep them out of GRB/ATW/MTW. Moisture and pollutants
trapped under the inversion will also result in some MVFR
(possibly IFR) fog development overnight into early Friday, with
the lowest vsbys over central and north central WI. The low clouds
and fog look to mix out during the morning hours; however, model
soundings show this might be tough to do over north central WI.

The threat for LLWS looks minimal as 2000 ft winds remain at or
below 20 knots through early Friday afternoon.



SHORT TERM.....Skowronski
AVIATION.......Bersch is the U.S. government's official web portal to all federal, state and local government web resources and services.