Area Forecast Discussion
Issued by NWS Green Bay, WI

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163
FXUS63 KGRB 141724
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1124 AM CST Tue Feb 14 2017

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 330 AM CST Tue Feb 14 2017

Quiet mid-winter weather expected, with generally above normal
temperatures into next week.

The upper flow across central and eastern North America will
remain split during the period as a positive upper height anomaly
shifts from western Canada into north-central Canada. The forecast
area will remain primarily under the influence of the northern
branch of the split, at least until the very end of the forecast
period. This will result in little precipitation through the
weekend. The upper flow across central Canada is currently
northwesterly due to the positive anomaly/ridge out west. After
another mild day today, a couple cooler days are expected as the
forecast area gets grazed by the southwest flank of a cold air
mass driven southeast by the northwest upper flow. Once that
air mass moves through, readings should warm back to
significantly above normal levels for the rest of the period.
&&

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 330 AM CST Tue Feb 14 2017

A westerly flow of air is expected across the area today as a
cyclone shifts east across Ontario. Cold advection aloft will
steepen lapse rates and result in gusty winds, but the incoming
colder air mass is well to the northwest so temperatures should be
able to warm to above normal again today. Some snow or mixed rain
and snow showers are possible, especially this afternoon.

Flurries are possible tonight as the colder air becomes
established across the area. Trajectories will be favorable for
some lake-effect in the Lake Superior snowbelt, but fairly strong
large scale subsidence is expected to limit accumulations. The
snow showers and flurries will probably linger into early
Wednesday in the snowbelt.

For temperatures, started with a broad-based blend of guidance
products and then adjusted toward the ECMWF and it/s bias-
corrected and MOS derivative products, which have verified well
lately.

.LONG TERM...Wednesday Night Through Monday
Issued at 330 AM CST Tue Feb 14 2017

The medium range models indicate that split flow will encompass
North America for much of the next week, with above normal 500mb
heights predominately from Friday through early next week.  As
troughing moves across the west, expect quiet and above normal
temperatures for much of the aforementioned time.  The ecmwf and gfs
agree well through the weekend, and then differ in regards to how
quickly they bring in troughing from the west.  Will give a slight
lean to the gfs for later periods.

Wednesday night through Thursday night...Surface ridge axis will be
shifting east across the state on Wednesday night.  Warm advection
will be occurring aloft as mid-level heights rebound, and a band of
6-10 kft clouds should spread east in this warm advection zone.  The
gfs is more ambitious with the degree of saturation within this warm
advection zone compared to other guidance, and consequently spits
out light precip on Thursday.  With high pressure at the surface,
think much of the lift will go towards saturating the atmosphere,
with any precip drying up as it falls.  Will therefore keep the area
dry.  Will still have plenty of mid and high clouds above 12 kft
around on Thursday night.  As winds shift to the south, should see
warmer low temps in the 20s.

Rest of the forecast...Mild and dry air originating from downsloping
off the Rockies will move into the region on Friday and hang around
through Monday.  A decaying front/trough is projected to move across
the region on Saturday, but the airmass looks too dry for any chance
of precip.  As the western conus trough finally moves into the
center of the continent, the next chance of precip will occur in the
Monday-Tuesday time period, with precip being mostly rain.  Temps
should fall back some behind the system by the middle of next week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1124 AM CST Tue Feb 14 2017

The passage of a cold front and mid-level shortwave trough will
bring a few snow showers or a rain/snow shower mix to the area
this afternoon. Colder air will then sweep into the area for
tonight with perhaps a lake effect snow shower or a few flurries
across the RHI TAF site. The remainder of the region is forecast
to be dry tonight into Wednesday. Mainly VFR conditions are
expected, however as the colder air sets up over WI, cloud bases
may drop into the MVFR range late tonight into Wednesday morning
across northern and central WI.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MPC
AVIATION.......AK



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