Area Forecast Discussion
Issued by NWS Green Bay, WI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS63 KGRB 211719

Area Forecast Discussion
National Weather Service Green Bay WI
1119 AM CST Wed Feb 21 2018

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 336 AM CST Wed Feb 21 2018

Low clouds will exit eastern Wisconsin before daybreak as drier
air arrives from the west. Lake effect clouds straddling the
Michigan border should also dissipate or move north as winds back
more to the west. High clouds are very high (above 300 mb or so)
and will not keep skies from being mostly sunny for most of today.
Cold advection will make for a day about 5 degrees below normal.

SKies will start clear this evening, but middle and high clouds
will increase later as warm advection arrives ahead of shortwave
energy lifting northeast from the central Plains. It should get
quite cold in the far north where there is still decent snow cover
and skies will be clear for much of the night. Lows should fall
below zero in the far north but hover in the single numbers and
teens elsewhere.

Clouds will continue to increase Thursday as warm advection
continues. Light snow is possible in the far southwest portion of
the forecast area but little or no accumulation is expected until
Thursday night. Highs will be near normal.

.LONG TERM...Thursday Night Through Tuesday
Issued at 336 AM CST Wed Feb 21 2018

Expect above normal temperatures to prevail throughout this part
of the forecast as flow aloft remains mainly out of the southwest
before becoming more zonal early next week.

Differences in the 00Z model runs started to show up early in the
forecast, so confidence is only medium with the first system and
low with the weekend system. Precipitation type issues are
evident with the system impacting the area Thursday night into
Friday morning. The model blend started out with snow and then a
switch to more freezing rain or a mix later in the night. Looking
at the 00Z NAM time/height sections and soundings it looks like
more freezing rain, or sleet changing to freezing rain, in the Fox
Valley and Lakeshore areas with sleet changing to snow in parts
of central Wisconsin. The 00Z GFS showed mainly snow.

A change to rain should occur in the southeast half of the
forecast area Friday morning as temperatures warm, but freezing
rain and/or snow is still expected for the rest of the area. Snow
totals Thursday night through Friday morning should range from
less than an inch from the Fox Valley east to Lake Michigan, to 2
to 3 inches in far north central Wisconsin. The rest of the area
should see 1 to 2 inches of accumulation. Some ice accumulation
may occur but totals should be less than 0.1 inch.

The GFS continued to show a much stronger surface low moving into
the region than the 20/00Z ECMWF or 21/00Z Canadian. The track was
also farther north than the others. Stuck with the blend due to
the significant model differences. Looks like temperatures will
warm up enough on Saturday to switch any snow to rain or a mix of
rain and snow before precipitation changes back to snow Saturday
night before it exits the area. Mainly dry weather is then
expected into early next week, though there may still be some
lake effect snow showers in north central Wisconsin on Sunday.

.AVIATION...for 18Z TAF Issuance
Issued at 1118 AM CST Wed Feb 21 2018

VFR flying conditions should prevail through the TAF period. Some
high clouds will stream across the area today and tonight, with
mid-level clouds returning Thursday morning. Conditions will
likely deteriorate later Thursday evening as a quick moving
system brings in snow and mixed precipitation.



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