Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 210937
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
337 AM CST Thu Feb 21 2019

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 326 AM CST Thu Feb 21 2019

A brief break in the active weather through tomorrow, then a
major winter storm will bring widespread precipitation and strong
winds to the area this weekend.

The large scale pattern was dominated by high upper heights over
the northeast Pacific, which was resulting in splitting of the
flow downstream over NOAM. The southern stream was highly
amplified and dominant, with a trough over the Desert Southwest
and ridging over the southeast states. Subtle but important
changes will occur next week as the positive anomaly over the
northeast Pacific shifts NNE into Alaska and strengthens. Though
the developing upper anticyclone will be undercut over the eastern
Pacific, the downstream flow across NOAM is likely to merge back
together, with the negative anomaly from the Southwest U.S. upper
trough reforming in the Lake Winnipeg region late in the forecast
period.

The large scale evolution will result in a transition from the
current active southwest upper flow regime to a much colder
northwest flow pattern by the end of next week. Temperatures will
remain AOA seasonal normals through the weekend, then drop below
normal next week. Well below normal conditions are likely by late
in the week. While it remains in place, energy ejecting out of
the southwestern U.S. trough will bring several opportunities for
precipitation, resulting in above normal amounts for the period.
The most significant precipitation episode will be with a rapidly
deepening cyclone expected to cross the region during the weekend.
&&

.SHORT TERM...Today...Tonight...and Friday
Issued at 326 AM CST Thu Feb 21 2019

A relative lull in the active weather will occur during the
short-term part of the forecast. Snow showers and flurries will
linger for a time this morning (mainly across the north) before
ending. Otherwise, the main forecast issue will be cloud trends.
The specifics of those are somewhat muddled. For today at least,
the main issue is low clouds and those will be more plentiful
across the north, with more sun in the south. By tonight and
Friday, patches of middle and high clouds will be streaming across
at times as well. Trended toward mid-range skycon during those
periods.

Colder air was advecting into the area early this morning, on the
southern flank of the departing cyclone. Temperatures will
continue to fall until mid-morning, but should recover some this
afternoon. Temperatures tonight will depend on clouds, and thus
the low temperature forecast inherits the uncertainty of the
specifics of the skycon forecast. With a fresh snow cover and
relatively light winds, readings will likely drop sharply during
any periods of clear/mostly clear skies. But there is great
uncertainty in when/where those conditions will occur. Staked out
a middle ground with the low temperature forecast with the
expectation of at least some breaks in the clouds occurring.
Readings across the north could easily be 10 or more F degrees
colder if any prolonged clear periods occur.

Stayed close to a blend of top performing guidance products for
high temperatures on Friday.

.LONG TERM...Friday Night Through Wednesday
Issued at 326 AM CST Thu Feb 21 2019

Southwest flow at 500mb is expected at the start of the period,
then should transition to a northwest flow aloft by the middle of
next and continue into the weekend of March 2-3. Temperatures
are expected to be at or above normal into the weekend, then will
run below normal next week. Latest ECMWF/GFS indicating 850mb
temperatures of -20C to -30C, by the first few days of March, thus
it appears spring will take awhile to get here.

For Friday night, 850mb warm advection noted on the models which
should help produce precipitation late Friday night into Saturday
morning. Latest trends indicated a slower arrival of the
precipitation, not reaching until east-central Wisconsin until
after 12z Saturday. Kept areas near the lakeshore dry Friday
night, while chances of light snow are expected north and
west of the Fox Valley. There may be a little freezing rain
towards 12z across central Wisconsin. The chances of light
snow or freezing rain will continue Saturday morning, especially
north and west of the Fox Valley until pavement/air temperatures
rise above freezing. The 850mb warm advection shifts east of the
state Saturday afternoon. There may be a lull or break in the
precipitation until late in the day when the system from the
southwest approaches the area. Precipitation should be on the
increase again late in the day across central Wisconsin, then
overspread the remainder of the region Saturday evening.

Models in good agreement in bringing strong storm across the
Badger state Saturday night. Although in good agreement, there
are still differences in the storm track and how much warm air
wraps up into northeast Wisconsin. The GFS was the furthest west
with the 850mb 0C isotherm, while the Canadian/ECMWF had the
850mb 0C isotherm straddling Interstate 41 across the Fox Valley.
The subtle difference will have a major impact when precipitation
changes over to snow across the Fox Valley. Also, the heavier
band of precipitation is expected to move across the area later
Saturday evening into early Sunday morning, which could change the
rain or wintry mix over to snow sooner than expected. Confidence
is growing for a band of heavy snow of 6+ inches north and west of
the Fox Valley. Still some uncertainty if this band of heavy snow
would make it as far north as Vilas County. Still plenty of time
to sort out the details. As the system moves east of the area,
bufkit soundings indicating wind gusts over 40 mph are possible
across northeast and east-central Wisconsin late Saturday night
into Sunday. The combination of falling snow and strong winds
will make for hazardous conditions for travelers to continue
into Sunday afternoon.

For Monday, high pressure will move across the area bringing
tranquil conditions to the area. Next system is expected to
bring more snow to the area Monday night into Tuesday night. Low
confidence at this time with the storm track and snow amounts. It
will be cold next week with highs mainly in the single digits and
teens above zero.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 326 AM CST Thu Feb 21 2019

Scattered snow showers and flurries will taper off this morning,
then aviation conditions will primarily depend on the behavior of
low clouds during the remainder of the next 24 hours. There may
not be any clear-cut cloud trends, with areas of clouds likely
moving through the area. The clouds will be most persistent in the
north, with southern portions of the area more likely to see some
mostly clear periods.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Eckberg
AVIATION.......Skowronski


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