Forecast Discussion for GRB NWS Office
FXUS63 KGRB 250444

Area Forecast Discussion
National Weather Service Green Bay WI
1044 PM CST Sat Feb 24 2024

Updated aviation portion for 06Z TAF issuance


- A return to well-above normal early next week with many records
  possibly in jeopardy on Tuesday.

- Next chance for widespread precipitation comes toward the middle
  of next week. Still plenty of uncertainty on strength/track,
  but a few thunderstorms may be possible with this system, mainly
  Tuesday afternoon/evening, along with some gusty winds and
  snow/mixed precip behind a strong cold front.


Issued at 236 PM CST Sat Feb 24 2024

Short Term...Tonight and Sunday

Main forecast challenges to focus mainly on precipitation chances
late tonight and again Sunday afternoon.

The 19Z MSAS surface analysis showed a ridge of high pressure that
extended from the mid-MS Valley northeast into eastern sections of
the Great Lakes. A cold front was situated from eastern Manitoba
south into the central Plains. A tightening pressure gradient
existed between the high pressure and cold front with occasional
wind gusts of 15 to 25 mph.

Generally partly cloudy skies this evening will give way to
increasing clouds overnight as the cold front and a mid-level
shortwave trough move into the western Great Lakes. Most models
keep northeast WI dry, however there are a few meso-models that
do try to generate light snow or flurries over northern WI into
Door County. Previous forecast already head this potential, so
other than perhaps starting a couple hours earlier, have not
touched this part of the forecast. Southwest winds and increasing
clouds will bring milder temperatures tonight with evening lows in
the lower to middle 20s north, middle to upper 20s south, then
slowly rising temperatures overnight as clouds thicken.

The cold front/shortwave trough move northeast WI Sunday morning,
bringing a wind shift to the west-northwest and a continued small
pop (mainly flurries) to northern WI. Some brief clearing may
occur late morning, but the approach of another shortwave within
the west-northwest flow aloft and weak WAA looks to bring more
clouds to the area in the afternoon. Just do not see enough lift
or FGEN forcing to carry pops in the afternoon and after
collaboration with DLH and MQT, have gone with sprinkles or some
late day flurries mainly north of HWY 64. Temperatures will
continue to warm on Sunday with readings to range from the lower
to middle 40s north-central WI, to around 50 degrees south
(slightly cooler along Lake MI).

Long Term...Sunday Night Through Saturday

 The main focus of the extended period continues to be a low
pressure system forecast to cross Wisconsin Tuesday and
Wednesday. Rain and a few thunderstorms look possible with the
onset of this system, with a transition to snow/mixed
precipitation expected behind a strong cold front.

Precipitation...A weak shortwave propagating across northern
Wisconsin Sunday night maybe enough to initiate a few areas of
light rain across central and east-central WI. However, with limited
moisture available most models are keeping the area dry.

With a robust WAA regime setting up Monday ahead of the
aforementioned low pressure system there is another chance for a
few areas of light rain Monday afternoon as mid-level lapse rates
steepen to around 7-7.5 C/km. Guidance has also been pointing
toward a low-level jet pushing into the area Monday
afternoon/evening which could help support a few areas of rain,
but again with limited low and mid level moisture the window and
intensity of any showers that develop would be limited.

The best chance for precipitation is progged to arrive Tuesday
with the low pressure system mentioned above, however, both global
deterministic and ensemble models are showing the strongest
forcing with system staying south and east of the CWA. Sounding
also show rather dry profiles into early Tuesday afternoon. These
factors may point toward precipitation not initiating until later
Tuesday afternoon. Current guidance does support a short window
for some elevated convective activity Tuesday afternoon/evening,
mainly in a wedge between the Fox Valley and lakeshore. Elevated
instability and surface dew points in the mid to upper 40s during
this period may be able to support a few thunderstorms, however,
that window will end quickly as a strong cold front moves through
Tuesday night into Wednesday morning. As moisture and colder air
wrap in behind the front expect precipitation to transition to a
wintry mix then mainly snow before ending late Wednesday
afternoon. An initial look at probabilistic guidances shows a
30-50% chance for over 2" of snow north of Highway 29 Wednesday
with lower probabilities further south. Gusty north to northwest
winds are also expected behind the front.

An area of high pressure is forecast to move in Thursday keeping
the rest of the extended period dry.

Temperatues...The warming trend is expected to continue through
Monday and Tuesday with record setting high temperatures
possible. Wednesday is forecast to be much colder behind the
front with highs dropping 20-30 degrees from the previous day.
However, this cold spell looks rather short lived as winds become
southerly by Thursday afternoon and highs return to well above
normal by Friday.


.AVIATION...for 06Z TAF Issuance
Issued at 1044 PM CST Sat Feb 24 2024

Mid and high clouds will stream in across the TAF sites at times
during the TAF period, with SCT to BKN CIGs expected. A weak cold
front and mid-level shortwave will track through late
tonight/early Sunday morning, which could bring some flurries to
far northern Wisconsin. Despite the frontal passage, VFR
conditions should persist. Once the front passes through the area,
VFR conditions will continue through the rest of the TAF period
as the mid and high clouds scatter out.

South-southwest surface winds have eased across some of the area,
with some gusts of 15-20 kts at times at RHI/GRB. Surface winds
should dissipate late tonight across all areas. KGRB VWP and model
soundings indicate winds just above the surface are gusting to 35
to 45 kts, with winds aloft decreasing from northwest to
southeast overnight into Sunday morning. The cold front is
expected to reach central WI at sunrise and eastern WI mid to late
morning with a wind shift to the west-northwest.






NWS GRB Office Area Forecast Discussion