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
000
FXUS63 KGRB 251139
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
639 AM CDT Mon Mar 25 2024

New information added to update section.

.UPDATE...
Issued at 639 AM CDT Mon Mar 25 2024

Will end the Winter Storm Warning across north-central Wisconsin.
Visibilities are increasing across Vilas county with the arrival
of the low level dry air and therefore appears that the steady,
heavy snow has ended. A few upstream obs are showing indications
of mixed precip, which could indicate freezing rain. Reports so
far have been isolated and any freezing rain would be falling on
fresh snow. Therefore think impacts will be minimal if freezing
rain occurs.

&&

.KEY MESSAGES...

 - Snow will be ending early this morning over north-central
   Wisconsin. The greatest impacts to the morning commute will
   occur over central, north-central, and far northeast Wisconsin
   where 6 to 12 inches of snow has likely fallen since yesterday
   afternoon.

 - Mainly rain is expected from late morning through Tuesday,
   before changing over back to snow late Tuesday over north-
   central Wisconsin. Minor snow accumulations are possible, but
   with little to no impacts.

 - A few thunderstorms are possible over northeast Wisconsin on
   Tuesday. If thunderstorms develop, there is low potential for
   the storms to produce gusty winds to 40 mph.

 - SE winds increase late tonight through midday Tuesday. There is
   a 60-80 percent chance of wind gusts exceeding 40 mph over
   northeast WI toward the lakeshore.

&&

.DISCUSSION...
Issued at 246 AM CDT Mon Mar 25 2024

Short Term...Today...Tonight...and Tuesday

The latest RAP analysis and satellite/radar imagery show a strong
Rocky Mountain cyclone centered over western Kansas early this
morning. Ahead of this cyclone, shortwave impulses over eastern
Nebraska and Iowa are helping generate a 40-45 low level jet
across Wisconsin. Strong warm advection within this low level jet
in combination with mid-level frontogenesis and the right rear
quad of a 110 kt jet streak is supporting a potent band of precip
with snowfall rates in excess of 1 inch per hour stretching across
central to northeast Wisconsin. This band is lifting northward,
but snowfall reports are indicating snowfall amounts are above the
current forecast. Will therefore increase snow amounts across far
northern Wisconsin through 7 am.

On the other hand, dry air is rapidly lifting northwest as dry air
is entrained from the east coast high pressure system. This dry
air is creating a sharp cutoff to the precipitation, which will
continue to rapidly lift northeast and push the band into far
north central Wisconsin by 7 am. As a result, end times to the
current headlines look good, but will likely end the warning on
the southern flanks prior to 7 am. An additional 2 to 4 inches is
possible over far north- central WI by then.

Besides the beefy accumulations, forecast concerns revolve precip
trends, amounts, and potential snow accumulations on the backside
of the strong cyclone due to pass across the region through
Tuesday.

Today and Tonight...Low pressure will slowly move northeast across
the central Plains today and into the northern Mississippi Valley
tonight. Deep layer south flow with embedded shortwaves within
this flow will send waves of precipitation across the region.

The first wave will move into central Wisconsin later this morning
before spreading across the rest of the forecast area during the
afternoon. Then warm conveyor belt will target eastern Wisconsin
tonight with persistent showers.

Current surface temperatures indicate that the warming trend in
our latest forecast is on the slower side. While CAMS indicate
precip amounts will be little to none, thermal profiles suggest a
brief window for freezing rain is possible, mainly in the 7-10 am
hour across north-central WI. This would suggest that the
freezing rain threat is low, and will lower amounts in this
forecast.

Even with the surface low moving into the northern Mississippi
Valley tonight, forecast soundings indicate little to no
instability works into northern Wisconsin. Therefore, the chance
of thunderstorms is low through tonight.

However, southeast winds are expected to increase late tonight
into Tuesday morning. With decent pressure falls occurring,
probabilities have increased (50-70%) for wind gusts of 35 to 45
mph over northeast Wisconsin after midnight.

Tuesday...Low pressure will travel across northwest Wisconsin with
a cold frontal passage of mid-morning. Moderate to strong forcing
will continue in the morning with elevated instability of 100-200
j/kg projected to spread across northeast Wisconsin. Will add
thunder to the forecast. Although some timing differences are
apparent in the models, the possibility of some convection with
strong winds in excess of 35-40 kts aloft and unstable conditions
in the low level suggest gusty winds will be possible should
showers/storms develop along the cold front. Will add to the HWO.

Lastly, precip will likely start or change over to snow
completely over north-central Wisconsin on Tuesday afternoon.
However, the higher sun angle and temps in the 30s will make any
accumulations difficult prior to 7 pm.

Long Term...Tuesday Night Through Sunday

Sub 995mb low pressure will be lifting north across Lake Superior
Tuesday evening and farther over northern Ontario between Lake
Superior and James Bay through Wednesday. Rain changes to snow
quickly from west to east on Tuesday evening as colder air but
deeper moisture pulling away with the shortwave/sfc low point to
minimal snow accumulations. Even the top end of ensemble guidance
is an inch or less for accums Tuesday night. Temps appear to only
gradually fall below freezing and there is still some gusty winds
so though there may be some slippery spots on untreated surfaces
later Tuesday night, impacts should remain minor.

Not much change to sfc pattern into Thursday as low only slowly
lifts north across Hudson Bay while ridge persists from western
Canada to the northern Plains, upper Mississippi River Valley and
western Ohio Valley. Dry weather with gradual warming trend will
prevail Wednesday through most of Friday.

As flow turns more zonal by end of the week, guidance still likes
idea of weak trough and warm air advection yielding swath of
precipitation later Friday through Saturday from the upper
Mississippi River Valley to the western Great Lakes. Thermal
gradient maximizes across our area so forecast carries chance of
rain/snow at this time with greatest probabilities of only snow
staying over our northern zones. Given the east winds coming out
of the departing high holding down sfc temps while warm air works
in aloft, could see potential for wintry mix at times, but not
enough confidence to include mention of that right now. Next
chance of precipitation moves back in late weekend and again this
could have more ptype issues as well.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 557 AM CDT Mon Mar 25 2024

Poor flying conditions over the next 24 hours as a strong cyclone
slowly moves towards the region.

Snow over far northern Wisconsin will diminish by the start of the
taf period as dry air continues to surge in from the southeast.
Then, rain showers and IFR/LIFR conditions will return into the
area from west to east this afternoon and continue through
tonight, as moisture streams northward ahead of a strong storm
system over the Central Plains.

Low level wind shear is expected for much of the period with east
southeast winds around 15 knots at the surface and south winds of
40 to 50 knots at 2000 feet.

After midnight, southeast winds are expected to gust in excess of
30 kts from the Fox Valley to the Lakeshore, impacting terminals
at ATW/GRB/MTW.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE.........MPC
DISCUSSION.....MPC/JLA
AVIATION.......MPC


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