Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 131941
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
241 PM CDT Wed Mar 13 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Precipitation chances late tonight over parts of central and
  east-central Wisconsin, then spreads across the rest of central
  and east-central Wisconsin on Thursday. Precipitation may mix
  with some wet snow Thursday evening before ending. Best chances
  for precipitation to be across central and east-central
  Wisconsin.

- Temperatures begin downward trend Thursday while still
  remaining around 5 to 10 degrees above average through Saturday.
  More seasonal temperatures expected Sunday and Monday.

- A system dropping south out of Canada will bring several chances
  for wintry precip starting this weekend.

&&

.DISCUSSION...
Issued at 241 PM CDT Wed Mar 13 2024

Short Term...Tonight and Thursday

Main forecast challenge will be the northern extent of rain on
Thursday as low pressure heads toward the Great Lakes, but will
battle dry air from Canadian high pressure.

The 18Z MSAS surface analysis showed high pressure over southern
Manitoba with several areas of low pressure situated over central
SD, southern IA and the strongest one over the OK panhandle. A
warm front extended from the OK low east-northeast into the mid-MS
Valley. Visible satellite imagery indicated plenty of middle and
high clouds streaming over the region.

The main area of low pressure is forecast to lift northeast from
the southern Plains into the mid-MS Valley tonight with the warm
front to extend toward southern sections of the Great Lakes by
daybreak. An increase in moisture transport via a 40-50 southwest
low-level jet, coupled with increasing isentropic lift and mid-
level FGEN will bring precipitation into southern WI, but
questions remain as to how far north this precipitation will
reach. Two factors come into play. First, models show a convective
line develop in the warm sector which could slow the northward
movement of the warm front. Second, the Canadian high pressure
will continue to funnel dry air into northeast WI, thus slowing
the advance in moisture. Therefore, have removed any evening pops
and only mention a small chance pop for our southernmost counties
toward sunrise. Min temperatures tonight to range from around 30
degrees far north, middle to upper 30s south.

The low pressure is expected to move northeast toward southern
sections of the Great Lakes on Thursday, but lingering debate as
to how far north any precipitation can get. The meso-models favor
a northward cut-off from roughly Marshfield to Marinette. The
larger models suggest a more northward extent with precipitation
reaching up to Hwy 8. Prefer to leave most of northern WI dry with
highest pops over east-central WI. Temperatures to be held down by
clouds and a gusty northeast wind. Look for readings to only be in
the lower 40s near Lake MI, middle to upper 40s inland.

Long Term...Thursday Night Through Wednesday

Focus for the extended continues to be a cooler pattern shift
heading into next week. As Thursday`s system departs to the east,
attention then shifts to a Canadian low bringing several chances
for wintry precip to the forecast area this weekend through mid-
week. Temperatures will begin a downward trend during this time,
cooling to around 2 to 4 degrees below average by Monday.

Thursday night precip... Precip will gradually exit the forecast
area to the east through Thursday evening, leaving clearing skies
and drier conditions in its wake. Diurnal cooling Friday morning
may allow for a brief window where some wet snow could mix in
across east-central Wisconsin, although split flow looks to keep
most of the colder air to the north. Short-range model guidance
has also been trending down QPF amounts due to dry air intrusion
on the back edge of the surface low, therefore no significant
impacts or accumulations are expected. Likewise, ground and
boundary layer temperatures look to be too warm for any wet snow to
stick. Overall, leaning toward rain as dominant precip type.

Precip chances through mid-week... Several chances for wintry
precip arrive to the region beginning this weekend as multiple
shortwave impulses across Ontario and Manitoba pivot through the
upper Midwest. This weekend`s system is likely to come in two
phases as strong jet energy and confluent flow place a deepening
surface low with two trailing cold fronts just north of Lake
Superior. The first wave of light snow is expected to affect
mainly northern Wisconsin on Saturday as the first cold front
sweeps to the east. Gusty northwest winds will be possible behind
the front. More widespread snow chances are then possible on
Sunday as the secondary cold front drops south across Wisconsin
Sunday evening. There is a strong signal for lake enhancement
across the Northwoods Sunday into Monday as a cold air advection
regime sets up and winds veer to north/northwesterly. Lake surface
to 850 mb delta Ts will thus be nudged into the favorable 14 to
18 degree range during this time. Although exact snowfall amounts
are still uncertain, probabilistic guidance currently shows a 40
to 60% chance of exceeding one inch of snow in Vilas county with a
20 to 40% chance of exceeding two inches by Sunday evening. With
post- frontal temperatures cooling to the mid 20s across the
north, chances for snow overall look to be higher this time
around.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1234 PM CDT Wed Mar 13 2024

For the majority of northeast WI, VFR conditions are expected to
prevail through the TAF period. The exception will be east-central
WI as an area of low pressure lifts northeast toward southern
sections of the Great Lakes and brings a band of light rain into
the area. Cigs/vsbys may drop into the MVFR category, potentially
impacting the GRB, ATW and MTW TAF sites. High pressure over
southern Canada will feed dry air into WI, thus limiting how far
north this band of rain will reach. This system appears to exit
the region by Thursday evening.

Winds are forecast to be light into the evening, but be on the
increase later tonight through Thursday from the northeast. Gusts
could reach 20 to 30 knots with the strongest gusts over east-
central WI.

&&

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

&&

$$

DISCUSSION.....Kallas/Goodin
AVIATION.......Kallas


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