Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 121908
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
208 PM CDT Tue Mar 12 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Elevated fire weather conditions will continue through early
  this evening due to low humidities and gusty west winds.

- Precipitation chances arrive late Wednesday and last through
  Friday morning. Precip likely to start as rain, then transition
  to a mix of rain and snow or wet snow Thursday night. Overall
  confidence is low.

- Temperatures begin a slight downward trend Thursday while still
  remaining around 5 to 10 degrees above average.

&&

.DISCUSSION...
Issued at 207 PM CDT Tue Mar 12 2024

Short Term...Tonight and Wednesday

The latest RAP analysis and satellite/radar imagery show shortwave
impulses across northern Minnesota and northwest Ontario pushing a
cold front across central Wisconsin early this afternoon. Because
of 0-1km dewpoint depressions in excess of 15C, this cold front
remains expected to pass through dry for the rest of today. Breezy
southwest winds are bringing temperatures into the lower to
middle 60s at most locations this afternoon, with a possible
record high at one or two locations. A few readings have reached
70 degrees early this afternoon. With temperatures this high and
drying fine fuels, humidity levels have fallen to around 25
percent over the sandy soil areas of north- central WI. With an
otherwise quiet weather through Wednesday, forecast concerns
mainly revolve around elevated fire weather conditions.

Sky Cover and Temperatures: The shortwaves will bring scattered
high clouds to the region for the rest of the afternoon into this
evening, before departing for a time tonight. Then more clouds are
expected to arrive from the west late overnight and thicken from
west to east on Wednesday afternoon. Winds will shift to the
northwest tonight and to the north on Wednesday and gradually
usher in a cooler airmass to the region. Temps on Wednesday will
be cooler, and mainly range from the middle 50s near the U.P.
border to the middle 60s over central WI.

Long Term...Wednesday Night Through Tuesday

A cooler, more active pattern shift is expected for the extended
as two systems bring precip chances to the forecast area. The
first round of precip looks to arrive Wednesday night into
Thursday morning. Precip type with this system will be tricky,
although temperature profiles are trending toward mainly rain with
the potential for some wet snow to mix in across east-central. A
weekend system will then bring a second round of rain/snow to the
forecast area, although there is still uncertainty in timing and
location of precip.

Wednesday night through Friday precip chances... As a closed
upper- level low sits and spins across the Four Corners region
Thursday and Friday, a piece of shortwave energy will eject up
from New Mexico into central Wisconsin. This shortwave will drag a
surface low and attendant warm front from the southern Plains
into northern Illinois, generating a baroclinic zone and
concurrent FGEN band across central Wisconsin Thursday evening.
Additional synoptic support will be provided by favorable
placement under the right entrance region of an upper- level jet.
Precip types/amounts will be a hindrance to the forecast given
model discrepancy about thermal profiles, specifically boundary
layer temperatures. The current NAM solution is running much
cooler than other short to medium-range models (RAP-ext and HRRR-
ext), and is hence more aggressive with snowfall amounts and
timing of rain/snow transition. The influence of Hudson Bay high
pressure and dry air over Ontario introduces additional
uncertainty about precip type and location given backing
north/northwesterly winds Friday morning, suggesting that there
may be a sharp cutoff in precip to the north. Precip type is
expected to start as mainly rain through Thursday afternoon before
a window of cooler temperatures arrives Friday morning, signaling
the potential for some wet snow to mix in across central and
east-central Wisconsin. Opted to leave NBM snow amounts given
warm ground/boundary layer temperatures paired with low likelihood
of precip rates high enough to accumulate snow at these
temperatures. Likewise decided to leave out freezing rain.
Additionally, the GFS picks up on a near- isothermal layer at 0
deg/C to around 850 mb, suggesting that any minor fluctuation of a
degree or two may affect precip type. Overall, thinking rain will
be the dominant precip type, although confidence is low. Most
convective elements will be confined to our south near the warm
front where highest MUCAPE and lapse rates are; have thus have
decided to leave out mention of thunder for the time being.

Rest of the extended... Next chances for precip enter the
forecast area Saturday morning as a more robust shortwave is
progged to drop south across the US/Canada border. There is still
model discrepancy about timing and location of precip this far
out, although cooler temperatures suggest higher potential for
snow to mix in this time around. Otherwise, temperatures begin a
slight downward trend starting Thursday while still remaining
around 5 to 10 degrees above average.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1220 PM CDT Tue Mar 12 2024

VFR conditions are expected through the TAF period at the
terminals. Scattered to broken cloud cover will be relatively thin
above 15 kft.

A dry cold front will move across northeast Wisconsin this
afternoon. Gusty southwest winds from 15 to 25 kts will veer to
the west after the cold front`s passage. Winds will diminish this
evening and remain under 10 kts on Wednesday.

&&

.FIRE WEATHER...
Issued at 207 PM CDT Tue Mar 12 2024

Elevated fire weather conditions will continue into early this
evening until winds subside and humidity increases with nocturnal
cooling setting in. Cooler temperatures and lighter sustained
winds under 10 kts will alleviate fire weather concerns some on
Wednesday, but afternoon minimum humidities will again fall to the
25 to 30 pct range west of the Fox Valley and Bayshore areas.
Fine fuels continue to dry out as evident by increasing FFMC
values to around 90. Will continue to highlight fire weather
conditions in the HWO.

&&

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

&&

$$

DISCUSSION.....MPC/Goodin
AVIATION.......MPC
FIRE WEATHER...MPC


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