873
FXUS63 KGRB 091852
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
152 PM CDT Sun Mar 9 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Temperatures will continue to run well above average through the
  upcoming week. Several record highs are possible on Monday.

- The warm temperatures along with melting snow will elevate
  flows on area rivers and streams and lead to an increased risk
  for ice jams and minor flooding. The potential for widespread
  rain late this week will add to the risk.

- A strong system arriving later in the week will bring our next
  chances for widespread rainfall and a risk of thunderstorms.

&&

.DISCUSSION...
Issued at 151 PM CDT Sun Mar 9 2025

Short Term...Tonight through Monday Night

The latest RAP analysis and satellite radar imagery show low
pressure moving east across northern Ontario early this afternoon.
A relatively tight pressure gradient between this low and high
pressure over the mid-Mississippi Valley is leading to gusty winds
across northern Wisconsin. Gusts from 25 to 30 mph have been
observed early this afternoon as temps approach or surpass 50
degrees at most locations. With the northern jet positioned north
of the Great Lakes, focus in this part of the forecast generally
revolves around temps and gusty winds.

Temperatures: After a mild afternoon, temperatures are expected to
fall into the middle 20s to lower 30s tonight. Temperatures this
cold are below the afternoon cross-over temps, which will lead to
favorable conditions for fog. Guidance is pointing to lower
visibilities over parts of north-central to far northeast WI late
tonight, where snow melt will aid in augmenting low level
moisture. Patchy fog will be possible, so will continue to
highlight in the HWO.

Unseasonably warm temperatures remain forecast for Monday.
Downsloped air off the Rockies will surge into the state via
breezy southwest winds. 925mb temperatures are forecast to rise
into the 10C to 13C range which would put highs in the middle to
upper 60s. Probabilities of 925 temps greater than 12C are in
excess of 80% over central and east-central WI (highs near 66
degrees). With gusty winds in the boundary layer and mixing in
excess of 900mb, think high temps on the high end of NBM guidance
is warranted so raised them a couple degrees. Several high temp
records therefore remain possible on Monday afternoon.

A cold front will then moved through the region on Monday night,
which will result in gusty winds and much colder temps arriving
after midnight.

Gusty winds: Winds gusting from 25 to 35 mph will diminish at
sunset. A Small Craft Advisory has been issued for Lake Michigan
this afternoon. Then gusty southwest winds from 20 to 30 mph are
likely on Monday afternoon. Relative humidities are forecast to
fall to around 30% in the afternoon over central WI, but fine
fuels are still moist so concerns about fire weather are minimal
for the time being.

Long Term...Tuesday Through Sunday

Split flow will continue to be the predominate pattern across North
America during the upcoming week.  While the northern stream will
generally be north of the region, a potent southern stream cyclone
will provide the greatest impacts over the next week.

Shortwave energy moving across the Lake Superior region will push a
cold front across the region late on Monday night or Tuesday
morning.  A few light snow showers will be possible over far
northern WI closer to the strongest dynamics.  Other than this small
chance of precip, the front is forecast to move through dry.
However, the front will bring gusty northwest winds as strong cold
advection steepen low level lapse rates.  Gusts from 30 or possibly
35 mph will be possible right behind the front for a short period.

Temperatures cool down closer to normal on Tuesday which will likely
be the coldest day of the next week.  After high pressure exits to
the east by Wednesday, warm advection returns as the upper flow
reorganizes. As a result, temperatures will start a warming trend
which will continue through the end of the work week.

The warmest day will occur on Friday when strong south flow will be
present.  925mb temps are forecast to warm into the lower or middle
teens by 7 pm Friday.  Probabilities of 925mb temps greater than 13C
at this time range from 50-70% over central to east-central WI. If
mixing can occur to this height, temperatures ranging from the upper
60s to middle 70s will be possible.   However, placement of the warm
front will be very important as east flow will occur north of the
front with onshore flow off a 36 degree Lake Michigan.  Therefore
will remain conservative with temps over eastern WI.  It would seem
that central WI will have the greatest potential of reaching 70
degrees.

Dynamics with this system are very impressive. Given the run-to-run
consistency, confidence is higher than normal for this time range of
the forecast that thunderstorms will be possible with this system.
CIPS Analogs and CSU Machine Learning forecasts depict a severe
threat most likely remaining south of the region.  But given the
wind fields aloft, will need to monitor potential for strong winds
in any storms in subsequent forecasts.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1158 AM CDT Sun Mar 9 2025

While VFR flight conditions are generally expected through the
taf period (cloud bases above 15000 ft), concerns over the next 24
hours revolve around gusty winds at the surface and aloft.

Southwest winds are forecast to gust from 25 to 30 kts this
afternoon. Winds aloft (850mb) are forecast to reach up to 50 kts,
so included a LLWS mention at all taf sites through late
afternoon or early evening.

Winds will gradually diminish in the evening, then become gusty
again on Monday. Southwest winds to 25 kts will be possible by
18z Monday.

Lastly, patchy ground fog may develop over far northeast WI late
tonight for a short time, but only reduced visibilities at RHI to
MVFR.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......MPC