776
FXUS63 KGRB 290904
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
404 AM CDT Mon Apr 29 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Scattered showers will continue through late today before ending
  this evening. There is a small chance for thunderstorms this
  afternoon over east-central and northeast Wisconsin.

- Due to recent rainfall, rivers and streams will be on the rise
  through midweek, with a few of them possibly reaching bankfull
  stage.

- Lingering higher waves will result in conditions hazardous to
  small craft this morning on the central Bay and also on the Lake
  from Sturgeon Bay to Washington Island. Dense fog is possible
  over all the waters into this afternoon.

- There is a chance of showers and a few thunderstorms Tuesday
  night. Additional rain and thunderstorm chances are possible at
  times from late Wednesday night through Friday.

&&

.DISCUSSION...
Issued at 403 AM CDT Mon Apr 29 2024

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

Shower, thunder chances and temps today are main forecast issues.

Sharp shortwave trough is lifting across the northern Plains while
sfc low is over southwest Minnesota. Warm front tied to the low is
just beginning to lift into southern Wisconsin. Otherwise, the NE
flow enhanced by cool Lake Michigan and the rain that has occurred
at times since midday on Sunday has resulted in very stable low-
levels over much of Wisconsin. Thus, no thunder has occurred in
the cwa into early this morning. Rain being more off than on early
this morning has led to some patchy dense fog. The fog is more
widespread across the bay and lake and right along adjacent
shorelines.

Shortwave trough reaches northern Minnesota late today with occluding
sfc low making its slow trek to western Upper Michigan. Scattered
showers forming due to isentropic ascent/moist low-level advection
moving toward central Wisconsin should expand as they lift northward
as the forcing links up with weak elevated instability over the area.
Highest pops this morning will be north and northeast. Chancy pops
otherwise. Warm front will move northward across the badger state
through the day, but given occluding low and wealth of cool/moist
air on east/southeast winds ahead of the front think the push
northward will be sluggish, only getting into northeast Wisconsin
mid to late afternoon. High temps will be *highly* dependent on
frontal position this afternoon. Just take a look at wide varying
MOS guidance at GRB which ranges from a high of 55 on the NAM MOS
to a high of 66 on GFS MOS. Think the front makes it past GRB so
went toward the GFS MOS, but realize there is higher than normal
bust potential for highs today with the sharp front in the vcnty.
Farther southwest toward ISW and OSH, readings will close in on
70. North-central will see highs into the mid 50s as will Door
County where cool east flow ends latest.

Cold front south of the low will swing into east-central and
northeast Wisconsin mid to late afternoon. MLCAPEs of at least
500j/kg and effective shear well over 40 kts makes it prudent to
continue to include and slightly bump up TS mention. An isolated
strong storm is not out of question, though extent of shear and
dry air in mid levels may be too much given the forecast CAPE.
Will be something to watch though.

Rest of short term more straight forward. Lingering smallish pops
near the U.P. border early tonight as the occluded low moves past,
but otherwise dry as the system gradually pulls away. Tuesday is
dry as high pressure crosses. Unmodified W/SW low-level flow means
all areas will have a shot of seeing highs well into the 60s with
some more readings near 70 ISW to OSH.

Long Term...Tuesday Night Through Sunday

An upper level disturbance moving with the zonal flow will bring a
chance of showers and a few thunderstorms Tuesday night. Latest
trends is to slow the precipitation down and have trended this
way with 3 hourly pop grids to reflect the slower arrival time of
the rain. I may still be too quick with the precipitation as the
00z ECMWF doesn`t get the precipitation here until 06z Wednesday.
Best forcing will be across northern Wisconsin with the shortwave
energy. Of concern is the precipitation totals of the ECMWF are
pretty skimpy across east-central Wisconsin, thus there is concern
on the amount of coverage of precipitation across east-central
and portions of northeast Wisconsin. The shortwave should exit
the area late Tuesday night into early Wednesday morning. Kept a
small pop just in case the timing if even slower on the next few
model runs.

Will need to watch Wednesday for some fire weather concerns as
mild temperatures and humidity readings plunge across northern
Wisconsin. Humidity readings will be in the 30s percent, but could
go a little bit lower over the next day or two. Winds are expected
to be in the 10 to 20 mph range with gusts around 25 mph. On
Wednesday into Thursday, a 500mb trough will begin to deepen
across the Rockies into the central plains with ridging across the
mid- Atlantic states. A warm front is going to set up well south
of the area, from central Iowa into northern Illinois by 12z
Thursday. This is a tad bit further south than yesterday. Based on
the ECMWF, central and east-central Wisconsin will be on the
northern edge of the precipitation shield. By Thursday afternoon,
the ECMWF has the warm front pushing northward into southern
Wisconsin, bringing showers and increasing chances for
thunderstorms during the day. We will still be in the cool sector,
thus there could be a trend for slightly cooler high temperatures
in the coming days. There are some considerable differences
between the GFS/ECMWF/Canadian on the track of the surface low and
placement and timing of the heaviest QPF totals. There is plenty
of time to sort out the details, but heavy rain may be a
possibility Thursday and Thursday night. Model differences
continue this weekend, thus hard to discern this far out what day
would have the highest probability of rain, if any?

Temperatures will be seasonable for the most part, with Wednesday
possibly the warmest day while cooler temperatures are possible
over the weekend.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1054 PM CDT Sun Apr 28 2024

A low pressure system will move slowly from Southern Minnesota
to Upper Michigan by Monday evening. There will be scattered
showers and isolated thunderstorms late tonight through midday
Monday.

IFR ceilings are expected tonight through at least midday Monday,
with some improvement in east central Wisconsin in the afternoon.
Visibility will fall to around one mile over much of the area
overnight as a warm front lifts north. The visibility will
improve Monday afternoon as a weak cold front moves through.

&&

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

&&

$$

DISCUSSION.....JLA/Eckberg
AVIATION.......RDM