000
FXUS63 KGRB 280825
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
325 AM CDT Sun Apr 28 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Better chances for rain returns this morning and continues
  through Monday. Periods of moderate to heavy rain tonight into
  Monday morning, could result in isolated flash flooding in urban
  and low lying areas. Rivers will be on the rise through the
  middle of next week, with a few of them reaching bankfull stage.

- Conditions hazardous to small craft are expected into Monday on
  the Bay and Lake. Patchy dense fog is possible on the waters as
  well.

- There is a chance of showers and a few thunderstorms Tuesday
  night and at times late Wednesday night into next weekend.

&&

.DISCUSSION...
Issued at 324 AM CDT Sun Apr 28 2024

Short Term...Today...Tonight...and Monday

Leading shortwave trough is heading east this morning while
primary active frontal boundary has sunk into far southern WI. A
few showers are occurring over northeast WI, but next main area
of showers will not arrive until later this morning into early
afternoon from south to north as yet another sharp shortwave
trough ejects out of the central plains. By late afternoon main
sfc low will be over western Iowa with sfc warm front still stuck
over southern Wisconsin. Sfc high near James Bay and the low to
the southwest will result in increasing NE winds across all but
southern Wisconsin. The showers driven by mid-upper diffluence and
warm, moist advection aloft ahead of H85 low along with the NE
winds off chilly Lake Michigan and the bay will keep temps *much*
cooler than what occurred over most of the area on Saturday as
readings this afternoon will commonly be in the 40s. Elevated
instability limited today, but will support some rumbles of
thunder into the south half of the area this afternoon. Rainfall
amounts late this morning through the afternoon should top out
over 0.50 inch in many areas, but be hard pressed to reach over
0.75 inch. Still a soaking rainfall is on tap.

Tonight, wave of showers will lift to northern areas early this
evening and there may be a brief break for part of the evening.
However, another round of showers and some thunderstorms will
impact all the cwa from south to north as the warm front lifts
farther north. There are some differences in where axis of
heaviest rain streams northward. At this point, the NAM along
with WRF-ARW and FV3 shows more of a direct hit with the second
round of showers while the GFS, Canadian and ECMWF favor areas
just to our east. Showers will still occur, but this will impact
if our area sees heavy rain that could possibly cause minor
flooding issues in low-lying and poor drainage areas. Diving into
HREF probabilities, certainly a decent chance most areas over
eastern and northeast cwa see another 0.25 to 0.50 from the rain
later tonight, but probabilities drop off to around 30 percent
when looking at seeing amounts over an inch, which is what the
NAM, WRF-ARW and FV3 are advertising. Have added fog as well as
there are hints that we`ll see some fog either due to the
advection of marine fog onto land with persistent E/NE winds or
just with enhanced low-levels to the north advancing warm front.
Lows will be similar to what temps will be late this afternoon.
Temps will rise more into the 50s late over far south as the warm
front moves in.

On Monday, shortwave trough pivots northeast while sfc low lifts
into northwest WI. Parts of the area will break into the warm
sector of the low, but dry air will quickly be shifting eastward
across WI. Still, after the morning showers, could see a brief
window of sfc based development of showers and storms where Td
surge up into the 50s in the warm sector. MLCAPEs nothing too
notable at this point (maybe up to 300j/kg) but with effective
shear 35+ knots, can`t rule out an isolated stronger storm early
to mid afternoon. SPC Day2 only shows general thunder for our
area. Highs in the warm sector will reach well into the 60s over
east-central WI with a 70 over far southern cwa not out of the
question.

Long Term...Monday Night Through Saturday

A zonal flow at 500mb is expected at the start of the period,
with a system moving through the mean flow that would bring a
chance of showers and a few thunderstorms Tuesday night. A deeper
500mb trough will approach the area Thursday then across the area
Friday into Friday night, bringing a better chances for showers
and some thunderstorm activity.

For Tuesday night, the models have been consistent in bringing
rain into the area during the evening hours over much of the area,
thus the small chances of rain Tuesday afternoon were removed. The
better forcing with the shortwave energy will be focus across
north-central and far northeast Wisconsin which will coincide
with the highest QPF totals. The GFS bufkit sounding indicated a
few hundred J/KG of CAPE, so a few thunderstorms will be possible
with the passage of the system. Dry conditions are expected to
prevail on Wednesday before the next system approaches from the
west late Wednesday night and Thursday.

Building 500 ridge over the eastern seaboard with 500mb trough
eventually evolving into a negatively tilted system Thursday into
Friday should bring a few rounds of showers and thunderstorms.
At the surface, at 12z Thursday a surface low is forecast to be
across the central plains into Iowa with a warm front extending
to near (south) of the Wisconsin/Illinois border. An MCS is
forecast to develop north of the warm front which is expected to
clip the southern half of Wisconsin. Based on the models tonight,
we will be on the northern edge of the MCS which should keep most
if all severe weather south of the area. On Thursday, the surface
low will push slowly northward which should keep the surface warm
front along our southern counties or to the south which will
bring a continued chance of showers and thunderstorms. By the time
you get to Friday, there are significant difference in the track
of the main surface low. It is too early to determine if any of
the storms would become severe. Confidence is low on the next system
bringing chances for rain on Saturday, thus no changes made to this
period. High temperatures will need to be watched Thursday and Friday.
Rain, clouds and easterly flow could keep temperatures in check
on one or both days depending on the final storm track.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1043 PM CDT Sat Apr 27 2024

A low pressure system will move north from the central Plains
to Western Great Lakes and bring periods of showers and isolated
thunderstorms tonight through Sunday night.

Ceilings will become MVFR across most of the area by daybreak Sunday,
with IFR ceilings north of a Merrill to Iron Mountain line. IFR
ceilings are likely over most of the region Sunday and Sunday night.

&&

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

&&

$$

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