773
FXUS63 KGRB 062354
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
654 PM CDT Thu Jun 6 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Isolated to scattered showers and gusty northwest winds will
  continue across the region through this evening. Winds will
  decrease slightly overnight but remain breezy.

- Breezy conditions are expected Friday, with gusts to 25-30 mph.

- Conditions hazardous to small craft are expected Friday.

- Showers are possible at times this weekend, with a chance of
  thunderstorms Saturday afternoon.

- Additional showers and thunderstorms are expected Tuesday
  afternoon into Tuesday night.

- Below normal temperatures are forecast through early next week
  with warming temperatures by mid-week.

&&

.DISCUSSION...
Issued at 238 PM CDT Thu Jun 6 2024

Short Term...Tonight and Friday

Mesoanalysis...Ongoing isolated to scatter this afternoon are
being driven by cyclonic flow around a low pressure system
centered just east of Lake Superior and steep low-level lapse
rates around 8.5 to 9 C/km. Analysis soundings are showing mixing
this afternoon to around 800-850 mb which is driving the stronger
35-40 mph gusts with these showers, especially in central WI. In
addition to the gusts being produced by rain showers the pressure
gradient is tightening which is driving up the gradient winds as
well. With a lack of instability (SBCAPE < 200 J/kg) and weak 0-
3km shear(15-20 kts) none of these showers have been able to
produce much in the way of thunder, but won`t rule out a few
rumbles around peak heating this afternoon. Expect the showers and
gusty winds to continue across the region through the remainder
of the afternoon. Temperatures this afternoon will be held in
check by the abundant cloud cover and showers with most locations
reaming in the middle 50s to middle 60s.

Tonight...Isolated to scattered shower activity should come to
and end from south to north this evening with the lose of daytime
heating and stabilization. While winds will back down from the
peak gusts this afternoon, a tighter pressure gradient will
continue to create breezy conditions with gusts of 15-25 mph
overnight. Near normal temperatures overnight with lows dropping
into the middle 40s to low 50s across the region.

Friday...Dry and breezy conditions are expected Friday as the
region resides on the backside of an upper trough with the
surface low shifting off to the east. A strong 90-100kt upper jet
is forecast to move directly overhead during the day which will
bring plenty of energy into the region to drive stronger wind
gusts. Forecast soundings look similar to today with mixing to
around 1.5-2 kft which should be deep enough to bring some 25-
30 mph gusts down to the surface. In addition, the deeper mixing
should aid in lowering surface dew points down into the middle to
upper 40s. The lower dew points in combination with a surge of
WAA bringing warmer temperatures into the middle 60s to low
should make for a more fall like feel, rather than early summer.

Long Term...Friday Night Through Thursday

Main forecast focus remains on trying to time precipitation
chances, especially next week as models continue to waffle on the
direction/amplitude of the mean flow.

A pair of closed upper lows, one over Quebec and the second over
Alberta/Saskatchewan, will keep unsettled weather across the Great
Lakes through the early part of next week. A west-northwest flow
aloft will carry individual shortwaves across WI about every other
day, but exact timing is a bit tricky. A more pronounced change
has taken place for the middle of next week as models are not
building a ridge over the east-central CONUS, instead keeping a
flat, near-zonal flow across the CONUS. Temperatures to be below
normal through Tuesday, then rise at or above normal mid-week.

Friday night and Saturday...
Clouds will be on the increase Friday night as the next mid-level
shortwave trough dives southeast into the Upper MS Valley. Models
indicate models levels of both Q-G and FGEN forcing with a weak
frontal boundary to move into western WI after midnight. These
factors should be enough to bring chance pops through at least
central WI and perhaps reaching eastern WI toward daybreak. Min
temperatures to be in the upper 40s to around 50 degrees north,
lower to middle 50s south. This shortwave trough/frontal boundary
push across WI on Saturday and bring a chance of showers across
the entire forecast area. Instability looks weak at best with
MUCAPES < 200 J/KG. However, shear is very strong (70-80 kts over
central/east-central WI). Therefore, have kept thunder in the
forecast for Saturday afternoon, but severe does not look likely
as the mid-level shortwave trough to be exiting the area during
peak heating. Max temperatures Saturday to be in the middle to
upper 60s north, upper 60s to lower 70s south.

Saturday night and Sunday...
A few showers may linger into Saturday evening, but most location
should be dry Saturday night as we lose daytime heating and there
is no other trigger present. Sky cover will become mostly clear to
partly cloudy with min temperatures in the upper 40s north, lower
to middle 50s south. The combination of cyclonic flow, weak
surface trough dropping south and cold air aloft to generate weak
instability may be enough to spark a few afternoon showers across
northeast WI on Sunday. Cool north-northwest winds will continue
to keep temperatures in check with readings on Sunday in the lower
to middle 60s north-central WI, upper 60s to around 70 degrees
elsewhere.

Sunday night and Monday...
High pressure is forecast to build into the western Great Lakes to
begin the new work week, thus mostly sunny skies and dry
conditions are expected on Monday. Max temperatures will warm up a
bit with middle to upper 60s near Lake MI, lower to middle 70s
inland.

Monday night and Tuesday...
Dry conditions should hold through Monday night as the high
pressure begins to shift east. By Tuesday, the next shortwave
trough is progged to move into the Upper MS Valley with a cold
front reaching the MN/WI border by 00Z Wednesday. Models differ a
bit with the timing of this system as the GFS already has
precipitation chances Tuesday morning, while the CMC is dry
through the day. Have a minimal chance of showers/thunderstorms
for the afternoon hours, but this may be tweaked in later
forecasts. Max temperatures Tuesday to be around 70 degrees near
Lake MI, lower to middle 70s north and middle 70s south.

Tuesday night through Thursday...
Best chance of seeing precipitation would be Tuesday night as the
shortwave trough and cold front cross WI. Of course, the faster
GFS ends the precipitation faster than other models, but this
timing issue will be resolved with time. Model issues then persist
for mid-week as they continue to waffle on whether an upper ridge
will build over the east-central CONUS in response to an upper
trough hitting the West Coast. Latest guidance does not show this
ridge developing, instead keeping a near-zonal flow across the
CONUS. This pattern could bring yet another shortwave trough into
the Great Lakes Tuesday night into Wednesday. A northward moving
warm front could also bring showers/storms to the area on
Thursday, so the wet forecasts look to persist next week.
Temperatures are forecast to go above normal for both Wednesday
and Thursday.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 654 PM CDT Thu Jun 6 2024

Scattered showers will diminish this evening, but a
northwest flow of cool air aloft will produce mostly cloudy skies
across much of the area through midday Friday. MVFR ceilings are
possible northeast of a RHI to SUE line, with VFR ceilings further
south.

Mostly clear skies are expected Friday afternoon and evening.

&&

.MARINE...
Issued at 238 PM CDT Thu Jun 6 2024

With a similar syntopic set-up to today breezy conditions are
expected near Lake Michigan Friday, strongest south of Sturgeon
Bay. However, with no rain showers expected mixing may not be
quite as efficient which would keep peak gusts more in a 25-
30 kts range. A Small Craft Advisory will likely be needed during
the late morning and afternoon period before winds diminish
Friday night.

&&

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

&&

$$

DISCUSSION.....GK/Kallas
AVIATION.......RDM
MARINE.........GK