Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 191152 AAA

Area Forecast Discussion...UPDATED
National Weather Service Green Bay WI
652 AM CDT Thu Sep 19 2019

New Information added to update section

Issued at 641 AM CDT Thu Sep 19 2019

Although conditions will become less favorable for training of
storms and upstream regeneration later today when the 925-850 mb
flow weakens, it is still strong enough this morning to result in
a persistent band of convection from central into northeast
Wisconsin. Cells are starting to develop south of the main band in
east-central Wisconsin. That and the MCS developing over southwest
Wisconsin should lead to a gradual weakening and southward shift
in the position of the band. But that is not apparent yet. Luckily
the heaviest rains thus far have fallen over the Bay. Calls to
Marinette and Door county have not revealed any reports of
flooding yet. Will continue to monitor closely. If the position of
the band does not change substantially in the next 1/2 hour, the
Flood Advisory will at least need to be extended and perhaps
expanded south some.

Issued at 402 AM CDT Thu Sep 19 2019

Continued warm and rather humid with scattered showers and
thunderstorms the next few days, then turning a little cooler and
much less humid by late in the weekend.

A highly amplified upper pattern was in place across North
America, with a seasonably deep trough in the west and an
intense/expansive ridge from the lower Mississippi Valley through
western Quebec. The pattern will gradually lose amplitude and
become progressive as energy ejecting out of the western trough
rides northeast and flattens the ridge. The large scale flow will
evolve toward a lower amplitude/longer wavelength regime, with
broad ridging off the West Coast and a large shallow trough over
the central and eastern portion of the continent by the middle of
next week.

Southwest upper flow between the current western trough and
eastern ridge will maintain a feed of warm, moist air into the
area for a few more days. That will result in continuation of well
above normal temperatures and rather humid conditions through
Saturday. After that, a more westerly trajectory aloft will bring
much drier and a little cooler air into the area, through
temperatures are likely to remain above normal. Very high PWATs
will be across the area during the first portion of the forecast
period, and probably result in above normal precipitation amounts
for the period.

.SHORT TERM...Today...Tonight...and Friday
Issued at 402 AM CDT Thu Sep 19 2019

A weak/diffuse warm front was slowly shifting east across the
area, with mid-upper 60F dew points gradually overspreading the
area from the west behind the front. The cold front that was
advancing east into Wisconsin from the west was slowing and
weakening, and will likely wash out near the western edge of the
forecast area. That will leave a very moist and somewhat unstable
air mass across the forecast area until a stronger cold front
arrives this weekend. There will be upticks and lulls in the
showers and thunderstorms across the area as subtle forcing and
diurnal trends modulate the convection. Adding meaningful detail
to the PoP grids rapidly became difficult with time, and went with
a general trend toward low-end chance PoPs as the ability to
latch onto specific forcing for lift decreased with time.

In general, severe weather parameters were marginal at best this
morning and expected to weaken with time. Deep-layer shear was
20-30 kts early this morning, and will weaken to 10-20 kts. Wet-
bulb zero heights will remain high. Isolated gusty winds could be
generated by wet microbursts from cell mergers, but those will
most likely remain sub-severe. PWATS will be very high and
combined with the weak shear that will favor heavy rainfall. 850
mb flow was 25-35 kts this morning, but forecast to weaken later
today, making continued regeneration of intense rain producing
storms over the same area somewhat unlikely. So while locally
heavy rainfall is possible with the storms, the threat of
excessive rainfall does not appear great.

Trended toward a blend of the recent top performing guidance
products for temperatures, with some local modifications--
especially near the lake and bay.

.LONG TERM...Friday Night Through Wednesday
Issued at 402 AM CDT Thu Sep 19 2019

Warm and humid air ahead of an approaching surface cold front and
mid level trough will bring showers and thunderstorms to the area
Saturday and Saturday night. Generally dry but cooler conditions
will prevail the rest of the weekend into next week as surface
high pressure and a weak mid level ridge pass across Wisconsin.
Though it will be cooler, temperatures will still be near or a
little warmer than normal into the middle of next week. Another
passing cold front will bring chances for showers and storms back
to the area for Tuesday night and Wednesday.

.AVIATION...for 12Z TAF Issuance
Issued at 402 AM CDT Thu Sep 19 2019

Flight conditions will be quite variable, especially early in the
period as clouds of various heights and some fog persist across
the area. Some improvement is expected during the day. Statistical
guidance products were showing strong support for widespread low
cloud and fog formation overnight. While the low clouds and fog
producing IFR/LIFR conditions may develop, there is at least a
little uncertainty added by questions about how much lingering
middle and high cloudiness will remain over the top, and when and
where convection will occur.

Beach Hazards Statement until noon CDT today for WIZ022.


SHORT TERM.....Skowronski
AVIATION.......Skowronski is the U.S. government's official web portal to all federal, state and local government web resources and services.