Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 191109
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
609 AM CDT Wed Apr 19 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 326 AM CDT Wed Apr 19 2017

There will be a brief dry period this morning as a low pressure
system tracks along the cold front laid out across northern
Illinois, lifting it back north as a warm front tonight. Rain
chances this afternoon will be chancy, mainly confined to the
western and southern cwa as a shortwave tracks through the
western Great Lakes. Highs today will mainly be in the 50s, right
around normal for this time of year.

The best rain chances arrive tonight as the warm front lifts north
with very strong isentropic lift as winds are strong and
perpendicular to the isentropic surface. The warm air associated
with this system appears to have trended a bit farther north than
previous runs. This means thunder chances will be farther north
along with a marginal chance for severe across the extreme
southern cwa given very strong winds just above the surface as
MUCAPE values soar to 500 to 1000 J/kg tonight with winds of 60
knots just 3k ft off the surface. If thunderstorms can bring these
winds down to the surface they would have a good shot at wind
damage, however given the strong inversion in place this could be
an issue, hence the marginal threat for severe weather. What does
not appear to be marginal is the amount of rain we are looking at
tonight. The very strong dynamics and available moisture could
lead to an inch or more of rain during the overnight hours across
a widespread area with heavy rain expected at times. This will
likely exacerbate any flooding concerns across area rivers.
Therefore will issue an ESF to highlight the flooding concerns
expected with this system.

The low will lift northeast on Thursday, bringing cold air in
behind it and ending the precipitation chances during the day.
Given the continued northward trend of this low snowfall chances
continue to diminish with each run. This set of runs appears to
give a fairly small chance of a changeover, this combined with the
very wet ground that will be in place will keep snowfall
accumulations muted if there is any at all.

.LONG TERM...Thursday Night Through Tuesday
Issued at 326 AM CDT Wed Apr 19 2017

Rain chances linger into Thursday evening, mainly across northern
Wisconsin, as the upcoming system continues to move away from the
state. Rain may change to a little snow or a wintry mix near the
Michigan border before it departs by 12Z Friday.

Surface high pressure and a mid level ridge should keep things dry
over the weekend. There is a slight chance for rain and/or snow
across the north late Sunday night in warm advection ahead of the
next approaching surface low and mid level trough. There is a
chance for rain in central and north central Wisconsin starting
Monday afternoon with the approaching system. Rain chances spread
across the rest of the forecast area Monday evening and
precipitation chances continue throughout the night. There could
be some snow or mixed rain and snow in the far north during the
night. Rain chances continue into Tuesday morning in the north
before coming to an end during the afternoon as the system
departs.

Highs should be mostly in the 50s through the period and lows
will generally be in the upper half of the 20s and the 30s.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 608 AM CDT Wed Apr 19 2017

MVFR/IFR cigs this morning will improve to VFR as high pressure
brings drier air into the region. This improvement will be short
lived as a low pressure system approaches from the southwest late
this afternoon and into this evening. Showers and isolated
thunderstorms will advect in from the west, with lowering
conditions expected as the rain arrives. Timing appears to be a
bit slower with this run of models, therefore pushed back timing
with this set of TAFs. Rain could be heavy at times tonight.
&&

.MARINE...
Issued at 326 AM CDT Wed Apr 19 2017

A strong low pressure system will bring a tight pressure gradient
and gusty easterly winds as it tracks over southern Wisconsin
later tonight and Thursday morning. Gale force wind gusts are
expected near Death`s Door and around the northern portion of
Door County during this period. Therefore a Gale Warning has been
issued for the central Bay of Green Bay and the Lake Michigan
nearshore waters north of Sturgeon Bay. Farther south closer to
the low winds will gust to 20 to 25 knots along with higher waves.
A small craft advisory has been issued for the rest of the zones
starting tonight and lasting through Thursday night for the Lake
Michigan nearshore zones.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....Kurimski
LONG TERM......MG
AVIATION.......Kurimski
MARINE.........Kurimski



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