Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 280839
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
339 AM CDT Wed Jun 28 2017

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 339 AM CDT Wed Jun 28 2017

A low pressure system will track over the upper Mississippi Valley
today, then continue east through the western Great Lakes tonight.
A line of showers and thunderstorms ahead of the low over
Minnesota is progged to continue east through the cwa during the
morning hours. These storms are not expected to be severe.

The main question for later this afternoon and this evening is how
much the atmosphere can recover for severe potential later in the
day. Given the high sun angle, a large window is not needed for
recovery. Models show MUCAPEs increasing to 1000 to 2000 J/kg
during the late afternoon and early evening hours as the warm
front associated with this low advects east. In addition a fairly
substantial PV anomaly will track through the area during the
afternoon and evening hours. Given the instability and lift there
is a slight risk for severe storms later today and into the
evening hours, particularly across central and east-central
Wisconsin given the proximity to the warm front and the axis of
greatest instability. Model soundings show the main threat will be
large hail and damaging winds, however isolated tornadoes are
possible given the proximity to the warm front and enhanced low
level shear this will provide. This will be highly dependent on
building enough instability after the morning convection comes
through, however it is enough of a risk to upgrade in line with
the latest SPC day 1 convective outlook.

The low will advect a moist airmass north over the western Great
Lakes today, as PWATs increase to 1.5 to 1.75 inches. The high
moisture content combined with the vigorous dynamics and the
several rounds of rain expected will bring the potential for a
substantial amount of QPF today and tonight.

Mostly dry weather is expected on Thursday as the low tracks off
to the east and drier air advects in from the west. Despite the
passage of a cold front temperatures are expected to be a bit
warmer during the afternoon hours with some sunshine expected at
times.

.LONG TERM...Thursday Night Through Tuesday
Issued at 339 AM CDT Wed Jun 28 2017

Active pattern expected to continue into early next week as 500mb
trough gradually moves across the area this weekend, then east of
the area early next week. The first wave of low pressure is
expected to approach the area later Thursday night into Friday
morning. A few of the models also depict convection breaking out
with the return flow, so there may be some showers and storms
Thursday evening ahead of the main system. Low pressure is
expected to move across the region on Friday. I was hoping for
better resolution of the details of this system which would
have impacts on potential severe weather and also problematic
for wind/wave forecasting on the bay of Green Bay and Lake
Michigan. Current thoughts system will pass overhead or just
to the south of the area during the day Friday. Showers and
storms are expected during the day which will also impact
high temperatures. If an easterly wind component develops
if system passes to the south would support high temperatures
several degrees cooler than the current forecast. Later shifts
can fine tune the details.

Northwest flow aloft and the next disturbance will bring a
chance of showers and thunderstorms on Saturday. The greatest risk
of thunderstorms would be Saturday afternoon into Saturday
evening. Precipitation would more than likely end Saturday
evening. The latest model trends are slow with system on Sunday,
bringing much of the precipitation into the area Sunday night into
early Monday morning. Continued a small chance of showers and
thunderstorms Sunday with higher chances on Sunday night.
Continued a small chance of showers and storms on Monday across
our southern counties. Dry conditions should prevail on Tuesday.
Only minor changes to max/min temperatures during the period.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1025 PM CDT Tue Jun 27 2017

Expect mainly dry and VFR conditions rest of the night as surface
high pressure drifts to the east and a mid level ridge moves to
central Wisconsin by 12Z. Increasing southerly winds just above
the surface will bring LLWS to central and north-central
Wisconsin after 09Z. Scattered showers and storms expected
starting Wednesday morning with lowering cigs and vsby. This
precip may be part of decaying convective system. Additional
storms may occur ahead of cold front later in the day, but this
development is conditional on extent atmosphere recovers after
earlier showers/storms.
&&

.MARINE...
Issued at 339 AM CDT Wed Jun 28 2017

Southerly winds will increase across the nearshore waters
today and tonight. This will cause winds to increase into the 25
to 30 knot range, with a few gusts around gale force at times,
especially across the Lake Michigan nearshore waters. Waves will
increase with the increasing winds, with the highest waves across
the Lake Michigan nearshore waters. Recent model runs have backed
off a bit on wind speeds, therefore will continue with the small
craft advisory as gale force gusts appear to be less likely with
this issuance. Any boaters planning on traveling today and tonight
should follow future forecasts closely.
&&

.HYDROLOGY...
Issued at 339 AM CDT Wed Jun 28 2017

Periods of heavy rainfall are likely with a widespread 1 to
2 inches across much of the state today and tonight. The greatest
potential for locally heavier rainfall will likely be with any
training thunderstorms along a warm front forecast to lift north
later today and this evening. This could cause rivers, that are
already above bankfull, to rise and bring the threat for flooding.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement from 9 AM CDT this morning through
Thursday morning for WIZ022-040-050.
&&

$$

SHORT TERM.....Kurimski
LONG TERM......Eckberg
AVIATION.......JKL
MARINE.........Kurimski
HYDROLOGY......Kurimski


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