Area Forecast Discussion
Issued by NWS Green Bay, WI

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929
FXUS63 KGRB 281628
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1128 AM CDT Fri Apr 28 2017

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 344 AM CDT Fri Apr 28 2017

Rather cool the next several days with another round of soaking
rains this weekend.

A powerful and energetic band of westerlies has been in place
across the CONUS for the past week, with ridges off the West Coast
and along the East Coast, and a strong trough over the southern
Plains. A slow progression of the features will begin as an
intense cyclone ejects out of the Plains trough this weekend. The
cyclone will result in another widespread soaking rainfall across
the area this weekend, and above normal totals for the period.
Temperatures will remain well below normal through the weekend,
then return closer to normal next week.
&&

.SHORT TERM...Today...Tonight...and Saturday
Issued at 344 AM CDT Fri Apr 28 2017

Moist, deep cyclonic flow was generating scattered light
precipitation across the area early this morning. Obs suggest it`s
falling as flurries, sprinkles and some drizzle (freezing where
temperatures are cold enough). Will continue with it in the
forecast until mid-morning. Cloud trends are also problematic as
guidance is obviously trying to get rid of the clouds too quickly.
Satellite imagery shows increasing breaks in the clouds and some
erosion of the main area of clouds to the west. Even so,
the improvement will take a while to get here and may never make
it all the way into the north. Adjusted toward a cloudier
forecast.

The next shortwave ejecting out of the Plains trough will head
toward the area today and then weaken/shear out in confluent upper
flow tonight. Most of the precipitation with the wave will pass
south of the area, and the majority of the guidance kept the area
dry. But the ECMWF and GFS were in agreement in brushing the south
with some light precipitation late today and this evening. That`s
a hard combination to ignore, so brought low Pops across the
southern part of the forecast area. Temperatures should be warm
enough to prevent any freezing precipitation.

Northeast winds will begin to increase Saturday in advance of the
strong cyclone developing in the southern Plains. Stuck with the
broad-based blend of guidance products which brought low PoPs back
into the south late in the day.

.LONG TERM...Saturday Night Through Thursday
Issued at 344 AM CDT Fri Apr 28 2017

Models are in very good agreement with the strong upper low within
a broad upper trough that will lift northeast and impact northeast
WI weather from Saturday evening through Tuesday. This system will
pull copious amounts of gulf moisture into the Great Lakes with
locally heavy rainfall a definite possibility, especially Sunday
night when WAA and mid-level forcing to be maximized. As this deep
cyclone begins to slowly pull away Monday night, we could see the
rain either mix or change to all snow over parts of northern and
central WI. Even beyond this system, a mean longwave trough will
remain over the central CONUS, thereby keeping temperatures below
normal and the weather somewhat unsettled through next Thursday.

System of interest continues to organize over the southern Plains
Saturday night. Increasing southerly flow will tap gulf moisture
with precipitation becoming heavy in the vicinity of a quasi-
stationary front draped from MO to the eastern Great Lakes. The
northern edge of this precipitation shield will get into central/
east-central WI Saturday night, but the rain would be on the light
side. Northern WI will see clouds increase, but remain dry until
perhaps toward daybreak as dry northeast winds to keep the rain
away. Min temperatures to be in the lower to middle 30s north,
middle 30s to around 40 degrees south.

The system begins to lift northeast on Sunday with a strengthening
area of low pressure over the central Plains/Mid-MS Valley and an
upper trough closing off into a closed upper low over eastern KS.
The persistent south winds ahead of the system will continue to
pump gulf moisture into the Great Lakes with PW values climbing
over 1 inch. The quasi-stationary front is forecast to start
slowly lifting north as a warm front and reach the WI/IL border by
00z Monday. A tight baroclinic zone to exist north of this warm
front with an increasing frontogenetical forcing signal located
just to our south. Highest pops will be placed across east-central
WI where up to one-half inch of rain is possible. Max temperatures
are expected to be stuck in the lower to middle 40s north, middle
to upper 40s south.

Sunday night simply looks very wet as the system becomes
vertically-stacked over the Midwest and the warm front reaches
southern sections of WI into central Lower MI. Plenty of lift
available between the warm front and a diffluent flow aloft,
coupled with the mid-level frontogenetical forcing and strong
moisture transport, all point to rain across northeast WI. Some
of this rain may become locally heavy at times and will need to
watch flooding potential (both flash and river) as grounds are
saturated already. Another concern could be precipitation type
across the north with surface temperatures only a few degrees
above freezing. While a little snow may mix with the rain at
times, do not expect any accumulation as temperatures aloft are
also above freezing.

Any mixed precipitation would transition back to rain showers on
Monday as the stacked system moves into WI. Just about the only
noticeable difference will be the lighter winds as the surface low
to essentially move into northeast WI and the pressure gradient
becomes baggy. Otherwise, more of the same with several rounds of
rain and temperatures running 10 to 20 degrees below normal. The
heavier precipitation should be north and east of the forecast
area on Monday, however hydro conditions will continue to need
close watching.

As the system begins to pull away Monday night, northeast WI to
reside on its cool, cyclonic side with wrap-around moisture
bringing additional precipitation chances to the region. As cooler
air gets pulled into WI, look for the rain to mix with or change
to all snow across northern and central WI. Cannot rule out a
light accumulation over parts of northern WI, but too early for
any specifics. This cool, cyclonic flow lingers into Tuesday, thus
expect at least a chance of mainly rain showers over the forecast
area through the day.

A broad upper ridge over the western CONUS will bring a northwest
flow into the Great Lakes Wednesday into next Thursday. The models
hint at several weak shortwaves diving southeast within this flow
which could set off a few light showers. Hard to time these small
features this far out and none of these shortwaves appear very
strong, thus any precipitation would be light and not aggravate
any river flooding. Temperatures will remain below normal through
Thursday, although there a signs of a warm-up at the end of next
week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1126 AM CDT Fri Apr 28 2017

Cigs will continue to lift to VFR levels from south to north this
afternoon as the cyclonic flow with a low pressure system departs
further northeast of Lake Superior. A west to east ridge of high
pressure will drift northward across the area this afternoon
into Saturday for an overall quiet weather regime. Another low
pressure region tracking over the mid mississippi region this
afternoon into tonight may be close enough to produce a few light
showers south of highway 10 this evening. Otherwise mainly VFR
conditions to prevail into Saturday.
&&

.HYDROLOGY...
Issued at 344 AM CDT Fri Apr 28 2017

This strong system is expected to pull copious amounts of gulf
moisture north into the Great Lakes during the Saturday night
through Monday time frame. PW values may approach 1.5 inches over
east-central WI Sunday night. A widespread one inch of rain is
forecast across northeast WI, with higher amounts across east-
central WI where isolated totals may approach two inches. Ground
conditions are already saturated from previous rain and snow
events and the threat for flash flooding or river flooding will be
enhanced late this weekend into early next week. Those with
interests along area rivers, streams and creeks should keep
abreast to the latest forecasts and be prepared to seek higher
ground if any flooding does occur.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Kallas
AVIATION.......TDH
HYDROLOGY......Kallas



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