Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 141740
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1240 PM CDT Sat Oct 14 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 303 AM CDT Sat Oct 14 2017

The cold front that passed through the region yesterday and
stalled to the south will push back north as a warm front today as
a low pressure system moves northeast through the western Great
Lakes region tonight. POPs will increase from south to north
today as the front and associated low move towards the region,
with widespread moderate to heavy rain expected during the
overnight hours. Around an inch or so of rain is expected to fall
during this period, however given the area is in the abnormally
dry category according to the drought monitor, therefore the
impact from this much rain is expected to be low across northeast
Wisconsin.

The southern portion of the cwa could briefly enter the warm
sector later this afternoon and into the evening hours, bringing
the possibility for thunderstorms to central and east-central
Wisconsin. However the best instability is expected to stay to the
south so severe weather is not anticipated.

As the low pulls away on Sunday, rain chances will decrease from
west to east as northwest winds increase precipitously late
tonight into Sunday morning. Winds across Door County are expected
to be close to Wind Advisory criteria for much of the day on
Sunday, therefore headlines are possible for this area in
subsequent forecasts if current wind speeds hold up.

.LONG TERM...Sunday Night Through Friday
Issued at 303 AM CDT Sat Oct 14 2017

Model guidance continues to show the mean flow to transition from
modest western CONUS upper ridge/strong eastern CONUS upper trough
early next week, to a strong western CONUS upper trough/modest
eastern CONUS upper ridge late next week. This pattern switch will
change the northwest flow aloft into WI through Monday, into a
southwest flow aloft into WI by Wednesday. Do not see much in the
way of precipitation chances as Pacific systems are forecast to
pass to our north. Temperatures would start the work week around
normal, but then trend upward thereafter reaching 10 to 15 degrees
above normal by late week.

Models continue to advertise the passage of a quick-moving
shortwave trough across WI Sunday evening before shifting farther
southeast after midnight. While the atmosphere will be too dry for
any precipitation to develop, the expected cloud cover associated
with the trough could impact the areal coverage of frost
potential across northeast WI. Latest thinking is to increase
clouds during the evening, then decrease the clouds after midnight
and with plenty of cold air in place, there would be enough time
for frost to form, especially over central WI where temperatures
could drop into the middle 30s. East-central WI should see
temperatures dip into the upper 30s with only patchy frost
expected. Parts of northern WI could drop into the upper 20s, but
since the growing season has officially ended there, the only
potential frost advisory would be over central WI Sunday night.

High pressure is forecast to stretch from TX northeast into the
Ohio Valley on Monday, bringing a west-southwest wind at the
surface into WI. WAA pattern to take over our weather, but the
cold start to the day with a northwest flow aloft, will temper the
warming process. Even under mostly sunny skies, look for max
temperatures in the middle 50s north, middle to upper 50s south.

A system moving across Ontario Monday night is forecast to drag a
weak cold front into the western Great Lakes region. Once again, a
lack of moisture would preclude the mention of precipitation with
only a subtle wind shift to denote the front`s passage. The dearth
of moisture will even have trouble developing any clouds, thus
mostly clear skies to hold with min temperatures to range from the
upper 30s to around 40 degrees north, lower to middle 40s south. A
weak surface ridge slides across WI on Tuesday and will continue
to bring mostly sunny skies to the region. The mean flow aloft is
expected to flatten and turn more westerly into WI, bringing a
persistent low-level WAA pattern into the state. Expect max
temperatures to respond by reaching the lower 60s north/near Lake
MI, middle 60s south.

The only potential issue with the extended forecast occurs at
mid-week as another system passes to our north and pulls another
cold front toward WI. Some models prefer to wipe this front out,
while other models sweep this front into the region on Wednesday.
The dry air mass in place, coupled by a lack of any mid-level
forcing, will prevent any precipitation from forming either way.
However, the difference would be in temperatures especially by
Wednesday night as 8H temperatures over northeast WI could range
from +6 to +13C. Pre-frontal warming on Wednesday would still keep
max temperatures well above normal with middle 60s north/near Lake
MI, middle to upper 60s south. It would be temperatures Wednesday
night/Thursday that would be impacted by the model disagreement.
Do not see a plausible reason why this cold front would simply
disappear, therefore have hedged toward the cooler air
infiltrating the forecast area with max temperatures on Thursday a
few degrees cooler than Wednesday.

The region is expected to return to a southwest flow (both aloft
and at the surface) as a new upper trough moves into the western
CONUS and upper heights build over the central CONUS. At the
surface, high pressure locked over the Mid-Atlantic states to
bring WAA back in full force by Friday with 8H temperatures
returning to the +12 to +14C range. Max temperatures for Friday
should reach the middle 60s north/near Lake MI, upper 60s to lower
70s south.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1240 PM CDT Sat Oct 14 2017

At midday VFR conditions prevailed across the northern part of the
area as MVFR ceilings, ahead of approaching showers, moved into
central and east central Wisconsin.

Conditions are expected to deteriorate across the area the rest of
the day and tonight, with IFR/LIFR ceilings and MVFR or IFR
visibilities in showers. Thunderstorms cannot be ruled out, but
probability is too low to include in TAFs. Locations in central
and north central Wisconsin should start to see improvement to
MVFR or VFR Sunday morning as a mid level trough axis passes to
the east.
&&

.MARINE...
Issued at 303 AM CDT Sat Oct 14 2017

An intensifying area of low pressure will move through the
region tonight into Sunday morning. Initially, east winds are
expected to increase this morning and afternoon reaching small
craft criteria everywhere, with waves reaching small craft
advisory criteria on Lake Michigan today, then the bay tonight.
Given the increased winds and waves on the Bay will expand the
Small Craft Advisory to the central and southern Bay this
afternoon and tonight.

The winds may briefly diminish this evening as low
pressure moves across Wisconsin. As the surface low departs later
tonight, winds are forecast to rapidly shift to the northwest and
become gusty into Sunday. A period of gale force gusts are
expected from late tonight through Sunday afternoon. The Gale
Watch remains in effect for everywhere during this period.
&&

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

$$

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



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