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259
FXUS63 KGRB 261956
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
256 PM CDT MON SEP 26 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Tuesday
Issued at 253 PM CDT Mon Sep 26 2016

An unsettled weather pattern will continue into mid-week as a
nearly vertically stacked system slowly drops south through the
Great Lakes. This system is forecast to bring plenty of clouds and
periodic rain showers to the area.

The 19z MSAS surface analysis showed a strong area of low pressure
over southwest Ontario with high pressure extended from the
northern Rockies to the central Plains. As a result, there was a
tight pressure gradient stretched from the northern Plains east
into the Great Lakes with wind gusts surpassing 40 mph at times.
Visible satellite imagery indicated thick clouds across the
northwoods with more of a diurnally driven cumulus field over
central/eastern Wisconsin. Radar mosaic had picked up on several
bands of generally light rain showers rotating around the surface
low (and an associated upper low), primarily across the north.

This nearly vertically stacked surface/closed upper low to edge
south into northern sections of Lake Superior tonight. Cyclonic
flow to persist through the night which will continue to send
several bouts of light rain showers across the forecast area,
especially over the north which will be closer to the system and
stronger forcing. Have continued the forecast trend of highest
pops near the U.P. border, to little or no pops over our southern
counties. Do expect sky conditions over the south to go partly
cloudy for a time this evening as daytime cumulus dissipates upon
sunset. However, clouds should return later tonight as the system
slowly sags southward. Winds are also forecast to diminish
overnight, but remain in the 10 to 15 mph range. Min temperatures
should be fairly uniform with most locations residing in the
middle to upper 40s at daybreak.

The deep/cyclonic flow persists through Tuesday as the system only
sinks south into Upper Michigan by 00z Wednesday. Cold pool aloft,
with daytime heating and additional shortwave energy rotating
around the upper low, will again bring a mostly cloudy/unsettled
weather day to northeast Wisconsin. The air mass is cold enough
such that northern parts of the area will struggle just to crack
50 degrees. For now, have gone lower 50s north-central, upper 50s
east-central Wisconsin. West-northwest winds are not expected to
be as gusty as Monday due to less mixing with thicker clouds in
the area. Nonetheless, sustained winds of 10 to 20 mph with gusts
to around 25 mph can be expected.

.LONG TERM...Tuesday Night Through Monday
Issued at 253 PM CDT Mon Sep 26 2016

THE NUMERICAL MODELS ARE IN GOOD AGREEMENT ABOUT
MOVING THE UPPER LOW SOUTH FROM LAKE SUPERIOR TUESDAY NIGHT TO THE
OHIO RIVER BY WEDNESDAY NIGHT. THEN THERE IS DISAGREEMENT AboutHOW
MUCH IT Retrogresses AT THE END OF THE WEEK. LIKELY YESTERDAY,
THE GFS KEEPS IT FAR ENOUGH TO OUR EAST FOR IT TO BE DRY SATURDAY
AND SUNDAY, BUT THE ECMWF BRINGS IT ALL THE WAY NORTHWEST TO
CENTRAL INDIANA, PRODUCING SHOWERS ACROSS EASTERN WISCONSIN. HAVE
NOT SEEM VERY MANY SYSTEMS MOVE AS FAR WEST AS THE ECMWF SOLUTION
SO TEND TO SIDE WITH THE GFS FOR NOW.

AS THE UPPER SYSTEM MOVES RIGHT ACROSS OUR AREA TUESDAY NIGHT
THERE WILL BE A GOOD AMOUNT OF SHOWERS AS THE COLDEST AIR ALOFT
TRANSLATES ACROSS THE REGION. SOME THUNDER IS NOT OUT OF THE
REALM OF POSSIBILITIES BUT LEFT IT OUT FOR NOW. ABOUT A TENTH OR
TWO OF RAIN LOOKS LIKELY. THE PROBABILITY OF RAIN SHOULD DECREASE
WEDNESDAY EXCEPT IN EASTERN WISCONSIN WHERE SOME LAKE EFFECT
SHOWERS ARE POSSIBLE. DRY AND MILD WEATHER LOOKS LIKELY THURSDAY
AND FRIDAY REGARDLESS OF WHETHER THE GFS OR ECMWF ARE CORRECT.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1234 PM CDT Mon Sep 26 2016

A strong system located just north of Lake Superior will continue
to bring gusty winds to northeast Wisconsin this afternoon. Gusts
to around 35 knots can be expected, especially over central and
east-central WI where better mixing to bring stronger winds down
to the surface. Otherwise, cigs are forecast to range from MVFR
north to VFR south this afternoon with light rain showers mainly
confined to northern WI.

The gusty winds are expected to diminish this evening as mixing
subsides upon sunset. MVFR cigs with scattered rain showers will
continue across the north, while cigs to remain VFR with only a
spotty shower or a few sprinkles in the south.

The nearly vertically stacked system is only forecast to sink
south into Upper Michigan on Tuesday. This should bring a repeat
of both clouds and precipitation to the region, although more
clouds and a better chance of seeing precipitation to reach
central and east-central WI. Winds are not expected to be as
strong on Tuesday with more clouds inhibiting mixing.
&&

.MARINE...
Issued at 253 PM CDT Mon Sep 26 2016

Gusty west winds tonight into Tuesday as a strong area of low
pressure slowly moves south into northern sections of the Great
Lakes. Gale force gusts are possible at times tonight across the
coastal waters of northern Door County. Winds should begin to
decrease later Tuesday afternoon and Tuesday night. In addition,
cold air aloft in combination with the approaching upper low, could
bring a chance of waterspouts across the nearshore waters later
Tuesday night and into Wednesday.
&&

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

$$

SHORT TERM.....Kallas
LONG TERM......RDM
AVIATION.......Kallas
MARINE.........Kallas