Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 190335

Area Forecast Discussion
National Weather Service Green Bay WI
1035 PM CDT Thu May 18 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 255 PM CDT Thu May 18 2017

A few lingering sprinkles are possible late this afternoon as a
low pressure system exits the Great Lakes region. Behind this low,
high pressure will build in across the western Great Lakes region
during the overnight hours. This high will bring clearing skies
and light winds to the region tonight, providing for ideal
radiating conditions across much of the forecast area. Given
temperatures across portions of north central Wisconsin are
already in the lower 40s and 850 mb temperatures are forecast to
fall into the low single digits or even below zero, there appears
to be a fairly high confidence in a frost/freeze situation across
much of the area. Across the north lows are expected to fall into
the middle to upper 20s, with lower to middle 30s across central
and portions of northeast Wisconsin. Therefore will issue a Freeze
Warning across the north, with a Frost Advisory bordering the
warning to the south and east. Across east central Wisconsin and
Door County it appears surface winds will be a bit higher with
warmer low temperatures in the upper 30s. Therefore will leave
these areas out of the current headlines.

Friday will start out dry as the high exits to the east while a
developing low pressure system brings mid and high clouds and a
small chance for light rain showers to the southern fringes of the
cwa during the afternoon hours. However even if it does rain the
impact appears to be minimal given the feed of dry air from the
high off to the northeast. The continued cold airmass and
increasing clouds will keep highs on Friday a good 10 degrees
below normal, limited to the 50s.

.LONG TERM...Friday Night Through Thursday
Issued at 255 PM CDT Thu May 18 2017

Models concur in the orientation of the mean flow, consisting of a
West Coast upper ridge, central CONUS upper trough and western
Atlantic upper ridge. This pattern will continue to bring above
normal precipitation/below normal temperatures to northeast WI
well into next week. Main forecast focus to be on precipitation
trends, including potentially heavy rain Saturday into Saturday
night. This would aggravate the river flooding over the Wisconsin
and Menominee rivers which are high already.

As the high pressure starts to shift east into western Quebec
Friday night, it will lose its influence on northeast WI. This
will allow for moisture ahead of our next weather maker over the
central CONUS to thicken clouds across WI with the leading edge of
light rain showers to reach at least central WI after midnight.
Increasing south winds will help to lift the 8H warm front into WI
with strong WAA aiding in the precipitation development. Better
instability to remain to our south overnight, thus have kept
thunder out of the forecast for now. Min temperatures to be in the
middle to upper 30s north, lower to middle 40s south.

Showers appear to be a good bet on Saturday as a surface low moves
northeast into the Midwest and the associated surface warm front
lifts north toward central WI by Saturday afternoon. PW values are
forecast to climb into the 1.25-1.50" range on Saturday, thus a
potential for heavy rain does exist, especially if enough
instability can get generated to support thunderstorm activity.
The 12z model blend produces one-quarter to one-half inch of rain
on Saturday which could create additional hydrology problems. May
add a hydrology section below and mention the flood threat in the
HWO to alert people of flooding potential. The combination of
clouds and precipitation will keep temperatures well-below normal
with readings in the lower to middle 50s north/lakeshore, middle
to upper 50s south.

The surface low will continue to move north-northeast into the
Upper MS Valley/western Great Lakes region Saturday night,
accompanied by a cold front sweeping into WI and a mid-level
shortwave trough reaching the Upper MS Valley. A good chance or
likely pops will persist into Saturday evening, then tend to
diminish later Saturday night as a dry slot rotates into WI.
East-southeast winds will veer southwest overnight and help to
usher in some drier/cooler air. Min temperatures to range from the
lower to middle 40s north, to around 50 degrees east-central WI.
While central/east-central WI look to be mainly dry on Sunday,
there is still some concern for scattered showers over northern WI
as the system slowly tracks into southern Ontario and a weak
cyclonic flow resides over the region. Any further precipitation
would be light and not add to any river issues. Even if no
precipitation does occur, Sunday should see plenty of clouds which
would keep temperatures in check as CAA will have overspread the
forecast area. Look for readings to reach the middle to upper 50s
north-central WI, lower 60s elsewhere.

Only spotty shower activity expected Sunday night into Monday
morning as the old system lingers to our north. However by Monday
afternoon, we will be watching a new shortwave trough drop
southeast into the Upper MS Valley, preceded by a cold front that
is progged to reach toward central WI late in the day. This could
bring a small chance of showers to the forecast area and maybe
even a stray thunderstorm. Max temperatures should be able to warm
into the lower 60s north-central/lakeshore, upper 60s to around 70
degrees east-central WI. This would make Monday likely the warmest
day of the extended forecast.

Questions begin to surface as to the movement/location/strength of
the mid-level shortwave trough as some models keep the trough an
open wave, while other models close this trough off into a closed
upper low to our south starting Monday night. Anticipate at least
a chance of showers Monday night as the cold front moves through
the area, followed by a chance of showers/slight chance of
thunderstorms on Tuesday as cold air aloft associated with the
mid-level trough increases instability. Max temperatures on
Tuesday to cool down once again with readings in the upper 50s to
around 60 degrees north/lakeshore, lower to middle 60s south.

Depending on how fast this mid-level trough hangs around the Great
Lakes, unsettled weather could linger over northeast WI into
Wednesday before finally pulling far enough east to allow
precipitation to end. Model/forecast uncertainty to carry over
into Thursday as the GFS is already racing a weak system southeast
into WI, while the ECMWF is dry. Prefer to go optimistic here and
hold off on any additional precipitation chances on Thursday.
Temperatures to remain below normal for both Wednesday and

.AVIATION...for 06Z TAF Issuance
Issued at 1033 PM CDT Thu May 18 2017

Low clouds have dissipated rapidly during the past couple hours.
The remaining low clouds near the lake and bay may be a little
more persistent. Once the remaining low clouds exit/dissipate, VFR
conditions expected for the rest of the TAF period.

Issued at 255 PM CDT Thu May 18 2017

Recent heavy rainfall has brought some rivers in northeast
Wisconsin above flood stage. Additional rains expected late Friday
night into Saturday evening could aggravate this river flooding
and keep river levels high into early next week. People living
along or near rivers or streams should keep alert to any possible
flooding and be ready to move to higher ground if flooding is

Frost Advisory until 9 AM CDT Friday for WIZ020-030-031-035>037-

Freeze Warning until 9 AM CDT Friday for WIZ005-010>013-018-019-


SHORT TERM.....Kurimski
LONG TERM......Kallas
HYDROLOGY......Kallas is the U.S. government's official web portal to all federal, state and local government web resources and services.