Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 291725
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1225 PM CDT Wed Mar 29 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 332 AM CDT Wed Mar 29 2017

Satellite imagery shows mid to high level clouds associated with
a strong storm system tracking form the central plains to the mid
mississippi valley region will increase across the area today.
This storm system will likely produce severe weather across the
central and lower Mississippi Valley region the next few days. For
this area, available observations and web cams this morning not
showing any low stratus or fog this morning so far. Fog and
stratus was noted across southeast Wisconsin, and across far
eastern upper Michigan working into the far northern portion of
Lake Michigan. Will watch to see if there is any expansion which
could impact part of the area this morning.

Otherwise focus with this forecast is the rain/snow mix potential
starting tonight as the northern precipitation region of the
storm system works into central and east central Wisconsin, and
then further northward Thursday. The leading edge of the
precipitation is already into Iowa at 3 am, so will continue the
trend of light rain working into central wisconsin later by this
afternoon. Boundary layer temperatures suggests precipitation will
start out as light rain across central and east central
wisconsin late today into this evening, but then turn to a mix as
evap cooling saturates the column to mostly snow. To complicated
snow amount totals, will be dealing with the warm ground and snow
melt on impact. Precipitation will likely turn to mostly snow by
early Thursday morning. Will issue a sps for a heads up for the
morning commute. Trend of these models have been to edge up the
snowfall totals, and if this trend continues, headlines may be
needed for part of the area.

Thursday will continue to be challenging with precipitation type
across the area. Boundary layer temps increase enough to produce
a mix and perhaps change to mainly rain for the day. LFQ of an
upper jet nudges into east central Wisconsin Thursday morning, so
lift into the higher snow growth may produce periods of snow.
lowered max temps a little for Thursday due to the precipitation.

.LONG TERM...Thursday Night Through Tuesday
Issued at 332 AM CDT Wed Mar 29 2017

Models continue to show an active split flow across the CONUS with
an upper ridge over the extreme eastern Pacific into western
Canada and a series of systems dropping southeast into the
southwest CONUS before moving northeast across the rest of the
CONUS. The first system will already be starting to pull away from
the Great Lakes at the beginning of the extended forecast with
system #2 expected to impact the Great Lakes during the Monday
night-Tuesday time frame. Precipitation type could again become a
nighttime issue when temperatures fall close to the freezing mark.

The first system is expected to slowly move east-northeast from
the Mid-MS Valley to just north of the lower reaches of the Ohio
River Valley Thursday night. Other than north-central WI, we
should still see precipitation linger over the rest of northeast
WI through at least Thursday evening with light rain becoming
mixed with light snow or light freezing rain as temperatures begin
to fall. Little of any accumulation of snow or ice is anticipated,
but will have to watch for possible icing on area roads as any
ponding of water could freeze as temperatures drop below freezing.
Min temperatures are forecast to be in the middle to upper 20s
north-central WI, lower to middle 30s elsewhere.

Due to the overall slow movement of this system (only forecast to
reach central/eastern OH by 00z Saturday), it is not unconceivable
that a little light rain or mixed precipitation could carry over
into Friday morning over parts of east-central WI before finally
pulling away in the afternoon. A weak ridge of is then expected to
move toward the western Great Lakes later on Friday and bring
decreasing clouds from northwest to southeast through the day,
although this clearing line may not make it to east-central WI
until late afternoon. Northeast WI will still be dealing with a
prevailing northeast wind, thus max temperatures to range from the
lower 40s near Lake MI, to the upper 40s north-central WI where
the sun to arrive first.

The surface ridge remains over the region Friday night, bringing
mostly clear to partly cloudy skies, light winds and seasonal
temperatures. Look for mins to be in the middle 20s north to
around 30 degrees south. Quiet weather conditions will continue
into Saturday as the surface ridge starts to slide to our east.
Depending on the timing of a weak northern stream shortwave trough
(the GFS is faster than other models), there could be an increase
in clouds across the area. Do not have enough confidence on the
timing of this feature to justify carrying any pops at this time
and prefer to remove the previous pops placed over the far north.
Max temperatures for Saturday should be in the middle 40s near
Lake MI, mainly lower to middle 50s elsewhere.

Northeast WI to be on the western fringes of the retreating
surface ridge while upper heights also build during the latter
half of the upcoming weekend. Generally partly cloudy skies are
expected with temperatures slightly above normal. This would take
max temperatures on Sunday into the upper 40s near Lake MI, lower
to middle 50s most other locations. There could be a few upper 50s
west of the Fox Valley if more sun can win out over the clouds.

Forecast becomes more complex early next week as a southern stream
system is progged to move from the southern Plains northeastward
through the OH/TN Valleys toward the New England states. The main
issue is a trailing northern stream shortwave trough and whether
these two systems will stay apart or attempt to phase. If these
systems stay apart, precipitation potential for northeast WI
Monday and Tuesday would be minimal as the southern system would
pass too far to our south. IF these systems do interact with one
another, we would be in for a stretch of unsettled weather both
Monday and Tuesday. The consensus of models would favor keeping
the systems separate, however either solution is still plausible.
Therefore, have kept a low chance pop in the forecast for now both
Monday and Tuesday. Obviously, temperatures would be completely
dependent on which solution ends up being correct with max
temperatures either in the 40s with rain or 50s with sun.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1213 PM CDT Wed Mar 29 2017

A storm system will pass to the south of the area later tonight
and Thursday. This system will bring rain and snow to much of
the area, except possibly the far north. Ceilings should fall into
the MVFR/IFR category across much of the area later this evening
or overnight and continue into much of Thursday. Heaviest snow
totals are expected south of highway 29. Conditions will improve
some Thursday night as the storm pulls away from the area. Also,
gusty northeast winds of 15 to 25 knots are expected Thursday
into Thursday evening across the Fox Valley and lakeshore region.

&&

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

$$

SHORT TERM.....TDH
LONG TERM......Kallas
AVIATION.......Eckberg


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