Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 250335

Area Forecast Discussion
National Weather Service Green Bay WI
1035 PM CDT Sat Mar 24 2018

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Sunday
Issued at 241 PM CDT Sat Mar 24 2018

The latest RAP analysis and satellite/radar imagery show high
pressure stretching from James Bay into the northern Great Lakes
early this afternoon. Meanwhile, a band of precipitation is
extending from northern Iowa into the southern Appalachians.
Central and northern WI remains on the northern edge of this storm
system, with broken cirrus extending across northern WI. The
clouds in combo with east winds have cooled temps several degrees
from yesterday. As high pressure continues to be the main
influence of the weather across the region, temps and low
humidities remain the main forecast concerns.

Tonight...The storm system will continue to track southeast across
the Ohio Valley. As a result, will see the blanket of high clouds
gradually thin out during the evening, then skies will become mostly
clear overnight. But even with clearing skies and a dry airmass
in place, do not think temps will tank in the northwoods due to
persistent 5 kts of east flow. Lows ranging from around 10 above
in Vilas county to the mid 20s near Lake Michigan.

Sunday...Should see temps moderate some as the surface high moves
further east of the region and with more sunshine. Mixing should
tap into very dry air aloft, leading to widespread low dew
points, some as low as zero in north central WI. This will lead to
very low relative humidity in the 15 to 25 percent range in the
sandy soil regions. The combination of low humidity and breezy
east to southeast winds will result in elevated fire weather
conditions, especially in the grassy areas of central and east
central WI, where there is little or no snow cover. Warmer highs
ranging from the mid 30s near Lake Michigan to the middle 40s over
central WI.

.LONG TERM...Sunday Night Through Saturday
Issued at 241 PM CDT Sat Mar 24 2018

Boundary layer high pressure will drift eastward Sunday night
into Monday morning for continued dry conditions. Southwest flow
aloft develops Monday as the upper ridge shifts east to start a
brief pattern change.

Clouds and then the chance of rain will be on the increase from
west to east Monday afternoon into Monday evening as return flow
and develops ahead of the next low pressure system. Best forcing
arrives later Monday night as the southerly LLJ works into the
area. Will keep pcpn type all rain due to a warm start Monday
afternoon, but a few locations across the north may have a brief
snow mix due to evap cooling effects from the departing dry air
mass. Best combination of forcing and pwats 0.75 to 1.00 inches
arrives late Monday night into Tuesday. Isold storms possible
late Monday night into mid day Tuesday as total totals climb to
the 45 to 50 range. ECMWF is a bit quicker with the departure
east with the precipitation later Tuesday afternoon due to a
trough system. The GFS is slower but has shifted from a closed
low system to trough as well Tuesday.

Cold northwest flow returns for the remainder of next week with
several chances of a mixed precipitation. Confidence with timing
and strength of these systems remains low.

.AVIATION...for 06Z TAF Issuance
Issued at 1032 PM CDT Sat Mar 24 2018

Good flight conditions are expected the next 24 hours. Winds over
east-central Wisconsin have decreased since late afternoon.
Decoupling will probably limit gustiness overnight, though it may
return on Sunday. But winds won`t be as strong as Saturday. Dry
air at low and middle-levels will limit clouds to just cirrus.

Issued at 241 PM CDT Sat Mar 24 2018

With the exception of shaded forested areas south of highway 8,
only snow cover left across the forecast area is mainly over
areas northward. Even that snow cover has likely been worked over
some the last few days due to the sublimation process with the
dry Hudson Bay east flow. For snow less areas, continued cold
overnight low temperatures and a lack of a penetrating rain, has
allowed a healthy frost to remain several inches below a thawed
surface layer. A system tracking over the northern Great Lakes
region Monday night into Tuesday continues to indicate a
widespread nearly half inch of rainfall. This rainfall will make
a good attempt to knock the frost out, but run off will be above
normal for this amount of rain resulting in some small streams
and creeks rising. Across the north, above freezing overnight
lows Monday night along with the rain will reduce the snow cover.
River flooding issues should be minimal with these conditions, but
will be monitored.  Thunderstorms are possible across parts of
East Central Wisconsin, so rain amounts may be locally higher but
confidence is low at this time for storms.



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