Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 210859
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
359 AM CDT Tue Mar 21 2017

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 356 AM CDT Tue Mar 21 2017

Much cooler today, with the cooler weather lingering through the
rest of the work week. The next significant chance for
precipitation will arrive late in the week and continue into the
weekend.

The persistent eastern North American upper trough will undergo
one last amplification the next couple days, before finally shifting
off to the east. A split flow regime will expand east across
North America in the wake of the departing trough, and continue
for the remainder of the forecast period.

A strong anticyclone from northwest Canada will push across the
area the next couple days, driven southeastward by the short-
lived northwest flow into the departing eastern trough. Once the
high shifts east, temperatures should return closer to seasonal
normals. But they may be held back some during days with
widespread precipitation. Total precipitation for the period is
likely to be above normal, primarily due to a slow moving southern
stream cyclone expected to affect the area late this week into the
upcoming weekend.
&&

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 356 AM CDT Tue Mar 21 2017

A secondary cold front will shift southeast across the area this
morning. A fresh surge of cold air from Canada will push into the
area behind the front. Winds will also turn northwest and increase
with the passage of the front. The temperature forecast for today
is tricky, because readings haven`t fallen off much in the
westerly flow in advance of the front. The northwest part of the
area should still drop off before daybreak, but the southeast may
just see readings hold steady this morning. A vigorous mid-level
shortwave was passing across Ontario, but it`s influence should
remain north of the area. Delayed the onset of snow showers and
flurries in north-central Wisconsin to allow time for some lake-
effect to develop. Diurnal destabilization could could also be
sufficient to result in some snow showers and flurries as well,
especially in the north and northeast parts of the forecast area.

Cold air will be in place across the area tonight. PWATs fall
considerably. The sky condition forecast is a little tricky,
because winds at 5k ft will probably veer north and possibly
north-northeast during the night. That could bring some clouds
from lakes Michigan and Superior into the area. Given the incoming
dry air, trimmed temperatures in the north with the expectation
that there will be at least some clear periods. Of course if
clouds are more prevalent, the min temperature forecast will be in
trouble.

Will need to carefully monitor how much cloudiness off Lake
Michigan works into eastern Wisconsin Wednesday morning, and if
the clouds produce any flurries. For now, accepted the lower
skycon forecast of the blended guidance, and stuck with max temps
derived from a broad-based blend of guidance products.

.LONG TERM...Wednesday Night Through Monday
Issued at 356 AM CDT Tue Mar 21 2017

Precipitation timing and type are the main forecast concerns
starting with the system that is expected to impact the area late
Thursday.

QPF fields from the 00Z models were not the most consistent even
at the start of this forecast period. The ECMWF already had QPF
across northern Wisconsin on Wednesday night. This appeared to be
associated with a short wave in the northern branch of the upper
flow and a low pressure system moving across Canada. The NAM, GFS
and Canadian were generally drier until strong warm advection
ahead of an approaching surface system brings a chance for
precipitation to the area Thursday night. A wintry mix is possible
across much of the area as temperatures drop below freezing during
the night, except in the Fox Valley and Lakeshore areas where
rain is expected. A change to all rain should occur by mid morning
on Friday as temperatures warm.

Precipitation type is a concern again Friday night as a cold front
pushes south across the area. Have snow becoming the main
precipitation type for the north, with rain and/or snow across the
rest of the area. A brief period of dry weather is possible
in far north central Wisconsin late Friday night. Warming during
the day on Saturday should change any snow or mix back to rain as
the surface low and 500mb low pass south of the forecast area.
PoPs start to drop Saturday night as the surface and upper systems
depart but precipitation type issues continue, with a change to
snow overnight and then back to rain on Sunday as precipitation
exits all but far eastern Wisconsin. Confidence in this scenario
is not particularly good considering the differences among the
models and the large areas of QPF the ECMWF and GFS were showing.

Looks like lows will be mostly in the 20s to mid 30s, with highs
generally in the 40s.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 356 AM CDT Tue Mar 21 2017

Expect some clouds with MVFR bases for form across the north this
morning. The main question is whether cloud coverage is sufficient
to produce a ceiling. Plan to just have a brief period with an
MVFR cig at RHI, and VFR conditions at the other TAF sites.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MG
AVIATION.......Skowronski



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