Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 230907
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
407 AM CDT Thu Mar 23 2017

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 404 AM CDT Thu Mar 23 2017

Freezing rain is likely to result in hazardous travel conditions
across the north tonight, while just rain falls elsewhere.

The upper flow across North America was evolving into a split flow
pattern. The mean trough position in the southern stream will be
over the southwestern United States. As a result, the southern
stream systems that manage to track far enough north to affect the
forecast area will be slow moving and weakening by the time they
arrive.

Temperatures will probably stay fairly close to seasonal normals
the next several days, then warm a bit early next week. Total
precipitation for the period is likely to be above normal over the
southern part of the forecast area, which will be closer to the
southern stream storm track. Totals across the north are more in
doubt.
&&

.SHORT TERM...Today...Tonight...and Friday
Issued at 404 AM CDT Thu Mar 23 2017

Clouds and some some snow showers/flurries generated by the
isentropic lift over the retreating cold air mass were moving
across the area this morning. But dry air low-levels was limiting
the amount of precipitation reaching the ground. The initial surge
of precipitation should shift off to the northeast this morning,
allowing for a lull before additional precipitation moves in from
the west. The exact timing of things in the rest of the short-term
is unclear. There appears to be a sufficient influx of moisture
and forcing to result in precipitation at times from late this
afternoon through Friday. Very steep mid-level lapse rates edging
in from the west suggest precipitation will be in the form of
small clusters/areas of showers. Scattered thunderstorms are also
possible, especially late today and this evening. The main issue
is temperatures across the north tonight, as readings are likely
to fall enough to result in freezing rain and some icing of
roads, especially since low-levels will initially be relatively
dry. Though confidence is not as high as it could be, the threat
seemed high enough to warrant posting a Winter Weather Advisory
for the north for overnight into early Friday.

Temperatures should warm enough Friday morning to bring the
threat of freezing rain to an end across the north. A cold front
dropping south across the area will usher in increasing northeast
winds during the afternoon. There is likely to be a sharp
temperature gradient across the front. Lowered maxes some in areas
where the front is likely to arrive early enough in the day to
affect maxes.

.LONG TERM...Friday Night Through Wednesday
Issued at 404 AM CDT Thu Mar 23 2017

Northern extent of precipitation and its type are already a
concern Friday evening.

Drier air associated with surface high pressure to the north
looks like it should keep the northern part of the forecast area
drier than the rest of Wisconsin, at least until the high moves
off to the east. Most of the 00Z models kept north central
Wisconsin dry Friday night but the 00Z NAM had some of its highest
QPF values there Friday evening before backing off during the
overnight hours. Have lowest PoPs in north central Wisconsin
Friday night and highest in east central. There are precipitation
type issues since low temperatures are expected to be at or below
freezing during the night over about half of the area.
Temperatures aloft are too warm for snow, so type would have to
change from rain to freezing rain/drizzle at some point during
the night before surface temperatures warm up during the day on
Saturday and put an end to any freezing precipitation.

00Z models were pretty consistent in showing a surface low and
500mb low passing across Illinois Saturday night/Sunday morning,
though the NAM was farther to the south than the NAM/ECMWF/Canadian.
QPF fields were still quite different but all had some measurable
precipitation across at least part of the forecast area. Blending
this all together results in a prolonged period of PoPs over
most, if not all, of the area. The same precipitation type issues
show up overnight Saturday night and Sunday night, though QPF
gradually tapers off over the weekend.

Models bring a mid level trough toward Wisconsin after the larger
system departs, so not sure if there is a forecast period when
there won`t be at least slight chance PoPs through the end of the
forecast. This will have to be fine tuned a little later.

It should be warmer than normal for this part of the forecast,
with the exception of Saturday when highs will be a bit below
normal.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 404 AM CDT Thu Mar 23 2017

Given the dry low-levels and precipitation falling primarily as
liquid, feel the guidance is too aggressive in dropping ceilings
and especially visibilities overnight. LLWS will also develop
across the area as southwest winds increase ahead of the cold
front dropping into the region.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 10 PM this evening to 9 AM CDT
Friday for WIZ005-010>013-018-019.
&&

$$

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


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