Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 212322
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
622 PM CDT Sun May 21 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 237 PM CDT Sun May 21 2017

The latest rap analysis and satellite/radar imagery show low
pressure centered over the western Upper Peninsula and an occluded
front extending southeast into lower Michigan.  Widespread showers
and a few storms exited earlier this morning, but additional light
showers/sprinkles are moving east across central and north-central
WI within the comma head of the system.  Additional shortwave
activity is diving south over the eastern Dakotas, to the west of
the center of the upper low. As this shortwave moves into the area,
shower chances/trends are the main forecast concerns.

Tonight...Upper level low pressure will continue to spin across the
western Great Lakes, with one particular strong shortwave moving
across the state after midnight.  Deeper moisture will continue to
wrap around the southern periphery of the low, causing skies to
remain broken to overcast over the region. Spotty showers will
mostly be confined to central and north-central WI during the
evening, but should become more widespread and push into eastern WI
after midnight with arrival of the shortwave. Low temps falling into
the low to mid 40s.

Monday...Mostly cloudy conditions with isolate to scattered showers
will be present at the start of the morning.  As the shortwave
trough exits, showers should retreat to the northeast by mid to late
morning, while warming low level temps should lead to partial
clearing taking place over central and northeast WI through early
afternoon.  But with increased solar insolation, clouds will build
again as convective temps are surpassed.  This should lead to
scattered showers developing during the afternoon, perhaps initially
over north-central WI before spreading south and east.  With ml
capes up to 500 j/kg over central and east-central, could also see a
few thunderstorms develop during mid to late afternoon.  Highs
ranging from the mid 50s in the far north to upper 60s south.

.LONG TERM...Monday Night Through Sunday
Issued at 237 PM CDT Sun May 21 2017

Precipitation trends are the main forecast concern.

The combination of a slow moving cold front, deep upper trof
and surface wave developing along the boundary, will result in
periods of showers through midweek. Have boosted pops to likely
over our western CWA late Monday night, over most of the forecast
area on Tuesday, and over our southeast counties Tuesday night.
Thunder is also possible over central and east central WI Monday
evening, and over the Fox Valley and Lakeshore areas Tuesday
afternoon.

A brief period of dry weather is expected Wednesday night into
Thursday evening, as a narrow ridge of high pressure crosses the
region.

WAA will bring a small chance of showers back to the region late
Thursday night into Friday night, but most of the precipitation
should stay to our south, closer to a warm frontal boundary.

After a dry day on Saturday, models diverge for the rest of the
weekend, with the GFS exhibiting convective feedback with a deep
low pressure system moving through the forecast area Saturday
night into Sunday. The ECMWF seems more plausible, with an upper
trof and associated frontal system bringing a chance of showers
and thunderstorms.

Below normal temperatures during the midweek period will moderate,
and should get slightly above normal for Friday/Saturday/Sunday.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 622 PM CDT Sun May 21 2017

Mainly MVFR cigs to prevail in the cool moist cyclonic
flow. A disturbance rotating around the low pressure area over the
northern Great Lakes Region this evening may generate a period of
IFR cigs with isolated mvfr vsbys due to showers and fog.
Conditions expected to improve to a lower end VFR later Monday
morning. There is a chance for more showers later Monday as a weak
front slides over the area.
&&

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

$$

SHORT TERM.....MPC
LONG TERM......Kieckbusch
AVIATION.......TDH



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