Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 212027
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
327 PM CDT Mon May 21 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Tuesday
Issued at 326 PM CDT Mon May 21 2018

Upper level shortwave/trough (seen nicely on the water vapor)
will approach from southern MN this evening, while a surface wave
passes into Lower Michigan. These will continue to spread showers
across much of the area, with only far north central WI staying
dry. However, very dry air (dewpoints in the 30s/40s) continue to
eat away at the leading edge of the showers. Meso-models all in
pretty good agreement showing the large area of showers slowly
shrinking as it moves northeast. This makes sense as the dry air
has been pretty impressive so far, especially over far northeast
WI, but the last hour or two an uptick was noted in the activity.
So still think most spots will get wet late this afternoon into
the evening, but amounts will diminish the farther north/east you
go.

Patchy/areas of fog are expected tonight, except for the far
north. With all the clouds around, do not think the fog will
become dense in most spots, but can`t rule out some dense fog,
especially where the most rain falls across central and east-
central WI and if any breaks in the overcast can develop. Fog is
also expected on Lake Michigan, as water temps are still in the
upper 30s and 40s, but drier air will filter in as winds turn
northeast, so the most widespread fog is expected south of
Kewaunee.

A cloudy/foggy start is expected on Tuesday. A few showers are
even possible as the trough exits and moisture lingers. Drier air
eventually works in from north to south across the area, allowing
for partial clearing, especially across northern WI.

Temps tonight will be much warmer than last night, mainly in the
40s to around 50, due to cloud cover and shower activity. Highs
on Tuesday look to rebound nicely for most locations that saw the
rain today, reaching the upper 60s to middle 70s (coolest in the
Fox Valley and near the Bay). The warmest temps are expected once
again across northern WI, with a few spots approaching 80, if
there is a little more sunshine than forecast. The only locations
that will miss out on the warm day will be near Lake Michigan with
temps mainly in the 50s.

.LONG TERM...Tuesday Night Through Monday
Issued at 326 PM CDT Mon May 21 2018

The pattern becomes active by the end of the week and into the
first part of the weekend as upper level ridging flattens out and
a mid level trough tracks through the western Great Lakes. The
main issue that continues to plague the forecast is the timing of
rain as NWP models offer up different solutions regarding when and
where rain will fall. Given the model uncertainties will continue
with chancy POPs during this period.

There is the potential for strong storms Friday through Saturday
as MUCAPEs rise to 1000 to 2000 J/kg. However bulk shear will be
fairly weak, on the order of 10 to 20 knots. Therefore organized
severe weather is not anticipated, rather pulse type thunderstorms
will be possible with gusty winds, heavy rain and hail.

Ridging will re-establish itself across the western Great Lakes
region for the second half of the weekend into early next week,
which should keep the weather dry. High temperatures during this
stretch will be above normal, ranging from the upper 70s to middle
80s at times.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1255 PM CDT Mon May 21 2018

Rain and low clouds have continued to slowly push north late this
morning and early afternoon. The northward progression has been
slowed by the very dry air over northern WI. The slow northward
progression of the showers and low clouds will continue the rest
of the afternoon and evening. Only the far north (RHI) may be
spared from the low clouds, with IFR/LIFR CIGS expected elsewhere.
Confidence is lower regarding how much fog will develop. Best
chances to see IFR/LIFR fog will be across locations across
central and east central WI, especially where the most rain falls.
Did not include any VLIFR VSBYS, but would not be surprised to
see a few locations drop under 1/2 mile at times overnight.
CIGS/VSBYS will slowly improve Tuesday morning, with increasing
amounts of sunshine expected very late in the morning and
afternoon.
&&

.FIRE WEATHER...
Issued at 326 PM CDT Mon May 21 2018

Rainfall amounts over the next few days are not expected to
alleviate the abnormally dry conditions across the north. Dry
conditions are expected through Wednesday, resulting in elevated
fire weather conditions and worsening drought conditions.
Relative humidities are expected to rebound some to the 25 to 40
percent Tuesday and Wednesday. Some relief is expected by the end
of the week as a low pressure system is expected to bring cloud
cover and the chances of showers and thunderstorms to the region.
Depending on how much rain falls late in the week, fire weather
concerns could re-emerge early next week if a healthy dose of rain
doesn`t fall across the north as high pressure and dry weather
return to the region.
&&

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

$$

SHORT TERM.....Bersch
LONG TERM......Kurimski
AVIATION.......Bersch
FIRE WEATHER...Kurimski



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