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FXUS63 KGRB 190922

Area Forecast Discussion
National Weather Service Green Bay WI
322 AM CST Sun Feb 19 2017

Forecast discussion for routine morning forecast issuance

Issued at 319 AM CST Sun Feb 19 2017

Unseasonably warm through the mid-week, with some rain Monday
afternoon and Monday night. Then turning colder with some rain and
snow late in the week.

The positive upper height anomaly associated with the highly split
flow currently across North America will consolidate over James 
Bay the next few days, then rapidly weaken and shift east. As it
does so, the southern stream will strengthen and expand northward
across the CONUS. The result will be a colder and much more 
active weather pattern for the latter part of the forecast period 
and beyond. 

Temperatures will remain well above normal the next several days,
though readings will be tempered some Monday due to clouds and
east winds. Readings will return to seasonal normals by next
weekend. An influx of moisture and a strong shortwave crossing the
region will bring some rain Monday into early Tuesday. Late in the
week, a powerful cyclone in the strengthening southern stream 
is expected to affect the area. Since both those systems look 
like good precipitation producers, totals for the period will 
probably end up above normal.

.SHORT TERM...Today...Tonight...and Monday
Issued at 319 AM CST Sun Feb 19 2017

The main short-term forecast issues are again temperatures and the
timing of the onset of rain on Monday. Satellite suggests there
will be quite a bit of sun this morning, with more high clouds
this afternoon. Temperatures aloft will be similar to yesterday,
but with a cooler start and a developing east wind, readings will
probably be a little cooler than yesterday. The exception will be
central Wisconsin, which stayed a little cooler than other areas
yesterday and may get warmer today. Continued east winds and
increasing clouds tonight will temper mins, so stayed close to a
broad-based blend of guidance products. With clouds, incoming 
rain, and strengthening east-southeast winds, guidance actually
looked a little too warm on Monday. So edged temps back a bit--
especially near the lake.

Differences among the models in the arrival time of the rain on
Monday are pretty typical of what occurs about 36 hours out. 
Tried to stake out a middle ground--which is similar to the timing
of the ECMWF.

.LONG TERM...Monday Night Through Saturday
Issued at 319 AM CST Sun Feb 19 2017

Forecast concerns revolve around temperatures and precip chances for 
the upcoming week.  A blend of the ecmwf/gfs will continue to 

Monday night through Tuesday night...A cold front will push east 
across the area Monday evening.  The front will have ample moisture 
to work with (pwats above 1.0 inches), so rainfall amounts above a 
half inch remain possible before the rain pulls out late Monday 
night. Not unreasonable to think that a few rumbles of thunder could 
occur within the stronger showers. The ecmwf has been blowing away 
the competition in regards to temperature verification, so relied on 
the ecwmf products for high temps on Tuesday. Temperatures will 
remain mild behind the front, as west winds continue to bring in 
downsloped air off the Rockies.  So raised temps into the middle 50s 
north to lower 60s south.  Based on 925mb temps, these forecast 
highs could still be several degrees too cool.  Continued quiet and 
mild through Tuesday night.

Rest of the forecast...Low pressure will move across northern WI or 
Lake Superior on Wednesday and an accompanying cold front will drop 
south across the area on Wednesday night.  Small precip chances will 
occur along the front over northern WI, but looks doubtful 
elsewhere.  Temps will likely fall back with more clouds and precip 
chances over northern WI, but central and east-central WI could see 
highs in the low 60s. Depending upon how far south this front 
reaches will help determine the track of a large cyclone at the end 
of the week. Potential is there for parts if not most of the area to 
be impacted from wintry weather with this system, but nature of the 
split flow pattern will make the track tough to pin down until later 
in the upcoming week.

.AVIATION...for 12Z TAF Issuance
Issued at 319 AM CST Sun Feb 19 2017

Considerable high and middle clouds have prevented any fog across
the area thus far. But with the bulk of the clouds shifting east,
some fog with MVFR visibility restrictions could still form until
a little after sun up. Will monitor the obs for that and make an 
issuance time decision on how to handle it in the 12Z TAFs. Fog 
with MVFR visibilities is also possible late tonight as moisture 
begins to increase from the south. Otherwise, the main aviation 
concern will be LLWS developing across the western part of the 
area late tonight.



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