Forecast Discussion for GRB NWS Office
FXUS63 KGRB 212249

Area Forecast Discussion
National Weather Service Green Bay WI
549 PM CDT Sun Oct 21 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 205 PM CDT Sun Oct 21 2018

The latest RAP analysis and satellite/radar imagery show surface
high pressure shifting into the central Great Lakes and a cold
front moving into northern Minnesota early this afternoon. Area of
mid clouds continue move southeast within a warm advection zone
ahead of a shortwave trough north of Minnesota. Farther west,
clear skies are prevailing along the front, as area soundings
show ample dry air below 700mb. Because of this dry air, forecast
concerns mainly revolve around cloud cover and temps in the short

Tonight...Weak shortwave energy will continue to move across Lake
Superior and the Upper Peninsula. Meanwhile, the weak upstream
front will lose definition as it progresses across the state.
Since Gulf moisture is shut off, no sign of any moisture surging
north along the front, and progged soundings remain dry through
the column. As a result, mostly clear skies are anticipated. Winds
are projected to fall off late, so trended toward the colder
statistical guidances for low temps. This lowered temps by a few
degrees, mainly over central WI and the northwoods.

Monday...Stronger shortwave energy will be diving southeast across
northern WI. Moisture will remain extremely limited, but a cold
front will quickly drop into the area in the afternoon. Some low
clouds will likely arrive behind the front over north-central WI,
but mid-levels remain dry. Will keep precip chances out of the
forecast for now. Warmer temps mainly in the 50s.

.LONG TERM...Monday Night Through Sunday
Issued at 205 PM CDT Sun Oct 21 2018

No major weather impacts expected through much of the extended
portion of the forecast. The next chance of significant
precipitation will be toward the end of the week into next weekend.

Monday night into Tuesday: A trough axis will remain nearby allowing
850mb temperatures to cool to around -6C to -7C. This, along with
Lake Superior surface temperatures around 6C to 7C and northwest
flow, will lead to light lake effect rain/snow potential over
north-central WI. This will be especially true over Vilas County.
No major system forcing is expected, so any precipitation should
remain fairly light with inversion heights/moisture remaining at
or below 4 kft. Only a small portion of the convective cloud
layer is expected to reach near the -10C isotherm, so any of the
snowflakes that form should remain small and give low snow to
liquid ratios at best. Outside of some increased cloud cover along
with MI/WI border, the rest of the CWA is expected to remain dry.
Monday night lows will be in the 30s with highs expected to be in
the 40s for Tuesday.

Tuesday night through Wednesday night: High pressure will move
across the area through this time period, both aloft and at the
surface. This will allow for dry conditions, partly cloudy skies and
relatively calm winds. This will allow for some cold temperatures
Tuesday night with ideal radiational cooling conditions. Lowered
temps a few degrees to trend that way. Temperatures will remain well
below normal with overnight lows dropping into the low to mid 20s
northwest to low 30s southeast. Daytime highs will be in the upper
40s to around 50.

Thursday into next weekend: Return flow will kick in on the back
side of the departing high pressure system. This will lead to
increasing moisture and cloud cover across much of the CWA ahead of
the next system. There will also be a steadily increasing chance of
precipitation across the area. An initial upper level wave is
expected to slide through the CWA Thursday afternoon into Thursday
night, which may bring some light rain or rain/snow. (all rain
during the day) The next more organized system will be Friday
night into Saturday as the next area of low pressure slides
through the area. At this point, it looks like temperatures will
be warm enough at the surface and aloft to keep most of the
precipitation in the form of rain. Model consensus was the way to
go with this forecast package, along with mainly chance
precipitation, as significant model differences remain.

.AVIATION...for 00Z TAF Issuance
Issued at 544 PM CDT Sun Oct 21 2018

A weak surface trough will drop southeast into the area tonight,
but moisture will be limited, so little in the way of cloudiness
will accompany the feature. An upper shortwave digging southeast
toward the region tomorrow will likely lead to some cloudiness
spreading across the north during the afternoon, but bases should
remain VFR through 00Z. Increasing flow across Lake Superior may
result in some MVFR ceilings across the north tomorrow night, but
that will be after the end of the current 00Z TAF period.



LONG TERM......Cooley

NWS GRB Office Area Forecast Discussion