Area Forecast Discussion
Issued by NWS Green Bay, WI

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988
FXUS63 KGRB 180552
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1152 PM CST Fri Feb 17 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Saturday
Issued at 234 PM CST Fri Feb 17 2017

Forecast challenge tonight and Saturday concern potential stratus
development and influence on temperatures. A patch of stratus did
develop over northeast wisconsin early this morning but did not
hang around long. Upstream over Minnesota, no stratus or even
patches of dense fog developed under the upper ridge. Likely too
much mixing with the surface trough sliding over this same region.
This surface trough with strong winds aloft slides over tonight
and will likely hold down stratus development overnight. Still
possible a band of stratus may develop due to convergence as the
trough slides over but likely would be minimal at this time when
considering upstream ground truth.

Weak caa for Saturday will lead to more mixing in the boundary
layer and inversion to keep the warming trend going.

.LONG TERM...Saturday Night Through Friday
Issued at 234 PM CST Fri Feb 17 2017

Highlights for this period is the stretch of well above normal
temperatures through mid week next week, and precipitation
potential Monday through Monday night and then again late next
week.

Building upper ridge this weekend into early Monday will provide
a quiet and very mild pattern. Forecast max temperatures will be
dependent on cloud cover, but relatively low surface dewpoints
indicate more sunshine expected. High level clouds may start to
spill over the ridge late Sunday into Sunday night ahead of the
short wave trough. Clear skies will also provide cool overnight
low temperatures and morning inversions to overcome.

Dewpoints will be on the increase Monday ahead of a frontal system
and short wave trough working into the flattening upper ridge.
Latest progs suggest a band of rain ahead of a cold front to
sweep over the area mainly Monday night with up to a half inch of
rainfall on average. Even though the 925-850 mb air mass is
cooler Tuesday, warm start and mixing will continue the mild
temperatures. Easterly component of the wind Sunday and Monday
may lead to cooler by the lake wording for February.

A brief split flow regime develops mid week with a weak front
from the northern stream sliding over the state. Temperatures
will be still be above normal but slightly colder air settles
southward later next week ahead of a stronger system possible
late next week, to produce a mix potential at the onset Thursday
night into Friday.

Medium range models in somewhat better agreement with some
elements of the storm system late next week with the 850 low
sliding over the state and then colder air wrapping into the state
in its wake to end the mild trend. With the deepening 850 low,
thunder possible in the warm sector of the system or over the
southeast portion of the state. Total total values reach the
lower 50s over the Southeast portion of Wisconsin. This mornings
12z GFS run was becoming more aggressive with a warm front lifting
northward into the state Thursday night. Trends suggest a strong
dry slot sliding over the eastern half of the state, with more
snow over the northwest portion of Wisconsin and especially into
Minnesota.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1152 PM CST Fri Feb 17 2017

Potential for IFR conditions due to low clouds and fog is the
main concern during the TAF valid period.

Expect the strong low level inversion to persist through Saturday
evening. Winds develop more of a westerly component as a surface
low passes north of the state tonight. This should result in some
downslope across the eastern half of the area, which should
suppress low cloud development there. 00Z NGM MOS guidance wasn`t
indicating any LIFR visibility, just some MVFR conditions at
worst. MTW has had some MVFR category visibility in fog which I
think is from onshore flow, though their observation had no wind
data. Have generally gone with some MVFR fog for most inland
locations toward morning. VFR conditions should prevail for the
late morning and afternoon on Saturday.

Some LLWS can be expected overnight as southwest winds at 925mb
increase and eventually veer northwest. Speeds should be in the 35
to 40 knot range.
&&

.HYDROLOGY...
Issued at 234 PM CST Fri Feb 17 2017

Runoff due to snowmelt and rain early next week may produce
crests just below flood stage for a few of the main stem rivers.
More of an issue is the ice break up and unstable ice conditions
that could develop next week. Began adding ice break conditions
as per request of Central and Northcentral Wisconsin Hydro partners
in the HWO for starters today.
&&

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

$$

SHORT TERM.....TDH
LONG TERM......TDH
AVIATION.......MG
HYDROLOGY......TDH



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