Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 171923

Area Forecast Discussion
National Weather Service Green Bay WI
223 PM CDT Thu May 17 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Friday
Issued at 222 PM CDT Thu May 17 2018

The main forecast focus to be on fire weather concerns on Friday
as temperatures are expected to warm, dry air to stay in place
and winds to be marginal.

The 19Z MSAS surface analysis showed a broad area of high pressure
located over much of Ontario into Quebec. The southwest flank of
this high pressure reaches into the western Great Lakes and
preventing any precipitation from developing. The radar mosaic had
picked up on two areas of showers/thunderstorms. One area was
located over the Dakotas/MN associated with WAA/8H warm front. The
other area was located over the Ozarks/MO associated with a
nearly closed area of low pressure. None of this activity will
impact northeast WI over the next 24 hours.

Quiet conditions are expected across the forecast area with the
high pressure holding on. Expect the instability mid clouds to
dissipate early this evening, leaving just high clouds from the
system to our south. Therefore, mostly clear skies with
diminishing winds are forecast for tonight with min temperatures
in the upper 30s to lower 40s north, middle to upper 40s south.

Dry conditions should hold through Friday as the influence from
the high pressure begins to weaken. The main concern continues to
be related to fire weather conditions as afternoon relative
humidities fall into the 25 to 35 percent range away from Lake MI.
It does not appear that we will be able to mix as high on Friday,
so wind speeds should be a bit lower. Nevertheless, northern WI
will see near-critical fire weather conditions due to the ongoing
dry conditions, low humidity levels and green-up has not finished.
Max temperatures on Friday to range from the middle 60s near Lake
MI, to the middle to upper 70s over central WI.

.LONG TERM...Friday Night Through Thursday
Issued at 222 PM CDT Thu May 17 2018

Focus is on weekend/early week precipitation chances followed by
another stretch of dry weather.

After some changes in the models over the past day, the latest 12Z
runs are somewhat more consistent in showing opportunities for
showers Saturday through Monday.

First, models are in decent agree that a piece of energy moving
up from the mid-Mississippi Valley Friday night could produce
light showers across our southeast forecast area, affecting
east- central Wisconsin, mainly east of Interstate 41. QPF amounts
would be light, less than a tenth of an inch, where rain does
fall. This wave moves out by Saturday afternoon, and the next
question is if showers will reach north- central Wisconsin
Saturday afternoon as another weak wave ejects out of the north.
Models diverge in solutions here and stuck with a blended
solutions which keeps a chance/slight chance mention in the
forecast through Saturday night.

The best chance for rain looks to arrive with a potentially
stronger shortwave that approaches Wisconsin from the southwest
sometime Sunday/Monday. The ECMWF depicts a weaker wave which is
gone by Monday afternoon; whereas the GFS and Canadian solutions
are slower, stronger, and keep showers over more of the area
through Monday night. Overall, confidence is still medium to low
on getting rain during any specific time period due to the
sporadic nature of the models, but expect at least the southern
half of the forecast area will get rain at some point. Confidence
is lower across the north. Thunderstorm chances are nearly gone
from the forecast for the weekend, with perhaps a few rumbles
possible in the far southern area on Sunday with MUCAPES up to
300 J/kg from Waushara east Manitowoc County.

Beyond Monday, models are in general agreement than a ridge builds
over the western Great Lakes keeping the forecast area dry for
most if not all of the week, with the ridge breaking towards the
end of the week. This brings up the continued potential for fire
weather concerns as the far north is now listed as `Abnormally
Dry` and have yet to fully green up. Relative humidity may
approach near critical values through the week in the north (25 to
35 percent) but the winds are expected to remain on the lighter
side (5 to 10 mph). Of course, conditions could still change this
far out but will be something to watch in the coming days.

Temperatues will be at or just below normal through Sunday due to
more clouds and possible rain. Highs will then warm into the 70s
through the midweek, although cooler along the lakeshore.

.AVIATION...for 18Z TAF Issuance
Issued at 1230 PM CDT Thu May 17 2018

VFR conditions are expected over the next 24 hours as northeast WI
remains on the southwest flank of an area of high pressure
situated over eastern Canada. Mid deck of clouds should gradually
dissipate this evening, while high clouds to persist due to a
system located well to our south. Gusty northeast winds should
also diminish this evening, however LLWS was added to all TAF
sites for portions of tonight as winds aloft remain strong.

Issued at 222 PM CDT Thu May 17 2018

Near-critical fire weather conditions are expected across northern
WI on Friday. Max temperatures in the 70s, relative humidities in
the 25 to 30 percent range and wind gusts to around 20 mph are
forecast for Friday afternoon.



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