Area Forecast Discussion
Issued by NWS Green Bay, WI

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065
FXUS63 KGRB 180338
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1038 PM CDT Mon Jul 17 2017

Updated aviation portion for 06Z TAF issuance

.SYNOPSIS...
Issued at 219 PM CDT Mon Jul 17 2017

Warm and humid with periods of thunderstorms for the rest of the
work week and into the upcoming weekend.

The upper flow across the northern CONUS and southern Canada is in
the process of flattening as a trough from the Pacific progresses
eastward through the persistent ridge position over the
intermountain West. Though the lower amplitude pattern will
remain in place for pretty much the rest of the forecast period,
the medium range models have reached a consensus that the western
ridge/eastern trough pattern will re-appear next week.

A frontal boundary forecast to push southeast across the area
tomorrow is expected to stall to our south and linger there along
the southern edge of the westerlies. That will provide numerous
opportunities for precipitation, and likely lead to above (north)
to much above (south) normal amounts for the period. Warm and
humid air is expected to dominate the area. Temperatures will
probably be near to modestly above normal most of the time, though
readings will be held back on any days with widespread clouds and
precipitation.
&&

.SHORT TERM...Tonight and Tuesday
Issued at 219 PM CDT Mon Jul 17 2017

The latest RAP analysis and satellite/radar imagery show high
pressure centered over the central Great Lakes, and a cold front
positioned from northwest Minnesota to western Nebraska early this
afternoon.  Skies are mostly clear across the the eastern half of
Wisconsin, though there are scattered clouds popping over western WI
in an area of greater moisture return.  Looking upstream, scattered
convection is firing along the cold front over northern MN, and
mesomodels indicate a more organized complex developing later this
afternoon in this area.  As the front moves southeast, thunderstorm
trends and the possibility of severe weather on Tuesday afternoon
are the main forecast concerns.

Tonight...The cold front will continue to sag southeast across the
northern Plains and into northwest Wisconsin late.  Ahead of the
front, hourly high res models continue to indicate that the
thunderstorm complex over northern Minnesota will dive to the south
into the instability and miss north-central WI to the west late in
the evening into the overnight.  Both the nam/arw move this complex
very close, however, to Vilas/Oneida counties, so will leave a small
chance in the forecast.  Otherwise, a warm front will move east
across the region tonight and could see areas of 4-5 kft move in
with the front.  Some potential for lower stratus to develop as
well, similar to this morning over western WI, but not confident in
coverage or location.  Will increase sky cover some though.  Warmer
lows in the upper 50s to low 60s.

Tuesday...After some patchy or scattered low clouds, the cold front
will continue to move southeast into northwest Wisconsin during the
morning and into north-central WI during the afternoon.  May see a
few showers pop up in the morning ahead of the front over north-
central WI.  But the main show will occur from mid-afternoon onward
as convection develops along the front from western WI to the
western U.P. Guidance depicts 1500-2000 j/kg of ml cape and 25-35
kts of deep layer shear ahead of the boundary, which would be
sufficient for severe storms. Looking at damaging winds and large
hail as the main threats, though cannot rule out an isolated spin up
given the low lcls, while 1-2 inches of rain is also possible. As
storms grow upscale, some acceleration of the line is possible late
in the afternoon, but tough to say how far east they will push by
00z. Think they could be approaching the Door and Fox Valley by this
time.  Warmer and more humid, with highs ranging from near 80 in the
north to mid or upper 80s in the south.

.LONG TERM...Tuesday Night Through Monday
Issued at 219 PM CDT Mon Jul 17 2017

This pattern just does not lend itself to adding much detail to
the forecast beyond the first day or two.

The first round of storms will continue into Tuesday evening as
the front presses south across the area. The severe threat will
continue along the front through the evening, but should wane
later in the night. The steady southeast progression of the front
combined with a substantial veering of the 850 mb flow will limit
the potential for training of storms and flash flooding. But,
PWATs rising to near 2 inches suggest localized heavy rainfall
will occur, especially in the vicinity of significant storm
mergers. That could result in some flooding in urban areas where
there is a lot of pavement.

There will probably be a lull in the precipitation chances
Wednesday as the front continues south. But given the flat upper
flow, it is not surprising that the models quickly generate
return flow behind weak high pressure crossing the region. The
upper flow never seems to back enough to allow the surface
boundary to lift back through the region during the rest of the
forecast. That will likely keep the excessive rainfall/flash
flooding threat focused to our south. But there will still likely
be several rounds of showers and thunderstorms across the
forecast area as shortwaves interact with the frontal zone.

No significant chances were made the forecast initialization
generated from a broad-based blend of guidance products.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1018 PM CDT Mon Jul 17 2017

A thunderstorm complex inches closer to north-central Wisconsin
this evening, while the meso models continue to insist it will
continue to die out as it heads over north-central Wisconsin.
Despite this insistence it refuses to completely die out,
therefore will put a tempo group for some showers at RHI with this
issuance. The blowoff from the thunderstorms will probably keep
fog in check at RHI, and quite possibly AUW/CWA. However will
maintain some MVFR fog at the central Wisconsin airports given
some breaks in the cloud cover. Otherwise clouds will continue to
increase from west to east as a warm front approaches with strong
to severe storms to develop over the area during the afternoon
and evening hours.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....MPC
LONG TERM......Skowronski
AVIATION.......Kurimski



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