Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 192013
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
313 PM CDT Thu Apr 19 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Friday
Issued at 312 PM CDT Thu Apr 19 2018

Forecast concerns include temperatures and fog potential.

Despite a deep snow cover over the entire forecast area,
temperatures have risen into the upper 40s and 50s away from Lake
Michigan, and dew points have mixed out into the single digits and
teens. With this in mind, have raised tomorrow`s high temperatures
above the previous forecast (50s away from Lake Michigan) and
lowered dew points considerably, though not nearly as low as
today.

The only other aspect of the forecast to consider is fog potential
late tonight into early Friday morning. The prevailing thought was
to expect an increase in low-level moisture due to melting snow,
but today`s mixing has mitigated that. Dew points will certainly
come back up overnight, and clear skies and light winds should
support at least patchy fog development. Several models indicate
more widespread fog over parts of central WI, where the surface
ridge axis will reside late tonight. Have worked this trend into
the forecast. Lows should drop into the teens and 20s.

.LONG TERM...Friday Night Through Thursday
Issued at 312 PM CDT Thu Apr 19 2018

The main concern for the long term is the warm-up in temperatures
resulting with possible rapid snow melt. Besides the warm-up, the
next chance for precipitation arrives late Tuesday afternoon.

A strong ridge of high pressure will remain over the region
through Sunday as a low pressure system tracks across the lower
Mississippi Valley. This high pressure system will keep
temperatures close to normal in the middle to upper 50s through
the weekend. It is also possible for patchy fog to develop during
the early morning hours on Saturday as well as Sunday due to the
melting snowpack to keep moisture in the lower atmosphere.

Temperatures will warm above normal for some spots on Monday and
Tuesday reaching to the lower 60s in some spots. These mild
temperatures associated with the higher April sun angle will keep
the snowpack melting through the beginning of next week.

The next chance for precipitation is associated with the arrival
of a cold front and its trailing shortwave trough late Tuesday
afternoon. Model guidance is not in agreement with the
precipitation associated with this system. However, there is
agreement with the evolution of the shortwave trough becoming a
closed upper level low and its track to the southwest of
Wisconsin. The ECMWF has all of the precipitation remaining well
to the southwest of Wisconsin compared to previous runs. On the
other hand, the GFS and Canadian show precipitation entering the
region late Tuesday afternoon through Wednesday afternoon. Due to
the uncertainty of this system, a blend of the models was favored
with slight chance pops continuing through Wednesday evening.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1226 PM CDT Thu Apr 19 2018

Melting snow and the arrival of a surface high should result in
at least patchy fog development late tonight into early Friday.
However, this is not a foregone conclusion, as daytime heating has
mixed some very dry air aloft to the surface, and this may offset
the increase in low-level moisture from the melting snow pack.
Models suggest that the best chance of fog will be southwest of a
Merrill to Oshkosh line, so added a TEMPO group for IFR VSBYs at
AUW/CWA.

Otherwise, VFR conditions and patchy high clouds are anticipated
for the rest of the TAF period.
&&

.HYDROLOGY...
Issued at 312 PM CDT Thu Apr 19 2018

Warming temperatures are expected to produce significant melting
of the current snowpack over northeast WI. This will lead to
runoff and a gradual rise of area rivers and streams. Recent RFC
forecasts indicate the Wolf River to reach bankfull this weekend
and reach flood stage on Tuesday. People living near rivers and
streams should keep a close eye on the anticipated river rises and
keep up to date on the latest river forecasts.
&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......Hykin
AVIATION.......Kieckbusch
HYDROLOGY......Hykin



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