Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 221652
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1152 AM CDT FRI JUL 22 2016

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 330 AM CDT Fri Jul 22 2016

Hot the next few days. A little less humid today, but high
humidities returning during the weekend. Another round of
thunderstorms is likely Saturday night.

The large scale pattern across North America will change little
during the period. A zonal band of westerlies will remain over the
northern CONUS and southern Canada, while the subtropical ridge
holds across the southern CONUS.

Hot weather will persist through the weekend, then temperatures
will gradually trend downward, likely returning close to seasonal
normals by the end of next week. Precipitation amounts are tougher
to evaluate since they will probably depend on a couple convective
episodes. High moisture values in place as an MCS crosses the area
Saturday night should yield another substantial rain in most
locations. But storms Sunday will be scattered, and then at least
a few days of dry weather are expected before the next chance for
precipitation. So totals for the next week will likely depend
primarily on what falls Saturday night.
&&

.SHORT TERM...Today...Tonight...and Saturday
Issued at 330 AM CDT Fri Jul 22 2016

The weather early this morning is much quieter than yesterday,
with the nearest MCS well south of the area and moving away.
Patchy fog will persist a little past sunrise, and a patch of high
AC should shift across the area during the morning. The weak
boundary across the area should drift off to the south as the flow
aloft tilts a little more northwesterly and weak high pressure
builds into the area. Dew points will mix down a little today,
though it will probably still be perceived as rather humid to most
people. Considered the possibility of a few storms developing near
the boundary before it exits the area, but support for that looked
too limited to justify adding to the forecast.

Clear skies and light winds will allow some patchy fog to form
again tonight. The main forecast issue then becomes how quickly
convection developing in the return flow to the west begins
affecting the area. The NAM, GFS, and Canadian models were the
most aggressive in pushing the convection east, while the 2 HiRes
WRFs and the ECMWF were slower. Preferred the latter. The NAM and
GFS did not handle Thursday morning`s MCS well and totally missed
the development of the MCS now over IL. The 2 HiRes WRFs had a
reasonable grasp on the current IL storms, and were really the
only 2 of the major models to correctly handle Thursday morning`s
storms.

Edged temps a little above a blend of the top performing guidance
products for today and Saturday as plenty of sun is expected. In
contrast, clear skies and light winds tonight supported trimming
temps a bit (especially across the north). Heat indices are
expected to top out in the upper 80s (N) to middle 90s (S) both
days, so no headlines will be needed for excessive heat.

.LONG TERM...Saturday Night Through Thursday
Issued at 330 AM CDT Fri Jul 22 2016

Low amplitude upper level flow is expected over the northern
Plains and western Great Lakes during this part of the forecast.

Thunderstorms for Saturday night and Sunday are the primary
concern in the long term as a surface low, passing through
southern Canada, drags a cold front through Wisconsin and a mid
level short wave trough moves across the region. 00Z models had
QPF across the entire forecast area during the 00Z-06Z Sunday
period, and again 06Z-12Z Sunday. 00Z NAM and GFS Bufkit soundings
around the area showed CAPE values well in excess of 1000 j/kg
early Saturday evening, with PWATs around 2 inches. With all this
in mind it appears that likely POPs are justified for Saturday
night. SPC day 2 outlook had a slight risk of severe in part of
central Wisconsin, with a marginal risk for the rest of the area
(except for Door County).

The models were pretty quick to move the rain out of the area, so
POPs rapidly decrease on Sunday, and Sunday night looks to be dry.

After a very warm, and wet, weekend a period of dry weather with
near normal temperatures can be expected for Monday through
Tuesday. There is a slight chance for thunderstorms on Tuesday
night, but the next chance for showers and thunderstorms should
be Wednesday through Thursday as another mid level short wave
tracks through the Great Lakes region. The timing and strength of
the short wave remain uncertain this far in advance so have gone
with chance POPs for Wednesday through the end of the forecast.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1152 AM CDT Fri Jul 22 2016

VFR conditions are expected under high pressure through Saturday
morning. Some fog is possible later tonight with light winds and
abundant low level moisture, possibly dropping conditions to MVFR
at times.
&&

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

$$

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



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