Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 152315
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
615 PM CDT Thu Jun 15 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 241 PM CDT Thu Jun 15 2017

Jet energy rotating around an upper low to the north
may produce isolated thunderstorms across northern Wisconsin this
evening despite decreasing low level moisture.

A weak surface low approaching from the central Plains combined
with weak upper support could produce scattered thunderstorms
Friday. While severe thunderstorms are not expected Friday, a few
could produce gusty winds and small hail.

Lows tonight and highs Friday will remain above normal for this
time of the year.

.LONG TERM...Friday Night Through Thursday
Issued at 241 PM CDT Thu Jun 15 2017

Models remain adamant in showing upper ridging from the eastern
Pacific into the southwest CONUS and over the western Atlantic.
This brings a general upper trough over east-central North
America. This pattern will bring a west-northwest flow into
northeast WI with a series of Pacific systems to impact the region
at regular intervals. Timing/extent of each system remains the
biggest forecast challenge. Temperatures will cool below normal
early next week, then rise closer to normal by mid-week.

Shower/thunderstorm chances will continue into Friday night as
another mid-level shortwave moves through the fast westerly flow
aloft. Forcing is a little better over central/east-central WI, so
have placed higher pops there, while parts of northern WI may not
see any precipitation at all. Plenty of clouds expected which will
keep temperatures on the mild side with readings in the middle to
upper 50s north-central WI, lower to middle 60s elsewhere.

There could be a brief break in the precipitation chances Saturday
morning, however the next round of showers/thunderstorms looks to
overspread northeast WI Saturday afternoon ahead of a strong
shortwave trough digging east-southeast through the northern
Plains. Capes by the afternoon could reach 1500 J/KG over central
WI with increasing deep-layered shear. We will need to watch the
intensity of these storms as a few could become strong if enough
instability is realized. Temperatures on Saturday are expected to
be cooler than previous days (more clouds), with readings in the
middle to upper 70s north-central/lakeshore, mainly lower 80s
elsewhere.

The best likelihood of seeing showers/thunderstorms will be
focused from Saturday afternoon through Saturday evening as the
shortwave trough arrives, accompanied by a surface low and cold
front. Even though instability weakens a bit with the loss of
daytime heating, there is lift from the cold front, sufficient
shear and moisture available for some of these storms to be strong
or even severe. Northeast WI is currently in a marginal risk of
severe thunderstorms, so anyone with outdoor plans late Saturday/
Saturday evening will want to keep an eye to the sky. For now,
will keep likely pops in the forecast Saturday evening, then begin
to taper pops down behind the cold front. Min temperatures to be
in the middle to upper 50s north-central, upper 50s to lower 60s
elsewhere.

Cool cyclonic flow to take over for the latter half of the
weekend. This cooler air aloft, combined with daytime heating and
the passage of a weak surface trough, will bring another chance
for showers/afternoon thunderstorms to much of the forecast area.
Temperatures are forecast to be markedly cooler (along with lower
dew points) with readings topping out in the middle to upper 60s
north-central, lower to middle 70s elsewhere.

Precipitation trends should diminish Sunday night upon sunset,
however activity is progged to redevelop on Monday as instability
increases once again with daytime heating. Hard to discern if any
mid-level shortwaves would be moving through the northwest flow
aloft, so have kept pops on the low side. Cooler temperatures to
persist with max temperatures Monday similar to those witnessed on
Sunday.

A weak surface ridge pushes across WI Monday night which would
briefly end the precipitation threat and allow skies to become at
least partly cloudy. Timing issues arise with the next weak
Pacific system approaching WI on Tuesday. The CMC is the fastest
of the models with this system (Tuesday morning), while the GFS is
the slowest (barely has precipitation into central WI by 00z Wed).
Will probably split the difference and bring small pops into the
forecast Tuesday morning central WI, Tuesday afternoon for eastern
WI. A slight backing of the winds from west-northwest to west-
southwest will allow for max temperatures to mainly be in the
70-75 degree range.

While timing is far from certain, indications are for another weak
ridge of high pressure to push across the western Great Lakes on
Wednesday and bring a dry day to northeast WI. This looks to
change once again by Thursday as the models show the next system
moving into WI with more shower/thunderstorm chances. Temperatures
by mid-week should be close to seasonal normals for late June.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 615 PM CDT Thu Jun 15 2017

VFR conditions are expected through the period as high pressure
slides through the area. Low pressure approaching from the south
will bring the chance for showers and thunderstorms Friday
afternoon and evening. However activity will be fairly isolated so
will opt to keep the TAFs dry with this issuance.
&&

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

$$

SHORT TERM.....RDM
LONG TERM......AK
AVIATION.......Kurimski



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