Area Forecast Discussion
Issued by NWS Green Bay, WI

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464
FXUS63 KGRB 271145
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
645 AM CDT FRI MAY 27 2016

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Saturday
Issued at 348 AM CDT Fri May 27 2016

Precipitation trends and temperatures are the main fcst concerns.

Ridging aloft brought dry conditions early this morning, with
mainly high clouds impacting the area. Light winds and abundant
low-level moisture was resulting in patchy fog development.
Regional radar mosaic showed showers and a few tstms developing
over southeast MN, eastern IA and northwest IL, in response to
increasing waa and moisture convergence, and a short-wave trof.

Patchy/areas of fog will dissipate early in the day. The band of
showers and embedded tstms is expected to arrive a little slower
than was previously advertised. Most of the meso-models suggest
that pcpn will hold off until around 15z in central WI, then
surge northeast as sfc/H8 warm fronts arrive in the late morning
and afternoon. Will carry likely pops for most of the fcst area,
with chance pops in our far eastern counties. Not expecting any
severe tstms, as instability will be weaker than the previous
couple days. Used a blend of the better performing guidance sets
for high temps, which yielded mid 70s to lower 80s, except upper
60s and lower 70s near the lakeshore.

It will be difficult to nail down specific pcpn trends tonight
into Saturday, due to a lack of significant dynamic forcing.
However, a very moist air mass will return to the region, with
precipitable water values increasing to 1.5 to 1.75 inches, so
it won`t take much to generate showers and sct tstms. Will
continue to carry high chance/likely pops over the entire fcst
area. There are some indications that another warm front will
lift into central WI Saturday afternoon, as low pressure moves
into the northwest part of the state. A dry slot may provide
partial clearing over c/ec WI in the afternoon, allowing
instability to build near the frontal boundary. With CAPE
increasing to 800-1200 j/kg, and deep layer shear of 30 to 35 kts,
will need to monitor for another round of isold severe tstms. High
temperatures should be in the 75 to 80 range away from Lake
Michigan.

.LONG TERM...Saturday Night Through Thursday
Issued at 348 AM CDT Fri May 27 2016

A prevailing SW flow aloft will continue into WI through Sunday
night, thanks to a shortwave trough that is expected to move from
the Central Plains through the Great Lakes. Expect to see
unsettled weather persist until this trough exits the region with
conditions becoming more stable as the mean flow turns more
westerly. Models show an upper ridge developing over the Western
CONUS early to middle part of next week and this will allow for a
downstream shortwave trough to push east across the northern tier
of states. This system would bring the next chance of showers/
thunderstorms to NE WI late on Tuesday into Wednesday.
Temperatures are forecast to remain above normal through mid-week
and then fall to or slightly below normal next Thursday.

The initial shortwave trough is forecast to move from the Central
Plains northeast to the Upper MS Valley/Midwest Saturday night and
into the Great Lakes on Sunday. This trough will be accompanied by
an eastward moving cold front that is expected to push across WI
on Sunday. Plenty of low-level moisture to be in place with dew
points in the upper 50s to lower 60s and with the lift provided by
the cold front and sufficient mid-level forcing provided by the
shortwave trough, anticipate at least a couple rounds of showers
and thunderstorms to move through the region during the Saturday
night/Sunday time frame. Look for min temperatures Saturday night
to be in the mid to upper 50s north/lakeshore, lower to middle
60s south. Max temperatures for Sunday should reach the mid to
upper 70s north, upper 70s to around 80 degrees south (cooler
lakeside).

Any lingering precipitation chances into Sunday evening should
come to an end as the cold front pushes east and the shortwave
trough continues to track northeast into Canada. The rest of
Sunday night and most of Memorial Day appear to be dry at the
moment with a weak area of high pressure drifting through the
region. The only concern for precipitation would be Monday
afternoon roughly over the southern half of the state where
instability increases and there is an upper diffluent flow aloft.
Will probably end up keeping a small pop over central/east-central
WI on Memorial Day for now. Sunday night`s min temperatures will
cool a bit with some clearing taking place as readings drop into
the 50-55 degree range north, 55-60 degree range south. Max
temperatures though on Memorial Day should again return to
readings similar to Sunday`s.

Any spotty precipitation chances would remain over southern
sections of WI Monday night, but shower/thunderstorm chances are
expected to increase on Tuesday as the next shortwave trough rolls
across the Northern Rockies. Winds will turn to the S-SE and begin
to pull gulf moisture northward toward WI. Modest isentropic lift
to be the primary mechanism for these precipitation chances on
Tuesday, but with the main forcing still well to our west, have
kept pops fairly low through 00z Wednesday. Increasing clouds
should balance the WAA, thus max temperatures on Tuesday to range
from the upper 60s to lower 70s near Lake MI, to the upper 70s
over parts of Central WI.

This latest shortwave trough is progged to move across the
Northern Plains Tuesday night and head toward the Upper MS Valley
by late Wednesday. A cold front is expected to preclude this
shortwave trough with the models showing this front possibly
reaching Western WI by 00z Thursday. While the timing of both of
these weather systems could change in the coming days, there
should be enough isentropic lift and mid-level forcing to provide
a good chance of showers/thunderstorms across NE WI Tuesday night
into Wednesday. Forecast becomes more uncertain thereafter as the
ECMWF is rather progressive with this system, whereas the GFS is
much slower. It appears that the GFS maintains a much stronger
Eastern CONUS upper ridge which would slow the upstream shortwave
trough. This is evident with the dry ECMWF versus wet GFS for
Wednesday night and Thursday. Fully expect the models to wrestle
with this scenario in the days to come, so have used the consensus
solution which keeps small chc pops for both Wednesday and
Thursday.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 637 AM CDT Fri May 27 2016

BANDS OF SHOWERS AND SCT TSTMS WILL LIFT NORTH INTO THE REGION AS
A WARM FRONT APPROACHES. THE FIRST BAND WILL SHIFT THROUGH C/NC WI
THIS MORNING, BUT ACCURATELY TIMING SUBSEQUENT PERIODS OF SHOWERS
WILL BE A REAL PROBLEM. EXPECT MAINLY VFR AND PATCHY MVFR
CONDITIONS DURING THE DAY, WITH FLIGHT CONDITIONS GRADUALLY
DETERIORATING TO IFR AND PATCHY LIFR OVERNIGHT. CONFIDENCE IN THE
TIMING AND OCCURRENCE OF TSTMS WAS TOO LOW TO MENTION IN THE TAFS
RIGHT NOW.

&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......Kallas
AVIATION.......Kieckbusch



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