Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 220001
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
701 PM CDT Thu Sep 21 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 258 PM CDT Thu Sep 21 2017

A warm front was lifting into southern MN and southwest WI
this afternoon. A band of low clouds was persisting north
of this boundary, and moving northward through GRB CWA.
Temperatures were in the low to mid 70s within the cloud band, but
in the upper 70s to lower 80s where there was sunshine. Despite
SBCAPE of 1000-1500 j/kg across the region, CINH of 75-100 j/kg
was capping off any convection.

The warm front is expected to lift north across the region tonight
and Friday morning. The front, combined with a developing 30-35 kt
low-level jet, should trigger isolated elevated thunderstorms
north of the boundary, as H8 LI`s of -3 to -5 C advect into the
region. Storms may be a bit more numerous over north central WI,
as some weak short-wave energy and the RRQ of 50-60 kt jet brush
past later tonight. SPC still has a small part of north central WI
in the Marginal risk for severe storms tonight, and this seems
reasonable, as deep-layer shear is strongest there (around 30
kts). Have added patchy fog across most of the region overnight,
with areas of fog in far northeast WI and on Lake Michigan, where
marine fog is already occurring.

The warm front will lift into the Upper Peninsula of Michigan
on Friday, ending the threat of thunderstorms. The resulting
clearing and gusty southwest winds will lead to strong heating,
with mixing through 900-875 mb supporting high temperatures
in the middle 80s to lower 90s, much above normal.

.LONG TERM...Friday Night Through Thursday
Issued at 258 PM CDT Thu Sep 21 2017

An amplified pattern will be in place for the conus until early next
week, thanks to a deep trough over the western U.S., and a ridge
over the east. The pattern does translate east, which will signal a
pattern change by the middle of next week across the region.
Although there are some timing differences in regards to when this
pattern change occurs, models are generally in good agreement this
far out, so will continue to use a multi model blend for this
forecast.

Friday night through Sunday...With a cold front nearly stationary
over Minnesota, and a warm front extending east over Lake Superior,
the entire region is expected to be located in the warm sector
during this period.  With mostly clear conditions and a breezy south
wind, temperatures will likely range from 15 to 20 degrees above
normal. Saturday should be warmer than Sunday, when a few 90s are
possible in the warm spots.  Heat indices in the low to mid 90s on
Saturday will fall back to the upper 80s on Sunday.

Rest of the forecast...Sunday night continues to look quiet and
warm. Then precip chances will gradually increase from west to east
on Monday and Tuesday when a cold front drifts closer to the region.
Storm chances look the highest on Tuesday along this front, but its
too early to assess a severe threat.  More seasonable temps return
behind the front for midweek.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 701 PM CDT Thu Sep 21 2017

Low clouds that were across central and east central Wisconsin
pushed northward during the late afternoon/early evening. Most
locations should have VFR ceilings, with MVFR fog and patchy IFR
fog developing overnight. MVFR ceilings may hang around northern
Wisconsin for much of the night, but still expect fog there with
dew points in the 60s at 23Z. Not sure about convective
development at this point. Looks like the closest convection is
what`s developing in northern Minnesota. Latest mesoscale models
did not have anything going on until later in the
evening/overnight and have just gone with VCTS for now, at least
until there is some development closer to the forecast area.
&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......MPC
AVIATION.......MG



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