Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 211959

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

Forecast discussion for routine afternoon forecast 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

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 18Z TAF Issuance
Issued at 1242 PM CDT Thu Sep 21 2017

Large patches of IFR/MVFR ceilings remained across the region at
midday, though VFR conditions were found over parts of northern
and east central WI. Latest satellite trends suggest that the
main area of stratus will continue to lift north this afternoon
and evening, resulting in improving flight conditions for all but
the RHI TAF site. The cold front that moved through the region
yesterday is expected to return north as a warm front later this
afternoon and tonight, and may produce isolated/scattered
thunderstorms. Confidence is only high enough to mention VCTS
in the TAFs at this time.

Have added LLWS to the RHI/AUW/CWA TAF sites from late evening
through early Friday morning, as low-level winds increase to
around 35 knots from the southwest.



SHORT TERM.....Kieckbusch
AVIATION.......Kieckbusch is the U.S. government's official web portal to all federal, state and local government web resources and services.