Area Forecast Discussion
Issued by NWS Green Bay, WI
FXUS63 KGRB 220337 AAA
Area Forecast Discussion...UPDATED
National Weather Service Green Bay WI
1037 PM CDT WED SEP 21 2016
New Information added to update section
Issued at 1037 PM CDT Wed Sep 21 2016
Considered trimming back the northern and eastern portion of the
Flash flood Watch this evening with current radar trends. After a
period of heavy convection over parts of Central Wisconsin early
this evening, precipitation has shifted to a stratiform type of
rain over much of the area including northern wisconsin. Radar
rainfall rates were much higher across the north compared to
ground truth. Recent nam has shifted rain to the north
tonight, so was reluctant to pull any headline at this time. In
addition convection was developing upstream over East Central
Minnesota and will be working into the state overnight and PWATS
were forecast to increase. Will let the overnight crew adjust
headlines with the next suite of data. Will likely cancel flash
flood warnings for now but head to areal due rising rivers.
.SHORT TERM...Tonight and Thursday
Issued at 226 PM CDT Wed Sep 21 2016
The latest RAP analysis and satellite/radar imagery show a surface
warm front snaking from southern Minnesota to northern Illinois
early this afternoon. Showers and thunderstorms continue to fire
along the boundary over the same areas that received heavy rainfall
last nite, namely southeast Minnesota and southern Wisconsin.
Additional storms are firing over western Wisconsin in a region of
low level moisture convergence. These storms will likely continue
to develop and push into the I-39/route 51 corridor later this
afternoon. An isolated severe storm will be possible from Lincoln
to Waushara counties with mu capes above 1000 j/kg and 0-6 km shear
of 45-50 kts. As a weak shortwave lifts across the Plains and into
the western Great Lakes tonight, thunderstorm trends and potential
for heavy rain/severe weather are the main forecast concerns.
Tonight...An active period of weather, with an atmosphere conducive
for heavy rainfall. A weak shortwave, currently over southwest
Nebraska will lift northeast and across the region late tonight.
Ahead of the shortwave, a strengthening 30-40 kt low level jet is
anticipated to ride over the slowly northward advancing warm front
later this afternoon into this evening. With ample instability and
shear as shown on mesoanalysis imagery, showers and thunderstorms
are expected to develop and expand upstream of the current
thunderstorm activity over southern and central Minnesota, before
sliding east through the night. Elevated capes of 1000-1500 j/kg
suggest a severe storm cannot be ruled out through the evening,
especially over areas from west of the Fox Valley and south of route
29. In addition, long duration of forcing combined with plentiful
moisture (pwats of 1.75 to 2.00) continues to imply that a flood or
flash flood threat is possible. The latest guidance shows that
central WI from Lincoln to Waushara counties have the most risk for
receiving heavy rainfall, with amounts of 1-3 inches possible
(locally higher). Though concerns are not as high for flooding
further east within the flood watch, potential for heavy rain will
remain, especially over the southern Fox Valley where rainfall over
an inch has already fallen early this morning. Temps ranging from
the mid 50s north to mid 60s south.
Thursday...Model guidance continues to show that the front will
remain stalled over central and northeast Wisconsin. Though weak
shortwave impulses will be passing to the east during the morning,
periods of showers and storms will likely continue through the day.
Weaker forcing and instability suggests rainfall only has a limited
potential to be on the heavy side, so thinking additional amounts of
a quarter to a half inch will be possible, locally higher in storms.
With the rainfall and clouds, temps will remain cooler in the mid
60s to mid 70s.
.LONG TERM...Thursday Night Through Wednesday
Issued at 226 PM CDT Wed Sep 21 2016
A frontal boundary that was just to the southwest of Wisconsin
early this afternoon is the main concern through the end of the
week before a surface low pressure system brings a cold front into
The approaching warm front will keep at least a chance for
showers and thunderstorms in the forecast through Saturday
morning. Central and east central Wisconsin will be the main
concern for heavy rainfall since the front is expected to be in
that general area before it finally makes a stronger push to the
northeast and clears the state late in the week. Looks like there
could be a period of dry weather, with not even a slight chance
POP, Saturday afternoon but confidence in timing is low.
Have shower and thunderstorm chances returning with the approach
of a cold front from the west, which may take a while to clear the
state. The 12Z GFS, ECMWF and Canadian all started to exhibit
significant differences for early next week but all looked quite
wet through the end of the forecast period.
Highs during the day should be within a couple of degrees of
normal, and lows should be warmer than normal due to all of the
clouds and rain.
.AVIATION...for 00Z TAF Issuance
Issued at 444 PM CDT Wed Sep 21 2016
A nearly stationary frontal boundary extending from west to east
over the state will be a focus of showers and storms tonight into
Thursday. Cigs and vsbys will continue to deteriorate tonight and
continue into Thursday.
Flash Flood Watch through Thursday evening FOR WIZ018>020-030-