Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 210819
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
319 AM CDT WED SEP 21 2016
.TODAY AND TONIGHT...Forecast confidence is medium.
Convection this morning is driven by strong h8-h7 warm and moist air
advection into the Upper Mississippi River Valley coupled with a
weak mid level short wave pushing through the zonal flow at that
level. The ongoing convection and its behavior this morning will
have a big impact on where redevelopment occurs later today and
tonight. This convection will lay out a decent cold pool,
essentially defining the location of the meandering frontal boundary
that will be the focus for repeated thunderstorm development over
the next few days. The mid level flow down to 850mb is southwest
into that cold pool, so the setup for repeated thunderstorm
development is there. The sfc front will likely get shoved south
into Illinois and northeast Iowa this morning and then lift a bit
north once the convection dissipates later this morning. More
activity should then develop along and north of it this afternoon
and evening. Therefore, look for the best chances of showers and
storms over the western and northern portions of the forecast area.
The timing and location of these episodic storms along the edge a
cold pool with persistent southwest flow impinging on it is
difficult to resolve perfectly. But, it`s a scenario that will
result in some heavy rain for some locations. Due to the training
echo potential, have decided to hoist a flash flood watch the
northern and western portions of the forecast area for today through
.THURSDAY THROUGH SATURDAY...Forecast Confidence...Medium
Deep moisture will remain overhead through the end of the week.
The highest precipitable water and CAPE values are progged to be
in the north on Thursday as a wave moves through. Highest pops
thus remain in the north.
Precip chances will keep going Friday as southern Wisconsin
remains between upper troughing to the northeast ridging to the
south. It won`t take much forcing to kick off more
The ridge should push in far enough by Saturday to result in a
return of dry weather.
Temps will generally remain above normal Thursday through
Saturday, though close to normal in the northeast half of the
forecast area Friday and Saturday.
.SUNDAY THROUGH TUESDAY...Forecast Confidence...Low
Models are in decent agreement in developing a closed upper low
early next week. The problem is the placement and movement of the
low. The GFS brings it overhead on Tuesday, while the ECMWF
lingers it much farther southwest. As a result, the GFS brings the
warm sector and precip through much quicker, while the ECMWF holds
onto the milder air and precip into mid-week. Pretty big
differences in model pops and temps. Generally tried to split the
difference between the solutions for now.
This will be an active period for showers and thunderstorms,
especially around KMSN. A round of convection should be moving
through around 12z this morning, then possibly a lull in the
activity until more redevelopment occurs this afternoon and
continues through the night. Timing of trends in a persistent
pattern that supports repeated thunderstorm development is very
difficult. In general, look for VFR conditions, but this
thunderstorm activity will bring periods of MVFR to IFR conditions
due to restricted VSBYS and briefly lower CIGS. Winds will remain
light, less than 10kts, outside of the convection.
.MARINE...Winds and waves will remain below small craft advisory
levels through the week.
WI...FLASH FLOOD WATCH through Thursday evening for WIZ046-047-051-
TODAY/TONIGHT AND AVIATION/MARINE...Davis
Thursday THROUGH Tuesday...DDV