Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 251143
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
643 AM CDT Tue Apr 25 2017
.AVIATION(12Z TAFS)...VFR conditions today followed by showers
developing tonight for S WI. Best chances for rain over south
central WI with lesser chances to far eastern WI. VFR conditions
early this evening with Cigs falling to 1-3 kft late tonight. MVFR
Vsbys will be possible with the rain.
.PREV DISCUSSION... (Issued 348 AM CDT Tue Apr 25 2017)
TODAY AND TONIGHT...Forecast confidence is high.
A shortwave trough will move newd across the state this morning
but with only few-sct high clouds over the area. For the afternoon
another shortwave trough will track from N IA to N WI with some
PVA to move across S WI. Went with only slight chance of showers
well west and north of Madison. Otherwise mostly sunny skies this
morning will become mostly cloudy but with more uncertainty in the
cloud cover to the east. Despite some clouds believe there will
still be enough heating for middle 70s inland from Lake MI
especially with mild temps to start the day.
For tnt, low pressure will develop along a n-s sfc trough from the
srn Great Plains to sw WI. The low will be near the WI, IA, MN
border around 12z Wed. Moisture transport on a 35 kt sly LLJ and
weak vorticity maximums within swly flow aloft will bring light to
moderate rain at times to south central WI but more sct in the
WEDNESDAY...Forecast confidence is medium.
A broad upper trough will sit over the western CONUS while an
amplified, negatively tilted upper shortwave ejects and pushes
through the Midwest. Meanwhile, a surface low pressure center will
slowly pass just to our northwest Wednesday morning. GFS, Euro, and
NAM all suggest that we will remain in the warm sector through at
least 00z Thursday, which will allow dewpoints to reach into the
upper 50s, and potentially into the 60s. Both the GFS and NAM show
PWATs reaching 1.5" by Wednesday afternoon, which exceeds the
daily maximum value by 0.4" on the SPC sounding climatology for
While precipitation is a near certainty, questions remain regarding
the convective potential for this system. First of all, with the low
just to our west at 12z, it looks like precip will be ongoing in the
morning. The evolution of the morning precipitation will play a
large role in how the afternoon develops. Additionally, it is likely
that we will be stuck under overcast skies through the day, limiting
instability. However, the system dynamics are quite strong, with 0-6
km bulk shear in the 40-50 kt range, and 0-1 km bulk shear close to
25 kts. If enough instability can build in, the lift, moisture, and
wind shear would support a severe weather threat. SPC day 2 outlook
has a marginal risk across our SE, which is reasonable given the
limited nature of the instability.
Aside from the potential severe threat, there are also concerns with
heavy rain. The extreme PWAT values mentioned earlier mean the
atmosphere will be primed for heavy rain production. It looks like
we`ll see at least 1" across much of the area, with locally higher
THURSDAY THROUGH TUESDAY...Forecast confidence is low.
Broadly cyclonic flow aloft will remain in place until the western
CONUS trough mentioned in the last section finally moves through
the region toward the end of the weekend. There is poor model
consensus with regards to the surface pattern for the end of the
work week, with the GFS and Canadian bringing another weak low
through while the Euro builds high pressure into the region.
Guidance actually comes back into decent consensus for the end of
the weekend as another strong low pressure system develops ahead
of the upper trough. Another prolonged period of precipitation is
expected from Saturday through Monday.
VFR conditions are expected through Tuesday. Mid and high level
clouds will move across the area at times through tomorrow. Models
backing off on the potential for fog near Lake Michigan later
tonight into Tuesday morning as higher dewpoints are slower to
Modest sely winds will prevail today into Wed nt with waves of 2
to 4 feet.
Today/Tonight and Aviation/Marine...Gehring
Wednesday THROUGH Monday...BSH