Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
311 am CDT Thursday Sep 3 2015
Today and tonight...forecast confidence is low.
Nearly all of the models are struggling with this weak flow/ample
low level moisture pattern. A lingering middle level trough with an
axis dropping south across the area late this afternoon and evening
further complicates things. The initiation of convection could
happen on the most subtle of features and that/S where the models
are getting their varied solutions. In the very near term...the
current convection pushing into the Fox Valley area of east central
Wisconsin looks like it/S finally getting some organized cold pool
dynamics and shifting to a south southeast movement. This would take
it across at least our far northeast forecast area...possibly
sneaking down the lake to Milwaukee. The NAM actually looks pretty
good with this early stuff.
Nearly all the models then diminish the activity through the morning
with regeneration possible this afternoon and evening along a
surface trough stretched more or less west to east across southern
Wisconsin. This is the remnant cold pool outflow. The NAM convective available potential energy of
4000j/kg or better look unreasonable as usual. This has been a
weakness this Summer with surface dew points running too high. Will
continue to carry smallish probability of precipitation this afternoon given lots of
uncertainty about if and where this convection will develop. Where
ever it rains...it should be fairly heavy with precipitable water/S in the 1.6 inch
Friday through Saturday... forecast confidence medium.
A middle level shortwave is expected to sit over lower Michigan on Friday
and not move much through Saturday. There is a chance that some positive vorticity advection
will extend back into southern WI during this time. With the
atmosphere primed with plenty of moisture and instability... it
would not take much to initiate a few thunderstorms thus kept slight
chance probability of precipitation each day. Left the overnight periods dry... but cannot
rule out a stray thunderstorm.
925mb temperatures will continue to be in the 22-25c range... warmest
toward western WI. Clouds will be a factor with the maximum temperatures... but
went with highs around 80 near the lake and upper 80s well inland.
Sunday through Monday... forecast confidence medium.
A strong upper low over the Pacific northwest will swing
northeast into Saskatchewan/Alberta Canada Sunday and Sunday
night. An associated surface low pressure trough will likely
initiate showers and thunderstorms over Minnesota and northwest WI Sunday aft/eve.
The trough/ cold front will drop southeast through WI Sunday night
into Monday morning. The upper level forcing will be weakening
during this time so still not too certain about precipitation chances in
southeast WI. The trough should clear southeast WI by Monday evening.
Tuesday through Thursday... forecast confidence medium.
A remnant shortwave originating in the southwest monsoonal flow is
expected to track into the upper Midwest sometime Tuesday... just
ahead of another shortwave trough tracking through the northern
plains. These features will lead to another round of shower and
thunderstorm chances for southern WI Tuesday into Wednesday. Precipitation
should be out of southeast WI by Thursday morning and much cooler/drier
air will be in place.
VFR conditions should generally prevail through this evening. There
is a chance of thunderstorms today as a weak surface trough moves
south across the area. Timing is difficult given the weak flow...but
we could see some showers/storms move across the far southeast
before about 15z this morning...then quiet down with more
development possible by middle afternoon into the evening. Weak flow
and ample low level moisture could bring IFR ceilings/visibilities to southern
Wisconsin after 06z Friday and linger for a while after sunrise
Areas of fog will be a constant threat through the weekend as very
moist air interacts with the cooler nearshore waters.
Today/tonight and aviation/marine...Davis
Friday through Wednesday...mrc