Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
852 PM CDT Wednesday Oct 1 2014
as mentioned in the previous discussion...weak warm advection
combined with a weak short wave pushing in is helping to trigger
some showers across the western forecast area this evening. The
low level jet is also drifting into the area and helping things
along. Overall the forcing is weak...so expect mainly scattered showers
with a thunderstorm possible. The hrrr is showing the scattered
stuff in the west fairly accurately. However...it seems to be too
far north and too strong with the precipitation moving across Illinois.
The hrrr brings this in across our southeast rather solidly and
this looks overdone. Given trends...I may have to back away from
the likely probability of precipitation and keep it more in the high chance category if
things Don/T start to expand over the next hour or so. It looks
like all of this will move out by about 4 am tonight with a lull
in the precipitation until the next round moves in during the afternoon
on Thursday. Temperatures won't drop much from here with the warm
there is a chance of showers or an isolated thunderstorm
overnight. Trends are looking a bit drier than the models
indicated earlier. These showers should move out by around 09z
Thursday with a lull in the precipitation expected until more
arrives Thursday afternoon. Winds fall off later tonight within a
weak trough moving in. Much of the model guidance is indicating MVFR
ceilings/visibilities developing between 09-10z Thursday and continuing through
about 15-17z Thursday. We may even see some IFR ceilings develop for a
short time...centered around sunrise. VFR conditions should return
ahead of the next round of rain by early Thursday evening. In the
outlook for Thursday evening...more MVFR ceilings/visibilities are
anticipated as low pressure moves overhead.
Previous discussion... /issued 341 PM CDT Wednesday Oct 1 2014/
Tonight and Thursday...forecast confidence high.
Warm advection aloft combined with a passing shortwave will kick off
showers and a few storms this evening into tonight. Best chance
based on latest mesoscale models seems to be from around midnight
until around daybreak. Kept temperatures on the milder side tonight due to
clouds and warm advection.
Looks like a lull in precipitation tomorrow morning...with more showers and
storms expected in the afternoon as low level jet Cranks up to the
south. Could see a few stronger storms...with models showing cape of
500-1000 j/kg and 0-6 km bulk shear of 40 to 50 knots. Plenty of
moisture to work with as well...with precipitable water values
increasing to at least 1.50 inches. Storm Prediction Center has kept the day 2 slight
risk south of the WI/Illinois border...with 5 percent probs across much of
the forecast area. Latest mesoscale model simulated reflectivity
seems to agree with stronger and more organized convection south.
Though temperatures aloft increase tonight into tomorrow...kept highs right
around 70 for tomorrow...as clouds and precipitation will limit heating.
Thursday night through Saturday...forecast confidence medium.
Cyclogenesis is expected Thursday nt from SW WI to Eastern Lake Superior
with cold frontal passage in its wake. The nose of the low level jet and
associated moisture transport will boost precipitable waters to 1.5 inches...with
MUCAPE up to 500 j/kg. Surface-850 mb moisture flux convergence and
frontogenesis will bring widespread showers and scattered thunderstorms from
Thursday afternoon into the evening. Storm Prediction Center day 2 slight risk remains to
the south but some strong storms are still possible given deep
layer shear of 40-50 kts with the aforementioned available cape.
The cold frontal passage will occur quickly from west-east after 06z. At least
light to moderate rain showers will continue much of the night as
an upper wave will approach from the SW while a much stronger
upper wave moves into Minnesota.
A large polar trough will become established over the north
central USA on Friday...slightly moving eastward on Sat. Light showers may
linger Friday am in far eastern WI while instability showers may be
possible Friday afternoon. A secondary cold front will then bring
good chances of showers Friday nt...followed by slight chances for
instability showers once again on Sat. Strong cold advection will
keep temperatures falling on Friday with chilly conditions into Sat as the
925-850 mb cold pool moves across the area.
Sunday through Wednesday...forecast confidence medium.
The large polar trough will slowly lift north into Canada by the
middle of the week. Before then...shortwave troughs in northwest flow
will bring small chances of showers at times. Temperatures will warm each
day but remain below normal with the exception of Wednesday.
A few showers may affect the western half of the forecast area
through late afternoon...with showers likely and a few storms also
possible later this evening and overnight. Based on model guidance
and upstream observation...may see lower ceilings move in overnight. Could also
see some patchy fog.
Looks mainly dry Thursday morning...with more showers and storms
likely Thursday afternoon into the night. Lower ceilings and visibilities
certainly possible at times through this period.
Could see a few wind gusts approach Small Craft Advisory levels
tonight...but winds will generally stay below criteria. Westerly
winds Friday will be gusty behind departing low pressure. A Small
Craft Advisory may eventually be needed for this period.
tonight/Thursday and aviation/marine...ddv
Thursday night through Wednesday...gehring