Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
331 am CDT Thursday Jul 31 2014
Today and tonight...forecast confidence - medium.
-Shra finally coming to an end near kmsn. Amazingly these -shra
were remnants of Wednesday evening convection cluster that affected northwest WI.
-Shra are diminishing as air mass further destabilizes. MUCAPE less
than 100 j over most of southern WI. Otherwise...will need to keep in low probability of precipitation
for afternoon/evening convection. Surface dewpoints should remain mostly in the low
to middle 50s resulting in MUCAPE of 200-500 j/kg. Middle-level lapse
rates slightly higher than Wednesday afternoon...reaching the 6-6.5 degree
range with elevated lifted index falling to around -2. Slightly
more cyclonic curvature as well as stronger short wave moves from
the eastern Dakotas through Iowa into northwest Illinois today and this evening.
Once again combination of clouds...boundary layer mixing and recent
dry conditions preventing significant fog formation across southern WI.
Webcams or surface observation not showing any fog yet. As clouds associated
with dissipating -shra continue to thin...some eastern areas could
experience several hours of light fog early this morning...especially
ksbm and kenw. Areas of fog likely in the WI River Valley for several
hours as well.
Prevailing west to southwest winds and sunshine should help
temperatures warm above Wednesday highs by a few degrees. Lighter
pressure gradient will allow lake breeze to develop which will halt
temperature rise by Lake Michigan this afternoon.
Friday - confidence...medium
upper trough remains across the area. This will result in more of
the diurnally driven instability shra/tsra. Hard to pick up on any
organized forcing during the peak heating time with primary vorticity
maximum arriving Friday night. Will keep rain showers chances going all night
due to the passage of the main vorticity even though better instability
Saturday - confidence...medium
positively tilted upper trough will be near southeast WI at 12z with a
slow shift to the east. Lingering vorticity and cold pool aloft
suggests keeping the chance of rain showers/isolated thunderstorms and rain in the grids. Best
chances for this activity would most likely be in the eastern County Warning Area
closer to the colder temperatures upstairs with the lingering upper
Sunday - confidence...low
upper trough well to the east in the Ohio Valley with more of a
northwest flow across WI. No discernible shortwaves to latch onto
for focusing precipitation. The frontal convergence remains to our north
though the GFS is still aggressive with quantitative precipitation forecast while the European model (ecmwf) and
Gem keep precipitation largely across northern WI closer to the low level
Sunday night through Tuesday - confidence...medium
frontal boundary is proggd to sag into the area and will potentially
serve as a focus for shra/tsra. Low level jet does not look strong
nor does the upper flow during this period. However frontogenetical
forcing in the lower levels will likely be the primary driving
force for any convection.
Tuesday night and Wednesday - confidence...low
flow becomes a bit more zonal with stronger piece of energy
proggd to take aim on the western Great Lakes region. The European model (ecmwf) shows a
faster and stronger low developing and tracking to our south.
Meanwhile the GFS is weaker and slower. While details vary amongst
the models the trend towards higher probability of precipitation from the allblend looks
Aviation/12z tafs/...mostly VFR conditions to continue but a brief
period of light fog may affect several taf sites early this morning.
Not expecting stratus development this morning as atmosphere drier
just above surface inversion compared to 24 hours ago. Boundary layer
winds will also remain light westerly. Still a small chance for afternoon
convection as air mass destabilizes weakly as weak middle-level low
pressure trough moves across region. Expect lake breeze to affect eastern
taf sites later this morning.
Marine...light pressure gradient and diurnal warming will result in
lake breeze and winds turning to the east-southeast later this morning...
continuing this afternoon.
Today/tonight and aviation/marine...mbk
Friday through Wednesday...collar