Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
326 PM CDT Tuesday Sep 1 2015
Tonight and Wednesday...forecast confidence...medium
Afternoon cumulus will diminish late afternoon and evening as
daytime heating is lost. Should be mostly clear then for at least
the first part of the night. Middle and high level clouds will then
likely increase later tonight into Wednesday as a shortwave
approaches. Winds will be a bit more in the lower levels than last
night. Between this and the possibility of clouds moving in...less
confident in fog. Pretty moist low levels though...so kept mention
of fog in the forecast for now. Similar to last night...lows should
be several degrees above normal values.
925 mb temperatures are prognosticated to be in the 24-26c range tomorrow...so
went with highs in the upper 80s to 90. Concerned about the
possibility of more middle/high level clouds with the shortwave than
currently in the forecast...possibly keeping highs down a couple
degrees. Banking on enough sunshine for now to mix down those warmer
temperatures. Kept some probability of precipitation going for mainly the afternoon hours as the
shortwave moves into the area. Best chance for storms should be in
the northern forecast area.
Wednesday night through Friday...forecast confidence medium.
A shortwave trough will slowly move across central WI Wednesday nt and
linger over east central and possibly southeast WI for Thursday. This area
will also be on the eastern periphery of a weak 850-700 mb
warm...moist advection zone. Precipitable waters will rise to 1.7 inches and many
models are responding with decent values of quantitative precipitation forecast over central WI.
The WRF mesomodels depict a cluster of convection over central WI
that will gradually move southeastward late Wednesday nt and probably into Thursday.
Thus increased probability of precipitation to 50 percent over the northern County Warning Area and eastern County Warning Area for
Wednesday nt and Thursday. Weak mean flow of 15 kts and northerly corfidi vectors
of only 5 kts combined with high precipitable waters would suggest heavy rainfall
with the thunderstorms. Rural areas can take a lot of rain this time of
year without flash flooding but a small threat would still exist
especially over urban areas.
The shortwave may then retrograde back into the area through Friday
given the weak upper flow so went with slight chance probability of precipitation Thursday nt-
Friday over eastern WI. Increased chances of rain and more clouds may
keep the temperatures down over the eastern half of WI for Thursday. More of an
onshore flow on Friday will also keep slightly cooler conditions in
the far east. The heat will likely remain over south central WI
with heat index values in the lower 90s for both afternoons.
Saturday through Tuesday...forecast confidence medium.
Stronger upper ridging should keep southern WI dry for Sat-sun with
continued very warm temperatures and humidity. A strong upper trough will
then lift northeastward from the western USA Sat nt and track northeastward to Ontario
Canada for Labor Day. This results in a weaker cold front for
Labor Day and only chances of thunderstorms at this time. Less humidity
and high temperatures in the 70s are then forecast for Tuesday as high
pressure builds into the region.
Could see some areas of fog again tonight...though maybe not as
widespread given a little more wind/mixing in the lower levels.
Otherwise...VFR conditions will prevail through Wednesday.
Could see some storms mainly in the afternoon tomorrow...the best
chance in the northern forecast area.
Latest webcams and satellite imagery show improved visibilities
south of Port Washington...with fog lingering north of there. With
southerly winds into at least early tonight...would expect the fog
to hang on for a while longer...so dense fog advisory for the
northernmost marine zone through tonight still looks good.
Lm...dense fog advisory until 7 am CDT Wednesday for lmz643.
Tonight/Wednesday and aviation/marine...ddv
Wednesday night through Tuesday...gehring