Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
858 PM CDT Tuesday Jul 22 2014
the front will exit the southeast corner of Kenosha County within
a few hours...by 03z Wednesday. Storms just couldn/T get going along the
front given a weak elevated cap that lingered into the late
afternoon and then once it disappeared...the forcing was just so
weak that storms could not be triggered nor sustained. There was
also a wind shift ahead of the front that brought prefrontal
westerly winds...a sure sign of weak low level forcing.
Anyway...look for cooler conditions behind the front overnight
with temperatures by morning dropping into the lower to middle 60s with much
lower dew points heading in.
VFR conditions expected through the taf period as high pressure
builds in behind a departing cold front. Winds will shift to the
northeast overnight and be a bit brisk during the day on
Wednesday...especially over the southeast taf sites of
northeast winds developing in the wake of the cold front...with
high pressure building in...will bring large waves by Wednesday
morning. Will hoist another Small Craft Advisory running from 06z
Wednesday...tonight...through Wednesday evening.
Previous discussion... /issued 355 PM CDT Tuesday Jul 22 2014/
Tonight...forecast confidence - medium.
Heat index values ended up exceeding 100 from Madison and west late
this afternoon after the low clouds cleared away. Madison reached a
high of 90 or greater for the first time this year.
Storm Prediction Center trimmed the slight risk a little further southeast again with
the 3 PM update. Mesoscale models continue to keep the area capped
/no convection/ until the front gets into far southeast WI or even
northeast Illinois late this afternoon between 22z and 00z. Storm Prediction Center
mesoanalysis rap is showing eroding cin along the front in central
WI...so I will continue the slight chance along the front as it
moves southeast through the mkx forecast area. We cannot rule storm
development given the high dewpoints...surface front...very high
cape over 4000 j/kg and signs of slight upstream cooling at 700-
The inhibiting factors for convection are: the cap. The westerly
winds just ahead of the surface and 850mb fronts are limiting the
low level convergence. We will have to sit and wait to see if the
cap breaks as the surface front reaches southeast WI. There is
limited bulk shear of 25 to 30 knots. Isolated severe hail and winds
will be possible. Precipitable water values around 2 will lead to
very heavy rain with any thunderstorms. Urban flooding will be
Precipitation chances exit with front late this evening with cooler and
drier air moving in. Temperatures down into the lower 60s and dew
points in the middle to upper 50s by Wednesday morning.
Wednesday...forecast confidence high.
High pressure...drier and and cooler temperatures will settle into
the region. Look for diurnal cumulus clouds to develop by late
morning and linger through early afternoon due to steep low level
lapse rates. Steady north winds will gradually diminish during the
afternoon. Winds will be highest near the lake.
Wednesday night through Thursday...forecast confidence - high.
The quiet and less humid weather will continue through Thursday as a
high pressure ridge and drier dewpoints hold sway across the western
gtlakes. Expect patchy fog later Wednesday night due to light boundary
layer winds and lingering dewpoints in the low to middle 50s. Expect
some locations to dip down into the 40s late Wednesday night.
Thursday night and Friday...forecast confidence - low.
Considerable differences between short term guidance in handling of
low to middle level forcing during this period. GFS only guidance in
bringing convection associated with warm front southeast across
southern WI on Friday. Meanwhile...Canadian maintains warm front
orientation farther south across MO/southern Illinois. Latest European model (ecmwf) a blend
between the two which clips portions of SW into south central WI
with convection generated by moisture and warm air advection return.
Will lean toward more southern solution and keep lower probability of precipitation in the
west and south during this period as leaning toward drier solution
with better chance for convection farther west and south. European model (ecmwf) and
NAM show stronger west-northwest flow steering flow across southern WI while GFS
stronger SW. GFS remains outlier at this point. Too many
descrepancies so confidence remains low.
Friday night through Tuesday - forecast confidence - low
trending toward medium.
Like NCEP wpc blended...prefer ensemble of medium range guidance for
this forecast period. Most of the medium range guidance is showing
somewhat better agreement than 24 hours ago...and are converging on
a somewhat similar solution.
Weakening middle-level ridge over northern plains continues to weaken
and flatten early this forecast period as low pressure moves across
southern Canada. GFS continues to phase this system with eastern
Canada long wave trough a bit quicker than Canadian/European model (ecmwf) solutions.
GFS brings short wave across WI Sat night into sun...while other
solutions are slower...later Sunday into Sunday night. Hence will
need to keep chance probability of precipitation going over the weekend as upper level
trough moves through region.
By Monday...northwest winds in the low to middle levels will have
ushered cooler and drier air into southern WI...however weak ripples in
fast northerly flow may generate -shra.
A cold front moving southeast through southern WI will bring a
chance of showers and thunderstorms along it late this afternoon.
The chance will increase as the front gets into far southeast
Wisconsin around 6 PM...especially Kenosha and then southward into
Any thunderstorms will bring MVFR ceilings/visibilities if they develop. Expect
very heavy rain. Winds will become northwest behind the front...
then north to northeast overnight. Expect a period of broken VFR
cumulus clouds Wednesday midday on steady northerly winds.
Marine...Small Craft Advisory in effect until 9 PM. Winds and waves
will rise on Wednesday in the wake of the cold front. A Small Craft
Advisory will likely be needed.
Beaches...Milwaukee...Racine and Kenosha counties will be in a high
risk of swimming hazards later tonight and Wednesday. Sheboygan and
Ozaukee County beaches will be in a moderate risk of swimming
hazards tonight and high risk Wednesday.
Lm...Small Craft Advisory from 1 am Wednesday to 1 am CDT Thursday
Small Craft Advisory from 1 am to 7 PM CDT Wednesday for lmz643.
tonight/Wednesday and aviation/marine...mrc
Wednesday night through Tuesday...mbk