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Area forecast discussion 
National Weather Service Milwaukee/Sullivan WI
340 PM CDT Thursday Aug 21 2014

Tonight...forecast confidence medium.

First of all...the models are all over the place for where they are
placing quantitative precipitation forecast and storms tonight. The 12z NAM seems to be too slow
with its quantitative precipitation forecast solution based on what already happened this
morning...so if I mentally change the time to be valid 6 hours
earlier...the NAM actually seems representative of what could happen
through tonight...which is developing storms over eastern Iowa and
tracking them across northern Illinois. The 12z regional Canadian model
develops strong thunderstorms this evening since it did not pick up
on the morning convection and clouds and is not a reasonable
solution.

The WRF-arw and WRF-nmm and a couple of other models still show
thunderstorms developing over west central WI that slide southeast
through southern WI late this evening. Kept chance probability of precipitation in forecast
to cover this scenario. There is clearing and destabilization going
on over southeast Minnesota this afternoon that could support this
scenario. If these thunderstorms develop...there would be moderate
cape...shear and helicity to support a few strong updrafts and
therefore isolated severe hail and wind. With precipitable water
values around 2 inches...expect very heavy rain with any
thunderstorms.

By Friday morning...convection should be south of the WI/Illinois border
as the low level jet veers west. The NAM and GFS forecast soundings are
showing high cape and moderate shear over south central WI Friday
afternoon. The problem is that there will be a small cap. A few
models develop convection along a lake breeze...but there is plenty
of uncertainty. The better chance for convection will be closer to
the surface warm front which should be over IA/IL.

Some expected sunshine will allow temperatures to reach their potential
with 925mb temperatures around 25c...with maximum temperatures in the upper 80s inland
and lower 80s near the lake.

Saturday - confidence...medium
588dm 500 millibar ridge continues to be anchored across the
western Great Lakes. Shortwave energy is focused in the
Dakotas/plains. Associated surface low will be in the plains as
well. A frontal boundary will extend eastward from the low...with
the best frontal convergence proggd closer to western County Warning Area. Best
925/850 baroclinicity located there. Core of 850 low level jet is well west
but western County Warning Area closer to the influence of this feature. 925 temperatures
range from 20c in NE County Warning Area to around 24c in the SW County Warning Area. Meanwhile
hottest airmass continues to build to our southwest with 925 temperatures
deep in into the 20s celsius. Best cwasp numbers well to our west
where better dynamics reside.

Sunday - confidence...medium
upper ridge continues to build and expand eastward through the
rest of the Great Lakes region. 850 hot produce extends further
northeast with hot and humid airmass encompassing all of the area
with best baroclinicity well to our north. 925 temperatures proggd to
range from 25c in the eastern County Warning Area to 28c in the western County Warning Area. So expecting
to see plenty of low to middle 90s for high temperatures in central and western
County Warning Area...outside of any lake induced cooling. If southeast winds Bend more
southerly may need to expand hotter temperatures further east within the
County Warning Area. Cwasp numbers focus well to our northwest closer to the
stronger southwest 500 millibar flow. So will go with a hot/humid
airmass with considerable capping in place. Given 90/70 degree
temperature/dew point potential may need a heat advisory for some within
the County Warning Area.

Sunday night through Wednesday - confidence...medium
upper ridge breaks down and looks like we will transition into
more of an active pattern...with southwest upper level flow. While
lead ripples within the flow may generate storms with meandering
frontal boundary...the 12z European model (ecmwf) has trended towards the GFS with
a more prominent trough approaching towards midweek. The Tuesday/Wednesday
period looks interesting...though still some timing differences
between the GFS/European model (ecmwf) with the European model (ecmwf) trending faster...getting the
front to the east by midday Wednesday.

Thursday - confidence...medium
emcwf shows surface high dominating with dry weather while the
slower solution of the GFS suggests some wraparound rain showers
potential. While some differences in the synoptic setup...both are
largely dry. Will stick with the allblend probability of precipitation but finally suggest
a break from the thunder potential.

&&

Aviation/12z tafs/...there is a chance that additional thunderstorms
will develop over west central WI early this evening and roll across
southern WI late this evening. If that does not happen...expect
quiet weather for the whole night into Friday morning. The moist
conditions will likely lead to some fog development late tonight.
Early morning fog and low ceilings will gradually dissipate and
lift to VFR by middle Friday morning.

There will be unstable conditions and some sunshine for Friday
afternoon...but it is not certain that we will see thunderstorms due
to a small capping inversion and lack of a strong front. The lake
breeze will need to be watched for potential convection Friday
afternoon.

&&

Mkx watches/warnings/advisories...
WI...none.
Lm...none.
&&

$$
Today/tonight and aviation/marine...mrc
Friday through Wednesday...collar

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