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Area forecast discussion 
National Weather Service Des Moines Iowa
250 am CDT Wednesday Jul 23 2014

Short term /today/...
issued at 239 am CDT Wednesday Jul 23 2014

High pressure will build into the state today and provide dry and
pleasant conditions. By this afternoon...expect dew points to be
15 to 20 degrees less than Tuesday dew points resulting in much
more comfortable conditions. Leaned toward a blend today for maximum
temperatures as models were in decent agreement with respect to temperatures. May
see a few middle-level cumulus develop this afternoon...mainly around
5000 feet.

Long term /tonight through Monday/...
issued at 239 am CDT Wednesday Jul 23 2014

Cool front expected to be well south of the region by tonight with
high pressure building across the region and east of the area by
late tonight and early Thursday morning. Tonight...aloft a high
pressure ridge continue over the west Continental U.S. With ring of fire
short wave/thunder migrating across Oregon/Washington east to the
Dakotas with several short waves embedded in the flow. The first
in the series of waves will not reach our area but the second and
third now over Oregon and northern California will eventually
track into the northern plains by late Wednesday night and then
move east southeast along the rim of the hot dome to our west.
Models have been consistent with a portion of the second wave
moving into west/northwest Iowa by 12-18z Thursday and weakening...
while the third wave drives southeast and affects mainly the
northeast half of the forecast area Thursday evening through
Friday morning. While the winds aloft are increasing toward
Thursday evening...Lee side troughing with hot conditions will be
building back toward the area with a strong push of warm
air/thetae advection into the cooler air still leftover across
the Great Lakes. Models continue to key on intensifying h850-h700
frontogenesis with strong h850 inflow between 00z and 12z of 40 to
50kts. With forcing increasing...focus for a more concentrated
area of convection and rainfall is beginning to appear more likely
for the northeast. The cold front now south of Iowa tonight has
taken most of the moisture with it...subjective h850 analysis
shows pool of 15c dew points hovering along the Gulf Coast with
surface analysis showing 75f dew points clinging to the front in
Missouri. As the high retreats to the east and southerly winds
return...the moisture will quickly return as well with dew points
back in the middle to upper 60s by late Thursday evening south and
in the lower 60s northeast. As the system evolves for late
Thursday into Friday...precipitable water values will increase to
1.5 inches by 06z Friday and warm cloud depths will increase to 13
to 13.5 kft. Though there remains some uncertainty as to the which
model is capturing the location of the forcing best...based on
consensus it is appearing more likely that an mesoscale convective system may develop
across southern Minnesota or northeast Iowa late Thursday evening into
the overnight hours Friday morning. This would increase the
potential for some severe weather and heavy rainfall in this area
into Friday morning. The timing of increased instability will
lessen the overall threat for severe weather Thursday night...bufr
soundings at Kalo do show potential for locally heavy rains.
Currently the GFS/Gem are slower in bringing the period of heavy
rain/storms through the area...mainly 12z to 18z Friday with the
NAM and 22/00z and 23/00z Euro favoring Thursday night into Friday
morning. Currently am leaning toward the Euro which suggests 1 to
2 inch rainfalls possible nearer the boundary Thursday night. As
the warm air advection moves east Friday morning the system is
expected to quickly translate southeast with the warmest air
moving back southeast of the area by late day. Some residual
thunder will remain east Friday night...but the best dynamics
shifts east by then. Friday afternoon looks rather warm south and
southwest...with highs pushing back into the 90s once again and
heat indices nearing 100f southwest.

Following this system...the weekend continues to advertise a pacnw
h500 wave crossing the ridge and phasing with a stronger h500 low
over Hudson Bay Canada. As the systems phase...a cutoff low should
develop over the eastern Great Lakes with unseasonably cooler
weather returning to much of the Great Lakes and Central Plains.
Given that the Central Plains will be on the western edge of the
northwest flow...we will likely be pleasantly cool with h850 temperatures
in the lower to middle teens supporting highs in the 70s to near 80
and lows in the 50s to lower 60s. Depending on the position of the
system...we may also see some showers from time to time mainly
during the afternoon hours as the cooler air moves across the
region. The cooler weather will hold through the end of the
period.

&&

Aviation...23/00z
issued at 705 PM CDT Tuesday Jul 22 2014

VFR conditions are expected through the period with mostly clear
skies and light generally north winds. No precipitation or obscurations
are anticipated.



&&

Dmx watches/warnings/advisories...
none.
&&

$$

Short term...podrazik
long term...rev
aviation...Lee

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