Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 201750

Area Forecast Discussion
National Weather Service Des Moines IA
1250 PM CDT Wed Jul 20 2016

.SHORT TERM.../Today/
Issued at 405 AM CDT Wed Jul 20 2016

Hot and humid conditions and thunderstorms chances were the
main focus for today. Some ACCAS developing over eastern Iowa and
looks to spread further west into the eastern part of the CWA and
isolated storms may trickle into this are through 12-15z. Further
west, a weak shortwave has spawned some isolated storms in east-
central Iowa and the current trajectory looks to be place these
storms across the north later this morning, if they hold together.
The 20.07z HRRR fizzles out these storms, but does depict a broad
area of convection developing over northwest Iowa between 09-13z.
However, this maybe too early and have delayed pops across the north
a couple hours until after 11z over the far north. The 20.00z ECMWF
and GFS have convection developing later this morning into the
afternoon across the far north and east, which are in decent
agreement with the hires models such as the HRRR. Regardless, low
confidence with widespread convection, thus heavy rain potential,
and cancelled the Flash Flood Watch over the northeast.

The cloud debris may stick around long enough to hold temperatures
in check for much of the day over the north to northeast, but dew
points remain high enough to place heat index values to 100-105 this
afternoon. Tweaked up dew points a degree or two across the area,
especially in locations where recent heavy rain fell.
Therefore, upgraded to heat warning for the entire forecast area.

.LONG TERM.../Tonight through Tuesday/
Issued at 405 AM CDT Wed Jul 20 2016

Main issue over the next few days will be the heat and subsequently
temperatures and dewpoints. Thermal ridge to build into the central
US today and begin to push into Iowa, with the main dome of hot air
moving over Iowa on Thursday. H85 temps warm into the mid to upper
20s Celsius with moisture increasing aloft as well. With the heavy
rain that has fallen across the state in the past few days,
evapotranspiration in full swing and low level flow meandering its
way off the gulf, boundary layer moisture to be quite high. This
should keep dewpoints into the mid to upper 70s in most sites
through the end of the week. Expect high temps in the mid 90s for
Thursday and overnight lows in the mid to upper 70s, which still
creates heat index values of around 110 for Thursday afternoon given
the high dewpoints. Therefore will continue with the heat warning
for Thursday.

Situation becomes a bit more muddied into Friday with
a weak cold front dropping further south a bit faster into Friday
into Friday night. Therefore could see some convection develop on
the nose of the LLJ Thursday night and potentially fester into
Friday. Additionally development possible Friday night into early
Saturday. Have decided to upgrade the watch to a warning for
headline simplicity and the fact that the heat and humidity will
be such a long duration. Some changes may be needed to the
placement toward Friday and Saturday given the chances for the
storms. Dry weather to return mainly Sunday into Monday, with
more seasonal temperatures expected. A larger upper level trough
to then push through the central US toward the middle of next week
which will allow the region to return to a more active pattern


.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1249 PM CDT Wed Jul 20 2016

Clouds and local MVFR may occur in vicinity of KALO/KMCW this
afternoon otherwise VFR conditions will prevail today. Winds will
become breezy this afternoon from the south/southwest. The wind
will diminish tonight before becoming breezy again on Thursday.


Excessive Heat Warning until 7 PM CDT Saturday for Adair-Adams-

Excessive Heat Warning until 7 PM CDT Friday for Audubon-Black
Hawk-Bremer-Butler-Calhoun-Carroll-Cass-Cerro Gordo-Crawford-
Kossuth-Palo Alto-Pocahontas-Sac-Webster-Winnebago-Worth-Wright.



SHORT TERM...Podrazik
LONG TERM...Beerends
AVIATION...Donavon is the U.S. government's official web portal to all federal, state and local government web resources and services.