Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 192352
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
652 PM CDT Tue Jul 19 2016

.UPDATE.../Tonight/
Issued at 652 PM CDT Tue Jul 19 2016

Will be removing the FFA over the southeast. Threat for any
additional heavy rainfall has ended with only lingering impacts
from earlier rainfall today. /rev


.SHORT TERM.../Tonight/
Issued at 347 PM CDT Tue Jul 19 2016

MCS that has gradually been progressing southeast today will
continue with precipitation ending from northwest to southeast. The
bulk of the storms should be done by 00z though areas of heavy rain
and severe weather possible over the next 1 to 2 hours before
exiting. After this expect a lull in the activity for much of the
evening. The low level jet will increase this evening through Kansas
and Nebraska and veer into NW Iowa and SW Minnesota and this will
drive strong theta-e advection northeast into North Central and
Northeast Iowa. This will bring renewed chances for thunderstorms
over that area. PWATS hovering near 2 inches and warm cloud depth
around 14 kft will keep the potential for heavy rainfall and high
rainfall rates with any storms that develop.

.LONG TERM.../Wednesday through Tuesday/
Issued at 347 PM CDT Tue Jul 19 2016

An upper ridge will be building into the central CONUS early
Wednesday but a shortwave ridging the ridge top but a fairly broad
area of theta-e advection and some weaker forcing topping the ridge
over Southern MN will keep chances for storms going over far Eastern
sections of the forecast area.  Elsewhere...hot temperatures and mid
70 dewpoints will be surging into Southern and Western sections of
the forecast area during the afternoon hours pushing heat indices
above 105.  I have gone ahead and upgraded our watch to an excessive
heat warning for much of the area.  The exception to this is my far
Eastern portions of the forecast area...from Mason City to Waterloo
to just North of Ottumwa.   I keep the watch going for these areas,
though I expect to upgrade them to a warning tomorrow for Thursday.
The reason I haven`t included them right now is the uncertainty of
convection across the East and what they will do to temps/heat
indices.  If we get another MCS rolling down the ridge it`s possible
for cloud cover to negatively impact temps tomorrow enough to not
hit warning criteria.  The ridge remains in place over the Upper
Midwest through Friday keeping oppressive heat and humidity in place
across central Iowa through that time.  A couple of the medium range
models hint at a weak shortwave pushing across Iowa on Friday
which...if that does occur...we will be unstable enough for storms
to develop in that environment.  For now...confidence in that
happening is low and the heat threat far outweigh the potential for
storms at this time.

Friday night into Saturday the forecast becomes a bit more nebulous.
Upper ridging remains in place but a strong shortwave will sweep the
Northern Plains flattening the ridge.  In general, temps will be at
least a little cooler than the previous few days. However...very
high dewpoints will remain in place.  In addition, a cold front will
be approaching from the West and models are hinting at strong warm
850 temps surging into the state which may keep the oppressive heat
going.  If anything...the humidity will still be unpleasant so in
coordination with my neighbors, I have extended the watch across my
far Southeast through Saturday.  The front then pushes through
Saturday night into Sunday morning and with that will come
additional thunderstorm chances.  The rest of Sunday through Monday
will be nicer with high pressure overhead bringing in cooler temps
and more importantly, lower dewpoints.  The high will shift to the
East Monday night into Tuesday.  Warm advection will return to the
West and Southwest brining more chances for thunderstorms, though
obviously that far out confidence is low as to strength and coverage
of storms.  I`ve covered that with slight chance pops and low end
chance pops.

&&

.AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/
Issued at 652 PM CDT Tue Jul 19 2016

Main concern will be renewed chance of convection northeast aft
05z through 15z with potential for MVFR cigs aft 05z through 13z
at KALO and KMCW. Currently residual showers passing southeast
near KDSM otherwise cigs generally VFR with a few patches of MVFR.
Aft 05z cigs may again drop northeast at KMCW and KALO. Once the
warm front exits the region northeast aft 15z Wednesday focus
shifts to mixing winds and mid level clouds. SSW winds of 11 to 22
kts through the day with generally VFR cigs remaining over the
northeast. /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning from 1 PM Wednesday to 7 PM CDT Friday
for Adair-Adams-Appanoose-Audubon-Boone-Calhoun-Carroll-Cass-
Clarke-Crawford-Dallas-Davis-Decatur-Emmet-Greene-Guthrie-
Hamilton-Hardin-Humboldt-Jasper-Kossuth-Lucas-Madison-Marion-
Marshall-Monroe-Palo Alto-Pocahontas-Polk-Ringgold-Sac-Story-
Taylor-Union-Wapello-Warren-Wayne-Webster-Wright.

Excessive Heat Watch from Wednesday afternoon through Saturday
evening for Mahaska-Poweshiek-Tama.

Flash Flood Watch through Wednesday morning for Cerro Gordo-
Hancock-Winnebago-Worth.

Excessive Heat Watch from Wednesday afternoon through Friday
evening for Black Hawk-Bremer-Butler-Cerro Gordo-Franklin-Grundy-
Hancock-Winnebago-Worth.

Excessive Heat Watch from Friday evening through Saturday
evening for Davis-Wapello.

&&

$$

SHORT TERM...Donavon
LONG TERM...FAB
AVIATION...REV


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