Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 232337
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
637 PM CDT Wed Aug 23 2017

.SHORT TERM.../Tonight through Thursday/
Issued at 358 PM CDT Wed Aug 23 2017

Area of high pressure will continue to move of to the east
overnight and Thursday. Theta-e advection will arrive by early
this evening as return flow aloft develops. The mid-level moisture
return combined with forcing associated with an approaching short
wave should result in an area of high based shower development.
The primary focus for any shower development will be along
and north of Highway 30. Currently have low pops across that
region though latest CAM runs are beginning to reflect the
moisture and forcing arrival and suggest higher pops may yet be
warranted. The activity is expected to diminish on Thursday until
late in the day when additional showers/thunderstorm chances
arrive over western Iowa in the vicinity of the surface boundary.

Have kept overnight low temperatures a bit warmer that last night
due to the switch to southeast winds overnight and due to
increasing mid-level clouds. Patchy fog may again develop with the
most favored area over the east where the wind will remain the
lightest and will have the best chance for radiational cooling.
High temperatures on Thursday will be dependent on how persistent
the cloud cover remains.

.LONG TERM.../Thursday night through Wednesday/
Issued at 358 PM CDT Wed Aug 23 2017

Northwest flow aloft will prevail through much of the period and
will keep the the cool late summer in place. High temperatures in
the 70s to low 80s and low temperatures in the 50s to low 60s will
be common. The best potential for precipitation arrives over the
weekend as a strong short wave passes through the region. The
greatest chance for precipitation will be late Saturday afternoon into
early Sunday morning. This system may bring rainfall amounts of
one half to one inch or more to some areas. At this time, northern
Iowa would be the target area for the higher amounts.

Both the ECMWF and GFS solutions are having the weekend short wave
evolve into an upper low by early next week that will keep the
steep north/northwest flow in place across Iowa. This system
could have several impacts across Iowa and also well to the south.
For Iowa, likely a round of even cooler weather Monday and
Tuesday with the potential for sporadic diurnal showers
developing. The upper low in conjunction to an amplifying ridge
over the western CONUS will lead to current Tropical Depression
Harvey to stall over the southeast Texas coast that may result in
a tremendous rainfall across that region.

&&

.AVIATION.../For the 00Z TAFS through 00Z Thursday evening/
Issued at 637 PM CDT Wed Aug 23 2017

The primary concerns will be thunder, ceiling and visibility trends
associated with current Siouxland weak convection as it slowly
moves across northern Iowa near KFOD/KMCW/KALO into Thu.
Confidence is not there at any particular location for anything
beyond VFR VCSH right now until near term trends suggest
otherwise.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Donavon
LONG TERM...Donavon
AVIATION...Small



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