Area Forecast Discussion
Issued by NWS Des Moines, IA

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388
FXUS63 KDMX 301152
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
652 AM CDT Tue Aug 30 2016

...Updated Aviation Discussion...

.SHORT TERM.../Today/
Issued at 400 AM CDT Tue Aug 30 2016

Another day of isolated to scattered convection anticipated
as an unstable airmass remains in place across central Iowa. To the
south, a stationary boundary is draped west-to-east across northern
Missouri and may trickle northward through the morning hours to
provide some focus for thunderstorm development in southern Iowa.
Further north, a cold front over South Dakota through central
Minnesota will continue to sag southeast throughout the day and
look to creep into northern Iowa past 21z today. Further west, a
weak mid-level shortwave looks to push into western Iowa later this
morning and provide a little better deeper forcing for ascent over
the western half of the forecast area. Models might be overdoing the
amount instability building into the state today with much of the
cloud cover looking to hang around before the cold front clears out
the atmosphere later tonight. Still, enough instability with the
better forcing over the west to southwest late this morning into the
afternoon was enough to increase pops to likely. Models are in
agreement about the random convection later this morning into the
afternoon, with the 29.18z ESRL HRRR and 30.00z NAM12 seemingly
handling the convective trends slightly better. But the ARW/NMM-WRF,
RAP, and even the HopWRF have some sort of convection through the
afternoon, especially across southern Iowa.

Confident enough to mention the severe threat is low with the lack
of any significant shear. However, may get a few more funnel clouds
today with some low level vorticity and CAPE present this afternoon,
especially near the aforementioned fronts in the north and south.
The main threat is heavy rain. PWATs across central Iowa are near
2.0 inches with warm layer cloud depths around 3500 meters and with
the lack of any significant stearing flow and very weak Corfidi
vectors, fairly high confidence in some isolated 2-3 inch rainfall
totals. However, lower confidence in the location and thus held off
on any flash flood headline at this time. Potential there for some
localized flash flooding, especially if storms impact an area hit
from Monday`s convection.

.LONG TERM.../Tonight through Monday/
Issued at 400 AM CDT Tue Aug 30 2016

Forcing will persist across southern Iowa tonight with lingering
threat of storms. However, farther north, increasing subsidence
and drier air will minimize threat north of Interstate 80 with
clearing skies moving southward overnight as drier air pushes
through the state. Large Canadian high pressure will build into
the upper Midwest on Wednesday and this will continue to influence
the weather for the remainder of the work week. Temperatures will
be cooler along with a relatively dry airmass with comfortable
conditions.

Warm advection increases by the weekend as upper ridging slides
overhead as trof moves into the western United States. A big
shortwave will pass through the trof by later in the weekend and
into south central Canada. This will push a frontal boundary into
the vicinity of Iowa by Sunday. Thereafter, the boundary will
remain near Iowa with broad southwest flow persisting. This will
act as a focus for thunderstorms development from late Saturday
into early next week with the potential for heavy rainfall and
possibly severe storms.

&&

.AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/
Issued at 645 AM CDT Tue Aug 30 2016

Scattered convection anticipated today and have VCTS mentioned
through the early afternoon. Low confidence with mentioned any
visibility and ceiling restrictions as the location and timing of
storms is difficult to determine at this time. Cold front looks to
move through the state this evening and provide a wind shift to
the north.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

SHORT TERM...Podrazik
LONG TERM...Cogil
AVIATION...Podrazik



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