Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 191729
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1229 PM CDT THU MAY 19 2016

...UPDATED AVIATION DISCUSSION...

.SHORT TERM.../Today/
Issued at 302 AM CDT Thu May 19 2016

There will be little overall change in the weather from yesterday
with token precip chances the only concern. Water vapor imagery
does depict a trough upstream with the primary short wave
advancing through the Texas Panhandle. The forcing response will
only be weak to moderate however and mainly to our south with
little in the way of moisture. The thermal component of lift will
be very weak with limited moisture as well in only weak warm
advection. Several models do generate light QPF over western Iowa
but this is more in response to shallow weak convection rather
than large scale vertical motion. Carroll forecast soundings
reflect this nicely with steep low level lapse rates and some weak
CAPE. However it will be capped by a warm layer around 2.5-3km so
do not expect this to amount to much. Fully expect some very small
and isolated light showers, which are depicted by a few high res
models, but with areal coverage not even enough to warrant a
mention which would require around 20 percent pops.

Much like yesterday, the airmass over Iowa will be very
homogeneous with less than a five degree difference over much if
not all of the forecast area. Forecast highs are essentially
persistence plus three or so degrees.

.LONG TERM.../Tonight through Wednesday/
Issued at 302 AM CDT Thu May 19 2016

Main forecast concerns will be precipitation chances Friday and
Saturday...as well as precipitation and thunder/severe weather chances
next week. The long term period will be characterized by a gradual
warming trend as the weather becomes more active for the CWA
especially by the end of this weekend...and the upper-level flow
transitions to southwesterly.

At onset the southern stream CONUS shortwave will be traversing
the Great Plains on its way eastward. It will slide across the
region during the day on Friday. More coherent forcing than the
past couple days will bring a larger area precipitation potential
especially across the western CWA where moisture will be more
plentiful. Only carrying slight chance POPs in that area though.
Enough instability will exist to warrant the mention of at least
isolated thunder.

After the aforementioned shortwave departs the region...a quick-
moving...compact and coherent shortwave is still progged to drop
SE through the flow Friday night into Saturday. Have slight chance
POPs across the far western CWA in conjunction with that feature.
Instability will be lacking...so have gone with only RW no
thunder.

Brief omega block signature in the upper level pattern will setup
on Sunday before the western CONUS mean trof kicks out a shortwave
into the Northern Plains Sunday night into Monday. CWA falls under
the influence of SW upper-level flow which will result in WAA and
moisture return. Shortwave will bring chances of thunder to the
CWA Sunday night into Monday.

Thereafter the long term period will feature POPs for showers and
thunderstorms as southwest flow continues with occasional
shortwaves helping to focus the precipitation chances. Models
differ in timing of these shortwaves thus resulting in the broad-
brush POPs. Toward the end of the long term period...the western
CONUS trof ejects and slides eastward across the CONUS...nearing
the Great Plains on Thursday.

Severe weather potential will exist next week. Due to timing
differences of the features...exact timing and magnitude of severe
weather has yet to be determined but will have to be monitored.

&&

.AVIATION.../For the 18Z TAFS through 18Z Friday afternoon/
Issued at 1228 PM CDT Thu May 19 2016

VFR conditions will prevail through the entire TAF period as high
pressure dominates the weather pattern.

&&

.DMX Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...Small
LONG TERM...Zogg
AVIATION...Podrazik



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