Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 222320
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
620 PM CDT SUN MAY 22 2016

.SHORT TERM.../Tonight/
Issued at 404 PM CDT Sun May 22 2016

With upper level ridge still in control today...only slight changes
anticipated overnight through 12z. Trough over the Western Plains
will edge east tonight forcing the H850 low level jet axis to also
move into western Iowa by 12z. This will allow for some showers and
thunderstorms to drift into the region west of US 71 as diminishing
CAPE and weaker moisture transport exist on the eastern fringes of
the low level jet. Clouds will also be on the increase as moisture
advances east.  Overnight lows will warm as well with increasing
south flow by morning through the region and H850 temperatures
increase to 13-15C by morning. Lows tonight will warm to the mid 50s
northeast to the lower 60s west. Winds will remain light south at 5
to 12 mph overnight. Interesting week ahead. Already today H850
subjective analysis shows high-content moisture plume advecting
north just east of the Western Plains trough. H850 dewpoints already
15C to nearly 20C from western NE to Mexico coast. Progged PWAT for
much of the week running 1.0 to 1.5+ inches across the area. Week
definitely looks wet with periods of thunderstorms.

.LONG TERM.../Monday through Sunday/
Issued at 404 PM CDT Sun May 22 2016

A very messy, humid, and summer-like week is ahead as the DMX CWA
will be under southwesterly flow into next weekend.

Monday...
The messy week ahead begins Monday as gulf moisture returns begin
to make their way into the DMX CWA from west to east. For another
run, 12z Sun model output handles sfc dwpts well enough to where a
consensus model blend is sufficient. Though cloud cover will be
increased from Sunday, 850mb temps will rise to the +14C to +15C
range, good enough to keep temps near to slightly below
persistence.

Overall model trend over the past 36-hr or so has been to push back
precip arrival time. Thus, do not have precip arriving eastern CWA
until closer to 00z Tue at earliest. Strong to svr potential looks
best in west-central Iowa during peak daytime heating. The NAM is
the strongest with portraying a N-S oriented band of isentropic lift
with an overriding pocket of PVA. With CAPE values slated to be near
1500 J/kg. Though hail will be the biggest threat, tor parameters
suggest cannot completely rule out tornado as a distant secondary
threat. Lack of deep shear noteworthy, as 0-6km bulk shear values
struggle to reach 30 kts...not conducive for a widespread event.

Tuesday...
Models coming into somewhat of agreement with low-level
frontogenetical forcing coincident with a the nose of a LLJ and
+1 to +2 std dev PWATs for moderate precip along and south of
I-80.

By the afternoon, CAPE values remain high in all models, but models
begin to diverge on solutions. The GFS basically keep any precip to
the south as the dry air wins out in the north. The NAM brings a
pocket of PVA through the northern part of the CWA. Have leaned
towards a blend.

Wednesday through Friday...
Models continue to look murky and in somewhat of disagreement
Wednesday and beyond. The NAM and GFS kick up a sfc low which they
place over KS by Wed afternoon. The ECMWF and GEM are in the
Dakotas with this feature, although the GEM Ensemble clusters with
the NAM/GFS. Keeping storms in the fcst, but confidence not high
enough to get too specific. If the GFS/NAM pans out, svr threat
may obviously become more sfc-based. Should hopefully have more
confidence by this time tomorrow. 850mb temps remain in the +1 to
+2 std dev range at around +17C. this will keep us in the 80s into
the weekend.

&&

.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 620 PM CDT Sun May 22 2016

Clouds to increase through the period with a chance for showers
and thunderstorms during the day Monday. Have highlighted best
time for precip with VCSH at this time, and will narrow to a
thunder mention when have greater certainty of the timing. Winds
to pick up overnight into Monday as well out of the south. Low
level winds aloft around 30 to 45 kts late tonight across central
and western IA, so have continued the mention of LLWS across the
western taf sites.

&&

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

&&

$$

SHORT TERM...REV
LONG TERM...Kotenberg
AVIATION...Beerends



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