Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 261207
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
707 AM CDT THU MAY 26 2016

...Updated Aviation Discussion...

.SHORT TERM.../Today/
Issued at 425 AM CDT Thu May 26 2016

The ongoing severe convection looks to diminish and/or move east
of the forecast area by around 10z. Some lingering
rain/thunderstorms are possible through 13z at the latest. With
the storms clearing fairly quickly this morning, the atmosphere
should have plenty of time to recharge today. Went dry for much of
the forecast area today after 13z until storms look to initiate
after 19z over southwest Iowa. However, lower confidence in storms
entering the forecast area that soon, so did pull back the pops
considerably through 00z. The latest HRRR/HopWRF/NMM/NCAR ensemble
has convection rapidly developing b/t 19-23z over southwestern
Iowa.

Storm mode initially appears to be high-precipitation supercells but
likely to quickly morph into a MCS type scenario. Surface based
instability increases to 2500-4000 j/kg by 21z over much of central
Iowa. BUFR soundings suggest a fairly weak cap in place across the
southwest with moderately unstable low to mid-level lapse rates
ranging from 7-8.5C/km. Decent looking hodographs over southwest
Iowa per NAM/GFS/RUC CSQ sounding b/t 21-00z. 0-1km Bulk shear in
the 10-20 knot range, 0-3km and 0-6km Bulk shear near 40 knots.
Helicity values range from 100 to over 200 m2/s2 this afternoon in
southwest Iowa. The tornado threat certainly is viable in the
southwest corner of the forecast area with large hail and damaging
wind threat across the majority of the CWA.

.LONG TERM.../Tonight through Wednesday/
Issued at 425 AM CDT Thu May 26 2016

Much like the last couple days, complex forecast in the extended range
due to mesoscale uncertainty. Discussion will be abbreviated due
to ongoing severe weather.

Tonight: Forecast Confidence = Low to Medium

Challenging forecast for tonight as convective trends will likely
be tied to exactly what happens during the day today in terms of
airmass recovery, location of boundaries, and initial
convective development. Overall - feel that at least scattered
thunderstorm coverage will over western Iowa will gradually grow
upscale into one or more MCS into the evening as a 40-50 knot LLJ
intensifies. Combination of MUCAPE 1000-2000+ J/kg/ and roughly
35-45kts of deep layer should support a continuation of
strong/severe thunderstorms with a threat for primarily hail and
wind. The other concern will be heavy rainfall, as strong moisture
convergence over an west to east boundary could support several
waves of training storms. Forecast PWATs of 1.25" are about the 90
percentile for mid-May. Confidence not high enough to issue a
Flash Flood Watch at this point - but will include heavy rain
wording in the forecast and will pass along concerns to future
shifts.

Friday through Wednesday: Forecast Confidence = Medium

The unsettled weather pattern is expected to persist into the Memorial
Day holiday weekend. Periods of showers and thunderstorms are
likely on Friday and Saturday as the strong upper low slowly pivots
northward across the region. Details become more nebulous on Sunday
through Tuesday but at least a chance for showers and thunderstorms
will continue. Temperatures should remain mild, with readings in
the 70s and 80s.

&&

.AVIATION.../For the 12Z TAFS through 12Z Friday morning/
Issued at 705 AM CDT Thu May 26 2016

VFR ceilings forecast attm due to the low confidence in timing of
convection this afternoon. Certainly more confident in MVFR
visibility restrictions with the heavy rain anticipated tonight
into Friday morning.

&&

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

&&

$$

SHORT TERM...Podrazik
LONG TERM...Fowle
AVIATION...Podrazik


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