Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 272011
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
311 PM CDT Sun May 27 2018

.DISCUSSION.../Tonight through Sunday/
Issued at 311 PM CDT Sun May 27 2018

Have maintained isolated thunderstorms in our northwest counties
late this afternoon/evening, but confidence is low. Satellite
imagery depicts modestly agitated cumulus in that area and current
mesoanalysis indicates weak surface moisture convergence, so will
maintain inherited slight chance POPs up around Fort
Dodge/Algona/Estherville for the next few hours. Meanwhile
isolated storms have developed along the southern Iowa/Illinois
border region just two or three counties east of our forecast
area, however, satellite imagery and short-range environmental
forecast is less supportive of convection in that area and will
risk keeping the dry forecast in our southeast corner.

Other than the low chance for isolated thunderstorms, the big
weather story will be the continuing heat wave, which is
exceptional for this time of year. Both yesterday and today Des
Moines has recorded its highest temperature this early in the
season in more than 50 years. Temperatures will be similar
tomorrow, though perhaps just a couple degrees less and with a bit
more breeze. Overnight temperatures and forecast heat index values
for tomorrow do not support a continuation of the current heat
advisory beyond this evening, so will allow it to expire and then
overnight consider whether to reissue for tomorrow or not. With it
being a holiday and many engaging in outdoor activities, we will
continue heat safety messaging whether an advisory is in effect or
not.

Beyond Monday, the weather pattern appears continued warm, though
not quite as hot, for the rest of the week with sporadic
thunderstorm chances. Around Tuesday night/Wednesday a 500 mb
trough will deliver just a glancing blow as it moves over the
Dakota and Minnesota, but this trough will also scoop the remnants
of Subtropical Storm Alberto northward to around the Chicago area
by late Wednesday. Between these systems central Iowa will reside
in a region of broad moisture flux and weak forcing, which may
support scattered storm development. Have therefore maintained
fairly widespread chance POPs in the Tuesday night through
Wednesday timeframe, though no organized/severe convection appears
likely. Cloud cover should help hold temperatures down a bit
Wednesday as well, but with highs still in the upper 80s.

In wake of the midweek trough/s, another thermal ridge will build
in rapidly from Wednesday night through Friday night bringing a
return of heat with daily highs back up into the 90s. It appears
another 500 mb trough will then affect the region next weekend,
likely moderating temperatures again, but details are sketchy at
this range.

&&

.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1242 PM CDT Sun May 27 2018

VFR conditions expected throughout the TAF period. The only
caveat would be possible isolated thunderstorm development this
afternoon, however with low confidence in storm development have
left this out of TAFs. Otherwise, expecting high clouds and winds
remaining relatively light.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for IAZ059-060.

&&

$$

DISCUSSION...Lee
AVIATION...Hagenhoff


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