Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 230838

Area Forecast Discussion
National Weather Service Des Moines IA
338 AM CDT Sat Jul 23 2016

.SHORT TERM.../Today/
Issued at 340 AM CDT Sat Jul 23 2016

A large complex of showers and thunderstorms has been progressing
slowly eastward across Nebraska overnight and is nearing the
Missouri River valley. Ahead of this complex isolated showers and
storms have developed across Iowa as anticipated. Most global models
are not handling the Nebraska convection well, if they recognize it
at all, but some of the high-resolution short-term models like the
HRRR have a much better handle on it and continue to move it
eastward, albeit with decreasing intensity, across our area through
the morning hours to around midday. Have trended this way with a
significant increase of POPs this morning, especially in our western
and northwestern counties, as well as a lowering of temperatures to
account for rain and cloud effects. This leaves the excessive heat
warning looking a bit marginal, however with it being the fourth day
of the event and with some warming expected yet this afternoon and
evening, and a continuation of very high humidity, will leave the
headline as is given that heat index values should still peak above
100 degrees. Later today, after the morning rainfall, uncertainty
increases regarding the potential development of additional
thunderstorms toward this evening. SPC has maintained a slight risk
of severe weather across northern Iowa around this evening/tonight
but it will be conditional on how the airmass recovers and where
boundaries lie after the morning storms roll through.

.LONG TERM.../Tonight through Friday/
Issued at 340 AM CDT Sat Jul 23 2016

Couple of challenges in the near term including continued thunder
chances and temperatures. Tonight convection developing across the
high plains will track across MN and Wisconsin with trailing thunderstorms
developing into northern Iowa. With the main band of westerlies setting
up north of us the balance of the stronger storms should remain over
MN but there may be some entering northern Iowa late this evening. Over
the rest of the area as the trough swings southwest a few isolated thunderstorms
may develop along the wind shift though convergence will be rather meager
with winds nearly parallel to the boundary...some isentropic lift over
the boundary will also result in small chances for elevated convection
in southern Iowa Sunday morning and spreading back farther north during
the afternoon hours to near I80. The overall severe threat will drop
by Sunday with only general thunder anticipated. Lows tonight will continue
very warm with mid 70s south and upper 60s far north. Sunday H850 temperatures
linger in the 20 to 25C range south. Despite weak northwest flow aloft
and chances for convection highs will still push the 90 mark south of
I80 with mid 80s over the far north. Cooler and drier air arrives by
Sunday night northwest with lows falling into the lower 60s. Across
the south mid to upper 60s will linger until Monday night. On Monday
pleasant weather returns with high pressure in charge through Tuesday
morning. As the high recedes into the Great Lakes return flow along
with increased isentropic lift will result in increasing thunder chances
west Tuesday afternoon and regionwide Tuesday night into Wednesday.
Confidence in the extended begins to deteriorate as mesoscale processes
begin to dominate the pattern through the end of the period. Generally...the
frontal boundary dropping south tonight will linger over the mid Mississippi
River Valley with short wave energy approaching from the northwest Tues
night/Wed and again late Thursday into Friday. Though the models dont
completely dry things out on Thursday...chances for thunder should drop
between systems with the Tues night/Wed and Friday periods most likely
being the preferred timeframe for more generous coverage. Highs cool
to near seasonal normals in the mid 80s for highs and in the mid to
upper 60s for lows.


.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1145 PM CDT Fri Jul 22 2016

VFR conditions will prevail through the entire TAF period. No
mention of thunder due to the isolated nature and low confidence
in timing and location Saturday afternoon and evening.


Excessive Heat Warning until 7 PM CDT this evening for Adair-



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