Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 231533

Area Forecast Discussion
National Weather Service Des Moines IA
1033 AM CDT Sat Sep 23 2017

Issued at 1015 AM CDT Sat Sep 23 2017

Updated verbiage in today`s forecast text product to "record highs
today". Added "near-record highs Sunday" verbiage for tomorrow`s
max temperatures. Am still going to hold off on issuing a Heat
Advisory. Basically, we are a solid 10 or so degrees below
reaching criteria. Would be easier to issue if closer, but 10
degrees is a considerable amount to be short. For tonight, we will
likely be close to, but ultimately a degree or two shy in most
places, of record high minimum temperatures.

Here are a look at some record high max temperatures for today
and tomorrow:

Des Moines... Today: 92 (1892); Tomorrow: 89 (2016)

Waterloo... Today and tomorrow: 91 (1937 today, 1984 tomorrow)

Ottumwa... Today: 93 (1938); Tomorrow: 91 (1984)

Mason City... Today and tomorrow: 87 (1938 today, 1935 tomorrow)


.SHORT TERM.../Today through Tonight/
Issued at 331 AM CDT Sat Sep 23 2017

The primary concern today will remain temperatures with little
change anticipated from yesterday. Iowa will remain between the
western CONUS trough and Upper OH Valley ridge with insufficient
moisture and forcing for any precipitation through the period. In
fact, the current frontal boundary through the Siouxland area early
this morning is expected to nudge slightly westward into tonight as
mid level forcing expands into the Rockies and high Plains ahead of
the slowly advancing long wave trough.

Raw model temps and soundings with projected mixing suggest highs
today will be at or just below persistence, at or above the warmest
end of MOS guidance. Dewpoints should be slightly lower however with
heat indices peaking into the middle 90s. Although temperatures are
expected to be similar, record highs today are lower than yesterday
so expect record or near record highs which will be highlighted by a
headline in text products. Will also highlight this late season
warmth and subsequent precautions with a Special Weather Statement.

.LONG TERM.../Sunday through Friday/
Issued at 331 AM CDT Sat Sep 23 2017

Little by little the western deep trough will edge eastward,
pushing the ridge of the Plains and eastern U.S. further east.
Sunday still looks very warm though additional cloud cover will
likely keep temps from climbing much past 90 and more likely, the
upper 80`s. Beginning late Sunday night, the trough noses into
western Iowa bringing a chance for showers and storms to the
western third to half of the state by daybreak Monday.

The slow moving nature of things will keep thunderstorm chances
going across the forecast area through Tuesday. The severe threat
looks low at this point primarily due to a lack of deep shear over
Iowa. The better shear remains west with just pockets of deeper
shear over the forecast area. Another thing that was of interest
was soundings showing lapse rates that were marginal. One would
think that with as deep a trough and as strong a front pushing
through, lapse rates would be steeper. There will still be
opportunity from time to time for a strong to severe storm as this
system pushes east but widespread severe storms looks rather

Due to a prolonged period of periodic showers and storms there
will be some locations that get respectable rainfall amounts but
as dry as we have been in most locations, the flood threat is
marginal, still it will bear watching.

The cold front finally moves through late Monday night and
Tuesday. With it`s passage will come an end to the rain and much
cooler temps. Looks for highs mid to late week to be in the 60`s
and 70`s with lows in the 40`s to lower 50`s. After Tuesday the
remainder of the forecast will be dry.


.AVIATION.../For the 12Z TAFS through 12Z Sunday morning/
Issued at 639 AM CDT Sat Sep 23 2017

Little change is anticipated through the period with high
confidence in VFR conditions and minimal cloud cover. Winds will
remain S to SE with sustained speeds below 12kts.




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