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National Weather Service Des Moines Iowa
627 PM CDT Wednesday Sep 2 2015

Short term /tonight/...
issued at 328 PM CDT Wednesday Sep 2 2015

Winds will begin to decouple between 23z and 00z tonight
and expecting light south winds through tomorrow morning. With the
winds looking to strong enough (5-10 knots)...they will hold off any
fog developing overnight and keep temperatures closer to the warmer
NAM for lows.

Long term /Thursday through Wednesday/...
issued at 328 PM CDT Wednesday Sep 2 2015

No large scale changes were made to the long term forecast at this
time. Central Iowa will be under the influence of a large high
pressure system through late Saturday that will keep very warm and
humid air in place across central Iowa. Highs will be 5 to 10
degrees above normal for this time of year through Saturday. The
GFS is suggesting a weak shortwave riding the ridge Thursday night
and kicking off showers/storms across the far west but so far
none of the other models are picking up on the precipitation trends.

The bigger story will be the large scale trough digging off the
Pacific northwest and pushing the ridge axis east late in the
weekend allowing a surface low to drop a pretty strong cold front
through central Iowa. The models develop storms along the boundary
to the west of Iowa Saturday night and potentially brush the
northwest early Sunday before shifting northwest. The models push
the front into northwest Iowa around 18zbut the Euro continues to be the
fastest with its progressions through central Iowa. The GFS and
Canadian models all hold the front back across northwest Iowa
through 00z and bring it slowly across the County Warning Area through Monday
morning. Thus there are timing differences with the front and
precipitation chances. At this point the bulk of the instability stay
north but there will certainly be enough instability over Iowa for
storms to develop...especially late day through late evening. The
deeper shear hangs back and really doesn't come into Iowa until
overnight and Monday but given the strength of the front there
should be enough low level shear present. The question is whether
that will be enough to sustain updrafts to see any severe weather.
Soundings show precipitable waters increasing to 1.75 to 1.9 inches so stronger
storms will have a potential for heavy rain. Temperatures by Sunday will
drop from the 85-95 range to more 75-85 range and by early next
week highs are back in the middle 70s.

The rest of the long term remains unsettled as the front stalls
out somewhere in northern Missouri/southern Iowa which will keep
at least some potential for precipitation across southern Iowa.


issued at 632 PM CDT Wednesday Sep 2 2015

Minor concerns this period. Weak short wave tracking into southern
Iowa has produced a few isolated showers/thunderstorms which will diminish
prior to 04z and should not affect taf sites. Otherwise overnight
expect winds to decouple with potential for some 5sm br north. By
15z Thursday winds will again mix but bufr soundings show little
momentum Transfer to surface. VFR conditions are expected with scattered low
and high level decks due to continued high surface moisture and
approaching system into the weekend. /Rev


Dmx watches/warnings/advisories...


Short term...podrazik
long term...fab

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