Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 270924

Area Forecast Discussion
National Weather Service Des Moines IA
424 AM CDT Tue Jul 27 2021

.DISCUSSION.../Today through Monday/
Issued at 423 AM CDT Tue Jul 27 2021

Departing surface high pressure is centered over central Illinois
this morning while the upper high pressure is centered to the west
over western Nebraska. The low level jet is wrapping around the
surface feature through southeast South Dakota and into southern
Minnesota with a strong wave of theta-e advection moving thorugh
that area and into north central Iowa. The theta-e advection is
moving just ahead of a short wave that is moving southeast into the
region and is helping tilt an instability axis into north central
Iowa today. Therefore, there is some convective potential there
though despite the theta-e advection, the lack of deep moisture
remains a limiting factor.

High temperatures will be warmer today. The 850 mb temperatures will
be 2C to 3C warmer than Monday and in the 21-23C range. There is
also a patch of less smoke that will pass across Iowa today and
should lead to less filtered sun which will help provide better
insolation as well. Forecast highs today are in the low to mid 90s
with the highest temperatures and dew points over the northwest and
thus heat indicies. Have issued a Heat advisory for the far
northwest for heat indicies in the low 100s to near 105 and to align
with neighbors. Chances for thunderstorm development near the IA/MN
border is a boundary sinks into southern MN then move southeast into
northeast Iowa. This is the activity that SPC has issued a slight
risk for severe weather for mainly for large hail.

The storm potential will linger into Wednesday morning and could
linger some convective debris over the northeast. In addition,
another round of more dense smoke aloft will be passing over the
state while the thermal ridge leans further into the state.
Confidence remains low on dew points on Wednesday as better mixing
is expected and there is the potential for deep mixing over
northwest Iowa. The NBM dew points have been too high much of the
summer and Wednesday looks to be another example of that. Expect
highs in the mid to upper 90s on Wednesday with the smoke likely
knocking off a degree or two for potential highs. That said the deep
mixing over northwest Iowa still has the look of highs in the low
100s with dew points mixing lower closer to 60, which would
ironically have heat index values near or lower than today. Due to
uncertainties all around with several variables, have opted to keep
the Excessive Heat Watch in place with the most likely scenario
being a Heat advisory but some locations could fall below criteria
while still a chance a few areas approach the 110 Excessive Heat
Warning criteria.

Little change to the forecast Thursday and beyond. The boundary
settles through Iowa on Thursday with highs again in the 90s across
the south. The boundary will be capped to surface based convection
but won`t be immune to early morning elevated convection advecting
in over top of the cap. A better chance for storms over southwest
Iowa late Thursday night and again Friday night. High pressure will
move into the Northern Plains and provide a mostly dry weekend and
may persist further into early next week along with highs in the


.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1153 PM CDT Mon Jul 26 2021

VFR conditions to prevail through the period with S/SW wind at
around 10 knots.


Excessive Heat Watch from Wednesday morning through Wednesday
evening for IAZ004>007-015>017-023>028-033>039-044>050-057>062-

Heat Advisory from noon today to 8 PM CDT this evening for



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