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Area forecast discussion 
National Weather Service Des Moines Iowa
1140 PM CDT Monday Jul 21 2014

Short term /tonight/...
issued at 322 PM CDT Monday Jul 21 2014

Low stratus developed across northwest Iowa this morning just north
of a boundary and has persisted well into the afternoon. Moisture is
trapped under a strong inversion in an area of good warm advection
which has allowed it to persist into the afternoon. Soundings in the
northwest do gradually dry in the lower layers with time this
evening and should see some breakup of cloudiness...albeit
gradually. Otherwise...warm middle level temperatures have capped the forecast
area to any surface based convection. Any threat from precipitation overnight
would come from very high based activity that would move across the
state overnight as middle level trough passes through the upper Midwest.
Temperatures will remain well into the 70s overnight decent surface
flow remaining along with dewpoints holding in the 70s. No change in
headlines as heat index values likely higher across portions of the
forecast area into Tuesday.

Long term /Tuesday through Monday/...
issued at 322 PM CDT Monday Jul 21 2014

Little has changed in overall forecast thinking today. By Tuesday
morning a cool front will lie near the northwest corner of Iowa
with warm and humid conditions ahead of it. Overnight storms
across Minnesota should stay to our north and while some high
resolution models continue to try to spit out some isolated storms
early Tuesday morning...believe this to be unlikely and have thus
held probability of precipitation out of the forecast for that period. Regardless...after
sunrise the temperatures will rise quickly with dewpoints creeping
even higher than today in many areas...resulting in heat index
values peaking generally near 100 across the far north and in the
105 to 110 range central and south. No changes have been made to
the ongoing heat advisory.

Despite the front moving through a very unstable airmass on
Tuesday...warm temperatures aloft should cap any potential
convection and no storm development is anticipated until perhaps
late afternoon and evening in the south and southeast. The frontal
boundary will blow out into Missouri by midnight and thereafter
Iowa will see cool and dry weather for a couple of days on the
northeastern periphery of the large southwest U.S. 500 mb high
pressure dome. Between Thursday night and Saturday morning a
series of shortwaves moving across the Midwest will punch this
high pressure area further south...placing US beneath a more brisk
northwest flow aloft which should spark one or more rounds of
thunderstorms late in the week with some potential for severe
weather depending on the degree of destabilization. From around
Saturday night into Monday the GFS and European model (ecmwf) differ somewhat in
the details...but both of them eventually carve out increasingly
cool and cyclonic flow aloft and build a large standing 500 mb
trough across the eastern half of the continent. This will
eventually lead to several more days of unseasonably cool weather
next week.


issued at 1140 PM CDT Monday Jul 21 2014

A very strong capping inversion proved to win out over increasing
instability and shear. Any mention that was placed in the forecast
earlier has once again been removed. There will be a scattered to broken low
to middle cloud deck through much of the night. A cool front will
sweep the area through 00z Wednesday. The front should go through
dry with a middle to High Deck likely frontal passage. Surface wind will be 10-20kt
but diminish after 00z.


Dmx watches/warnings/advisories...
heat advisory until 7 PM CDT Tuesday for Adair-Adams-Appanoose-
Audubon-Black Hawk-Boone-Bremer-Butler-Calhoun-Carroll-Cass-
Cerro Gordo-Clarke-Crawford-Dallas-Davis-Decatur-Emmet-Franklin-
Kossuth-Lucas-Madison-Mahaska-Marion-Marshall-Monroe-Palo Alto-



Short term...cogil
long term...Lee

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