Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 192341
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
640 PM CDT Mon Jun 19 2017

.SHORT TERM.../Tonight through Tuesday/
Issued at 220 PM CDT Mon Jun 19 2017

Cyclonic flow aloft with a series of impulses embedded in the
flow to drop southeastward through the region tonight into
Tuesday. Afternoon CU field has bubbled up with the approaching
wave across south central/northeastern IA with a few isolated
storms firing on lingering boundaries from showers this morning
and then additional activity with the wave off to the north/east.
Expect any activity to remain mainly sub-severe with weaker
instability around 500-1000 J/kg and weak shear around 20-25kts. A
few small hail reports or wind gusts to 50 mph will still be
possible with a stronger storm through early evening. Expect
activity to push ESE as it diminishes in intensity toward early
evening and the wave moves into eastern IA/IL tonight. Second wave
upstream evident on WV imagery near the ND/MN border will drop SE
across northern/eastern IA toward Tuesday morning. This may allow
a few showers/storms to skirt the northeastern few counties after
sunrise into mid morning. It will drop an associated boundary
through the state by late Tuesday with waa and moisture advection
into far southern IA by late day. This may result in some
additional storms firing along the IA/MO border late Tuesday into
Tuesday evening. Therefore have several little pockets of slight
chance pops intermittently through the short term. Overall should
see generally warmer conditions for temperatures into Tuesday with
warmer air moving in aloft across the central/southern portions
of the area. This should allow highs to push into the mid to upper
80s.

.LONG TERM.../Tuesday night through Monday/
Issued at 220 PM CDT Mon Jun 19 2017

The focus on the extended forecast includes the potential for
strong to severe thunderstorms on Wednesday and Thursday followed
by additional chances for precipitation and below average
temperatures.

A shortwave trough digging through Saskatchewan will result in
height falls aloft and a tightening surface pressure gradient over
the Plains and the Midwest. Ahead of an advancing cold front, low
level moisture will be on the increase aided by southerly return
flow. Thunderstorms are expected to develop near and along the
advancing front in western Iowa late Wednesday afternoon with
thunderstorms continuing overnight aided by a strengthening low
level jet. Effective shear 30-45 knots, MLCAPE 2500-3000 J/kg and
steepening lapse rates will be supportive of a risk of damaging
winds and large hail.

Additional chances for thunderstorms possible Thursday and Friday
especially across Southern Iowa. Position of the frontal boundary
will be dependent upon previous convection with models depicting
boundary becoming parallel to zonal flow aloft. Thunderstorm
development will be aided by daytime heating and passing shortwave
moving through the Midwest.

A much cooler airmass will settle into the Northern Plains and
the Midwest over the weekend and early next week. Temperatures
will be about 10 degrees below average with highs in the 70s and
lows in the 50s. Showers and a few thunderstorms will be possible
Saturday with the passage of a strong shortwave and the deepening
upper trough. Drier and cooler air then overspreads the Midwest on
Sunday and Monday.

&&

.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 640 PM CDT Mon Jun 19 2017

VFR conditions expected through the TAF forecast period.  VCSH was
continued for KOTM thorugh 01Z as the last of the instability
showers is exiting the forecast area.  Winds diminish aft 02Z then
become southerly overnight and back to the NW on Tues. Potential for
a broken deck of mid clouds in the morning otherwise just sct
clouds.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Beerends
LONG TERM...Angle
AVIATION...FAB


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