Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 262335
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
635 PM CDT Fri May 26 2017

.SHORT TERM.../Tonight through Saturday/
Issued at 337 PM CDT Fri May 26 2017

Surface high pressure will continue to build into the state
tonight and looks to provide clear skies and light winds. Fog
potential across the east exist, but left out mention attm due to
the likelihood of high cloud cover moving into the state towards
morning with the approaching shortwave and mitigating the
radiational cooling. The RAP, ESRL HRRR, and NMM/ARW suggest fog
develop by around 09-10z Saturday across the east but quickly lift
past 12z.

The other concern is storm chances and even severe weather
potential Saturday late morning into the afternoon. The main warm
front looks to set up across Kansas into Missouri with the parent
surface low pressure tracking across Oklahoma. A fairly decent
vort max rides the upper level flow over central to southern Iowa
Saturday afternoon. The GFS is a little more bullish than the NAM
tomorrow with building instability into southern Iowa, but
regardless, instability is likely to be at a minimum tomorrow with
plenty of cloud cover. Maybe MUCAPE rises to 500-1500 J/kg across
the far south with moderately strong deep layer shear present.
0-1km and 0- 3km shear remain weak, albeit unidirectional.
Certainly elevated storms, some isolated severe possible, with the
LCL heights rising to 2500-3500 ft across the south. Can`t
completely rule out an elevated hail storm and possibly some brief
wind tomorrow over southern Iowa. Have the highest pops going
across the south during the afternoon.

.LONG TERM.../Saturday night through Friday/
Issued at 337 PM CDT Fri May 26 2017

The long term period will be characterized by upper-level
cyclonic flow dominating the CWA during much of the period,
transitioning to weak ridging by the end of the period. As a
result, temperatures will be near to slightly below their seasonal
normals.

Saturday night into Monday: Confidence Medium

The long term period will begin with residual showers and
thunderstorms Saturday evening and night especially across the
eastern CWA, in advance of a shortwave--and cold front reflection
at the surface--traversing the north central U.S. Quiet weather
will be found in the wake of the shortwave on Sunday into Sunday
night as the surface cold front settles south of the CWA.

Another shortwave rotates through the cyclonic flow on Monday
bringing renewed chances of showers and isolated storms mainly
across the northern CWA. Models are in fairly good agreement with
the timing and strength of both shortwaves.

Tuesday through Friday: Confidence Low to Medium

Model solutions begin diverging on Tuesday and continuing through
the end of the long term period. There is general consensus,
however, on upper-level cyclonic flow dominating the CWA with
occasional shortwaves rotating through the flow.

Although there are timing differences with the shortwaves,
moisture and forcing will not be sufficient for precipitation--
only increases in cloud cover--through Thursday morning. On
Thursday afternoon, slight chance POPs return to the southwestern
CWA due to return flow and the surface frontal boundary beginning
to return north. Slight chance to lower-end chance POPs continue
mainly across the southwestern and western CWA for the remainder
of the long term period.

&&

.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 633 PM CDT Fri May 26 2017

Sunk KALO, KOTM, KDSM into IFR for VSBY restraints tonight.
Thickest fog likely to be from KOTM to KALO and locations east.
May lower KDSM, but as of now, remaining conservative. Left
thunder out of at KDSM and KOTM... though this will possibly need
to be added by the 12z Sat aviation update. Time of thunder would
most likely be from 20z-00z or so for KDSM and 22z-02z or so for
KOTM.

&&

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

$$

SHORT TERM...Podrazik
LONG TERM...Zogg
AVIATION...Kotenberg



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