Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 301429

Area Forecast Discussion
National Weather Service Des Moines IA
929 AM CDT Sat Jul 30 2016

Issued at 922 AM CDT Sat Jul 30 2016

Isolated showers or sprinkles have started to develop over central
Iowa at 915 am. Have updated for small chance along with some
increased development in the afternoon w/small potential for iso
thunder as well during the mid to late afternoon. Overall
coverage expected to be small so will only go slight chance at
this time. /rev


.SHORT TERM.../Today/
Issued at 334 AM CDT Sat Jul 30 2016

The situation has changed little over the past few days with
interrelated cloud and temp trends still a concern. Forecast has
busted on both sides of expectations recently so confidence is not
great and have not strayed from guidance consensus. Hi Res ARW as
well as operational and experimental HRRRs all suggest clouds will
lift and go cellular by afternoon allowing for some heating.

The precipitation situation is quite similar as well. Most models
depict uncapped 500-1500 j/kg MLCapes by afternoon. Much of this
will be unfocused but some high res models do suggest the current
central IL surface trough will further build back into northeast IA
toward Waterloo and enhance convergence in that area. Areal coverage
is going to be minimal and the heavy rain environment is not
extreme, but with very light mean winds and instability greater than
yesterday, very localized heavy rain may develop much like occurred
in DVN`s area. Any storms would be very slow moving. Examination of
soundings suggest the moister end of solutions could also be
conducive for a funnel cloud/landspout environment during peak
heating along the weak convergence axis with 0-3km Capes pushing 200

.LONG TERM.../Tonight through Friday/
Issued at 334 AM CDT Sat Jul 30 2016

Little change was made to the forecast in the long term. A
building ridge to the West will send shortwaves across Iowa along
with warm advection increasing across the South and West. We
should see something similar to what is occurring across
central/Eastern Nebraska now, over Western/Southwest Iowa tonight.
This activity should wane through Sunday morning.

Then for Sunday night into Monday...the upper ridge begins to
shift East but a shortwave drops across the area and strong warm
advection takes place. In addition...much stronger forcing occurs
across Southern Iowa and thunderstorm chances look much better
Sunday night/Monday. In addition shear looks pretty impressive as
well so a few storms could be strong and produce heavy rainfall.
For Monday...a warm front will likely be near or across Iowa with
strong instability and deeper shear, Monday is still looking like
an interesting day and we could see some strong to severe storms
late afternoon into the evening.

Tuesday through Wednesday the upper ridge really amplifies over
the upper midwest and temps will be very warm through this period
with highs 85 to 95.

For Thursday a shortwave drops through the Northern Plains and
flattens the ridge bringing with it not only cooler temps North
but at least some potential for storms but better chances will
come later Thursday through Friday as a cold front drops through
the state. Strong to severe storms are possible along with the
frontal passage. Cooler temps will follow for Friday night into
Saturday but models diverge here. The GFS is more bullish on a
shortwave coming across Southern Iowa while the Euro wants to
rebuild the ridge. The GFS is suggesting that the front stalls
over Missouri on Friday then begins to lift back as a warm front
Friday night/Saturday which would also suggest a better chance for
storms during this period but confidence is low on any one
solution at this point. Seems like the ridge rebuilding is more
plausible but for now I went with persistence and kept the model
blended chance pops going across the South. Will watch for trends
again tomorrow.


.AVIATION.../For the 12Z TAFS through 12Z Sunday morning/
Issued at 709 AM CDT Sat Jul 30 2016

MVFR ceilings blanket much of the northeast half of Iowa this
morning with a few spots down to IFR/LIFR conditions. These
degraded conditions continue to drift south across the state
behind southern Great Lakes low pressure, but should improve
toward midday lifting to VFR in most locations. Scattered
convection may also form during peak heating but confidence not
there for anything beyond KMCW VCSH. Expect radiation fog
development early Sun morning, down to at least MVFR is most




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