Area Forecast Discussion
Issued by NWS Des Moines, IA

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233
FXUS63 KDMX 300912
AFDDMX

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

.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
j/kg.

.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 00Z TAFS through 00Z Saturday evening/
Issued at 639 PM CDT Fri Jul 29 2016

CIGS have lifted some this afternoon, but expect them to fall back
into the MVFR and possibly IFR categories overnight. Some fog may
develop late tonight through sunrise Saturday especially on the
outskirts of the cloud shield and in areas that may see some
partial clearing overnight. Have highlighted the northern tafs at
this point where the best chances are, and only brought down to
MVFR VSBYS which could be optimistic. Otherwise expect CIGS to
lift some during the day as winds become more easterly to
southeasterly.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Small
LONG TERM...FAB
AVIATION...Beerends



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