Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 260436

Area Forecast Discussion
National Weather Service Des Moines IA
1136 PM CDT SAT JUN 25 2016

Issued at 702 PM CDT Sat Jun 25 2016

Convection continues to bubble up over the west just ahead of the
boundary but other than instability...parameters remain rather
meager early this evening with weak surface convergence and
marginal 0-6km effective bulk shear. Hires models continue to
point to slightly better organization after dark...when brief
period of convergence aloft occurs as low level jet intensifies
over the boundary between 05-09z and then weakening toward 12z.


.SHORT TERM.../Tonight/
Issued at 336 PM CDT Sat Jun 25 2016

The primary concern will be how convective trends play out this
evening. There is high confidence the upper level divergence, DPVA
and a cold front aloft will combine with low level convergence
and trigger convection associated with the impending upstream
frontal passage. The question remains areal coverage and intensity
however. The convection that has already developed has not shown
any propensity to turn severe and elevated weak convection from
NE/KS into IA will likely continue to contaminate the
thermodynamic environment somewhat locally. The only maturation
area appears to be eastern Nebraska where nearly full sunshine
still exists. Visible satellite imagery notes linear CU moving
through Wayne NE, so this would be an area of concern in the short
term to monitor. The RAP suggests effective shear will remain
rather weak so anything that does strengthen will likely have a
rather short significant lifespan as daytime heating wanes. If the
aforementioned Nebraska location does not materialize it may
largely be below severe limits for Iowa this evening. Otherwise
damaging wind and large hail would both be possible immediately
along the front where there is a localized shear enhancement and
closer to steeper mid level lapse rates. Dry air below 1.5km does
linger for quite a bit and could potentially be realized in strong
downburst winds until the inversion eventually trims MLCapes

Little of the high resolution model QPF through 12z is impressive,
but with precipitable water values pushing two inches, RAP warm
cloud depths approaching 4.5km toward midnight and persistent 925-
850mb moisture transport locally heavy rains are possible if the
MCS is robust enough. These will all combine with favorably low
layer mean wind and backward propagating Corfidi vectors.

.LONG TERM.../Sunday through Saturday/
Issued at 336 PM CDT Sat Jun 25 2016

Main forecast concern was focused on temperatures through the
early part of the week and then precipitation chances mid to late
week. Models are in good agreement through the middle of the week
with the large surface high pressure building into the region and
with the central U.S. remaining in northwest flow aloft.

Sunday into Monday...Behind the cold front anticipated to push
across the state tonight...dew points drop roughly 10-15 by Sunday
afternoon compared to this afternoon. With the dry airmass
filtering into the state and some mixing developing in the
afternoon should put temperatures back to around 90. However, the
heat index values remain low due to the drier air mass. A
secondary push of cold air begins to move into the state during
the afternoon Monday and brings some welcomed relief to the heat
through the middle of the week. Timing of the front across the
forecast area looks to be late enough in the day to keep the
normal diurnal trend going over much of the forecast area. The far
northern couple tiers of counties may see some temperatures
holding steady with the fropa by around 21z Monday. However, no
mention of non-diurnal temperature trend attm as the fropa may
not be until after 00z Tuesday.

Tuesday through Friday...Surface high pressure builds into the
state Tuesday into Wednesday and will provide below normal for
much of the forecast area for the first time since June 7th. The
GFS and ECMWF try to bring a shortwave across western Iowa late
Wednesday into Thursday, but the surface high looks to remain
strong enough to keep this system far enough west to impact much
of the forecast area. Have a few chance pops going during the day
Wednesday and then slights over the entire cwa Wednesday night.
However, low confidence central Iowa will receive any
precipitation from this shortwave as models begin to diverge in
solutions and location of pops. A couple additional shortwaves
pass over Minnesota late in the week providing rain chances to
northern Iowa Thursday into Friday.


.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1136 PM CDT Sat Jun 25 2016

Main concern overnight will be coverage of convection. The
northern branch will quickly exit the area. Isolated convection
will continue between KALO and KDSM...with scattered convection
from KDSM southeast to KOTM through 12z. Brief MVFR cigs possible
south sites...otherwise VFR conditions aft 12z and light winds
remainder of period as high pressure builds into area. /rev


.DMX Watches/Warnings/Advisories...


LONG TERM...Podrazik
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