National Weather Service Raw Text Product

Displaying AFOS PIL: AFDDMX Received: 2018-07-12 04:05 UTC


811 
FXUS63 KDMX 120405
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1105 PM CDT Wed Jul 11 2018

.DISCUSSION.../Tonight through Wednesday/
Issued at 306 PM CDT Wed Jul 11 2018

The overall pattern has changed little since this time yesterday 
with anomalously high heights and moisture parameters into the 
weekend and our primary frontal mechanisms driven by fringe 
trailing effects of larger Canadian troughs tomorrow and again 
around Sunday. The only real change appears to be more emphasis on
a subtle MO Valley short wave into Friday evening. This pattern 
still looks to change to end the period however with lowering 
heights through the Great Lakes which will at least briefly inject
as respite from heavy precip with somewhat cooler and less humid 
conditions.

At onset early this evening, cumulus is beginning to build in the
low level theta-e axis NW where parameterized and non- 
parameterized models have suggested some peak heating development 
so have continued conditional isolated mention north. If anything 
does form, 2500-3500 j/kg MLCAPEs and weak winds through the 
column would result in slow moving storms with locally heavy rain 
and strong winds the primary threats. Anything that would form 
should dissipate into the evening with the loss of insolation. 
Much of the low level convergence and moisture transport should 
focus into MN overnight.

Into tomorrow, forecast soundings suggest highs will be a touch 
higher than today with the max dewpoint pool shifting a bit north 
and east. With steady south winds overnight leading to little 
relief and peak heat indices Thursday higher than today, have 
extended current Heat Advisory and/or issued anew across the 
entire forecast area. Peak Heat Indices 105+ may be fairly 
widespread. Into the early evening the attention will turn to 
convective trends with yet another high instability/weak shear 
environment sagging to the IA/MN border leading to mainly a 
damaging wind/heavy rain potential. Mean winds and Corfidi vectors
are low with 4-4.5km warm cloud depths and precipitable waters 
near two inches. The moisture transport is not strong, but does 
stay focused through the MO Valley into northern IA overnight so 
the heavy rain potential may linger even though the severe 
potential wanes. The situation looks to repeat itself into Friday 
but likely a bit farther south as the forcing mechanisms sag into 
Iowa. Please see Hydrology section for more information.

Possibly to a lesser degree, but this active pattern looks to 
continue right through Sunday with what's left of the boundary
nearby until heights lower and NW upper level flow begins to 
develop into Tuesday. This will usher in a somewhat cooler, drier 
airmass less favorable for severe weather and heavy rain. Although
confidence in this range is of course low, short waves in the NW 
flow will still be sufficient to re-introduce PoPs south toward 
the MO Valley baroclinic zone by Wednesday.

&&

.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1105 PM CDT Wed Jul 11 2018

Little change from the previous package. Main concern will be
onset of convection aft 20z. Hires models suggest that most areas
will remain dry through 00z...though some hint that convection may
affect KMCW aft 20z. Otherwise VFR conditions expected with bkn to
ovc conditions at KFOD/KMCW as increasing chances for thunder
return aft 00z. Winds continue from south with some mixing aft
15z...gusts 14 to 19kts at times for the area. /rev

&&

.HYDROLOGY...
Issued at 306 PM CDT Wed Jul 11 2018

Details in magnitude and locations are yet to be determined at
this point, but concerns about river flooding and flash flooding
will elevate again to end the work week. While there is
latitudinal disagreement about whether the heavy rain axis will
set up in southern MN or northern IA late Thursday Night, or from
southern MN to as far south as central IA Friday Night, the NAM,
GFS and CMC all depict the potential for one to two inch rainfalls
during these periods with locally higher amounts possible. Would
not be surprised to see WPC Excessive Rainfall outlooks nudged up
in the coming days so the situation will need to be monitored 
into the weekend with confidence in north to south placement hopefully
increasing as convection allowing models become valid in time.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT Thursday for IAZ004-005-015-023-024-
033>035-044>047-057>060-070>073-081>083-092>094.

Heat Advisory from 1 PM to 8 PM CDT Thursday for IAZ006-007-016-
017-025>028-036>039-048>050-061-062-074-075-084>086-095>097.

&&

$$

DISCUSSION...Small
AVIATION...REV
HYDROLOGY...Small