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FXUS63 KDMX 252016

Area Forecast Discussion
National Weather Service Des Moines IA
316 PM CDT Sun Aug 25 2019

.SHORT TERM.../Tonight through Monday/
Issued at 316 PM CDT Sun Aug 25 2019

Confidence: Medium to High

Models are coming together with a more coherent picture of what 
should occur in the next 36 hours despite some differences.  Early 
in the period old MCS over northern Missouri continues to drift 
north northeast spreading showers into southern sections while 
another weak MCV spreads showers into northwest and northern Iowa. 
Overnight light showers with possible iso thunder southeast will 
continue into the evening.  Thickening clouds will help to keep 
overnight lows in the lower to mid 60s over the region as dew points 
increase during the night. A well defined speed max over the Pacific 
Northwest/Rockies will move quickly southeast overnight and enter 
Iowa during the 18-00z timeframe Monday as mid level upper level 
wave/sfc reflection develops along the sfc pressure trough.  With 
speed shear increasing aloft, the combination of shear/instability 
over the south will lead to more organized storms between 19z and 
00z Tuesday. There is still some uncertainty as to where the sfc low 
will develop.  The NAM is farther north into southern Iowa with the 
sfc low while the Euro/GFS continue to keep the sfc low in northern
Missouri. This will have an impact on where the stronger storms 
develop. Currently the Day2 Outlook extends slightly farther north
into southeast Iowa reflecting this uncertainty. The various CAMs
are more supportive of the southern solutions with the exception 
of the NAM Nest model which reflects more closely the NAM solution.
The main threat appears to be wind/hail though nearer the Iowa-MO
border there may be a threat for an isolated tornado if the NAM 
is more correct. With increasing moisture transport into the 
region Monday and PWATs nearing 1.5 to 2 inches by late 
afternoon/early evening south; any of the storms that move across 
the region could drop a quick inch or two of rainfall. At this 
time storm movement appears fast enough to minimize higher 
rainfall totals over one area. Highs Monday are going to be held 
back with clouds on the increase again in the afternoon, though 
they should be higher than today with lower to mid 70s in the 
north to the mid to upper 70s south. The front will quickly move 
southeast of the area during the evening hours with precipitation 
coming to an end. Lows will fall into the 50s to lower 60s over 
the region. 

.LONG TERM.../Monday night through Sunday/
Issued at 316 PM CDT Sun Aug 25 2019

Confidence: Medium to High

The bulk of the week will remain quiet until Thursday night into 
Saturday. A large upper level trough over southern Canada is 
expected to dig south with time and amplify northwest flow over 
the region through Wednesday. There is no strong signal for rain, 
though the Euro suggests a few showers may develop in cyclonic 
flow over southern MN/extreme far northern IA Tuesday afternoon. 
Otherwise slightly below normal temperatures will remain in the 
area through midweek, then the ridge aloft begins to build into 
Thursday with H850 temperatures quickly recovering to 17C to 20C 
by mid afternoon just ahead of a sfc trough/front entering 
northwest Iowa. Instability increases Thursday afternoon through 
00z Friday with thunder chances over the south extending into 
Thursday night. Isentropic lift and a passing upper level wave or 
two will extend rain chances into Saturday over the region. Highs 
Thursday should ramp into the mid, perhaps upper 80s prior the 
frontal passage. Cooler temperatures return for the remainder of 
the period with highs in the 70s and lows dropping generally into 
the 50s along with possible 40s in the south.


.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1228 PM CDT Sun Aug 25 2019

Main concerns include lowering cigs, old MCS affecting southern
Iowa and scattered showers through 12z. Iso showers continue to
develop and move northeast without much impact. Old MCS drifting
into southern Iowa and may impact KOTM with iso thunder by 22Z.
Cigs expected to lower over south/southwest with MVFR conditions
generally aft 06-08z most sites. Main concerns aft 12z will be
cigs and increasing -TSRA risk. Some uncertainty on extent and
timing of 12z-18z thunder and will let later updates address in
more detail. /rev




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