Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 201737
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1237 PM CDT Sat Jul 20 2019

.DISCUSSION.../Today through Friday/
Issued at 353 AM CDT Sat Jul 20 2019

Main focus today will be on precipitation chances, temperatures and
the progression of the cold front across Iowa through Sunday.
Currently have the surface cold front stretching across southern
Minnesota back southwestward into northwest Iowa and is right near
the IA/MN border across north central Iowa. A few storms have fired
along the boundary through the overnight hours, but have not been
able to sustain themselves and have since dissipated completely. The
boundary is expected to waffle around southern MN/northern Iowa
through the morning into the early afternoon hours. An ongoing MCS
is moving through SD currently and is expected to continue push east
along the 850mb moisture gradient especially into the morning hours
as the moisture transport becomes more oriented into southern MN.
Expect the majority of this activity to remain across southern MN,
but could scrape the northern counties this morning, therefore have
reduced pops across the north. This system will reinforce the cold
front with additional activity expected to fire along the front into
this afternoon as it begins to push further south again and becomes
stalled out across central Iowa this evening. Mean flow will be
parallel to the front across central Iowa tonight, with storms
expected to backbuild and then likely train across the area. Given
the hot and humid conditions, large amounts of instability present
however bulk shear values will be limited. However given the large
instability, some severe storms are still likely across the area
with large hail, damaging winds and possibly even a tornado the main
threats. However the threat for heavy rainfall appears to be even
larger given the tremendous moisture in place with precipitable
water values around 2 inches or higher across the area later today
into tonight. Freezing levels will be up around 15-16kft yielding
deep warm cloud depths, and efficient rain production. These
parameters and the training storms expected, the potential for heavy
rainfall also seems likely. Overall given the dryness in many areas
the past few weeks to a month and full, mature crops in place the
threat of flash flooding will be somewhat dampened so will not issue
any flood headlines at the moment. However the threat will still
have to be assessed during the dayshift for a possibility. The main
worries would be heavy rainfall in a more urban areas and towns. The
majority of FFG across the area has 1,3,6 hour rainfall amounts of 2-
3 inches or higher, with some areas in the far south central pushing
5" FFG amounts for 6 hours.

Into Sunday, much cooler temperatures are anticipated as the frontal
boundary is expected to stall across central/southern Iowa with
continued chances for showers and storms. Highs are expected to top
out in the 70s to around 80. Some lingering storms still possible as
the front moves south Sunday night across far southern Iowa, however
a large, high amplitude upper ridge to build into the
western/central US early next week. This upper ridge will slowly
breakdown and shift east through the week which will allow for
cooler northwesterly upper level flow across the state and dry
conditions through much of the week. An upper wave will move through
the Canadian Rockies toward Thursday and will bring a frontal
boundary through the state by the end of next week/weekend which
will bring a return to some storm chances toward that time period.
Otherwise temperatures to remain cooler than the seasonal averages
through mid week and begin to moderate toward the seasonal averages
by the end of next week.

&&

.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1237 PM CDT Sat Jul 20 2019

Thunderstorms will affect the area periodically this afternoon
through tonight, producing localized MVFR or lower conditions
along with variable strong/gusty winds at times. Have reflected
short-term convective trends in the first several hours of the
TAFs, but amendments are likely and details for the overnight
hours will be fleshed out in later issuances. Conditions should
improve toward the end of the TAF period, during the day Sunday,
as storms gradually move out.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 7 PM CDT this evening for
IAZ026>028-035>039-044>050-057>062-070>075-081>086-092>097.

&&

$$

DISCUSSION...Beerends
AVIATION...Lee


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