Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 172358
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
658 PM CDT Sun Sep 17 2017

...Updated Aviation Discussion...

.SHORT TERM.../Tonight through Monday/
Issued at 342 PM CDT Sun Sep 17 2017

High pressure is moving across Iowa today after precipitation passed
across the region last night. The high pressure brought dry air back
to the state along with mostly clear skies except for the far south.
The area of high pressure will continue to slide east overnight.
Strong return flow will develop in the wake of the high pressure and
in advance of a vigorous short wave approaching from the west. The
best kinematic forcing associate with the short wave will arrive
late tonight into Monday morning as a theta-e advection is maximized
over the area. Expect widespread showers and thunderstorms to
develop as this occurs and a mostly damp and cool day for Monday.
The precipitation will end across the west during the afternoon.
Precipitation amounts of one quarter to one half inch are likely
with the potential up to an inch. No severe weather is expected.

.LONG TERM.../Monday night through Sunday/
Issued at 342 PM CDT Sun Sep 17 2017

Bottom Line Up Front...
Another hot week is in store for Iowa as temperatures will be a
solid 10 to 15 degrees above normal much of the week. Sporadic
shower and thunderstorm chances throughout the week, with the best
widespread rain chances Wednesday evening into Thursday morning,
and again next Saturday into Sunday.

Setup to start the long term features a longwave trough digging
all the way down through the Four Corners region and encompassing
the western half of the CONUS. Meanwhile, broad anti-cyclonic
ridging will encompass the eastern half of the CONUS through the
Ohio Valley region and into the Gulf of Mexico. This will place
Iowa in strong S/SW all work-week long. With the upper low at the
core of the longwave trough stationed over Alberta most of the
week, the thermal ridge will build all the way into southeastern
Manitoba...keeping Iowa firmly entrenched in 850mb temps around
the +17C to +22C range for this week. It is certainly worth noting
that this range of temperatures and overall setup bears a decent
enough resemblance to the end of last week, where much of the DMX
CWA was in the upper 80s to mid 90s. So, am thinking the currently
forecast temperatures in this long-term period are *still* 1-3
degrees too low, if anything.

Overall, spotty precipitation chances exist throughout much of this
long-term fcst period. Tuesday night into Wednesday morning, a broad
sfc low is slated to eject off the Rockies and push quickly to the
E/NE...making it into SW MN by 06z Wed, and western WI by 15z Wed,
falling apart over time. Meanwhile, an attendant cold front will
punch through Iowa, being located near I-35 during peak heating
Wednesday. Instability sufficient as MUCAPE values exceed 2500 J/kg,
low-level and mid-level lapse rates both very strong, and DCAPE over
2000 J/KG. Given this is Day 4, will not drill down too much... but
damaging winds seems like a solid primary threat, with large hail as
a secondary threat. Will need to keep an eye on this svr threat.

Next Saturday, another low looks to push across the upper Midwest,
with an attendant boundary to push through Iowa... similar to what
happened yesterday into this morning. This boundary looks to signal
the end of the well above-normal temperatures through next week.

Temperature records at Des Moines that may fall this week... Record
high minimum temperature on Wednesday of 74 (1895), record high min
on Friday of 68 (1937), the record high min on Saturday of 70
(1930), and the record high max on Wednesday of 92 (1931).

&&

.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 658 PM CDT Sun Sep 17 2017

Delayed the precip and MVFR ceilings slightly Monday morning for
all TAF sites. High confidence the rain and MVFR ceilings through
much of the last 12 hours of the TAF period. Lower confidence in
mentioning IFR/LIFR conditions but certainly cannot rule out a few
brief stints of these occurring if an airport gets under a decent
rain showers.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Donavon
LONG TERM...Kotenberg
AVIATION...Podrazik



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