Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 180503
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1203 AM CDT Mon Sep 18 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 06Z TAFS through 06Z Monday night/
Issued at 1158 PM CDT Sun Sep 17 2017

Continued to delay the onset of precip and MVFR ceilings for all
TAF sites. Still looking at closer to sunrise Monday morning of
rain at FOD, MCW and DSM and a bit later for OTM and ALO. Lower
confidence to mention any MVFR conditions at OTM as the bulk of
the forcing and rain looks to stay to the north. The hires models
are in good agreement with the precip, visibility, and ceiling
delay. BUFR soundings per the GFS suggest much of the event
remains VFR or around 5000-6000 ft during the day, but a few of
the hires models have periodic ceilings ranging from 1200 to 2500
feet mid morning into the afternoon, and this is mainly affecting
FOD, MCW, ALO and briefly at DSM.

&&

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

&&

$$

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



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