Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 081001
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
401 AM CST Fri Dec 8 2017

.SHORT TERM.../Today through Tonight/
Issued at 359 AM CST Fri Dec 8 2017

Weak shortwave currently moving through the
state early this morning is mainly bringing some mid-level cloud
cover. A few flurries maybe found over western to northern portions
of the forecast area, but with the cloud bases AOA 7000 feet, any
flakes that are produced are likely to not reach the surface. Only
have flurries mentioned through 12z this morning. The next shortwave
looks to push across Wisconsin this evening and quickly push east of
the area past 06z Saturday. Some light snow is possible b/t 00-06z
tonight across the northeast sections of the forecast area. MCW
forecast soundings suggests ice introduction by around 02z but loses
it by 06-07z time. The depth of the moisture is only to about 5000
feet but there is saturation with the dendritic layer.  Winds atop
the mixed layer increase to 35-40 knots and certainly cannot rule
out some visibility issues with the falling snow and blustery winds
developing. However, with the snow likely to be very short-lived, no
headlines are anticipated attm and could just be handled with a
Special Weather Statement.  Windy conditions remain throughout the
overnight hours with some wind gusts over 40 are likely across
northern Iowa prior to sunrise Saturday.

.LONG TERM.../Saturday through Thursday/
Issued at 359 AM CST Fri Dec 8 2017

The gusty winds will persist into Saturday though will be gradually
subside through the day as the pressure gradient relaxes and the
mixed layer winds diminish. Temperatures will be cold once again as
cold advection continues on Saturday with high temperatures in the
low 20s to low 30s. Ridge of high pressure will reach far western
Iowa by late afternoon and will move quickly east across the state
through the early evening. This will bring a switch to southwest
winds and the beginning of warm advection. Saturday night lows
should occur during the evening followed by steady to slowly rising
temperatures after midnight. A stronger push of warm advection will
arrive Sunday morning fueled by westerly winds and downslope flow.
The very warm air arriving around 850 mb will create an inversion
and will limit mixing potential to near 900 mb. Expect to have
passing mid-level clouds through the day. How persistent and opaque
these clouds are and how much sun is filtered will have an impact on
high temperatures. Downslope flow can offset some of the cloud
impacts. Considering all the above, have remained close to guidance
for now with highs in the upper 30s northeast to near 50 southwest.

The active northwest flow for next week still leading to a lot of
spatial and temporal variability for potential outcomes. Trending
to higher 500 mb height across Iowa next week which would shift
the more active weather further to the northeast and impact
Minnesota and Wisconsin and leaving Iowa in the drier side which
includes more subsidence and breezy to windy conditions for much
of the period. A strong cold front will arrive on Monday. The
boundary will be accompanied with stratus but very dry air above
700 mb. The moisture will be in a thermal layer warm than -10C
mitigating any flurry threat and profiles would not be conducive
for any other precipitation. The primary threat with the boundary
passage will be strong and gusty northwest winds. The wind
potential looks stronger than the potential for tonight and will
continue to monitor for headline potential. Hints that the large
amplified ridge over the western CONUS will break down late next
week as a strong system moving of the Pacific squashes it and
eventually leads to a warmer westerly flow for the Midwest beyond
the extended forecast period and towards next weekend.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1124 PM CST Thu Dec 7 2017

Continued with VFR conditions through tonight and tomorrow.
Flurry potential for this morning trending to be less impactful.
Continued with vsby above 6 SM and CIGS above 3000ft. Winds should
be near 10 kts all day today.

After 00z tonight, MVFR cigs will begin to infiltrate Iowa from
north to south... impacting KMCW. Additionally, wind gusts will be
increasing through tonight, peaking near sunrise tomorrow morning.

&&

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

$$

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



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