Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 151127

Area Forecast Discussion
National Weather Service Des Moines IA
627 AM CDT Sun Oct 15 2017

...Updated for 12z Aviation Discussion...

.SHORT TERM.../Today through Tonight/
Issued at 343 AM CDT Sun Oct 15 2017

Main 500mb trough axis is moving over central Iowa at this time
with the 250mb jet departing the area and placing Iowa under an
area of subsidence. Surface low pressure continues to move off to
the northeast and is nearing Lake Michigan with the cold front
being east of the state at 3am. Behind this front, much cooler and
drier air is being ushered in on strong, gusty winds from the
northwest. Winds have occasionally reached wind advisory criteria
at a few sites with gusts into the 40s (mph) with a recent gust at
Boone to 50 mph. Have issued a Special Weather Statement through
8am for these gusts as they have been fleeting. Otherwise, GOES-16
Nighttime Microphysics shows extensive cloud cover over the
state, though there may be a few breaks over western Iowa at this

Highs today will be lower than yesterday in large part to the cold
air advection. Winds will stay elevated and gusty through this
morning and will gradually decrease throughout the day from west to
east. Used a blend of CONSShort and CONSMOS to arrive at wind speeds
for today. Wind gusts through early this morning will be around 40
mph until 7 or 8am after which time gusts should start to drop as
the sustained winds also decrease. Sunshine will be limited early
this morning as the aforementioned clouds will be slow to clear. The
HRRR time lagged and 05z National Blend were handling the current
cloud cover extent well. So used a blend of these two models with
with manual adjustments based off of 925mb NAM RH for sky cover from
now through early this afternoon, after which time skies should be
mostly sunny.

By tonight, primary forecast concern is frost and associated
headlines. The sky will be clear with subsidence continuing on the
backside of the departed trough and ridging starting to move in
overhead. Temperatures will drop into the 30s over much of central
Iowa with the Des Moines metro and some spots over southern Iowa
near 40 degrees. Used a blend of the NAM, ECMWF, and National Blend
to arrive at these lows. Confidence is fairly high that there will
be areas of frost over northern Iowa and probably in the Nishnabotna
Valley and have included in grids/text products. In coordination
with our neighboring offices, it was decided to evaluate headlines
later today, but would expect headlines at least over northern Iowa
barring any major upward shift in low temperatures.

.LONG TERM.../Monday through Saturday/
Issued at 343 AM CDT Sun Oct 15 2017

The weather will be quite uneventful through the period with mild
temperatures and plenty of sunshine during the day. Fast, zonal
flow will be in place through midweek with the polar jet staying
to our north. A strong short wave will track across southern
Canada around Wednesday but our forecast will remain dry with
minimal moisture and forcing staying to our north. A weak front
will drop into Iowa late Wednesday, but will have little effect on
our weather. Heights will then build into the central CONUS to
end the work week with increasing southerly low level flow. A
very dry atmosphere and brisk south winds result in favorable
warming conditions to end the week with highs in the 70s forecast
area wide.

The forecast through the valid period remains dry, but there may
be a window for precip into Saturday Night. The 00z deterministic
ECMWF has swung around to yesterday`s phased, progressive
elongated through solution depicted by the GFS, which continues
this morning, but the 00z ECMWF ensembles still suggest the
potential for a weaker wave and closed low left behind from the
Four Corners region into the southern Plains into the weekend.
Regardless of preferred solution, little change in our pattern is
anticipated through at least early next week.


.AVIATION.../For the 12Z TAFS through 12Z Monday morning/
Issued at 626 AM CDT Sun Oct 15 2017

Strong, gusty winds from the northwest will gradually decrease
through the day today in the wake of a cold front that has swept
east of the state. Clouds with MVFR bases over central Iowa
presently will gradually lift and break into VFR from west to
east this morning into early this afternoon. Thereafter, VFR
conditions will prevail through the remainder of the TAF period as
winds generally settle under 10 knots tonight.




SHORT TERM...Ansorge
AVIATION...Ansorge is the U.S. government's official web portal to all federal, state and local government web resources and services.