Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 261746
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1146 AM CST Sun Feb 26 2017

.SHORT TERM.../Today through Tonight/
Issued at 346 AM CST Sun Feb 26 2017

The primary concerns through tonight will be temp trends and fog
potential. A short wave shows up nicely in the water vapor imagery
along the MN/Canada border with another wave through KS associated
with the jet through the base of the broad CONUS trough. Any precip
potential with either system should remain north and south of Iowa
respectively with our current mid and high cloudiness exiting by
midday. Weak high pressure will cross the MO River into Iowa tonight
with light and variable winds turning southerly into early Monday
morning. Although there isn`t great moisture return today or tonight
with mostly clear skies and light wind overnight conditions will be
somewhat favorable for radiation fog formation considering recent
snowmelt and continuing snow cover north. NCEP NMM/ARW models and
the SREF all suggest increasing fog potential so have added some fog
wording from late evening into early Monday morning.

Temp wise, the northern snow pack did have an influence yesterday
with north-south differences greater than climatology would suggest.
With some sun, a fairly dry airmass and favorable wind direction
there could be around a 15F difference north to south with low/mid
30s north and readings pushing 50 south. Do not have great
confidence in lows tonight due with fog and snow cover all
complicating things.

.LONG TERM.../Monday through Saturday/
Issued at 346 AM CST Sun Feb 26 2017

Not much change to the going forecast at this point.  Monday is a
still a transitional period as a deep trough pushes onshore across
the West buckling the flow and putting Iowa in a Southwest flow
aloft.  A surface low will develop to the West with an attendant
warm front somewhere across Iowa.  The whole area will be in weak to
moderate warm advection into Tuesday.  From 00Z Tuesday through 09Z
Tuesday an area of theta-e advection sweeps Northeast across
Southern into Eastern Iowa but forcing during this time is pretty
weak to marginal at best so not looking at much in the way of precip
at this point.  Temps across the North will be tricky but models are
indicating warmer temps both surface and aloft so much of the
freezing precip has been removed from the forecast though there
appears to be a brief window for this in the far NW towards daybreak
Tuesday.

During the day Tuesday a surface low will lift across the state
bringing even warmer air to the forecast area bringing a chance for
light rain to the area.  Colder air will push into the state behind
the surface low and coincident with the aforementioned deep trough
lifting out of the West Coast and through the Rockies.  This will
keep a chance for showers far Southeast with snow North and a
rain/snow transition zone that will push across central Iowa
overnight.  Not looking at much snow with this system with areas
Northwest of a Waterloo to Omaha line seeing maybe a half inch or
so.

Wednesday and Wednesday night the upper trough passes through the
state bringing colder air into the region and...for the most
part...ending the precip.  Ridging will quickly build to the West but
with the trough shifting into the Great Lakes and slowing
some...Iowa will be put in a Northwest flow and the models have been
pretty consistent with a shortwave dropping across Iowa in the
Thursday timeframe.  The location of the best chance for precip is
still somewhat in question but the favored area continues to be the
Northeast and Eastern third of the state.  The Southwestward extent
and some timing details still need to be worked out.

Another weak wave brushes Northern Iowa around Friday but confidence
really drops off by this time.  Temps during the mid to late week
will be in the 30`s North to 40`s South so the likely scenario for
precip during this time will be snow North and rain South.  A fairly
substantial warm up is expected next weekend with mid 40`s or so
North to the lower 60`s South as a low across the Northern Plains
sweeps a warm front through the area.

&&

.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1132 AM CST Sun Feb 26 2017

Warm air continues to stream across the area...with stronger WSW
winds over the south through 00z. Main concern overnight will be
fog potential. Hires models show a signal for areas fog...but
there is little consensus on location. Climatology favors northern
areas nearer snowpack...though light warm air advection overnight
may tend to inhibit widespread fog. For now have included 2sm
visby across north sites KMCW and at KOTM and 3-5sm at KALO/KFOD
through 13-14z with no mention at KDSM. Remainder of period will
see warming and VFR conditions. /rev

&&

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

$$

SHORT TERM...Small
LONG TERM...FAB
AVIATION...REV


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