Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 140553
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1153 PM CST Mon Nov 13 2017

.SHORT TERM.../Tonight through Tuesday/
Issued at 229 PM CST Mon Nov 13 2017

Lots of low level moisture hanging around today with moisture
advection expected to bring in additional low level moisture tonight
into Tuesday. Area of surface high pressure has shifted off to the
east across the Ohio Valley region, with an elongated area of low
pressure stretching from the Dakotas southwestward into the high
plains of Colorado. Southerly flow will continue to increase ahead
of this area of low pressure with a weak upper level disturbance
moving through the region currently. Another upper level shortwave
will dig into the northern Plains states into Tuesday with a surface
boundary expected to push into the state by late Tuesday. WAA and
moisture advection continues ahead of this boundary, with soundings
showing deep saturation in the lower levels through late Tuesday.
Isentropic analysis also showing widespread lift in the saturated
layer, thus expect a fairly decent chance for areas of drizzle and
fog tonight into Tuesday across much of the forecast area. With the
increasing moisture tonight, temperatures to remain fairly steady or
even warm into early Tuesday. Somewhat concerned with how much temps
will warm Tuesday with the stratus/drizzle expected to linger
through the day. However strong waa pattern and southerly to
southwesterly flow should hopefully be enough to still push temps
into the upper 40s northeast to mid 50s southwest.

.LONG TERM.../Tuesday night through Monday/
Issued at 229 PM CST Mon Nov 13 2017

Surface cold front will be over the northwestern part of the state
by early Tuesday evening with mid-level PV anomaly over the northern
Plains/Canadian prairies. Plenty of moisture will be present between
the surface and 850mb with drier air within the environmental mixed
layer up to 600mb over central Iowa. Best omega will be above the
saturated layer, but still should be enough to produce scattered
showers vs drizzle. Instability is essentially nonexistent so will
keep mention out. As the front clears the area early Wednesday
morning and the PV anomaly swings into the Great Lakes, lingering
clouds will move out as subsidence moves over the area with high
pressure building in from the Dakotas. Despite breezes from the
northwest, temperatures will still peak near normal for the middle
of November under a mostly sunny sky.

Cooler air will filter in on Thursday as the high pressure
transitions eastward and winds switch to the southeast. Clouds will
also begin to increase as a potent PV anomaly/shortwave trough
begins to move ashore the western US. As this moves eastward,
surface low pressure will form east of the central Rockies and move
northeastward towards the region. Differences remain significant
amongst the global models and will likely remain so as the main PV
anomaly is now over the Gulf of Alaska/north Pacific Ocean where it
will largely remain not sampled. One example of this large
difference is the location of the surface low pressure late
Friday. The GFS has the low closer to Madison, WI at 995mb, the
CMC closer to Omaha, NE at 992mb, and the ECMWF back towards
northwest Kansas at 993mb. Another example is the track with the
GFS/CMC bringing the low over the state in a northeast direction
while the ECMWF passes through central Missouri. It looks like at
this time by the time cold air is wrapped back into the system
regardless of solution, most of the precipitation will be rain
with perhaps a mix or brief changeover to snow limiting wintry
impacts. Overall, used a blend of models to arrive at the forecast
late this week until details become clearer. Of more certainty
are the winds that are expected to increase late Friday into
Saturday. GFS/ECMWF forecast soundings show winds at 925mb of 30
to 35 knots and at 850mb of 35 to 45 knots. Already initial
Superblend guidance was suggesting winds around 20 knots across
central Iowa and used CONSMOS to increase these winds. This
resulted in a rise on average of 3 to 6 knots yielding sustained
winds of 20 to 25 knots within the cold air advection regime
Saturday afternoon. Temperatures this weekend will fall back below
normal Saturday into Sunday as northwest flow persists aloft and
high pressure noses into the central US.

&&

.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1153 PM CST Mon Nov 13 2017

Little change to the aviation forecast with persistent low clouds
for the duration of the period. Widespread IFR to LIFR conditions
are expected in most locations although MVFR ceilings will occur
in far eastern portions of the forecast area overnight. South
winds will continue through the entire forecast period.

&&

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

&&

$$

SHORT TERM...Beerends
LONG TERM...Ansorge
AVIATION...Cogil



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