Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 122042

Area Forecast Discussion
National Weather Service Des Moines IA
242 PM CST Sun Nov 12 2017

.SHORT TERM.../Tonight through Monday/
Issued at 242 PM CST Sun Nov 12 2017

A large area of sfc high pressure to continue to build into the
state tonight, with clear skies and light winds expected. As the
high shifts off to the east southeast Monday, return flow will setup
across the state. WAA will kick in with some high clouds possible
into the afternoon hours. Still expected to see cooler temperatures
tonight with the clear skies and waa not kicking in until late
tonight. Very low level moisture to stick around especially in areas
where the low clouds hung around this afternoon, thus expect near
saturation tonight. With the light winds and moisture, could see
some fog develop across the southeastern third to half of the
forecast area late tonight into early Monday. Winds likely to pick
up a bit into the afternoon hours as well with some stronger winds
aloft, and a tightening pressure gradient. Therefore will add in
some gusts into the afternoon. With the south to southwesterly flow,
should see decent warming with temperatures pushing into the mid to
upper 40s and possibly even around 50 for highs Monday.

.LONG TERM.../Monday night through Sunday/
Issued at 242 PM CST Sun Nov 12 2017

The large area of high pressure will continue to move away from
Iowa over the eastern US/Canada Monday night. As the high moves
farther away, winds will become from the south and begin to draw
moisture northward within the warm air advection regime as a
shortwave trough approaches the area crossing the northern United
States. Soundings show this warming as well as an increasing
depth of moisture from the surface to 1500m/roughly 850mb by 12z
Tuesday. This will allow for plenty of clouds to be over the state
by early Tuesday morning. With the moisture in the column and the
surface temperature above freezing and weak omega, liquid
precipitation type in the form of drizzle or perhaps pockets of
light rain will be possible late Monday night into Tuesday. The
NAM has been the most aggressive with the high resolution windows
of the WRF as well as the global models also showing this light
precipitation. As the cold front--associated with the
aforementioned shortwave trough--moves across the state Tuesday
night, will have a better chance of rain showers, especially over
the eastern half of Iowa. Instability continues to be meager with
MUCAPE values of just a couple of hundred J/kg ahead of the cold
front and with a strong environmental mixed layer near 875mb,
thunder will be quite limited Tuesday night.

By Wednesday morning, the cold front and showers will be clear of
central Iowa while winds from the northwest bring in drier air
that will aid to clear out any lingering clouds over eastern Iowa.
Another area of high pressure will move across the northern
Plains/southern Canadian prairies Wednesday into Thursday. As the
high moves over Ontario/Great Lakes on Thursday, a potent PV
anomaly will be moving ashore the western US and will be
progressive in moving toward the central US. Surface low pressure
is expected to form east of the central Rockies and move toward
and over the region late this week/early this weekend. Despite the
PV anomaly being over the upper air network of northern Alaska at
12z this morning, significant differences remain amongst the
global models with timing, placement and evolution of the low.
Therefore, confidence in details late this week is low.


.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1120 AM CST Sun Nov 12 2017

Low clouds still in place at KALO, KDSM and KOTM should clear out
in the next 2-4 hours as drier air moves in from the north.
Northerly winds expected to shift around to south into Monday. VFR
conditions expected tonight into Monday.




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