Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 130535
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1135 PM CST Sun Nov 12 2017

.UPDATE...
Issued at 1135 PM CST Sun Nov 12 2017

Dense fog advisory was issued earlier for deteriorating
visibilities across the eastern third of the forecast area. This
fog is forecast to linger into Monday morning before gradually
lifting. Concern is that the advisory may need to be expanded a
bit farther west, especially on the southern end as light south
to southeast winds begin advecting the fog to the north and
northwest. This will be monitored closely overnight for any
potential updates. Temperatures were also too warm and knocked
down values overnight with good radiational cooling setup,
especially in the north and west.

&&

.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 06Z TAFS through 06Z Monday night/
Issued at 1135 PM CST Sun Nov 12 2017

Aviation weather will be somewhat poor overnight in the south and
east including KALO, KDSM and KOTM with fog the main restriction
to visibilities and ceilings. Other concern is stratus in Kansas
is beginning to advect northward on backside of ridge axis. This
appears that it will spread into much of the forecast area on
Monday which may continue some ceiling restrictions through the
day into the evening. This will need to be watched closely to see
if the trends continue.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CST Monday for IAZ039-049-050-061-
062-073>075-083>086-094>097.

&&

$$

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



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