Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 210952
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
352 AM CST Sat Jan 21 2017

.SHORT TERM.../Today through Tonight/
Issued at 352 AM CST Sat Jan 21 2017

09z Sat Water vapor imagery clearly depicting dueling shortwaves
over the upper Midwest keeping persistent pattern of fog/rain in
place this morning. The most southern shortwave, the one currently
influencing Iowa`s weather the most should be into Canada by 12z
Sun...leaving behind it weak large-scale subsidence and gradual dry-
air entrainment aloft.

Fog potential...
Confidence: Medium-High

Once again, fog will impact the DMX CWA through this morning, only
to return this evening into the overnight period. Expect similar
evolution of fog as past few mornings, with fog beginning to lift
northeastward around 15z-18z today, bringing area out of Dense Fog
Advisory criteria.

Scouring Bufkit soundings across the area, differences in tonight vs
this morning, is that low-level moisture/saturation does not look as
abundant tonight in locations south of around highway 20. This would
suggest lower probabilities/confidence in dense fog occurring.
Looking further into detail, fog type may even be different. At 04z
Sun, the KLWD RAP forecast sounding suggests radiation fog vs the
advection fog setup more likely at KMCW. Thus, will have to keep an
eye on mid-level cloud cover across the south. WV imagery picking up
on pocket of mid-level clouds over the Permian Basin of west Texas.
Obs verifies these clouds, and if they make it over southern Iowa,
which seems plausible, radiative fog processes would be hampered.


Rain potential...
Confidence: High

Rain ongoing across the central to northern portions of Iowa will
continue to propagate northeastward with the low... generally
exiting Iowa to the north around 18z or so today. Another shortwave,
presently located near the four corners region, will push
near due east across Oklahoma. As of now, it appears any sensible
effects and precip from this low should remain just south of
Iowa...Next update will handle precip chances near IA/MO border.

.LONG TERM.../Sunday through Friday/
Issued at 352 AM CST Sat Jan 21 2017

Fairly quiet to begin the long term, with only one system to focus
on by early next week. Have a large upper trough moving through the
southern US Sunday, with a weakening/dissipating low hanging around
the state. This will keep cloud cover around, but no precip
expected. Larger southern system to shove east into the Atlantic
coastal region, while brief upper ridging moves into the central US,
while a large upper trough digs into the western US. Upper ridge to
push east with return flow setting up into Monday night/Tuesday with
a piece of energy expected to eject across the central US as the
larger upper trough meanders eastward. This system to deepen as it
lifts through the state Tuesday into Wednesday. SFC low is expected
to track across south central to southeastern Iowa mainly Tuesday
night with cooler air moving in on the backside. Moisture lift
northward ahead of the system with some precipitation chances
beginning Tuesday. Then as colder air wraps into the system expect
def zone precip to linger across the state into Wednesday with the
system lifting ENE out of the area by Wednesday night into early
Thursday. Large cyclonic northwesterly upper low flow remains in
place through the end of the week. Therefore have widespread precip
chances mainly Tuesday into Wednesday, and mainly dry conditions
after that. Soundings indicating mainly rain central/south rain/snow
mix north for Tuesday, with a changeover to all snow Tuesday night
into Wednesday as cooler air moves in. Some light accumulations
could be possible with this system especially across the north where
precipitation will fall as mainly snow through the event.

Models hinting at another piece of the upper trough
swinging through late in the week could bring some light snow
showers/flurries. Overall though now mainly have increased cloud
cover for much of next week with the early week system and cyclonic
flow remaining beyond that. As for temperatures will continue to see
above average temperatures into early week. Colder air to move into
the CWA behind the early week system, with h85 temps dropping to
around -10C by late week. Therefore expect temps to return toward
the seasonal averages for late January by mid to late week.

&&

.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1133 PM CST Fri Jan 20 2017

LIFR cigs and vsbys will persist through 15Z before gradually
improving and Northern TAF locations may remain in LIFR conditions
through much of the day.  After 00Z a low pressure system will slide
East across Southern sections of the plains.  This will not impact
Iowa TAF`s directly but it will cause a wind shift to the Northwest
which may be responsible for more dense fog...especially over
Northern TAF locations.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CST this morning for IAZ004>007-
015>017-023>028-033>039-044>050-057>062-070>075-081>086-092>097.

&&

$$

SHORT TERM...Kotenberg
LONG TERM...Beerends
AVIATION...FAB



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