Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 191715

Area Forecast Discussion
National Weather Service Des Moines IA
1215 PM CDT Mon Mar 19 2018

...Updated Aviation Discussion...

.SHORT TERM.../Today through Tonight/
Issued at 351 AM CDT Mon Mar 19 2018

Complicated Nighttime Microphysics imagery from GOES-East early this
morning with mainly low stratus clouds over portions of central Iowa
being overspread by higher clouds associated with the precipitation
primarily southwest of Iowa. With light winds and ample near surface
moisture, there are areas of fog beneath these low clouds with
visibilities generally above 2 miles. Beyond monitoring the fog and
low clouds, other concern in the near term is the precipitation that
has been trying to work its way into our forecast area. This
precipitation is associated with a surface low that is currently
along the central part of the Kansas/Oklahoma border with a mid-
level shortwave over roughly the same area per GOES-East IR imagery
and derived motion winds at 8z. The 00z KOAX RAOB shows a moist
layer between 925mb and 875mb with a distinct dry layer above this
up to 700mb. This dry layer has been quite effective at evaporating
the precipitation keeping it mostly confined over southwest Iowa and
points south and west from there.

With the surface low tracking east into the Ozarks and Tennessee
River Valley and winds from the northeast and east in the low and
mid-levels that will keep delivering dry air into central Iowa,
expect the dry air to win out so forecast is dry from this morning
through this evening. Fog will lift toward mid-morning, but clouds
will remain quite plentiful today especially over western and
central areas. Mixing of the boundary layer up to 1 to perhaps 1.5km
per NAM and RAP soundings will help make temperatures higher than
yesterday with most areas in the 40s to low 50s.

Tonight, an inverted surface trough with a 500mb trough and
associated vorticity will move into the state. Clouds will thicken
as lift increases and precipitation in the form of primarily snow
will begin to arrive after midnight. The precipitation will make
slow eastward progression as dry air will continue to be advected
into Iowa from the east. However, over time saturation will become
sufficient for light snow with a dusty to perhaps half of an inch of
snow by sunrise Tuesday along and west of Highway 4 in our far
northwest and far west central counties.

.LONG TERM.../Tuesday through Sunday/
Issued at 351 AM CDT Mon Mar 19 2018

Fairly active mid/long range with high certainty for Tuesday into
Wednesday, and much less certainty with precipitation chances
Thursday and beyond as models continue to have a hard time
discerning the energy expected to top the ridge toward late week,
and then upper troughing to dig into the central US by the weekend
into early next week. Initially for Tuesday, another upper wave
still expected to drop through the state Tuesday with precipitation
likely ongoing in the far west/northwest at the beginning of the
period. This wave still expected to die off/shear apart through the
day as it moves east across the state. Therefore have highest pops
with precipitation chances earlier in the day, with precipitation
trends diminishing into the afternoon hours. Overall precipitation
expected to be lighter and still expecting around an inch or two
into the far west/northwest portion of the forecast area. A large
area of surface high pressure to then build into the state into
Wednesday with dry conditions expected into Wednesday night. Upper
ridging builds eastward through the Rockies and into the western
Plains. A quick shot of precip is possible Thursday as a weak wave
drops through the NW flow aloft across IA. Mainly rain is expected
with this fast-moving system.

Upper ridging moves east, flattens and almost a mini-Omega block
type pattern setting up for Friday into Saturday with energy
ejecting from the digging trough moving ashore over the Pac NW.
Another southern stream shortwave trough moving through the central
Plains and IA late Friday into Saturday. This system will have an
associated area of low pressure tracking across KS Friday into
Friday night and through northern MO into Saturday. A baroclinic
zone sets up across the state with additional precipitation chances
Friday into Saturday. Dry conditions then expected for a brief
period Saturday night as the upper wave moves east. Pac NW upper
trough to then move east and through the northern Plains/IA/MN by
Sunday into Monday. This will bring additional precipitation
chances. Majority of the precipitation with both the late week
system and again into the weekend system expected to be rain at this
time across the southern half of the state, with more of a rain/snow
mix in the north. Temperatures again to remain cool through the
entire period, with the warmest days Thursday into Friday with temps
into the 40s north and 50s south.


.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1212 PM CDT Mon Mar 19 2018

Main concern was with winds mixing throughout the afternoon and
have mention of gusts to near 20 knots for most TAF sites except
OTM were a bit more sunshine has allowed for deeper mixing and
slightly stronger gusts. Winds decouple by this evening. Have
introduced MVFR ceilings at FOD, MCW and DSM for incoming system
to produce some light snow.





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