Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 191148
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
648 AM CDT Sun Mar 19 2017

.SHORT TERM.../Today through Tonight/
Issued at 339 AM CDT Sun Mar 19 2017

High pressure moving eastward into the Ohio Valley and a weak area
of low pressure approaching Iowa from the west will foster gusty
breezes from the southeast and south over the state Sunday. These
southerly winds will also draw moisture northward and in this warm
air advection, plenty of clouds are expected to form beneath an
elevated inversion. Where more cloud cover is expected to persist,
have lowered high temperatures a few degrees from the previous
forecast.

By late tomorrow afternoon, a cold front trailing a stronger area of
low pressure traversing southern Canada provinces will be moving
toward the northwest part of the state. Ahead of this front, the
850mb low level jet will be strengthening to between 40 and 45 knots
by early Sunday evening. CAPE will be elevated with values generally
between 1000 and 1500 J/kg. In this environment, isolated to
scattered thunderstorms will develop with the main threat being
marginally severe hail. With the elevated inversion fairly stout,
this will likely limit the stronger gusts from reaching the surface.
Most of showers and thunderstorms will end toward sunrise as the
cold front will be nearly through the southeast part of the CWA.

.LONG TERM.../Monday through Saturday/
Issued at 339 AM CDT Sun Mar 19 2017

Monday through Wednesday.  Confidence Medium.

By early Monday the precipitation over the southeast will have ended
with clouds lingering across the area. Northerly flow with cooler
thickness/H850 temperatures will move into the area...keeping highs
generally in the lower 50s north to the lower 60s in the far south.
A mixture of clouds and sun can be expected once again. Late Monday
evening into Tuesday a weak H500 wave will track quickly east
southeast over the Central/Northern Plains.  The models have been
attempting to resolve this feature for the past few days with marginal
success...with wave placement and strength in question each day.
That...and the amount of cold air accompanying it is leading to
more uncertainty for Tuesday. For now...will continue on a track
for a chance for a rain/snow mix early in the event on Tuesday
across the west with light rain through the remainder of the day
over the south or southwest. The GFS/NAM are introducing rain and
snow to the south half of the forecast area on Tuesday while the
Euro is less focused on the the south half and more for the
southwest third. None the less...a cooler day with highs in the
40s to lower 50s southeast can be expected for the morning and
afternoon hours on Tuesday prior to high pressure pushing south
far enough to end the risk of any precipitation for at least
Tuesday night into Wednesday. Clouds will still be part of the
picture on Wednesday as another system approaches from the west
later in the day. For now the better chances for any precipitation
will either be over the far west late Wednesday or finally reaching
the area Wednesday night. Highs Wednesday will be cool with readings
mainly in the 40s.

Thursday through Saturday.  Confidence Low to Medium.

As has been advertised for the past several days...the late week
weather will continue to be active over the region. Significant
shortwave energy has been tracking across the Pacific and several
waves will be migrating onshore in the next 5 to 10 days as a
longwave trough becomes more firmly established over the western
Conus next weekend.  The first wave will reach the west coast by 00z
Thursday with both a north and south branch.  The southern wave is
expected to dig toward the four corners area by 12z Thursday with
the first significant push of warm air and accompanying moisture
into the Central Plains by Thursday/Thursday afternoon. With increasing
instability over the area...showers and possible isolated thunderstorms
will work into the area as a warm front lifts north into Iowa.
The very northern fringe of the precipitation band may contain a
brief rain/snow mixture...but confidence is low depending on model
output. The Euro reaches saturation only after the warm air is in
place while the GFS is a bit faster with the onset of precipitation.
Through the day a change over to all rain is expected with the
possible thunder as well. With a second more vigorous push of warm
air heading north Thursday night...a more well defined warm front
should form resulting in another round of thunderstorms and much
warmer temperatures by Friday. Thursday will the be transition day
with mid 40s northeast to upper 50s southwest...while with much
of the warm sector through the region on Friday...highs are
expected to reach the lower 50s north to the upper 60s southeast.
The evolution of the late week system is still in question. Though
the initial surface low develops in eastern Colorado...a second
weaker low moves northeast into Iowa Thursday night and Friday
while the Colorado low begins to dig southeast with H500 upper
level support providing the lifeline for the remainder of the
event. This feature eventually fills and moves into Arkansas
cutting off the Gulf moisture to the area by late Friday night and
Saturday. Though instability will be present from time to time
from Thursday through Friday afternoon...the period of better
upper level forcing/jet winds maximized and collocated appear to
be on Friday and mainly over the southeast of the forecast area.
Generally from eastern Oklahoma northeast into eastern
Kansas/Missouri/northwest Arkansas to southeast Iowa and then
toward Illinois. This may result in some stronger thunderstorms
Friday though the better opportunity for more organized severe
weather will probably be well southeast of the state. By Saturday
the system will pull east with a weak ridge of high pressure and
cooler temperatures moving into the area.

&&

.AVIATION.../For the 12Z TAFS through 12Z Monday morning/
Issued at 647 AM CDT Sun Mar 19 2017

Currently, VFR conditions at all terminals as some mid and high
level clouds stream over the state. However, lower level clouds
have been trying to move northward and have recently pushed up the
Missouri River Valley into western Iowa per satellite imagery.
These clouds are expected to expand with some high MVFR
ceilings at times today. Winds will also be gusty from the south
or southeast ahead of an approaching cold front. This front will
bring another round of at least MVFR conditions as it crosses the
late today and tonight. Scattered thunderstorms will develop with
the best chance over southeast Iowa. After the front passes, a
return to VFR conditions will occur, though that may be after this
TAF period for KDSM and KOTM.

&&

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

$$

SHORT TERM...Ansorge
LONG TERM...REV
AVIATION...Ansorge



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