Area Forecast Discussion
Issued by NWS Des Moines, IA

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796
FXUS63 KDMX 231133
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
633 AM CDT Thu Mar 23 2017

.SHORT TERM.../Today through Tonight/
Issued at 351 AM CDT Thu Mar 23 2017

High pressure over the eastern Great Lakes region will move
southeast today while an area of low pressure organizes across
eastern Colorado. This combination will lift a warm front north into
Iowa today along with strong theta-e advection. Good low level
saturation will occur below 700 mb however a wedge of dry air will
remain prominent generally from 700 to 500 mb. This dry layer and
associated inversion does leave some uncertainty today. Guidance is
suggesting instability today into tonight however much of this is
likely based from 850 mb and does not account for the warm nose
aloft which will inhibit vertical ascent. Possible forcing above the
dry layer could ignite isolated and highly elevated convection but
at this time, not seeing much chance beyond isolated at this point
as long as this dry/warm layer maintains. Chances for precipitation
lifting through the region this morning but likely to be more
drizzle to light rain with the forcing focused below 700 mb. The
precipitation chances will lift north and be mainly over the
northern portion of the area by later this afternoon into the
evening. The precipitation chances will settle back south into
central Iowa later tonight.

Temperatures today will be dependent on cloud cover. The low
ceilings should be north of Highway 30 by mid afternoon with the
warmer temperatures immediately behind this region. Highs still
looking in the mid 40s northeast to the upper 60s southwest.

.LONG TERM.../Friday through Wednesday/
Issued at 351 AM CDT Thu Mar 23 2017

The main forecast concern revolves around the system that will begin
to impact Iowa today.  Not much has changed with the overall
picture.  A deep trough over the West will develop a closed low as
it crosses into the Southern/central Plains.  A surface low will
develop a warm front that will extend from Kansas then Northeast
across Eastern Nebraska into Western and Northern Iowa by Friday
morning.  The frontal position has changed some by both the GFS and
Euro mainly being a little further West and North.  Deeper moisture
and pretty strong forcing will arrive by Friday afternoon across the
forecast area with some instability across the West and South. We
should see widespread showers by the afternoon along with some
thunderstorms...especially South.  Can`t rule out a strong to severe
storm either with large hail and damaging wind the main threats. The
better chance for severe will remain South of the state but given
the strength of the system and the amount of forcing with it, storms
should form.

Friday night and Saturday the low shift South and East of Iowa and
we will be in the cold sector of the storm.  While the thunder
threat will diminish, the slow movement of the system will keep Iowa
in the deformation zone and bring a prolonged period of moderate to
occasionally heavy rainfall to the area.  I would not be surprised
to see several rivers have significant within bank rises and a few
may even go into minor flood.  This is something we will certainly
be watching for.

The system will finally pull far enough East during Sunday morning
to bring an end to the precip.  The break will be short lived though
as a Northern and Southern stream shortwave merge over the region
and bring another shot of precip mainly to Southern Iowa.

Towards the end of the forecast period another strong low develops
over the Southwest U.S. and moves towards Iowa by the end of the
forecast period.  This system looks very similar to the one that
will impact Iowa through Saturday though there are significant .
model differences at this point.

&&

.AVIATION.../For the 12Z TAFS through 12Z Friday morning/
Issued at 633 AM CDT Thu Mar 23 2017

Cigs will lower ahead of a warm front that will lift into Iowa
today. A few showers and isolated thunderstorms are also possible
with the lowering cigs. Cigs may become MVFR to locally IFR at
times. Conditions will improve over southern and central Iowa this
afternoon and into the evening. The lower cigs and precipitation
chances will linger over northern Iowa through the overnight.
Expect breezy southeast winds today diminishing a bit overnight.

&&

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

$$

SHORT TERM...Donavon
LONG TERM...FAB
AVIATION...Donavon



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