Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 200549
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1149 PM CST Sun Feb 19 2017

...Updated Aviation Discussion...

.SHORT TERM.../Tonight through Monday/
Issued at 324 PM CST Sun Feb 19 2017

Low pressure over the lee side of the Rockies combined with high
pressure through the lower Ohio Valley have led to an increasing
pressure gradient and southerly flow into Iowa. Deeper gulf
moisture has been lifting rapidly north with the southerly flow
and into Texas and Oklahoma this afternoon. This moisture will
continue to surge north overnight as the low level jet
intensifies. A PV anomaly lifting into the region overnight will
bring decreasing static stability. This in addition to the
moisture advection and steepening mid-level lapse rates will
promote shower and thunderstorm development late tonight over
southwest Iowa then spreading northeast Monday morning. Some
activity may linger into the afternoon, mainly east of Interstate
35. Another line of showers and isolated thunderstorms may develop
late in the day in the vicinity of a frontal boundary that will
be passing through the state. A narrow ribbon of surface based
instability may develop in advance of the boundary. Clouds are
expected to be over the region for most of the day therefore have
trimmed back high temperatures closer to RAW guidance output.
Clouds in February are still a bit factor in temperatures. The
clouds certainly should limit the surface instability overall but
given high dew points in the 50s, the instability may still
develop.

PWAT values will be near 400% of normal on Monday and with melting
levels near 10 kft creating a seasonably deep warm layer, any
showers and storms will be efficient rain producers. That said,
storm motions will be around 50 mph and this will limit the
residence time.

.LONG TERM.../Monday night through Sunday/
Issued at 324 PM CST Sun Feb 19 2017

The passing of the shortwave will bring strong subsidence and
drying by Monday night as precipitation chances end across the
east. Tuesday and Wednesday will return to very mild and near to
above record temperatures. Wet ground on Tuesday from Monday`s
precipitation may slow the initial warmup, however, conditions
will be conducive to quick drying as profiles mix. Temperatures
in the 60s and 70s are expected both days.

The biggest challenge for the forecast period remains the storm
system for the end of the week. General trends have remained
consistent with a strong upper level system entering the Midwest
Thursday night and Friday. Temporal and spatial issues will
persist for the next several days though the window of
possibilities will continue to narrow. As of now, the potential
low pressure track is from central Iowa to northern Missouri. This
system will feature a very tight thermal gradient and the
potential for a strong overrunning event as the warm conveyor
wraps into the cold air. This would lead to significant snowfall
on the cold side of the system. These type of systems tend to have
a region of convective activity to the south, however they surface
boundary may be delayed which would limit the convection to the
south and allow for more moisture to be available for the
deformation precipitation. Will continue to highlight snow
potential over northern Iowa and a rain/snow mix central and
south. This could end up with temperatures in the upper 20s to
lower 30s north to 70s over southeast Iowa on Friday before the
cold advection sweeps across the state. An intense pressure
gradient and strong mixed layer winds would cause additional
potential issues as strong northwest winds develop. Temperatures
Saturday will be colder with highs in the 20s and 30s and a bit
warmer for Sunday.

&&

.AVIATION.../For the 06Z TAFS through 06Z Monday night/
Issued at 1144 PM CST Sun Feb 19 2017

Delayed the onset of IFR ceilings and MVFR visibility a couple
hours as hires models as well as current trajectory of storms in
OK look to impact the TAF sites closer to 12z Monday. Much of the
IFR to MVFR conditions will exit by around 21z.

&&

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

&&

$$

SHORT TERM...Donavon
LONG TERM...Donavon
AVIATION...Podrazik


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