Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kdmx 192125 
afddmx

Area forecast discussion
National Weather Service Des Moines Iowa
325 PM CST sun Feb 19 2017

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.

Precipitable water 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 18z tafs through 18z Monday afternoon/
issued at 1138 am CST sun Feb 19 2017

VFR conditions will persist through this evening along with
southeast winds. Cigs will increase and lower overnight,
especially after 06z. MVFR to IFR cigs are expected by late
tonight and through Monday morning. In addition, areas of fog may
develop along with a few showers and thunderstorms.



&&

Dmx watches/warnings/advisories...
none.
&&

National Weather Service Glossary of Abbreviations