Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Des Moines Iowa
1224 PM CDT Thursday Sep 18 2014

Updated for aviation...

&&

Short term /today/...
issued at 359 am CDT Thursday Sep 18 2014

Cool high pressure was located over western Ontario this morning
with a ridge extending south into the Tennessee Valley. High will
move east today with ridging extending back into the central U.S.
Some fog has formed in low lying areas and along rivers. Do not
expect to see widespread fog...but some local visibility down to 1/4
mile at times. Cool southeast surface flow out of the high will
hold temperatures back back to a few degrees cooler than yesterday
in many locations. Drier flow from the southeast will also keep warm air advection
precipitation to the west of the County Warning Area.

Long term /tonight through Wednesday/...
issued at 359 am CDT Thursday Sep 18 2014

Great Lakes high pressure will shift east into the northeast Continental U.S.
Late tonight into Friday. Strong Theta-E advection will commence
over western Iowa after 06z. Expect a few thunderstorms to develop
with the band of moisture advection. The chance for storms will
translate east Friday morning then should be out of the area by
the afternoon as the elevated mixed layer builds into the state
and effectively caps the area. The primary frontal boundary and
short wave arrive Friday night into Saturday. Forcing with the
system still looks to be modest with no strong convergence near
the front and a lack of kinematic forcing across the state. The
main focus for a statically unstable environment is from southern
Minnesota through northeast Iowa and into northern Illinois on
Saturday and should be a more primed region for more widespread
activity. There will likely be some decaying convection over
northern Iowa Saturday morning followed by peak heating
redevelopment over southern Iowa by middle afternoon. Not expecting the
boundary to be very active between the two periods. The moisture
axis is relatively narrow with the tropical elements blocked to
the south...thus any activity will be narrowly focused with most
of the day dry. Good mixing is expected Saturday as well with most
locations reaching the 80s.

Another large area of high pressure will follow Sunday and will be
the dominant feature through middle week. This high is of Pacific
origin thus will not be as cool as the past few systems and very
well may have highs in the low to middle 70s early next
week...therefore expect an outstanding start to the week.
Precipitation chances will creep back into the state late in the
period as the high shifts east and return flow begins to lift Gulf
moisture back toward the state.

&&

Aviation...18/18z
issued at 1217 PM CDT Thursday Sep 18 2014

Sky clear to a few cumulus...along with VFR conditions...expected through
09z Friday. Major forecast challenge will be fog for Friday morning. With
mainly clear skies expected across taf sites...especially sites
east of Interstate 35...dewpoint depressions will be zero to a few
degrees. Major inhibitor of fog will be winds...which will be
blowing in the 6kt to 8kt range. Lowest winds at kdsm...so went
3sm visibility there. Otherwise dropped rest of taf sites to MVFR
conditions with expectation of evening/overnight shift to tweak
tafs when forecast becomes more clear. Looks like fog should lift by
13z to 14z and strong southerly winds with gusts of 20kts to 25kts
to move in for the rest of Friday.

&&

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

$$

Update...MS Sep 14
short term...MS Sep 14
long term...donavon
aviation...kotenberg

National Weather Service Glossary of Abbreviations