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Area forecast discussion 
National Weather Service Des Moines Iowa
532 PM CST Friday Nov 21 2014

Short term /tonight/...
issued at 355 PM CST Friday Nov 21 2014

Large fetch of Theta-E advection entering southern Iowa
will continue to surge northward through the evening. Forecast
soundings still indicate fzdz/freezing rain potential over the eastern
sections of the forecast area...mainly east of i35. The hires models
in great agreement with timing and location of light precipitation tonight
into early Saturday morning and leaned toward a blend of the
hrrr/hopwrf/arw for probability of precipitation.

Looks to be a very brief period early this evening for some fzdz
over the far south...but latest Road surface temperatures well into the 30s
to around 40 and expecting the warm air advection to persist into Saturday
morning...there is a lower confidence with the much...if
accrual south of Highway 34 towards the Missouri border. Most likely
could cancel the advisory by around 03z time frame.

Further north however...Road temperatures along the i80 corridor toward
Highway 20 range in the lower to middle 30s and further north remain
in the 20s. Plus the ground/soil temperatures still below freezing in this
area due to the extended cold period over the past 10 days. There is
a higher confidence with a light glaze in the aforementioned area
even though temperatures from Ames to Des Moines have warmed into the
middle 30s. Think the ground is cold enough to quickly freeze any
precipitation this evening. The current trajectory of precipitation places it in
the Des Moines metropolitan between 02z and 04z tonight. Have the greater
fzdz/freezing rain chances from 02z-08z south to northeast tonight. Warm air advection and
good surge of surface dew points in the middle 30s...expecting the
freezing rain/drizzle potential to cease by around 06z along the i80
corridor and further northeast by around 09z. Have mention of the
fog overnight as well with the large area of moisture moving into
central Iowa.

Long term /Saturday through Friday/...
issued at 355 PM CST Friday Nov 21 2014

Will see first surge of Theta-E and warm advection departing on
Saturday morning. Some residual drizzle/very light rain remain
possible in the far southeast forecast area along with some fog
areawide as higher dewpoints move into the state. Much of Saturday
appears relatively dry before next surge of moisture and lift
arrive as main upper system lifts northeast Saturday night into
Sunday. This next surge begins Saturday evening with drizzle/very
light rain spreading northward across the forecast area as
isentropic lift increases. Moisture advection will also continue
and as this continues over the cold ground...fog seems as if it
should thicken overnight Saturday. Temperatures will likely fall
little if any and may actually rise into Sunday morning ahead of
approaching boundary. Precipitation will begin to consolidate on
Sunday morning with main wave lifting northeast into Illinois with
deformation precipitation along and east of i35 by afternoon. Cold
advection will also increase during the afternoon as front slides
eastward. Dry slot will overspread much of the forecast area by
Sunday evening with only threat of precipitation remaining in the
far east on backside of deformation axis. As cold air surges into
central Iowa...a brief transition to snow is possible however any
amounts appear light at this point.

Monday and Tuesday appear windy and cold with broad cyclonic flow
across the upper Midwest. Snow showers and some limited blowing
snow will be possible on Monday with soundings in dendritic growth
zone helping to promote snow development. At this point...there
appears only limited threat of precipitation late Tuesday night
into Wednesday morning as another wave drops into broad eastern
trough...however Thanksgiving appears dry at this point albeit cold.


issued at 528 PM CST Friday Nov 21 2014

Band of dz and fzdz will push into sites beginning early in the
period...bringing MVFR and lower ceilings and visibilities.
Ceilings and visibilities will primarily be MVFR...though may see
IFR and lower visibilities and ceilings at times with
precipitation...especially 06z-12z. Have continued to trend this
way at this time. In addition...MVFR visibilities and ceilings will linger
through 18z with ample low level moisture...though may lift to VFR
near 18z. Winds will be from the south and strong though much of
the period.


Dmx watches/warnings/advisories...
Freezing Rain Advisory from 9 PM this evening to 6 am CST
Saturday for Black Hawk-Boone-Bremer-Butler-Cerro Gordo-Dallas-

Freezing Rain Advisory until 3 am CST Saturday for Appanoose-



Short term...podrazik
long term...cogil

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