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Area forecast discussion 
National Weather Service Des Moines Iowa
540 am CST Sat Feb 13 2016

Short term /today/...
issued at 305 am CST Sat Feb 13 2016

Main concern will be the cold today and arrival of snow this
afternoon. Still clear east with some increase in clouds over the
southwest/west at this time. Isentropic lift beginning on the
western edge of the ridge over the plains with light snow breaking
out along the surface/upper level warm front now located over southwest
South Dakota northwest to the Lee side surface low in Wyoming. Early
today...winds are expected to remain light but wind chill values
will remain quite cold over the north. Will continue advisory
through expiration.

Clouds will be on the increase through the afternoon hours...but
enough sun will help temperatures rebound to about 10 degrees
northeast to the middle to upper teens central and southeast. The
synoptic models in general suggest isentropic lift/saturation will
occur between 21z and 00z this afternoon over southwest to west
central. GFS bufr soundings show deepening saturation at Creston and
Carroll from 5kft to 13kft but mainly outside of the dendritic
layer. Initially...expecting very light and fine dry snow to develop
prior to end of first period there. Nmm hires model lags synoptic
model in onset of snow...though arw coincident with synoptic
models and better reflects current initial conditions.

Long term /tonight through Friday/...
issued at 305 am CST Sat Feb 13 2016

Forecast concerns for the extended will revolve around
precipitation chances early in the period. Expect light snow to
be ongoing across southwestern portions of County Warning Area by beginning of
period. Still some concern over the onset of snow...especially
across the north with a large amount of dry air at middle and low
levels to overcome. Isentropic analysis shows moisture increasing
across the east and south quickly after 00z. In addition...forcing
will increase as system lifts north...with best forcing arriving
by 12z. Therefore...expect snowfall rates to increase quickly
after sunset and to continue into the day Sunday. Models have
trended further to the south and southeast with
precipitation...and have generally trended snowfall totals this
way as well...especially increasing totals across the southeast
where forcing is best and precipitation will linger the longest as
system pulls east. Winds will also increase tonight and could
result in blowing snow reducing visibilities...especially in the
north with existing snowpack. Therefore...will go ahead and issue
Winter Weather Advisory for tonight for areas where snowfall
totals are expected to be generally over 3 inches. Will set start
time to 03z...to correspond with best forcing and expected
increasing precipitation rates. However...with models trending
further south and southeast with system...advisory may need to be
adjusted by future updates to start earlier or include more southeast
continues. In addition...have a few locations with snowfall
totals near 5 inches...especially in the east...and will need to
monitor for potential upgrade to Winter Storm Warning. System will
push east by late Sunday...and have kept advisory through 00z
Monday...mainly for eastern portions and expect advisory to be
able to be dropped earlier in the west.

Behind system will see warming temperatures Monday. However...will
only see a brief break in precipitation chances as low pressure
system drops south quickly from Canada...impacting the area late
Monday night. Models are in good agreement with the placement and
timing of system...though GFS is most aggressive with strength of
system. Have therefore increased probability of precipitation Monday night and
Tuesday...with a quick shot of snowfall expected. Models bring
quite a bit of moisture with system. However...with warmer
temperatures ahead of system...at this time expect snowfall ratios to be
lower. System will need to be monitored.Stem will need to be
monitored. Another wave is expected to drop south Wednesday...but
do not have enough confidence in amount of moisture available to
include pop mention at this time. Beyond Wednesday temperatures will warm
quickly as ridge builds into plains. Good southerly surface flow
Thursday with strong southerly winds will allow for a nice warm up
with temperatures expected to be well above normal for the end of
the period. Guidance continues to be quite warm at this time...and have
trended temperatures up. Large upper level low will push east
across northern US bringing precipitation chance. At this time models
have system affecting Iowa on Friday...but models are in poor
agreement with timing and placement of low and have therefore kept
forecast mostly dry at this time.

&&

Aviation...13/12z
issued at 540 am CST Sat Feb 13 2016

Snow and wind will be increasing after 21z west...with ceilings and
visibility lowering to MVFR conditions as snow increase between 02-05z sun.
Snow will lift east-northeast across area through period...continuing beyond
12z. Gradient winds increase 14g24kt from 04z through end of
period over most of area. Brief IFR visibility may occur in heavier
band of snow after 04z. /Rev

&&

Dmx watches/warnings/advisories...
Winter Weather Advisory from 9 PM this evening to 6 PM CST
Sunday for Black Hawk-Boone-Bremer-Butler-Calhoun-Cerro Gordo-
Dallas-Davis-Emmet-Franklin-Greene-Grundy-Hamilton-Hancock-
Hardin-Humboldt-Jasper-Kossuth-Mahaska-Marion-Marshall-Monroe-
Palo Alto-Pocahontas-Polk-Poweshiek-SAC-story-Tama-Wapello-
Warren-Webster-Winnebago-Worth-Wright.

Wind Chill Advisory until 8 am CST this morning for Black Hawk-
Boone-Bremer-Butler-Calhoun-Cerro Gordo-Emmet-Franklin-Greene-
Grundy-Hamilton-Hancock-Hardin-Humboldt-Kossuth-Marshall-Palo
Alto-Pocahontas-SAC-story-Tama-Webster-Winnebago-Worth-Wright.

&&

$$

Short term...rev
long term...awb
aviation...rev

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