Area Forecast Discussion
Issued by NWS Des Moines, IA
FXUS63 KDMX 030948
AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
348 AM CST Sat Dec 3 2016
.SHORT TERM.../Today through Tonight/
Issued at 348 AM CST Sat Dec 3 2016
Surface ridge sliding over the state with light winds overnight.
Clouds have lingered across the north but some clearing is
advancing from the south as ridge axis slides through the state.
The low clouds will continue to slowly erode from south to north
this morning, however only to be quickly replaced by mid and high
clouds ahead of an approaching system. Temperatures will be a bit
warmer than Friday with the thinning lower clouds and some weak
warm advection. By later in the day, increasing isentropic lift
will lead to deeper saturation across western Iowa with light rain
developing by late afternoon. This area of precipitation will
continue to expand slowly north and east this evening as the lift
and moisture moves into the state. Mid-level forcing takes off
after midnight with moderate to strong lift across the southeast
2/3rds of the state through sunrise and continuing in the east
through late morning Sunday. This strong forcing will increase
precipitation rates overnight as the shortwave advances into the
state. The big question continues to be precipitation type!
Soundings are all below freezing throughout the deep of the
troposphere except the near surface layer. Therefore, this will
be a rain/snow event determined by precipitation intensity and
surface temperatures. Initial precipitation this afternoon is
expected to be rain with surface readings in the mid 30s or
higher. However, as evening progresses and the atmosphere
continues to saturate, surface cooling will continue with readings
dropping into the low to mid 30s despite ongoing warm advection.
Farther north, readings will drop to freezing with snow or rain
changing to snow this evening and then continuing overnight.
Farther south where temperatures are warmer, rain may persist for
a while. However, as strong synoptic lift arrives and
precipitation rates increase overnight, dynamic cooling and the
higher rates is expected to push the near surface soundings to
near freezing with any remaining rain changing to snow by late
evening or early morning hours. The snow will continue through
sunrise, although it will diminish across the west late tonight.
Accumulations are expected across much of the forecast area with
under an inch in the northwest to around 2 or 3 inches along the
far eastern border areas. This may approach advisory criteria,
especially given that it will be the first substantial snow of the
season. However, warm ground temperatures may keep overall amounts
lower than what they would be in the dead of winter.
.LONG TERM.../Sunday through Friday/
Issued at 348 AM CST Sat Dec 3 2016
Snow will persist mainly east of I35 through mid morning Sunday
with precipitation ending quickly in the rest of the forecast area
by midday. There may be a transition back to light rain before the
precipitation ends as temperatures will be climbing into the mid
to upper 30s by lunchtime. The warmer conditions will persist into
Monday as thermal ridging builds toward the state. May have some
concern with fog potential on Sunday night as melting snow cover
and light winds may lead to fog development. A cold front will
arrive late Monday night with some threat of light snow across the
area along with a surge of much colder air. The push of cold air
will continue into midweek with a polar airmass overspreading the
state. Temperatures will drop well below normal by Wednesday and
this will persist into Thursday with brisk northwest winds. There
remains a chance for light snow across mainly southern Iowa later
Wednesday/Wednesday night although both GFS and Euro are
suggesting the bulk of precipitation with this system will be to
the south of the state.
.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1150 PM CST Fri Dec 2 2016
Widespread MVFR ceilings above 2000 ft are in place over the
forecast area with spotty VFR conditions as well. Confidence is
fairly high this will continue overnight. However the western edge
of the stratus is expected to continue slowly advancing eastward
with conditions eventually becoming VFR at TAF sites this morning.
Attention will then turn to another drop to at least MVFR
conditions west to east Sat evening however as stratus and rain
and/or snow develops into IA with the next system.