Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Des Moines Iowa
706 am CST Thursday Dec 25 2014
issued at 704 am CST Thursday Dec 25 2014
Little change was made to the forecast at this point. Some
adjustment to cloud cover due to stratus tailing back across the
Short term /today/...
issued at 356 am CST Thursday Dec 25 2014
Satellite is showing the stratus steadily pushing to the east and
out of central Iowa. Des Moines had scattered out around 3am and
the clearing line as of that time ran from Estherville to just east
of Des Moines to just east of Centerville. By 12z the south should
be clearing from the stratus. The north is a little more
problematic and I believe locations north of Highway 20 will see
stratus for a fair part of the morning.
While the stratus will likely be gone by the afternoon...pretty
strong warm advection is underway and will continue through today.
Middle and high clouds currently over Nebraska and the Dakotas will
move into Iowa and while there should be a fair amount of sun and
plenty of breaks in the clouds it will not be a bright sunny
day...at least for the most part. Soundings hang on to low level
moisture and do increase middle level moisture by the afternoon which
is expected as the warm advection increases. The NAM is more
bullish while the GFS does not hold on to the moisture as much. Hi-
res short term models like the rap and the hrrr also indicated less
cloud cover today...especially south.
Surface winds will become widespread 10 to 20 miles per hour with gusts to 25 or 30
miles per hour at times. Temperatures today will be quite nice with highs in the middle
30s north to the middle 40s south. Enjoy todays temperatures because model
soundings crash temperatures beginning tomorrow.
Long term /tonight through Tuesday/...
issued at 356 am CST Thursday Dec 25 2014
Cold front will settle slowly southeast into Iowa tonight but bulk
of forcing will have moved northeast of the state with initial
warm advection surge and associated shortwave. Low clouds will
drop into the far northwest overnight behind the boundary beneath
the shallow frontal inversion. The front is expected to slow on
Friday as main shortwave begins to eject from the inter-mountain
west. Low clouds will continue to gradually expand southeast
across the forecast area on low level northwest winds. NAM most
aggressive with deeper low level saturation while GFS/Euro not as
moist. Not real confident about the possibility of freezing
drizzle/drizzle given the model discrepancies but have included
some patchy areas starting late morning in the northwest per NAM
given the deeper saturation. This spread slowly southeast into the
afternoon...however the precipitation will be very light until the
main system arrives on Friday night.
Precipitation will be on the increase Friday night as the main
shortwave approaches. Middle level qg forcing intensifies rapidly
Friday evening across the west and propagates primarily across the
west and north overnight. This area will see the best coverage of
snow overnight with 1 to 3 inches likely across the north...mainly
along and north of Highway 20 with highest amounts along the
Minnesota border. Farther south...another precipitation area is
expected near the surface front in the far southeast forecast area
near Ottumwa with light rain initially changing to snow late.
Amounts will remain quite light with only a dusting of snow.
Temperatures will cool with a surge of Canadian air behind this
system. However...the bigger push of cold air will arrive Sunday
night into Monday as a cold front slides through the state. There
will be some threat of very light snow on the backside of the
boundary on Monday...however the push of colder air will be the
bigger issues with temperatures dropping below normal for much of
the week as a polar airmass overspread the Midwest.
issued at 554 am CST Thursday Dec 25 2014
Stratus currently from just east of kmcw to just west of kcid and
will continue to push east today. Middle level cloud cover will
increase in warm advection today producing VFR ceilings. Southerly
winds will increase today in strengthening warm advection ahead of
the next system which will move into taf locations by late in the
period. Ceilings will once again go back to IFR with a wind shift to