Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Des Moines Iowa
1155 PM CST Sat Jan 31 2015
issued at 824 PM CST Sat Jan 31 2015
Am going to extend the warning the rest of the way across the
state. Amounts coming in this evening are higher than
expected...though will likely see amounts a little less after
midnight. Some tweaking with amounts...but not major.
Short term /tonight/...
issued at 329 PM CST Sat Jan 31 2015
Main concerns continue the timing of the changeover and eventual
snowfall rates/amounts in the next 12 to 24 hours. Will continue
with headlines for long duration event with snowfall rates of near
1/2 inch or slightly higher per hour overnight once the mix changes
over to all snow. A surface boundary continues over the region from
Carroll to near Waterloo at 20z. Temperatures northwest of the
boundary have cooled a few degrees and the precipitation has changed
over to snow there. The boundary continues to drift south this
evening as isentropic lift increases as the h850 approaches from the
southwest. By 06z the low will be over northern Kansas with modest lift
continuing into the boundary overnight. Initially the better lift is
above the dendritic layer south of Interstate 80 before 03z. After
03z a broad zone of modest lift develops in the dendritic layer and
continues through Sunday. Looking at a xsect from Carroll...across
the west and northwest there is already some lift in the dendritic
layer which generally remains modest during the evening and
overnight hours. As the low deepens Saturday morning there is also a
hint at a deformation axis and weak trowal developing over south
central toward east central areas. This may help to enhance snowfall
amounts along Interstate 80 just to the east of Des Moines after 06z
through Sunday morning. Overall...snowfall amounts should be higher
across this area for the storm total. Model quantitative precipitation forecast has been generally
consistent with a range of .35 northwest to near 0.70 south/east
overnight. With snowfall ratios of 12 to 14 overnight...about 4 to
nearly 7 inches of snow is likely by 12z Sunday given some of the
precipitation will fall first as rain...some melting and compaction issues
as well. Winds overnight remain modest initially between 10 to 15
miles per hour through 12z southeast but increase over northern and
northeastern sections to 15 to 20 miles per hour toward 12z. Given the wet
nature of the snow some blowing and settling will occur...but not
expecting more than patchy blowing snow until 12z northwest
sections. Elsewhere across the south this shouldn't pose any
additional issues. With temperatures beginning above freezing in the
southeast/south and dropping this evening...roads may become
slushy/slick prior to snowfall accumulating to a great degree. Thus
travel may become hazardous early due to this rather than completely
snow covered roads initially.
Long term /Sunday through Saturday/...
issued at 329 PM CST Sat Jan 31 2015
Snow will be ongoing Sunday as the surface low slowly drifts eastern
Missouri. The snow will gradually end from northwest to southeast
through the day but should linger in the southeast for a fair
portion of the afternoon. The upper level wave will take its time
pushing east and by 18z it will barely be across the middle section of
the state. The brunt of the forcing will be exiting the east
shortly after 18z so the heaviest snow will fall by then but we will
still see light accumulations in the southeast through the middle-
afternoon. Between 6am and 6 PM we will get another 2 to 4 inches
across the southeast. I have lingered snow in the far southeast
through early evening. Although we lose most of the forcing...the
GFS hangs on to some of it across our area in the 700-500 mb layer
and the axis of the upper level wave will still be in the far
southeast portion of the forecast area.
Winds continue for Sunday night and Monday with wind chills solidly
in the -10 to -20 range through Monday morning. While this is not
quite advisory criteria it will be cold.
The pattern remains active through much of the long term period.
All the models are depicting another shortwave dropping down the northwest
flow over the region. This one is not any where near the strength
of the weekend system but there is some forcing with it and while
moisture is lacking there should be enough forcing to squeak out
some light snow Monday afternoon through Monday evening.
After that passes a low developing in the plains and a warm front
will try to establish itself across Missouri. While we will not see
the real warm air we will be considerably warmer Tuesday than we will
be on Monday. However...I think models are a bit optimistic with
all the fresh snow cover. Another shortwave drops down into the
state on Tuesday and with the warm advection will come a little
better moisture so we will be seeing some measurable snow again
Tuesday afternoon into the evening.
Canadian high pressure will then settle into the state for Wednesday
into Thursday and more cold air will be in place. Temperatures go into the
cooler again with highs in the teens and 20s and lows in the single
digits above and below zero.
Another short wave was suggested by some of the medium range models
for Thursday/Friday but there was no consensus on precipitation and since
forecast soundings were very dry I left precipitation out of this period.
For the start of the weekend another surface low and warm front
develops over the plains and this time the boundary shifts into
Iowa. Temperatures will be warmer once again...but tempered by ground
cover of the previous snows.
issued at 1150 PM CST Sat Jan 31 2015
Low pressure over central Kansas will move across northern MO Sunday
and to the east Sunday night. Widespread IFR to LIFR conditions in
stratus and snow tonight and Sunday. Improvement from the west
with the northwestern taf sites becoming high MVFR in the evening and the
southeast sites remaining IFR well into the night.
Outlook...high pressure will bring clearing late Sunday night into
Monday. Series of weather systems will bring snow and lower clouds
Monday night and late Tuesday and Tuesday night.
Winter Storm Warning until 9 PM CST Sunday for Adair-Adams-
Update...MS Jan 15
aviation...MS Jan 15