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Area forecast discussion 
National Weather Service Des Moines Iowa
543 PM CST sun Nov 23 2014

Short term /tonight/...
issued at 333 PM CST sun Nov 23 2014

Several challenges with overnight forecast as rather dynamic and
fast evolving system moves through the central US tonight. Lead wave
is already moving nearly due north out of la with second wave over
Kansas slowly beginning to deepen this afternoon. Third wave over the
western Dakotas/Wyoming border will be the main energy for any
accumulating snowfall over the region by late tonight and early
Monday morning. First cold front heading into the area now with band
of showers developing along the boundary near i35. This will
continue to move east this evening. Fog is increasing ahead of the
front due to moisture pooling along the boundary. Once the front
drives east...the visibility will improve as a push of strong
northwest winds increases. Within the past hour winds have increased
to 15 to 30 miles per hour just behind the boundary with gusts to near 40. Most
of the night will be windy. Gradient winds over the northwest will
be quite strong and will increase to 30 miles per hour or higher across the
northwest third and remain strong on Monday. The remainder of the
area will remain below wind advection criteria. Have considered the
potential for more impacts with any snowfall...but amounts look low
enough to keep advection as wind and for now not a Winter Weather Advisory. As
Kansas shortwave tracks northeast this evening...weak deformation axis
now developing over Nebraska back SW into Kansas will expand
northeast with time. Have increased pop chances regionwide with the
best chances still southeast. The third wave over the western
Dakotas will be the source for cold air and the rain/snow
changeover. Timing of the arrival puts a rain snow mix over the
northwest by 01-02z and into the i35 corridor by 05-06z and into the
southeast by 08-09z. Complete changeover should take 1 to 2 hours
longer. The net result will be a short window of light to moderate
snowfall rates with generally light accumulations. Currently
amounts of up to an inch west and between 0.5 and 1.5 inches east
of Highway 63 by morning. Some concerns about impacts nearer
Sunrise East with winds remaining rather strong overnight. For
now...will handle with an Special Weather Statement and let the evening/overnight crew
evaluate with later data. The main concern overnight is the
potential for the trailing wave to bring a quick 2 to 3 inches of
snow southeast as it rotates northeast out of MO into western
Illinois. If the changeover to snow is quicker... this will result
in slightly higher totals in the far southeast and bigger impacts
by morning...especially for the commute. The current light amounts
may stick and freeze on contact...making for some slick
travel...but any higher amounts may also result in some blowing
snow and more issues. Presently low confidence that this will have taken a more measured approach for now.
Temperatures overnight return to recent memory with lows in the
lower 20s northwest to the upper 20s southeast. Combined with wind
by morning...some wind chills will drop to zero to 5 above the teens elsewhere.

Long term /Monday through Sunday/...
issued at 333 PM CST sun Nov 23 2014

Monday's forecast is a little less complicated than last nights
forecast. Cold air should be in place across central Iowa so ptype
should be all snow. However...the models have shifted their focus
for accumulating snow more to east central and southeast the deformation least from 12z-15z. After 15z
the system departs with a strong west to northwest wind at
25-35 miles per hour continuing over mainly the northern third of Iowa.
Still not confident we will get enough snow to have blowing snow
in this situation but there could be some drifting across roads
that would make surfaces slick. Current thinking is that now we
will see 1 to 2 inches along our eastern County Warning Area border...mainly from
Waterloo to Ottumwa with lighter amounts elsewhere...especially
east of I-35.

Deep trough remains roughly in place over the upper Midwest keeping
temperatures cold through the week...though there is no real Arctic air
behind this system so highs Tuesday and Wednesday remain in the
30s with lows in the teens and 20s. There is a clipper system that
all the models track...dropping into the upper Midwest but they
all vary as to intensity and track of the surface low. The GFS
digs the upper wave deeper and right over Iowa than the other
models. The Euro and sref are similar while the Canadian is
weaker and further north with the wave...just brushing northern
Iowa. The GFS and to some extent the Euro as well have higher quantitative precipitation forecast
over Iowa this run. I pretty much discounted the Canadian models
and a blend of the rest brings a band of snow across central Iowa
from 06z Wednesday through 18z with just some lingering snow beyond
18z across our east. We could see a couple inches out of this
system but just where the snow will fall is yet to be pinned down.

Thanksgiving day appears to remain dry and slightly cooler behind
the clipper system. Warm advection returns Friday as the upper flow
turns more zonal and another shortwave heads towards the upper
Midwest. The various models are nowhere close to a consensus on any
precipitation but with warm advection in place and several subtle waves in
the upper flow the period will not stay completely dry. Timing and
location this far out however is near impossible and any precipitation
would be light. The best chances right now appear to be Friday
and Sunday but my confidence is not high enough for anything more
than slight chances at this point.


issued at 538 PM CST sun Nov 23 2014

Persistent precipitation will remain across sites through much of
period...with northern sites kmcw/Kalo seeing most prolonged
precipitation. Precipitation will be rain changing to snow late.
Conditions will be primarily MVFR...though could see IFR or LIFR
with falling precipitation. Will see low VFR conditions at western
sites for beginning of period before falling back to MVFR or
lower. Winds will be strong and gusty with gusts over 30kts
possible in the afternoon. Strong winds may combine with -sn to
reduce visibilities but have kept mention out at this time.


Dmx watches/warnings/advisories...
Wind Advisory from 3 am to 6 PM CST Monday for Calhoun-Carroll-
Cerro Gordo-Emmet-Greene-Hancock-Humboldt-Kossuth-Palo Alto-



Short term...rev
long term...fab

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