Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 251023

Area Forecast Discussion
National Weather Service Des Moines IA
423 AM CST Sat Feb 25 2017

.SHORT TERM.../Today through Tonight/
Issued at 359 AM CST Sat Feb 25 2017

Although some shallow blowing snow lingered early this morning, all
it all conditions were much more tranquil than this time yesterday
with the main concern temperature trends into tonight. All of the
previous system`s forcing has exited the area with surface high
pressure moving from the central Plains into the mid-lower MS Valley
by this evening. There are two short waves which will impact the
forecast, but neither looks to have sufficient moisture or lift to
introduce precip as of yet. The first currently crossing the Rockies
will reach IA by late afternoon already flipping our regime to weak
forcing and warm advection. This will increase mid/high level
moisture and cloudiness with 1-3km lift and moisture following
behind resulting in insufficient moisture depth for precip.

The next short wave currently moving through Alberta/Saskatchewan
should reach the northern Plains re-enforcing the warm advection
with greater mid level kinematic contributions. Soundings suggest
the column would be on the brink of sufficient saturation for
precip, but not quite there as of yet. Thus the forecast remains dry
tonight with better chances north of IA, but would not be surprised
to see flurries in our northern areas eventually.

Temp wise, stayed toward the cooler end of guidance based on current
verification and model warm bias and did shade things even further
down north in the deeper snow cover.

.LONG TERM.../Sunday through Friday/
Issued at 359 AM CST Sat Feb 25 2017

A shortwave trough will pass across the state Sunday/Sunday night
with a high pressure ridge at the surface shifting off to the
East. Skies will clear during the morning hours Sunday but despite
the sun...temps across the snow pack will not respond thus highs
were lowered North on Sunday. Depending on how much melting occurs
South today...some of those highs may need to be adjusted as well.
Winds will drop off Sunday night and switch around to the South
but again with clear skies the southerly wind will have little
impact on the snowpack areas. Lows across the North Sunday night
were also lowered as a result.

A deep trough will move into the West Coast and this will buckle
the flow across the Plains and Upper Midwest and putting Iowa in a
Southwest flow and driving temps back up...with the usual bias
over snow covered areas but in general, warmer for the first part
of next week. Monday night into Tuesday a surface low develops
over the Plains and while models differ quite a bit on the
location of the low and attendant warm will draw
moisture over the area. Ptype will come into question...especially
North. Currently with models all over the place, the blends are
putting freezing precip across the North. At this point confidence
is low in any one solution and in keeping with collaboration with
neighbors, I left what the blends gave but with their propensity
to overdo freezing precip I would expect this to change with time.

Tuesday evening the low passes to the East and we get colder air
spilling into the state. In addition...the upper trough will move
East Wednesday and Wednesday evening. Temps will be colder from
Tuesday night through Thursday but temps will moderate after that
with readings climbing back into the 40`s and 50`s. Even during
the colder midweek period...temps will be near normal as opposed
to much above normal. Concerning precip...the remainder of the
forecast period from mid-week on should be mostly dry. A shortwave
is evident in on all models and they all try to sweep some light
qpf across the state but that is too far out to place much
confidence in when, where and how much. We had slight chances
going for Thursday afternoon across the North and East and I left
that as is for now.


.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1128 PM CST Fri Feb 24 2017

Mainly VFR conditions through the TAF period with some light snow
still possible at KOTM initially. High clouds to remain through
the period, with northwesterly winds diminishing some into
Saturday. Winds to then shift to the southwest to south Saturday




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