Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Des Moines Iowa
332 am CDT Sat Aug 2 2014
Short term /today/...
issued at 307 am CDT Sat Aug 2 2014
Similar setup for much of today as the past few days though some
hints of change develop late in the period. Broad surface high pressure
is still over the state this morning but it will begin to nudge
slowly east by the afternoon as low pressure moves into western
South Dakota. Upper level northwest flow will persist today and it
remains littered with embedded weak short waves. The weakly capped
environment remains however less instability is in place today along
with the lack of forcing will result in a dry day for most
locations. Still possible for an isolated short lived thunderstorm
or two this afternoon however the majority of the activity will
remain north into Minnesota. High temperatures today similar to
Friday with readings in the low to middle 80s.
Long term /tonight through Friday/...
issued at 307 am CDT Sat Aug 2 2014
Ridge across rockies will remain in place throughout much of the
period with northwesterly flow across Iowa. Several waves will
make their way southeast across Iowa through the weekend...before
stronger low pressure system will begin to break the pattern for
late in the period. Models are in generally poor agreement
overall for period...especially in near term.
Weak wave will push southeast to the west of Iowa tonight. Best forcing
and moisture remains near the Missouri River valley...and have
kept probability of precipitation confined to the west late tonight...though may still be
too early on precipitation...pushing eastward into the County Warning Area near
12z before dissipating. With generally weak surface flow and
little forcing through the afternoon hours...have kept probability of precipitation in the
afternoon across northern County Warning Area Sunday where best forcing and
instability will be. However...models are beginning to pull system
further south...and have brought probability of precipitation south through the late
afternoon and into the evening as another weak wave pushes
through. System is very slow moving and kept probability of precipitation through Monday.
Additional wave pushing through Monday night...mainly focused
across the northwest and have kept probability of precipitation higher there. However...have
mainly kept probability of precipitation slight chance to chance as have uncertainty in
timing and location of ... expect generally scattered precipitation
through beginning of period.
Better chances for precipitation arrive middle week as low pressure
system begins to work eastward. Again models have very poor
agreement in handling of this system...with GFS/Gem developing
low across Dakotas...pushing eastward across southern Minnesota
with two rounds of precipitation across Iowa with associated
frontal boundaries. However...European model (ecmwf) drops system further south
with more broad precipitation across Iowa as boundary shifts south
through the state. This will need to be monitored as models
hopefully begin to settle on a solution. However...for now have
trended towards GFS/Gem solution with probability of precipitation for extended Wednesday
and Thursday. Will likely see breaks in precipitation between
system...though have kept probability of precipitation fairly consistent in forecast. In
addition...could see good rain with this system...though given dry
antecedent conditions do not anticipate flooding concerns.
Temperatures will be consistent through the beginning of the
week...cooling behind low late in period...though remaining near
normal for early August.
issued at 1121 PM CDT Friday Aug 1 2014
Little change to previous package. Dew points jumped 5 degrees
between 23z and 02z...but have settled back a few degrees. Most of
the area continues with light winds and dew points holding in the
lower 60s. Patchy fog/some areas fog with visibility down to 1/2sm
possible by morning with valley areas near Kalo and kotm more
likely. Weak wave across the Dakotas and convection expected to
dive south ovn with few thin cirrus clouds over west after 12z.
Otherwise scattered-broken VFR conditions after 17z most areas. There
remains a weak signal for some convection after 17z...but
confidence and coverage not certain enough to include at this