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Area forecast discussion 
National Weather Service Des Moines Iowa
631 PM CDT Wednesday Jul 1 2015

Short term /tonight/...
issued at 400 PM CDT Wednesday Jul 1 2015

A very quiet night expected across the dmx County Warning Area. A very weak
shortwave is exiting the County Warning Area to the east and taking with it -
ra/virga. Soundings show a lot of dry air in the low levels
and...subsequently...high cloud bases. Surface dewpoint depressions also
approaching 10f. All of this equals bad news for rain trying to
reach the ground and will thus keep with -ra/virga through 02z Thursday
or so.

NE flow from a surface high located in the Northwoods of WI will keep
with dry air advection in low levels of the atmos. This is best
highlighted at 850 mb on forecast soundings/cross sections. Am expecting
middle-level to high level clouds to be present across most of County Warning Area as a
jet streak is approaching from the northwest. This will largely inhibit
radiational fog overnight.

Long term /Thursday through Wednesday/...
issued at 400 PM CDT Wednesday Jul 1 2015

Although there are other token precipitation chances early and again
late...the primary sensible weather through the period will be
Sunday night into Monday night. At onset current South Dakota and southern
Alberta/Saskatchewan short waves will continue their treks down the
MO River Valley reaching or approaching Iowa Thursday morning. There will
be little if any thermodynamic support with what forcing there is in
the middle levels and still fairly weak. Instability parameters
including k index and MUCAPES are low so any thunder would be
limited and certainly no severe weather. This scattered and weak
convection would mainly affect western 2/3rds of the forecast...and
eventually exit by late evening.

There is little large scale support or low level convergence for
precipitation Friday or Sat. Bufr soundings do suggest uncapped MLCAPES over
1k j/kg...but with weak flow and little focus feel any coverage
would be quite isolated and not Worth a blanket slight chance. The
situation will change considerably by the end of the weekend
however. Return flow will strengthen sun with the return of a
more seasonal airmass...boosting dewpoints and instability. Models
are still trying to come to a timing consensus into early next
week...actually flip flopping their respective fast vs slow
solutions...but this only appears to result in minor sensible
weather concerns. Expect peaking surface based convection to fire
upstream into South Dakota during peak heating...moving southeast and reaching northwest
Iowa into the night. A lobe of fairly deep forcing associated with
maturing Canadian long wave trough will dip into the upper MS
valley and should be sufficient to sustain the mesoscale convective system overnight with
deep moisture convergence and extended cold front/Theta-E gradient
aloft. This will likely continue into Monday...so while the
convergence will be there for additional surface based development
during peak heating...that will be conditional depending on the
amount of convective debris which may not be minimal. GFS/European model (ecmwf)
deep shear seems weaker than yesterday...so while MUCAPES would be
there for strong to severe storms the overall event outlook may be
diminishing slightly. The signal for locally heavy rains has been
persistent however with warm cloud depths and precipitable waters both
increasing. This should be limited to only an event or two however
with pattern progressive with only token lighter precipitation expected
south into Tuesday and Wednesday...if that.

&&

Aviation...02/00z
issued at 630 PM CDT Wednesday Jul 1 2015

Few concerns this period. Remaining showers over northeast
sections drifting east by 02z. Surface high over Great Lakes will
provide east northeast flow with some partial clearing toward 12z
northeast. Small area of MVFR ceilings tracking over central Iowa at 23z
and may briefly affect kdsm with a few hours of bkn025-030. Main
stationary front and storm track remains west of area for now...
this should result in better instability...forcing to remain west
of the state through end of period. VFR conditions expected for
remainder after band of stratus passes south of kdsm after 02z. /Rev

&&

Dmx watches/warnings/advisories...
none.
&&

$$

Short term...kotenberg
long term...small
aviation...rev

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