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Area forecast discussion 
National Weather Service Des Moines Iowa
657 PM CDT Thursday Aug 28 2014

Short term /tonight/...
issued at 315 PM CDT Thursday Aug 28 2014

Primary forecast question for tonight is coverage and timing of
precipitation. Recent radar trends and high resolution models such
as the WRF and hrrr have indicated a significant decreasing trend in
precipitation coverage late this afternoon and evening...however most short
range models continue to forecast an increase once again after dark
tonight. This is consistent with the synoptic scenario characterized
by broad upper level diffluence over a saturated atmosphere. Have
carried generally chance probability of precipitation/scattered wording through the night
given the support for redevelopment...but have little confidence in
details of timing and location thus the pop forecast is broadbrushed
for now. Otherwise little change was made to the ongoing forecast.

Long term /Friday through Thursday/...
issued at 315 PM CDT Thursday Aug 28 2014

With upper level trough still west of the area through early
Saturday morning...likely to see some additional rounds of
thunderstorms across the region through that time. Over the next 24
to 36 hours...the highest precipitable water values will gradually
shift east of the region as h850 moisture transport begins to shift
east as well. By 12z additional wave...the kicker
wave...will be located over southeast Kansas/western MO. This should
lift northeast during the next 24 hours resulting in increasing lift
over the region Friday afternoon and evening. In combination with
that a cold front and upper level low over southern Canada will
drift southeast and also aid in displacing the trough across the
Great Plains. Through the period Friday into early Saturday...
another half inch to inch of rainfall is likely to fall with the
heavier totals over the north and northeast portion of the forecast
area. With rainfall rates slowing down...flash flooding is probably
no longer a threat...but saturated ground may lead to some minor
runoff problems at times including some ponding of water and minor
street flooding in areas of poor drainage. Temperatures tomorrow
will likely warm a bit in the southeast in the lower 80s...ahead of
the wave with warm air advection and some potential breaks in the
cloud cover in the southeast. As the cool front moves east precipitation
chances should end across the region Saturday morning with some
sunshine returning to the area by morning. Highs will be slightly
warmer...but still within the a few degrees of highs of Friday with
more sunshine...but some slight cool air advection. Models in
general agreement with the next strong wave expected to arrive by
Sunday afternoon....with a rather warm day ahead as h850 rise to
near 20c by afternoon. The GFS shows that precipitable waters will once again rise
to near or slightly above 2 inches along the boundary as it moves
into western Iowa by 00z. Upper level wind fields again show a
modest increase as a modestly strong wave approaches from the
southwest with 0-6km bulk shear over 40 kts across the area. This
should be enough to promote severe storms during the late afternoon
and evening hours. Another round of storms with over an inch of rain
in some of the heavier storms is expected. Finally...the remainder
of the forecast suggests that a break from the active weather will
return from later on Monday through Wednesday...with some potential
for a quick moving storm again by Thursday.


issued at 657 PM CDT Thursday Aug 28 2014

All elements will be a concern through the period...especially
tonight. Confidence will be low as well due to scattered
convection and variable visibilities and ceilings. 00z surface analysis shows
warm front from northwest into east central Iowa with hit tafs north and east of
those locations the hardest with IFR/LIFR conditions by early Friday
morning with at least MVFR likely elsewhere due to high low level
moisture levels. Expect scattered convection mainly tonight and again
Friday afternoon. Possible other periods as well but tried to
highlight those rather than blanket the entire period with
vicinity wording.


issued at 315 PM CDT Thursday Aug 28 2014

Several additional episodes of rain are expected through Saturday
morning and again another Sunday afternoon through Monday morning.
At this time expected rainfall amounts through Saturday morning with
each event should be light to moderate. This will limit the likelihood
of flash flooding but still have some effect on rises on small stream
and area rivers. There is a greater risk of more substantial rainfall
over portions of the forecast area Sunday evening. This time period
will be monitored for both short term flooding and river flooding
over the upcoming Holiday weekend.


Dmx watches/warnings/advisories...none.



Short term...Lee
long term...rev

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