Area forecast discussion
National Weather Service Des Moines Iowa
641 PM CDT Sat may 25 2013
Short term.../tonight /...
issued at 314 PM CDT Sat may 25 2013
The precipitation had ended over central Iowa by middle afternoon. An
area of subsidence west of a mesoscale convective vorticity maximum which is
exiting the region should help keep it dry over central Iowa into
this evening. The warm front was well defined this afternoon from
far northern Nebraska southeast along the Missouri River into
northern Missouri. Expect another mesoscale convective system to develop this evening and
then move into central Iowa tonight. Exact evaluation of the system
is uncertain...but confidence of it occurring is high. As for the
forecast...went with high probability of precipitation tonight and a small diurnal
temperature range. Primary threat will be heavy rain with the mesoscale convective system.
Convection should be elevated and severe parameters are not
favorable.
Long term.../Sunday through Saturday/...
issued at 314 PM CDT Sat may 25 2013
active weather pattern will continue over the next several days
as upper level ridge remains in place across the central portion
of the country allowing for southwest flow to dominate the weather
pattern. Leaned toward a blend...as models are at least agreeing
on overnight/early morning convection during the next several
nights...but disagree on location of heaviest rain.
Sunday through Tuesday...ongoing mesoscale convective system expected to develop tonight
will push into northeast Iowa Sunday morning. Have confined highest
probability of precipitation through 18z Sunday in the northern and eastern sections of the
forecast area. Moisture transport vectors and Theta-E advection
continue Sunday morning before diminishing by the afternoon hours.
Cut back on probability of precipitation b/T 18z Sunday through 00z Monday with a brief
period of subsidence settling in over central Iowa Sunday afternoon.
Another shortwave and 500 mb vorticity maximum...combined with low level jet and
moisture transport increasing Sunday evening into Monday
morning...kept with high probability of precipitation through 18z Monday. Warm layer cloud
depths reach 12000 feet by 12z Sunday and again by Sunday night into
Monday. This...combine with precipitable water values ranging around
1.50 inches will lead to some efficient rain producers Sunday
morning and late Sunday night into Monday. Another round of
efficient rain producers sets up Monday night into Tuesday with a
very similar pattern as tonight and Sunday night. Cut back on probability of precipitation
Tuesday during the day as shortwave is a bit quick to move northeast
past 12z Tuesday.
Wednesday through Saturday...GFS and European model (ecmwf) are coming together with
much stronger vorticity maximum and 500mb shortwave to push across the region
Wednesday night into Thursday. The 00z European model (ecmwf) is slightly slower than
the 12z GFS...but concerned about precipitation amounts on top of
anticipated quantitative precipitation forecast over the next few nights. The very active weather
pattern continues with the GFS/European model (ecmwf) both keeping the forecast area
under southwest flow and a series of shortwaves to affect Iowa
Thursday night into Friday...and again Friday night into Saturday.
Hydro issues will remain a concern in the extended period.
&&
Aviation...26/00z
issued at 641 PM CDT Sat may 25 2013
Mainly IFR stratus shield will prevail much of the night and it is
likely to hold through Sunday over the northern sites. Kdsm and
kotm have the potential to scatter with the warm front nearing
these locations. Chances for precipitation will increase again
tonight mainly after midnight into Sunday morning with areas of
thunderstorms developing. Another round of precipitation will
likely develop by middle to late Sunday afternoon. At this time have
not focused high detail with this late period activity. Potential
remains with some areas of lower visibilities under the stratus.
&&
Hydrology...
issued at 314 PM CDT Sat may 25 2013
This mornings rainfall was significant in spots across central Iowa
with an over 5 inch report in Marshall County. Heavy rain forecast
tools suggest that the storms associated with tonight/S mesoscale convective system should
be very efficient rainfall producers. Both the GFS/NAM shows a deep
warm cloud layer...high precipitable water and good moisture
transport over the warm front. Although the 850-700 mb Theta-E
advection is not as strong as this morning...there is enough to
support elevated convection. In addition...corfidi vectors are
pointing south tonight into the low-level just suggesting some
back building potential of the mesoscale Beta elements. With all
of this considered...we have issued a Flash Flood Watch for the
areas threatened by heavy rain and areas which had heavy rainfall
last night.
&&
Dmx watches/warnings/advisories...
Flash Flood Watch from midnight CDT tonight through Sunday
morning for Audubon-Black Hawk-Boone-Calhoun-Carroll-Crawford-
Dallas-Greene-Grundy-Guthrie-Hamilton-Hardin-Jasper-Mahaska-
Marion-Marshall-Polk-Poweshiek-SAC-story-Tama-Wapello-Webster.
&&
$$
Short term...Johnson
long term...podrazik
aviation...donavon
hydrology...Johnson
