Area forecast discussion 
National Weather Service Des Moines Iowa 
355 am CDT sun may 26 2013 


Short term.../today /... 
issued at 322 am CDT sun may 26 2013 


Shortwave lifting across Iowa this morning has set off a decent line of 
thunderstorms and rain on the 800 mb front. Lack of northeastward progress of the front and 
continued feed of moisture has lead to some big precipitation amounts in 
the area east kdsm. Next area dropping southeast out of northwestern Iowa may 
enhance development for a few hours before the low level jet weakens. Also 
scattered convection over north central MO will likely lift/spread 
into southern Iowa this morning. Will limit probability of precipitation by later this morning and 
afternoon over the south but keep the clouds in. Rain chances 
continue through the day over the northeast. Went below MOS and 
closer to the European model (ecmwf) for temperatures today with a very slow rise expected. 
A decent rain range in temperatures for late may however. 




Long term.../tonight through Saturday/... 
issued at 322 am CDT sun may 26 2013 


Persistent probability of precipitation for the extended will lead to many issues/concerns 
with extended. Increased confidence in prolonged 
precipitation...with high precipitation rates possible at times across 
the County Warning Area. Precipitable water values remain high through the period...near 1.5 or 
higher at times...which is well above climatology for late 
may/early June. 


Tonight will see another shortwave lifting northeast along the MO 
valley...with Theta-E advection ahead of shortwave...spreading into 
central Iowa along with good moisture transport on nose of low level jet. 
Soundings also indicate deep warm cloud depth layer...especially 
across the north overnight and anticipate heavy rainfall rates. 
May need a Flash Flood Watch again for the overnight 
period...however have held off for now with current 
headlines...and northern portions of County Warning Area have not received as much 
rainfall as central. 


Expect precipitation to continue into the day Monday as Theta-E 
advection and moisture transport increase ahead of an approaching 
frontal boundary. Near frontal boundary in the far west...sb cape 
values support chances for severe weather...with shear increasing 
18-00z along boundary. System lifts again NE across the 
state...with highest precipitation chances/quantitative precipitation forecast again across the 
north...though deep layer saturation wains towards 12z Tuesday. 
However...areas of heavy rain again look possible as southerly 
flow persists...with additional flood/flash flood headlines 
potentially needed. 


Frontal boundary lingers into Tuesday...with additional chances 
for precipitation. Again...near frontal boundary could see 
strong/severe storms...but shear is a bit weaker. Currently...best 
chances for precipitation across the north...though still model 
disagreement on location of the front...and may be further south. 


Large area of low pressure is set to impact the region for the 
middle/end of the week. May see a break between systems ahead of 
secondary low for Wednesday and early Thursday...though have kept 
lingering probability of precipitation with model uncertainties. Low expected to dig into 
southern Dakotas for Thursday...with frontal boundary spread 
across Iowa...slowly lifting northeastward through Friday as 
negatively tilted trough. However...there are still significant 
model discrepancies in timing/location of low and frontal boundary 
for Thursday/Friday...but period has potential to be active with 
severe storms possible. This will need to be closely monitored by 
future shifts. 




&& 


Aviation...26/06z 
issued at 1159 PM CDT Sat may 25 2013 


An area of thunderstorms across central Iowa will continue to 
become more focused farther north overnight and generally impact 
the northern sites. Drier air advecting in from Great Lakes high 
pressure has helped ceilings increase to VFR over eastern Iowa and 
into the eastern sites. While some IFR conditions are possible yet 
through the period...the drier air should trend ceilings to MVFR and 
VFR. Precipitation will mainly be focused through middle Sunday 
morning then again Sunday evening. 


&& 


Hydrology... 
issued at 322 am CDT sun may 26 2013 


Strong moisture flux into the state continues to focus on the 800 mb warm 
front and should continue to present problems for the next few 
hours. Doppler estimates suggest rainfall of 3 to 5 inches may have 
occurred in parts of Jasper County. The current Flash Flood Watch 
will continue through 14z. Feel flooding threat will diminish once 
the low level jet weakens. For that reason would want to hold off until at 
least middle day before issuing additional headlines. 


Overnight tonight low level jet again kicks up nosing into Iowa with Theta-E 
advection and continued strong moisture transport ahead of a 
shortwave. Potential again exists overnight for areas of heavy 
rain with efficient rain producing storms as precipitable waters  remain high. 
Chances for flash flood again exist overnight especially in areas 
which have already received substantial rainfall. In 
addition...pattern looks to persist into Monday night...though 
further north. May see rivers begin to react to heavy 
rainfall...especially in the northeast where rivers are running 
high...with river flooding possible. 


&& 


Dmx watches/warnings/advisories... 
Flash Flood Watch until 9 am CDT this 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...MS 
long term...awb 
aviation...donavon 
hydrology...MS/awb