Area forecast discussion National Weather Service Des Moines Iowa 624 PM CDT Wednesday may 22 2013 Short term.../tonight/ issued at 353 PM CDT Wednesday may 22 2013 Upper low is moving very slowly to the east tonight and as a result will likely see light showers across the north this evening and far east much of the night. Still expecting some light showers or sprinkles elsewhere as well but these will be much lighter and much more hit and miss than north and east. The nam12 shows another wave of Theta-E advection pushing south across the County Warning Area this evening but forcing is weak if there at all. This should provide for a brief period of better shower activity across the north through middle evening before everything finally pushes east overnight. With expansive cloud shield in place and low ceilings in place...I would expect the lower clouds to linger for a fair part of the night with clearing expected across the north late. Temperatures will need to be monitored if we clear out a little quicker as the airmass in place is pretty cool for late may. Temperatures could fall quicker and farther with a faster clearing sky. Long term.../Thursday through Wednesday/ issued at 353 PM CDT Wednesday may 22 2013 Primary concern will be convective trends and precipitation from the weekend right on through the middle of next week. Period will begin with a few days of fair weather however as current system exits and Iowa remains under the influence of upper level ridge. Progression of ridge and introduction of prolonged intermittent warm/Theta-E advection will begin Friday night however and last from the Memorial Day weekend right into the middle of next week. With heights gradually lowering in persistent west-southwest flow between slow moving western trough and departing MS/Ohio Valley ridge...this will place Iowa into what looks to be a nocturnal maximum pattern with soundings showing only minimal potential for surface based convection. Difficult to provide too many details yet...but Sat night into Sun morning is one period of concern with regard to severe weather and heavy rains with low level jet and 300k inflow right into western Iowa. GFS elevated convective available potential energy approaching 1500 j/kg with seasonally high precipitable waters and warm cloud depths up to 12kft will provide favorable environment for efficient rainfall. Storm movement will not be much either with mean wind 20kts or less. Do not expect mcss every night but pattern really changes little into the middle of next week with 850 mb flow remaining focused from Southern Plains into Iowa. Thus have kept prolonged period with chance wording and...unfortunately...little confidence in when to highlight particular periods with higher or lower probability of precipitation at this point. Elevated convective available potential energy are not as impressive as Sat night for following nights...but stagnant pattern will keep potential for at least weak mesoscale convective system activity in the forecast. Cumulative rainfall will keep things wet with little hydrologic recovery and at least some potential for additional flooding. && Aviation...23/00z issued at 624 PM CDT Wednesday may 22 2013 Upper level low continues to move slowly east. MVFR/IFR ceilings will remain overnight and gradually improve by 10-12z west/northwest with improvement for remainder of area from 14-18z. Winds will vary from northwest near 12kt to at times higher overnight with visibility generally VFR to MVFR with passing showers/drizzle. As upper level system departs skies will become broken VFR to sky clear after 18z with winds diminishing as well. && Dmx watches/warnings/advisories... none. && $$ Short term...fab long term...small aviation...rev