Area forecast discussion National Weather Service Twin Cities/Chanhassen Minnesota 741 am CDT Monday may 20 2013 Short term...(today and tonight) issued at 400 am CDT Monday may 20 2013 Today-tonight...broad upper level central Continental U.S. Trough will slowly meander toward the east...with its cutoff low wobbling over western Minnesota and the eastern Dakotas. Several shortwave spokes will rotate around this upper low...swinging through the mpx County warning forecast area today into tonight. The main issues are around timing of precipitation and potential for severe weather in far eastern Minnesota into western WI. Scattered showers this morning will continue to develop and dissipate as models indicate dry slotting to shift NE into the region this morning...lasting through at least middle afternoon. This would halt any widespread precipitation but isolated to scattered showers/thunderstorms certainly cannot be ruled out. Once this dry slotting shifts well into northern Minnesota and northwest WI by this evening...another swath of moisture will br dragged into the region which will be ably tapped to produce additional bands of precipitation...if not a large precipitation shield. One determining factor will be the placement of the surface low under the upper low. The surface low looks to remain primarily near the ND/SD/MN triple point... and this position would keep the bulk of the precipitation along and north of its latitude. As for severe weather potential...the eastward shift of the upper trough puts the best jetting and exit region over far eastern Minnesota and western WI. In addition...the break in the precipitation may allow for a few breaks in the overcast...allowing for additional instability...especially in western WI where precipitation has now virtually shut down everywhere. This will allow a reloading of the atmos to generate MLCAPE in the 2000-2500 j/kg range with little capping...while central-western Minnesota will be dealing with less impressive lapse rates and instability parameters. Still have a slight risk in place per Storm Prediction Center in their swody1 for all of far eastern Minnesota through WI which is very reasonable. As for temperatures and dewpoints...with the warm front continuing to lumber northward through the County warning forecast area and its trailing cold front still in the Dakotas...another warm/humid day can be expected. Will look for highs from around 70 in western Minnesota to the lower 80s in western WI... with lows tonight again mild in the middle 50s to lower 60s. Dewpoints will again reach the lower 60s...keeping an unseasonably humid airmass in place. Long term...(tuesday through sunday) issued at 400 am CDT Monday may 20 2013 It isn't until Tuesday night/Wednesday morning that we finally see some slow eastward progress with the trough over the central Continental U.S.. during this time the surface low slowly fills and moves from Minnesota to WI. However...before then...during the day on Tuesday...we expect scattered showers across primarily central Minnesota and northern WI. Just like this morning...where we see good drying showing up in the water vapor imagery across eastern NE and western Iowa...Tuesday should see a dry slot across the southern half of the forecast area. Better q-vector convergence and slightly better fgen is located across the northern forecast area just north of the dry wedge shifting northeast during the day. As a result...kept high chance probability of precipitation or likely probability of precipitation in the forecast for the northern County Warning Area...but lowered probability of precipitation or went no weather in the southern County Warning Area Tuesday/Tuesday night. Lingering instability in eastern Minnesota and western WI warrants thunderstorms for the weather type on Tuesday...but even before Tuesday night the MUCAPE slides farther easy and diminishes. Therefore...kept the thunder out of the forecast in most locations Tuesday night and Wednesday. We also cooled temperatures a bit on Wednesday...especially across central Minnesota...where light showers may be more widespread and hang around longer. Also...with east-southeast shift to the system on Wednesday...the better large-scale forcing should get pulled across the area. So wednesday's probability of precipitation are actually higher than tuesday's and are comparable to the probabilities forecasted today. However...the quantitative precipitation forecast is low. Looks like we'll get a brief reprieve from the wet weather Thursday and Friday with a surface high building in trough...ridge...trough pattern setting up across the Continental U.S.. the weather prediction center prefers a GFS/gefs/ec/ec-mean blend in the extended and to that seems reasonable given the relatively small spread in the long wave pattern...even with an anomalously deep trough along the West Coast. By the weekend...a warm front is forecast to move east across South Dakota/NE and approach western Minnesota. Most of the forecast area takes some time to moisten in light of the drier east-southeast flow under the ridge. Nonetheless...with at least some moisture place...the warm advection could kick off some showers by Saturday...especially in western Minnesota. && Aviation...(for the 12z tafs through 12z Tuesday morning) issued at 711 am CDT Monday may 20 2013 Another day of radar monitoring and fairly frequent amendments. Little bit of a tricky start with IFR/LIFR ceilings over much of the area and determining any improvement and when. Main culprit is the still-rotating expansive low pressure system centered over the eastern Dakotas into western Minnesota. This system will slowly drift east today while its associated warm front lifts north and the cold front lingers near the wrmn Minnesota state line. Low clouds will gradually lift into MVFR range with precipitation slowly coming to an end...especially for eastern Minnesota into western WI. By this afternoon...enough daytime heating will allow convection to develop across the entire region. Have held off timing to mainly around 20z and afterwards. If/when any thunderstorms move across a terminal... conds can easily be worse than what is advertised but did not want to go too hard at this time. More showery precipitation is then expected overnight with conds again degrading to at least MVFR tonight. Kmsp...tricky start as conds have bounced between lower-end MVFR... including below 1700 feet...and VFR at initialization. Have covered this using a tempo group at the start and will monitor trends to see if additional tweaks are needed. MVFR conds likely to hold from midday Onward...with precipitation re-developing around msp later this afternoon. Few thunderstorms at the start then more persistent rains expected after 00z. Still some timing/duration complications so some changes to the latter half of the taf would not be unexpected. Winds start out southeast...become S...then become southeast again during the early morning hours...and speeds will be gusty this afternoon. /Outlook for kmsp/ Tuesday...VFR/MVFR ceilings. Rain showers/thunderstorms and rain likely. S-SW wind 5 kts. Wednesday...VFR/MVFR ceilings. Rain showers likely. NE wind 5-10 kts. Thursday...VFR. NE winds 10 kts. && Hydrology... issued at 249 am CDT Monday may 20 2013 Have maintained Flash Flood Watch as-is through this forecast pkg but confidence is waning that actual flash flooding may be achieved due to dry slotting moving into the region this morning. This has cut into additional quantitative precipitation forecast expected. That said...much of the area has received 2-4 inches of rain with locally higher amounts the past couple of days...so soils are certainly close to if not completely saturated. There may not be the quintessential flash flooding that develops...but quick rises in rivers and streams along with urban flooding due to runoff certainly cannot be ruled out as another one half to one inch is expected today in much of the area covered by the watch...especially in central Minnesota. Even though the forecast is loaded with showers through Wednesday. Today appears like the last remaining chance to get any kind of quick response to local rivers and streams. We lose the environment for vigorous deep convection Tuesday and Wednesday and should just get scattered light showers with lower quantitative precipitation forecast totals on both of those days. && Mpx watches/warnings/advisories... Minnesota...Flash Flood Watch until 7 PM CDT this evening for mnz041>045- 047>053-057>063-066>070-075>078-084-085-093. WI...Flash Flood Watch until 7 PM CDT this evening for wiz014>016- 023>028. && $$ Short term...jpc long term...clf aviation...jpc hydrology...clf