Chase Forecast: May 21/22

TWISTEX will become active tomorrow as all involved prepare for several days of active severe weather in the western plains. Chris Karstens and I will depart Ames early tomorrow morning and hit I80 to the west through Nebraska, hopefully arriving mid-afternoon. Although Wednesday does hold some potential for severe weather, mainly for large hail, the day will mainly be a travel day unless something drastic can occur with the forecast. Nonetheless, the option will be there to go after a storm that may be able to form along the high plains of NE/CO, maybe Wyoming?

Wednesday should feature a deepening low over northeastern Colorado, which in response will allow for strong moisture return into the high plains. The corresponding moisture return will lead towards a very narrow axis of a warm sector just east and north of the low. Currently the SPC outlooks indicate the best chance being north and northeast of the low, with lesser concern on areas just east of the low. Further south along a trough, or pseudo-dryline the capping will be of major concern with very warm 700 temperatures and thus no risk has been outlined. The tornado threat is likely minimal with the lack of shear and overall instability that will be featured, thus a large hail threat is the main concern for this forecast. Likely to have multiple clusters of thunderstorms to the north of the low over the Nebraska panhandle and southeastern Wyoming where surface based CAPE values between 500-1500 J/kg will yield storms capable of producing large hail. Further south to the east and southeast of the low, while moisture and overall instability should not be a problem; 700mb temperatures of 11-15C will likely hamper development. This area may be an area to watch though, as if a storm can breach the capping inversion it does seem that conditions are favorable for severe storms as well. Beings the terrain of southeastern Wyoming is not that favorable, plus the idea that the threat on Thursday will also be near the NE/KS borders it does look like we'll play along the NE/CO/KS corners and hope for that rogue storm.

Thursday is coming together for a significant severe weather event along the high plains. Continued low pressure system in northeastern Colorado will continue to be in place, with the aid of a strong warm front and dryline will focus the severe weather threat.


Strong moisture return as indicated by the green arrows will continue throughout the day on Thursday, providing mid 60s dewpoints throughout the warm sector. Upper level support with good vorticity advection and strong divergence should be located across western Kansas and Nebraska. The best low level and overall shear does however seem to be limited the further south you go, indicated by the blue-lined area on the map. This confines the best tornado potential to the southwestern portions of Nebraska, with perhaps a good threat somewhat south along the dryline in the northern half of Kansas. Capping should be in place throughout the warm sector, however, a breakable cap does seem to be indicated by models over the northern half of Kansas and throughout Nebraska in the warm sector. Storm motions are likely to be north/northeastward, with any strong supercells being able to move east/northeast instead. For this reason, the best tornadic target area is likely to be placed in southwestern Nebraska and northern Kansas along the dryline (indicated by black outline). Large hail seemingly will be the main threat of the day, with damaging winds also likely. A lot of time for details in the forecast to be worked out and I will continue to update the forecast tomorrow and on Thursday morning.