:: Waiting for Signs
Tricky June convection forecast coming our way for the mid week. 48-72hr period in current model runs showing many ingredients for a widespread severe weather event coming together. Having shown these elements this far out, SPC has issued threat assessments for the area both Wednesday and Thursday.
Main culprit is a longwave trough currently pushing its way into the Pac-NW, and an associated surface low now developing on the lee side of the Cascades. As the system sweeps across the MT mountain ranges, and high pressure anchors over the Appalachians, a strong southerly low level flow will develop over the plains and the upper MS valley. The low level flow will usher in high dewpoints and warmer temps from the Gulf of Mexico, and as slight blocking sets up to our east, the surface low will slow its eastward progress a bit and a well defined cold front should set up. As that front pushes east, upper jet dynamics will remain mostly zonal across the front (according to GFS), while low level flow remains firmly in place ahead of it. The potential for deep layer shear is high. Development of supercell structures will be limited to the ability of the low level flow to work its way into the H70-H50 spectrum. Some model outputs are suggesting a very elevated warm layer.
Nonetheless, I think that concurrence with the professional offices is warranted for a slight risk of severe weather for the Wednesday overnight and Thursday afternoon. Timing of system will need to be tweaked up tonight and tomorrow morning. But three day outlook is a cinch for generalities today...
Tuesday...Mostly Sunny. High 74. Calm winds turning WSW 5mph. Low 53.
Wednesday...Partly cloudy. High 83. Gusty southeast wind 10-20mph. After sundown a 40% chance of showers and thunderstorms, some with heavy rain and damaging wind. Low 55.
Thursday...Mostly cloudy. High 80. Showers and thunderstorms likely in the afternoon, some could be severe. Southeast wind 10-15mph turning southwest 5-10. Rain ending after sundown. Low 50.