*Blog written at 4am CT May 19, 2013*
Sunday, May 19, has the potential to be a severe weather outbreak in the Plains and Midwest. Water vapor imagery currently shows a negatively tilted trough, with the trough axis running from southeast ID through northwest TX. Forecast models continue to show a closed low forming and setting up over NE/SD by tomorrow afternoon. A secondary shortwave trough will round the base of the synoptic trough/low and will be the culprit of the severe weather set-up tomorrow in the Plains. Surface cold front will sag south/southeast and will be draped across central KS and northwest OK by early evening, Sunday. The front will likely stall in that position. A dryline will be also be set-up in west-central Oklahoma throughout the day. It is still relatively unclear where and when storm initiation will happen. However, the most likely area for all modes of severe weather will be form central OK, through northern MO. Severe weather will be possible across 11 states in the Plains and Midwest, but not all areas will have the same severe probabilities. Overall, hail and destructive winds will likely be the main threats Sunday, but isolated and perhaps scattered tornadoes will be possible in OK, KS, and MO. This is where the best set-up will be. Below is the Storm Prediction Center’s (SPC) Day 1 Outlook, issued at 06z May 19 and valid Sunday 12z to Monday 12z. A “Moderate” risk of severe storms has been issued for parts of OK, KS, MO and extreme southeast NE. A “Slight” risk of severe storms surrounds the “Moderate” risk area. This graphic will likely change throughout the day. The “Moderate” risk area has the best chance at seeing all modes of severe weather tomorrow: hail, damaging winds, and tornadoes, possibly some strong (EF2-EF5).
On Monday, May 20, yet another shortwave will be rounding the base of the main cut-off low that will be centered over the northern Plains. The main surface low will also be set-up in the northern Plains. It will have cold front that will be stalled over the southern Plains, in central OK through central MO. A dryline will also exist, though it is tough to know exactly where it will be by Monday evening. Regardless, areas in the warm sector will be vulnerable to another severe weather outbreak. Areas in the warm sector include central OK, eastern OK, northwest AR, southern & western MO, and eastern KS. Storm initiation will depend on where the surface boundaries set up on Monday afternoon and locations of upper level jet streaks occur. The surface boundary locations will depend on what happens on Sunday. However, once again, SPC has issued a “Moderate” risk of severe storms for Monday afternoon/evening. Atmospheric environment will heavily favor destructive supercell in the warm sector. If tornadoes develop, they can be strong. Below is SPC’s Day 2 outlook, issued at 06z May 19 and valid Monday 12z – Tuesday 12z. This graphic will also change over the next 24-36 hours.