Tuesday, May 21, 2019

Active Pattern to Continue Severe Weather Threats

An active weather pattern is expected to continue threatening severe weather over the contiguous United States for the remainder of this workweek into the weekend and even next workweek, following up on my long-range forecast issued the other day (click here to read). Click on any image to enlarge it.

Latest analysis of the jet stream over the Northern Hemisphere.
Source: San Francisco State University
A look at the jet stream over the Northern Hemisphere spells out how the remainder of the week should bring continued threats for severe weather. The Pacific jet stream remains strong and extended west of the current trough that produced yesterday's severe weather, recording wind speeds in excess of 160 knots just off the West Coast. Maximizing that jet streak is the presence of another storm system making its way into the Pacific Northwest, which will be shunted south into the Southwest over the next day or two as a Rossby Wave blooms northward into the Gulf of Alaska. This particular storm system is expected to pose a threat for severe weather by the end of the workweek, something the Storm Prediction Center has already highlighted as shown below.

Severe weather outlook for Thursday, May 23rd.
Source: Storm Prediction Center
Long-range severe weather outlook for Friday, May 24th.
Source: Storm Prediction Center
As this storm system ejects into the Plains and Midwest to wrap up the workweek, a second trough is forecasted to make its way into the Southwest over the weekend.

500 millibar geopotential height anomalies for Sunday evening, May 26th.
Source: Pennsylvania State University
Indeed, on Sunday night model guidance projects strong negative geopotential height anomalies to once again be present over the Southwest, indicative of the presence of a storm system in that region. The positioning of a ridge over the Central and Eastern U.S. should locate this storm system's severe weather threat again over the Plains and Midwest to kick off the next workweek (about a week from today), essentially placing the same cities and states under the gun that have seen severe weather threats for the past few days now.

Just when it seems like it might quiet down, ensemble guidance then sees yet another storm system entering the Southwest by the end of May, which could pose yet another severe weather threat in these same areas for the beginning of June. However, model discrepancies become too large to have any material confidence in forecasts beyond the end of next workweek.

To summarize:

- An active weather pattern is expected to persist through this workweek and weekend into next workweek.
- Multiple severe weather threats are expected to evolve over the Southern and Central Plains into the Midwest and Great Lakes regions, as a train of upper level lows ejects from the Southwest and are pushed north into those areas due to a high pressure stationed over the Southeast.
- Severe weather threats are expected to continue through next workweek, but the potential for further threats may continue into the opening days of June.