May 7th-8th Potential Severe Weather Threat

It's looking more like we can expect a severe weather threat around the May 7th-8th period.

Tropical Tidbits

(The following is copied from a May 1st post) On the afternoon of May 2nd, we see a small but still-substantial ridge of high pressure pushing over Japan, as a strong storm system to the west begins pushing in the direction of the island nation. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. Seeing as this ridge appears on May 2nd in Japan, we can expect some warm weather around May 8-12th.

Tropical Tidbits

By May 3rd, we see a strong storm pushing into Japan in the wake of the ridge we saw in the image above. Looking at the trough, it looks like the system is negatively tilted, as seen by the pressure contours pushing in a south-east direction. If this trough reflects on the United States in about a week, which it very well may, the negative tilt may result in a pretty substantial severe weather threat. Locations of this threat are unknown at this time, but be cautious for some severe weather in this timeframe. (End copied portion)

The Storm Prediction Center has outlined an area of enhanced severe weather risk on May 8th from Oklahoma into southern Wisconsin. This threat area includes cities such as Chicago IL, Milwaukee WI, and Wichita KS, just to name a few. 

The surface analysis forecast from the Weather Prediction Center for May 8th shows a strong low pressure system moving northeast into Minnesota, dragging a warm front to the north, which should allow for a warm, moist and unstable atmosphere to flow over the area. To the west, we see a cold front draped across the Central and Southern Plains, with a dryline denotation in western Oklahoma and Texas. I expect that we will see the cold front be the main cause for this severe weather event, while the dryline to the south may provoke additional activity in the southern Plains. I anticipate the highest tornado threat to remain in the southern Plains, as dryline features typically can retain more tornadic cells than cold fronts, but we will analyze that idea later on. The Storm Prediction Center indicates we can expect the main threats to include damaging winds and hail, with a tornado threat still present, as is indicated below.

AS MODELS BRING THE UPPER TROUGH EWD INTO THE PLAINS DAY 6 /THU 5-8/
   HOWEVER...MORE COMPLETELY MODIFIED GULF MOISTURE APPEARS LIKELY TO
   HAVE SPREAD INTO THE CENTRAL U.S. PERMITTING DEVELOPMENT OF MORE
   SUBSTANTIAL CAPE.  AS THE SURFACE LOW SHIFTS NEWD ALLOWING A
   TRAILING FRONTAL ADVANCE ACROSS THE CENTRAL PLAINS
   VICINITY...DEVELOPMENT OF AFTERNOON SURFACE-BASED STORMS APPEARS
   LIKELY.  WITH THE GREATEST JUXTAPOSITION OF FAVORABLE SHEAR AND
   MODERATE CAPE LIKELY TO EXIST FROM ROUGHLY OK NEWD ACROSS KS/MO/IA
   AND INTO IL AND SRN WI...IT APPEARS THAT INCLUSION OF A 30
   PERCENT-EQUIVALENT RISK AREA CAN BE INTRODUCED ATTM WITH MODERATE
   CONFIDENCE...WITH HAIL/DAMAGING WINDS LIKELY ALONG WITH SOME TORNADO
   POTENTIAL.

I do believe we may see another severe weather outlook posted for May 7th for areas further to the west, as we take a look at rank-analog tornado probabilities off of the GEFS modeling system. Out of the four panels, the one which highlights the overall tornado probability is in the top-left corner, and we can see in that panel that Nebraska and Kansas may be in line for as high as a 10% chance of a tornado, which would certainly warrant a severe weather outlook.

If we take a look at the same four-panel forecast image, now valid on May 8th, we can see how the Storm Prediction Center is highlighting areas in Oklahoma into Wisconsin. It appears that the tornado threat here is weaker and displaced farther west than the SPC outlook for this day, but as was mentioned earlier, the main threats should be damaging winds and hail. I find that the threat for this day is more accurately highlighted in the other three panels, which calculate different values for ingredients of severe weather and general thunderstorms.

Overall, we are looking at a severe weather threat on May 8th (and potentially May 7th) over the Plains and Midwest regions.

Andrew