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

Long Range Severe Weather Threat Looming

I'm watching for a severe weather threat in about a week's time.

Tropical Tidbits

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.

Andrew

Analysis of the Tupelo Tornado on April 28, 2014

On April 28th, 2014, a supercell moving northeast across northern Mississippi became tornadic, and exhibited multiple signals of a large, violent tornado before it struck Tupelo, MS.

At approximately 2:44 PM Central Time/3:44 PM Eastern Time, radar indicated a supercell with a defined hook echo signature located in the immediate vicinity of Tupelo, as indicated above. This supercell was exhibiting a tornado debris signature (TDS) at the time it struck Tupelo, indicating that a tornado was already on the ground and doing damage. The already-dynamic environment, which later warranted a rare 'High Risk' of severe weather designation by the Storm Prediction Center, provided a sustaining mechanism for this tornadic supercell which eventually did strike Tupelo.

At approximately 2:54 PM Central Time, or 3:54 PM Eastern Time, the supercell had now moved past Tupelo. Radar imagery indicated a much more defined TDS, culminating into the appearance of a debris ball, in which a tornado is present and is throwing debris high up into the air, which then appears on radar. Note that the debris ball is significantly more defined at 3:54 PM in comparison to the previous radar scan at 3:44 PM. This development, combined with further analysis which detailed a more specific track, eventually led to the realization that this tornado had directly hit the city of Tupelo, Mississippi.

The correlation coefficient, a tool of dual-polarization radar, also indicated the presence of a debris ball. Using two methods of scanning from the radar tower, the radar is able to pick up the likelihood of a debris ball. When looking at a correlation coefficient (CC) chart above, one would want to observe values below 0.800 or so (seen as blues on this chart) to identify a potential debris ball. As this CC image from 3:54 PM ET shows, the debris ball is clearly evident in the white circle, seen as a deep blue dot. This nearly confirmed the possibility that this tornadic supercell had struck Tupelo, producing significant damage.

According to the governor of Mississippi, 131 homes and numerous businesses had been damaged in Tupelo as a result of this tornado. Dozens of injuries were reported as a result of this storm, but none were told as life-threatening.

Additional analyses of other tornadic supercells will be released in coming days.

Andrew

Significant Tornado Outbreak Expected Sunday, Monday

A significant tornado outbreak is expected on Sunday and Monday, with strong to violent tornadoes expected on these two days.

The Storm Prediction Center has issued a moderate risk of severe weather for northeast Texas, northern Louisiana, eastern Oklahoma, southern Missouri, and most of the state of Arkansas. This moderate risk comes as a strong upper level low brings moisture and other destabilizing factors up to the Plains, likely resulting in one of the more significant tornado events in recent memory. The Storm Prediction Center has indicated that long-tracked and strong tornadoes are possible if this event comes to fruition, and an upgrade to the agency's highest risk level, the High Risk, will come tomorrow if model guidance continues to hone in on this severe weather event.

The image above shows the East WRF-ARW model forecast for maximum updraft helicity over its entire 48 hour forecast period. The idea of highlighting the maximum updraft helicity values is to identify where potentially tornadic supercells may strike for this severe weather event. A look at this image, showing maximum updraft helicity for the Sunday event, gives a clear indication of what we could be facing with this situation. This particular model shows multiple long-tracked, rotating supercells moving northeast from Texas into Arkansas. Based on the high helicity values, it looks like some of the most intense cells may be able to put down some strong tornadoes, but it will take another round of model guidance to confirm or reject this idea.

A look at the Storm Prediction Center's SREF (short range ensemble model guidance) projection for the probability of strong tornadoes only worsens this threat. We see the chance of a significant tornado at or above 75% in Arkansas, but there's a very small speck in the middle of Arkansas, where it seems to increase another contour level. The next contour level above 75% is 90%, meaning that this model run indicates there is a 90% chance of a significant tornado in central Arkansas. Predicting tornadoes is a very difficult endeavor, but this graphic gives us an idea of where the worst tornado threat may be.

On Monday, we see another moderate risk area, now located just to the east over northeastern Louisiana, much of Mississippi, and western Tennessee. This moderate risk area also has the potential to be upgraded to a High Risk, as many of the same dynamics that look to produce a potentially deadly environment on Sunday will be in place again on Monday. If you or someone you know resides in the moderate risk area for either Sunday or Monday, please alert them to this severe weather. This outbreak may be one of the more significant ones of the last few years, and should be dealt with with extreme caution.

The SPC SREF projection for the probability of significant tornadoes is also startlingly high for the Monday evening event, as the graphic above shows. We see the highest probabilities placed in far northeastern Mississippi into northwest Alabama, located a bit east of the current Monday moderate risk area. While this forecast may see slight adjustments in the near future, the trend of a significant tornado event on Sunday and into Monday remains clear.

To summarize:
• A significant tornado event is expected Sunday and Monday.
• Long-tracked, violent tornadoes may occur on either of those days.
• Anyone in either of the moderate risk areas on Sunday or Monday should immediately prepare for potentially extreme weather, which may threaten lives and property.

Andrew

April 26-30 Severe Weather Outbreak: Monday Outlook

This forecast is solely for the severe weather on Monday, April 28th. For the Sunday, Monday and Tuesday outlooks, please look at the bottom of this post for links.

The Storm Prediction Center has outlined a rather large area of potential severe weather to kick off the workweek on Monday, April 28th. This is a continuation of the severe weather events on Saturday and Sunday, as a strong upper level low continues to ravage the country. When the SPC issues these sorts of long range outlooks, they highlight areas with a 30% chance or more of observing severe weather within 25 miles of any given point. This means that any of the areas highlighted in Arkansas, Louisiana, Mississippi, Alabama, Tennessee, Kentucky, Indiana, Illinois and Missouri may see some formidable severe weather, with a lesser-but-still-present severe weather threat surrounding this circular shape.

A look at the projected 500mb isobars and wind speeds for late Monday evening continues to exemplify why this event will be a multi-day, potentially significant severe weather outbreak. We see a long strand of anomalously high wind speeds extending from Oregon, rounding the closed low and punching into the area we're watching for Monday's severe weather risk around Missouri and Illinois. Although the closed low does not have a negative tilt that could then intensity the situation further, it does look like this piece of the Pacific jet stream will be what keeps the severe weather going, even though the closed low won't be doing much, other than continuing to pull moisture up from the Gulf of Mexico.

A look at 700mb winds, just a few thousand feet off the ground for the same time as the 500mb image shows strong lower-level winds over the area we're watching for the severe weather threat Monday evening. Considering the streak of 40 to 60 knot winds in the Midwest and southern Plains will only continue to intensity during Monday evening, as it is the nocturnal Lower Level Jet stream (LLJ), the severe weather threat will likely continue as well, at least through Monday evening.

A look at projected dewpoints and the Lifted Index for Monday evening really emphasizes the moisture this system has to work with. We see the projected dewpoints in shaded colors, and the dark blues represent the highest dewpoints, and thus some pretty muggy air. This all bodes well for severe weather potential, which is confirmed by the very low Lifted Index values, some as low as -9. The Lifted Index, also called the LI, is a measure of buoyancy of the air- in other words, when the LI is negative, air tends to rise and thus create thunderstorms. When the LI is positive, it indicates a stable atmosphere, suppressing thunderstorms. Seeing numbers close to double-digit negatives tells me this closed low will be keeping the severe weather fireworks going well into the workweek.

To summarize:
• A potentially significant severe weather event is possible on Monday.
• Those in the outlined area may want to review severe weather preparations and watch for further updates on this situation.

Other posts pertaining to the April 26-30 Severe Weather Outbreak:
• Saturday Severe Weather Outlook: Click Here 
• Sunday Severe Weather Outlook: Click Here
• Tuesday Severe Weather Outlook: Click Here (Coming soon)

Andrew