Cool, Stormy Weather To Give Way to Summery Warmth by Late May

I'm expecting some cool and stormy weather in mid-May to eventually give way to a shot of above-normal temperatures, before a cool spell returns for late May.

* A quick note, I have had at least 8 comments telling me that my late April-early May forecast was wrong, with more than a couple of these comments delivered with a less-than-enticing attitude. I've been receiving these comments for 2 weeks now- enough is enough. I don't expect myself to be correct 100% of the time, and I certainly hope no one else expects that of me, either.

Tropical Tidbits

The latest GFS Ensemble forecast above, valid on the evening of May 6th, shows troughing and cool weather present over Japan. By using the East Asia / Typhoon Rule, we can estimate that cool and stormy weather is can be expected around May 13-17th or so. Judging by the weak negative 500mb height anomalies, I'm only expecting a weak chill in the US, with the strongest cold weather allocated further north.

Tropical Tidbits

By the morning of May 9th, we see that the western portion of that elongated trough, seen in eastern China on the first image we analyzed, as now become a closed low and is progressing through Japan. If we once again apply this correlation, it is understood that a strong closed low may traverse the United States between a May 15-19th period. When this low comes through, I'm estimating we see it hit primarily the northern and central thirds of the nation, if you were to slice the US into thirds, horizontally. Cooler than normal temperatures can be expected with this, as well.

Tropical Tidbits

We finally do get relief in mid-late May, we a massive ridge of high pressure pumps up over Japan on May 11th, sticking around for a little while. This tells me we can then anticipate a period of anomalously warmer than normal weather in the United States around May 16-22nd or so.

Tropical Tidbits

Unfortunately, long range ensemble guidance supports the return of troughing and associated cold weather in Japan by May 16th, leading to potentially cooler and stormier weather in time for Memorial Day weekend.

Andrew

El Niño Beginning to Reach Surface

It looks like the much-anticipated El Nino is currently reaching the surface in the eastern Pacific.

Latest sea surface temperature anomalies (SSTAs) over the globe show our El Nino beginning to blossom in the sporadic areas in the waters west of Ecuador. This has been a long time coming, as we have been discussing extensively the Kelvin Wave that has been producing record-breaking temperature anomalies, as high as 6 to 7 degrees C above normal! The wave has been slow to push northward due to a not-as-favorable environment above the surface, but now that we are seeing the El Nino evolve, it can be expected that we will be in at least moderate El Nino territory by the time we hit late autumn.

Mean water temperatures along the equator from the surface to 500 meters down (top),
and anomalies for the same cross-section region (bottom).

If we take a look at sea surface temperature anomalies, now diagnosed on a cross-section along the equator from the surface to 500 meters down, it is evident that this Kelvin Wave-produced warm water is quickly upwelling to the surface. We see anomalies as high as 6 degrees C above normal about fifty meters below the surface, as is seen on the bottom panel in the top-right corner. As this body of warm water continues to push to the surface, we will likely see gradual weakening of these anomalies, but they should still be strong enough to propel us into our first El Nino event in multiple years.

Andrew

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