Active Severe Weather Potential Looming for Mid-June

I am still monitoring the potential for a period of active weather in mid-June.

The image above shows a long range forecast of outgoing longwave radiation (OLR) anomalies over the equatorial region of the globe, valid on June 14th. In both of these images, the yellows represent positive OLR, or suppressed tropical convection, while the blues denote negative OLR, or enhanced tropical convection. We can see a strong active Madden-Julian Oscillation (MJO) signal on the bottom panel, with deep blues indicating abnormal convection occurring over southern India into the waters east of the subcontinent. The placement of this enhanced convection tells me we are looking at a Phase 2 MJO, as the OLR composite shows below.

OLR anomalies for each MJO phase

Now, outside of the fact that Phase 2 MJO events have been known to increase the risk of violent tornado outbreaks in the spring months, the mid-level pattern during a June Phase 2 MJO event also signals the potential for severe weather.

The image above, produced by Americanwx, shows 500mb height anomalies over the northern hemisphere when the Madden-Julian Oscillation is in Phase 2 during the month of June. In this image, warm colors indicate high pressure/calm and warm weather, while cool colors denote stormy and cooler weather. During a typical MJO Phase 2 event in June, we tend to see ridging set up from the Bering Sea to the Great Lakes, enhanced slightly by weak troughing in the West. Because of this weak West US troughing, warmth and moisture are pumped north into the Central and East US from the Gulf of Mexico. This action then feeds into the increased potential for severe weather. Based on this composite, I do feel this time period may be defined by some active severe weather.

More evidence for an active severe weather period in mid-June arises when we take a look at the long range CFS severe weather forecast. The dates on the right display the date the forecast was made on, and the dates on the bottom legend indicate when this forecast is valid for. Warmer colors indicate the higher potential for severe weather. For instance, if I want to know the severe weather potential for May 30th on a forecast made on May 5th, I go up the legend on the left to find May 5th, then scroll on the corresponding horizontal line to find the May 30th box. In this case, we have been seeing the majority of recent forecasts highlighting the June 10-25 period as the one to watch out for, as the varying-colored boxes show on the upper-right corner of this image. Sometimes, there is safety in numbers in the weather world. In this case, with the relative consistency of these forecasts for the mid-June timeframe, I feel comfortable raising the concern of a potential active period for the aforementioned timeframe.

Andrew

Potential Severe Weather Outbreak Projected for Mid-June

I'm seeing an increased probability for a severe weather event, potentially an outbreak, for the middle of June.

The image above shows a long range forecast of outgoing longwave radiation (OLR) anomalies over the equatorial region of the globe. In both of these images, the yellows represent positive OLR, or suppressed tropical convection, while the blues denote negative OLR, or enhanced tropical convection. We can see a strong active Madden-Julian Oscillation (MJO) signal on the bottom panel, with deep blues indicating abnormal convection occurring over southern India into the waters east of the subcontinent.

If we take a look at MJO composites for each phase, with blues once again defining enhanced convection and oranges signifying suppressed convection, it would seem that storms just east of India fit in best with a Phase 2 or 3 MJO event, seen on the left panels of this graphic above. Considering there has been a link observed between the MJO being in Phase 2 and violent tornado outbreaks occurring consequentially, there is reason to monitor this period for potential severe weather.

The image above shows projected 500mb height anomalies over the northern hemisphere. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. In the image above, if we look towards the Bering Sea, we can see a very strong ridge of high pressure, seen by the splotch of red around the Aleutian Islands. This image is valid for May 13-14, and if we extrapolate it out 2-3 weeks using the Bering Sea Rule, we can expect high pressure and warm weather to appear in the East US. This extrapolated timeframe looks to fall around the time when this potential severe weather outbreak may strike, and the presence of strong high pressure migrating across the Eastern and Central US may amplify the potential for active weather.

Another device we can use to predict potentially active weather is this grid chart. The dates on the right display the date the forecast was made on, and the dates on the bottom legend indicate when this forecast is valid for. Warmer colors indicate the higher potential for severe weather. For instance, if I want to know the severe weather potential for May 20th on a forecast made on May 5th, I go up the legend on the left to find May 5th, then scroll on the corresponding horizontal line to find the May 20th box. In this case, we have been seeing elevated supercell composite values around the June 15-20 period for some time now, as the red box indicates. This is a long range forecast, but as you can see with severe weather events further to the left on the image, we can get a feel for severe weather potential a long way out, with more accurate forecasts usually coming a few days to a week prior to the event.

This potential event will be updated in coming days as more information becomes available.

Andrew

Summerlike Warmth Returns for First Days of June

I'm expecting summerlike warmth to come back for the first week or so of June.

The image above shows projected 500mb height anomalies over the northern hemisphere. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. In the image above, if we look towards the Bering Sea, we can see a very strong ridge of high pressure, seen by the splotch of red around the Aleutian Islands. This image is valid for May 13-14, and if we extrapolate it out 2-3 weeks using the Bering Sea Rule, we can expect high pressure and warm weather to appear in the East US.

If we look at another 500mb height anomaly forecast graphic, this one valid on May 19th, we now see that our strong ridge has shifted west into the middle of the Bering Sea, with cooler, stormier weather now protruding into western Alaska. This tells us that we can expect warm temperatures in the first several days of June in the middle of the country, with cooler conditions along the Eastern Seaboard.

This warmth is supported by long range modelling of enhanced tropical convection around the central Pacific, which is typically associated with warmer than normal weather in the Central and East US in the May-June-July time period. The bottom panel in the graphic above demonstrates the enhanced convection (blue) present in the Central Pacific.

Andrew