Saturday, June 21, 2014

Quiet Period Expected for Severe Weather

A quiet period in the realm of severe weather is looming on the horizon.

CFS Long Range Severe Weather Forecast
The image above shows 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 July 20th on a forecast made on June 5th, I go up the legend on the left to find June 5th, then scroll on the corresponding horizontal line to find the July 20th box. We have been going through an active period of severe weather, which was predicted earlier by the CFS model, as those red and yellow boxes on the left side of this chart show. However, long range forecasts in the top right corner show a distinct drop-off in colored boxes, indicating a quieter weather pattern.

The image above shows 500mb height anomalies across the Northern Hemisphere, valid on Monday, June 23. In this image, we see below normal height anomalies across the Japanese/East Asian region, located in the top-left corner of this graphic. These negative height anomalies indicate a cooler and stormier regime, something that will carry over in the United States 6-10 days later using the Typhoon Rule. This particular ensemble set, referred to as the PSD Ensemble guidance system, continues the negative height anomalies for multiple days ahead, meaning that the correlation period is extended and the cooler pattern should persist in the US. At this rate, the CFS forecast and PSD Ensembles do match up in the general quieting down of the weather pattern; the CFS model shows the supercell composite values across the nation dwindling, going from colorful boxes to dark blue boxes, and the PSD ensembles keep cold & stormy conditions over Japan for multiple days, meaning cold and stormy conditions can be expected in the US 6-10 days later, and then for a longer time period.