Severe Weather Discussion for Sunday, June 29

Sunday is being monitored for potentially significant severe weather.

SPC

The Storm Prediction Center has highlighted portions of the Plains and Midwest for severe weather on Sunday. The Slight Risk covers eastern Nebraska, northern Kansas, northwestern Missouri, Iowa, southeast South Dakota, much of Missouri, Wisconsin, and the Upper Peninsula of Michigan. The most elevated risk inside this overall outlook area extends from eastern Nebraska to west-central Wisconsin.

Instant Weather Maps

Projected instability values off of the NAM model show figures in excess of 4000 j/kg situated from Kansas to Iowa, which should be more than enough to fire off these storms as a disturbance propagates eastward across the northern Plains. Shear from the surface to the 500mb layer looks to grow to upwards of 60 knots across the northern Plains and Upper Midwest, with spots of 70 knots also being found. It does appear that the initial storms that fire look to have some substantial tornado potential, with the aforementioned instability and shear present. As the night wears on, the expectation is for these cells to coagulate into a mesoscale convective system, which will then likely shift off to the east overnight. A strengthening nocturnal lower level jet stream should enable this eastward progression to continue.

Andrew

Long Range Guidance Supporting Snowy East Coast Winter

In a marked change from previous forecasts, long range guidance is now indicating that the East Coast is in line for a snowier than normal winter.

The image above shows the average precipitation anomaly forecast for January 2015 from multiple forecast guidance models. In this image, we see a textbook El Nino precipitation pattern. This pattern is complete with a drier than normal Pacific Northwest region, leading into a wetter than normal Southwest. This wetter than normal Southwest area would likely arise from the enhanced subtropical jet stream, a result of the El Nino phenomenon, and bring quite a beatdown to the drought ravaging the West US. We see these wetter than normal anomalies transpiring throughout the Southern US, and along the Gulf Coast, before cutting up the coast. As I have previously discussed, sea surface temperatures close to Greenland are becoming increasingly supportive of a pattern which could bend the jet stream and induce additional opportunities for coastal storms in the East. These long range models would seem to confirm this theory, and will have to be monitored in the near future.

Andrew

Update on Winter 2014-2015 Forthcoming

An update to the 2014-2015 winter season will be released tomorrow at 2:00 PM Central Time. 

Andrew 

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.

Andrew

Global Sea Surface Temperatures Supporting Cold Winter Ahead

Global sea surface temperature anomalies continue to point towards an increased likelihood for a cold winter ahead.

ESRL

There are four specific items I want to review that are pointing towards this cold winter idea.

1. El Nino
It's been discussed countless times already by countless weather agencies and enthusiasts, but we'll discuss it again here. The anomalously warm waters appearing west of Ecuador, nicknamed the El Nino phenomenon, look to be a crucial piece to this puzzle indicating a chilly winter ahead. In typical El Nino situations, we tend to see warm weather confined to the North and West US regions, while cool anomalies prevail in the South and East. Considering the El Nino retains the highest confidence for still being present in the coming winter, confidence in a cooler than normal winter for the aforementioned regions rises in response.

2. Cooler than Normal West Pacific 
This factor doesn't constitute an oscillation or index, per se, but will likely play into what we see happen this winter. The past cold season, I based the majority of my long range posts off of storms I was seeing hit Japan, based on the Typhoon Rule popularized by Joe Renken. It only takes a simple understanding of the relationship between high/low pressure patterns and sea surface anomalies to recognize what this means. The presence of below normal water temperatures extending eastward from Japan could very well mean that we see a stormy pattern over Japan this winter. Translating that through the Typhoon Rule, it means that the prospects of a stormy (and consequentially cooler) winter are enhanced.

3. Positive Water Temperature Anomalies in the Gulf of Alaska
In addition to the waters off Ecuador, the Gulf of Alaska is also experiencing above normal water temperatures. However, the placement of this particular body of warm water is key. Last winter, well above normal water temperature anomalies in the Northeast Pacific resulted in consistent high pressure along the West Coast, which provoked the polar vortex and incredibly cold air to push south, affecting much of the United States in the process. Barring any significant changes this summer and fall, a similar situation could unfold this next cold season.

4. AMO
The Atlantic Multidecadal Oscillation, abbreviated as AMO, is the wild card this winter. In recent months, it has reversed from its positive phase, which appears as warm waters along the coast of Greenland and into the Arctic Circle, into its negative phase, which features cold water temperatures in those same areas. The two conflicting masses of water are outlined clearly on the image above, and right now, it looks like the warm water is winning the fight. If it does hold out, we can expect increased probabilities of high pressure being sustained over Greenland, which would buckle the jet stream to the south and allow for cold air to penetrate deep into the Eastern US. Again, however, this is the wild card, and we likely won't know if this will happen for another handful of months.

Andrew