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3.23 LR/AG: Active pattern with multiple severe weather chances

A happy Thursday evening to you all! We hope you’ve had a wonderful day and are sitting down to read and chat with us regarding the upcoming long range weather pattern. We’ve got a lot to cover and will do our best to lay it out in an understandable and explanatory format. For a few weeks now, our forecasters have been discussing a change to the atmospheric pattern across the Northern Hemisphere during the end of March. These changes are still likely to occur and will lead to a much different weather pattern than the one we’ve been observing over the past few weeks.

From early March up until today, the pattern over the Northern Hemisphere has been essentially altered by the presence of high latitude blocking. This is better defined as the presence of ridging, or “blocking” high pressures in the atmosphere across parts of Canada, Greenland, and the Arctic. These are critically important because they alter the atmospheric flow in those regions and dislodge cold air, usually bottled up north, further south into the USA. The presence of this blocking has resulted in a colder pattern, particularly across the Northeast, in March.

Things are about to change.

What’s happening as we speak?

That very same blocking has begun to decay, and as it does so, the atmosphere will begin to undergo modifications and changes. While cold air may still hang on across the Northeast states, ridges will build northward with more ease across the Central and Southern USA. This will lead to warmer temperatures throughout those regions as the end of March approaches.

Analysis from today shows little to no blocking in the high latitudes, allowing the Pacific Ocean to dominate the weather pattern in the USA.

Analysis from today shows little to no blocking in the high latitudes, allowing the Pacific Ocean to dominate the weather pattern in the USA.

But more importantly, looming in the distance will be a change in the Pacific Ocean. A very impressive upper level jet extension will surge eastwards from the Central Pacific into the Western United States. Persistent jet streaks will lead to troughs across the West and Southwestern USA from the end of March into early April. With ridging to their east and troughs digging into the Southwest US with some consistency — low pressure systems seem poised to frequently eject into the Plains states. And that spells trouble for the Central and Southern AG Belt.

Why do we look so far west to understand the pattern?

The Pacific Ocean is one of the most critical components to the weather throughout the United States, and this is especially true for the AG Belt and Central United States. When the jet stream amplifies like this, the Pacific can be a huge transporter of moisture and energy. Forecast models have begun to key in on the potential for multiple disturbances to emerge out of the Pacific Ocean and into the Western United States.

The atmosphere works like a wave pattern — so as the troughs dig into the Western USA, ridging will develop to the east (like a dip and rise in the ocean waves). This will lead to a thermal gradient, or boundary of temperature, developing from the Plains into the AG Belt. Low pressure areas love to ride these thermal gradients and produce precipitation near and along them.

Forecast models show a large amount of disturbances moving into the USA as the Pacific pattern ramps up.

Forecast models show a large amount of disturbances moving into the USA as the Pacific pattern ramps up.

Accordingly, the threat for severe weather appears likely to unfold from the Southern and Central Plains eastwards through the Arklatex and into Southern USA. But individual threats remain extremely uncertain at this time. We simply don’t know the exact track of these low pressure systems yet, and their positioning and intricate details will determine when and where the potential for severe storms will develop on a more widespread basis.

What reservations do we currently have?

As is the case for almost any forecast, there are still plenty of uncertainties. Being able to communicate these to you is one of our top priorities, so while we make forecasts with confidence, we always try to communicate the forecast risks. As this particular pattern unfolds, our main reservation comes from the placement of the thermal gradient and intricate handling of individual systems.

After analysis of all of our forecast methods and model guidance (including properly weighting and understanding this guidance), our confidence in an active and wetter than normal pattern across the Southern and Central AG Belt is moderate to high. But there are still plenty of risks with the forecast, and those include the potential for the thermal gradient to shift. The thermal gradient serves as an area where enhanced lift for precipitation often occurs, and its exact placement will be critical in determining where the wetter than normal pattern develops.

For instance, if the thermal gradient is further north, storm systems will have a propensity to track further north through the AG Belt — and if it is further south, they will have a tendency to track likewise. So while we are confident in its development, and the development of a wetter than normal pattern overall, we’re working hard to pinpoint exactly where the wettest pattern will develop through Mid-April — and we’ll be updating as we get closer with more confidence on where exactly that will be.

What is the forecast over the next few weeks?

Firstly, make sure you check our client-based Weekly Outlook page and subscribe for our daily briefings. These include week-by-week breakdowns of the weather pattern across the Lower 48 through a 45 day advance period. They are updated fully three times a week and tweaked with new discussions every day.

For the purpose of this post, however, we’ve laid out a general theme over the next few weeks in terms of “hazards” as Plant 17 approaches. The simplistic way to look at it is that we are forecasting a wetter than normal weather pattern across much of the AG Belt through at least Aprils second week. Temperature departures on a large scale should be cooler in the west and warmer in the Southeast, while the Central US and AG Belt will lie right along the gradient. We’ll start to pinpoint local variations as we get closer to Aprils first day.

Stay tuned for more information and make sure to head over to our Live Blog for a 24/7 stream of the latest weather models and thoughts from our team of meteorologists.