Since we are in meteorological spring, I'd like to briefly recap the weather across the United States for the past three months. For the entire winter season, most of the Eastern United States has been above to well above normal on average. Only the far Southwestern United States has averaged even slightly below normal from December 1, 2012 through February 28th, 2013. This winter has also been characterized by above normal precipitation in portions of the Ohio Valley, Great Lakes, and lower Mississippi Valley.
And we all know how winter went for the Ohio Valley and Great Lakes. For the Ohio River region, snowfall was above normal due to the prevalence of clipper systems in that region, as well as Southwest Flow Events. The lower Great Lakes largely ended with well below normal snowfall over a large area (discounting the Western Michigan snow belts), with most of the snow falling this winter over portions of the Central Plains, and Upper Midwest, as well as Southern New England.
The first spring outlook will be rather brief, but I'll explain a few of the factors involved.
The first two factors I will talk about is the PDO (Pacific Decadal Oscillation) and the ENSO state (El Nino/La Nina Southern Oscillation). For the weather geeks out there, the general SST anomaly pattern that you see in the above image clearly indicates a re-strengthening negative PDO. Although the PDO index progressively rose since October, it seems now that it may be going back negative once again as the climate wind patterns shift to allow for the fledging development of a weak, east-based La Nina. With the ongoing warm SST anomalies in the Caribbean, as well as the enhancement of the Northern Pacific jet, this seems to suggest that spring will be rather warm and wet over a large portion of the Untied States.
The EPO continues in its negative phase, as well as the WPO, which is the reason why we continue to see a large vortex situated near Alaska. This is the main reason why we haven't been able to see a more suitable pattern for winter weather all winter. This will largely act to "recreate" the Bermuda ridge, which will likely dominate the United States during the middle and second half of spring.
Other factors in the spring forecast include the North Atlantic Oscillation, the Arctic Oscillation, and the Pacific North American index. The trends in all of these variables seem to clearly indicate that a warmer pattern is on the horizon. In fact, its likely that in combination with widespread drought across the United States, most of the country will end up above normal in temperatures for a large portion of the spring.
Here's my official forecast:
The first spring outlook will be rather brief, but I'll explain a few of the factors involved.
The EPO continues in its negative phase, as well as the WPO, which is the reason why we continue to see a large vortex situated near Alaska. This is the main reason why we haven't been able to see a more suitable pattern for winter weather all winter. This will largely act to "recreate" the Bermuda ridge, which will likely dominate the United States during the middle and second half of spring.
Other factors in the spring forecast include the North Atlantic Oscillation, the Arctic Oscillation, and the Pacific North American index. The trends in all of these variables seem to clearly indicate that a warmer pattern is on the horizon. In fact, its likely that in combination with widespread drought across the United States, most of the country will end up above normal in temperatures for a large portion of the spring.
Here's my official forecast:
- March 2013- As we've already seen, March 2013 will likely remain cooler than normal, or near normal through the middle part of the month. With an active, progressive pattern likely, precipitation will be near to slightly above normal, providing a few more chances for snow and rain across the area. By mid-March, temperatures are likely to rebound to normal, or possibly above normal. This will be in accordance with a deepening, east-based La Nina, a strengthening -PDO, and a relaxation in blocking across the Arctic. The Pacific jet will remain active, providing above normal precipitation to the region, and keeping drought conditions away from the area.
- April 2013- April will likely see more fluctuation than March will. In fact, it's likely that April remains near to slightly above normal as well, especially if we see long-term "after-effects" of stratospheric warming, which could allow blocking to rebuild for a brief time. Even so, this will be more likely in the earlier part of the month, with warmer conditions towards the end of the month. Fluctuations in the PDO, PNA and the ENSO will lead to varying strengths in the jet stream, and thus, its likely that we see near to above normal precipitation for the month of April. Overall, temperatures and precipitation won't be too far from normal. The warm latter part of April will also lead into May (note: When I mention warmth, I mean departure from normal, and not actual temperatures.).
- May 2013- May will likely be a warmth month, and more than likely, very similar to May 2012, which was incredibly warm, but also incredibly dry. Due to changing climate patterns, its likely that the drought re-extends farther east once again this summer, likely leading to intense heat once again. Several analogues seem to suggest that we could see at least one heat wave towards the end of May (much like last year). Early May could feature wetter conditions due to an active severe weather season as well, but transition to much drier conditions towards the end of the month.
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