Looking A Month Ahead: March Week 2
It’s Monday evening and the new Euro weeklies are out, so it’s time to look ahead at what the rest of March may have in store, as well as early April. Despite all the El Niño talk and discussions of 1998, that continues to not be a strong analog given observations, trends and forecasts. Through the second week of March, the pattern includes ridging across the East with above average temperatures, as an anomalously far south cutoff low pivots through Mexico and the southern Plains. This pattern will favor excessive rainfall from parts of East Texas into the lower Mississippi Valley. A few bouts of severe thunderstorms are also possible, although the setup is fairly messy with considerable convection and mixed storm modes.
The pattern reloads over the weekend with the next western trough taking a bit of a father north path than that of this past weekend. This will favor periods of rain and snow from Northern California into the Northwest. As the trough ejects east, areas of low pressure are progged to track from the central Plains into the Upper Midwest next week. These systems may ultimately produce some severe thunderstorms between the Plains and Mississippi Valley.
The dominant pattern may break down for a time, as the trough transverses east across the Great Lakes. This pattern would suggest cooler temperatures return to the East for a few days, but without significant downstream blocking, guidance suggests the pattern turns warmer again for the last 5-8 days of March. The last few panels of the GEFS appear to be in agreement with this as well. Keep in mind that confidence lowers with time, but eastern ridging has more or less been the expected pattern for late March for quite some time.
Into early April, there is no reason to believe that the general pattern undergoes any major changes. The weeklies suggest generally positive height anomalies over the eastern CONUS with troughing in the west. Should this verify, expect more West Coast stormy weather with a continued periodic threat for central U.S. severe events. While not terribly far from climo, the seemingly steady pattern is a bit ahead of schedule in the season and may gradually support threats as far north as the central Plains and Midwest from late March into early April.
Quick NAO/PNA notes
The NAO pattern has been slightly positive ever since late January, favoring generally at or above average temperatures across the eastern half of the U.S. with an active pattern, including more winter severe threats than recent years. The NAO projections show a large spread, but generally point to neutral to slightly positive NAO persisting into early April. The PNA has also remained slightly positive and is projected to fall to near and hover around neutral.
These projections are not guaranteed and if anything, the ensemble spread and tendency for a near-neutral NAO/PNA suggests that we are not following closely to the 1997-98 strong El Niño. This can be noted with the upper level pattern that has not been a close match over the past 1-2 months. Likewise, severe thunderstorm and tornado frequency has been on a much faster pace in early 2016 than it was into early spring 1998. As mentioned last week, the ensemble projections going forward and their respective analogs do not follow 1998.
The bottom line is that we are in an interesting pattern. One that doesn’t want to “follow the rules,” as we’ve seen with the Mexico cutoff low this week and otherwise April-like setups in February to early March of this year. Despite the uncertainties and other tricks the North American pattern may have in store, prospects for severe thunderstorm activity remain optimistic over the next month or so.
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