The tropics are quite active now as we gradually move towards the climatological peak (mid September) of the Atlantic Basin hurricane season. There are three tropical systems in the Atlantic Ocean and one of these is likely to completely dissipate in the next few days, a second may impact the northern Caribbean Sea or the Southeast US/Bahamas region, and a third is likely to strengthen significantly as it treks towards the US. The front runner system is Tropical Depression Fiona and it is of least concern as it shows little sign of intensification. On its heels is another tropical system that is of some real concern as it is entering an area of very moist air and it will take a southern route towards very warm waters of the western Atlantic or Caribbean Sea. The third system is far out in the eastern Atlantic and it will take more of a northern route towards the US east coast and it should strengthen noticeably in the near future; however, it is unclear as to whether it will ever even make it close to the US coastline.
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The official Atlantic Basin hurricane season has just begun and it may be more active than normal and more active than recent years as El Nino fades in the tropical Pacific Ocean and La Nina conditions develop (see tropical outlook). Tropical Storm "Bonnie" formed this past weekend and lasted as a minimal tropical storm for little more than 14-15 hours before making landfall Sunday morning near Charleston, SC. “Bonnie” has actually re-developed this morning into a tropical depression and is likely to produce additional heavy rainfall over coastal eastern North Carolina during the next 6-12 hours. In addition, signs indicate a new tropical storm is likely to form in the eastern Gulf of Mexico by early next week and then cut across Florida potentially producing several inches of rain for a good portion of the state. If this next system were to become a named tropical storm, it would be called “Colin” and be the third of the 2016 Atlantic Basin season (“Alex” formed in January).
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Let me paraphrase poet T.S. Eliot and say “April can be the cruelest month”. The long winter season is over, baseball is about to begin, trees are blossoming, and colorful early season flowers dot the landscape, yet all it takes this time of year is the passage of a strong cold front to put the Northeast US back in the deep freeze. Or, a simple shift of low-level winds to an onshore direction can bring about a quick twenty degree drop in temperatures as the ocean remains quite cold this time of year (i.e., the dreaded back door cold front). Indeed, just when it appeared that we were on the door step of sustained warmth in the Northeast US, it looks like the first 10 days or so of April will feature multiple cold air outbreaks and there may be numerous chances for snow.
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There is a blizzard raging today across the Rockies and it’ll greatly impact the Northern Plains and Upper Midwest over the next 12 to 24 hours or so with significant snow and wind. By no means, however, is this winter’s last gasp for that part of the country and indeed, there are numerous signs for a major cold air outbreak for much of the central and eastern US as the calendar turns from March to April. Multiple “teleconnection” indices support the idea of a pattern change to colder-than-normal around here by the time April begins and it could last right into the second week of the month. Looking even farther ahead, once this upcoming cold spell disintegrates likely by the middle of next month, we could very well go from “winter-like” to “summer-like” in a hurry.
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The 12Z GFS Ensemble forecast map of 500 millibar height anomalies for Thursday morning (above) shows three major players across the North American playing field in terms of upper atmosphere lows (blues) and highs (oranges). To begin, a strong upper level high will be situated over the Northeast US. This relatively slow moving system contributed to “atmospheric blow torch” conditions on Wednesday in the Northeast US and Mid-Atlantic region and there will many more records broken on Thursday as well in this part of the country. Elsewhere, one strong upper level low will be sitting over Mexico and another will be located over the northeastern Pacific Ocean. These two systems have already contributed to an “atmospheric firehose” feeding copious amounts of moisture into both California and the south-central US. In addition, the strong upper low spinning over Mexico is associated with an air mass that is nearly 30 degree below normal for this time of year and this is resulting in many higher elevation locations receiving highly unusual snowfall amounts.
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A chaotic weather pattern is shaping up for next week and it will be a very challenging forecast period. The weekend will begin on a very mild note with temperatures flirting with the 60 degree mark in some spots along the I-95 corridor and there will no doubt be a feeling of spring in the air. Colder air will then filter back into the region from the northwest late Sunday night and early Monday and it looks like a sneaky low pressure system may accompany that cool-down. After that, it appears we may have to deal with two separate low pressure systems later next week in the eastern US with odds favoring rain in the I-95 corridor.
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January will end and February will begin on a mild note here in the Mid-Atlantic region with temperatures well above normal for this time of year in the Sunday to Wednesday time period. High temperatures by Sunday afternoon should climb well up into the 40’s and those mild conditions will continue right through mid-week. In fact, Wednesday looks especially mild with temperatures likely 20+ degrees above normal in the Mid-Atlantic region (above). Snow should continue to melt around here at a pretty good clip given the expected (temporary) break from winter and that’s a good thing since there is the threat for a heavy rain event by the middle of next week. The potential heavy rain event will be produced by a powerful El Nino-enhanced storm and its associated strong cold frontal system that will cross the nation next week and have significant implications all along the way. Behind the storm, a widespread Arctic air outbreak will envelope much of the eastern half of the nation by Thursday and Friday of next week.
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One of the ways to monitor the potential for Arctic air outbreaks in the northern U.S. is to follow what is happening in the stratosphere over the polar region of the northern hemisphere. Sudden stratospheric warming (SSW) events are large, rapid temperature rises in the winter polar stratosphere occurring primarily in the Northern Hemisphere. They have been found to often set off a chain of events in the atmosphere that ultimately lead to Arctic air outbreaks from northern Canada into the central and eastern U.S. Indeed, there is stratospheric warming taking place right now over portions of the polar region and another significant warm up in the upper part of the atmospheric is predicted ten days from now. This unfolding stratospheric warming event provides reason to believe that after a bit of a break in the winter weather pattern in the eastern U.S., cold air outbreaks will return in full force for much of February beginning as early as late next week.
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This week’s Arctic air outbreak is only the opening salvo. Old Man Winter was pretty embarrassed by his performance during December in the eastern half of the nation and is primed to make up for it with multiple Arctic blasts during the month of January and perhaps even considerably longer than that. The overall weather pattern underwent a significant change around New Year’s Day from the record-breaking warmth of December in much of the eastern half of the nation and the end result will be much more in the way of sustained cold air outbreaks. In fact, there are signs for widespread Arctic air next week with an initial shot arriving early in the week following a Sunday storm and then a reinforcing shot at mid-week. By the middle of next week, colder-than-normal conditions will extend from virtually coast-to-coast.
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