Winter 19/20 Thinking for our Area
December will be a month where the 500 MB pattern will become highly volatile. While I can’t rule out a winter storm this month, the best potential for a major Nor’Easter type storm will likely be towards the second half of the month. The first half of the month will feature several fast-moving clipper-type low-pressure systems with shots of Polar air masses invading. I’ll be keeping an eye out for the rogue clipper redevelopment threat throughout this month. Snow threat will be moderate.
This month will feature two periods of enhanced threat for major winter storms. The first period will be at the start of January when high latitude blocking will be peaking. This will be followed by a relaxation period that I am expecting for the middle of the month followed by another period of high threat potential for winter storms for the last third of January. Look for the words Polar Vortex to be mentioned frequently with an arctic blast a high threat. Snow threat is high.
February will feature an active weather pattern throughout this month. Look for maximum amplification of high latitude blocking and influence from Polar and Arctic air masses. Snow threat is very high.
March is a wild card month, especially with warm neutral ENSO states. If the MJO is favorable, keep an eye out for a major winter storm in the first half of the month. Snow threat is moderate.
The regions are described above on the map. Naturally, the closer you are to the coast, the higher the threat for warm air to create mixing of snow, sleet, and rain.
My point for region one is depending how the high latitude blocking evolves, there could be several coastal storms that track too close to the coast, which will mean that the interior is the focus for most of the snowfall while the coastal plain has a high threat for snow to rain or snow to ice events that end as snow. A key factor will be how fast low-pressure systems transition to the coast. The slower the transfer, the warmer the storm and the less snow on the coast compared to the interior. At the same time, this transition factor will mean that locations over interior southeastern Pennsylvania may be caught in between the old precipitation shield and the new one forming to the east, which would reduce snowfall potential in a storm.
Miller B type storms will be a primary type of storm this winter with low-pressure systems redeveloping along the Mid Atlantic coast. Other storm tracks will be Miller A storms tracks out of the Gulf of Mexico and Alberta Clippers from central Canada.
PRIMARY FORCING MECHANISMS
Unlike in previous years, this year will not have a strong influence from an El Nino nor a La Nina. As a result, the tropical forcing features are going to be highly volatile to nail down this year with the primary focus being the MJO phases. Meanwhile, the sun has gone dead quiet and is now at record levels. The stratospheric evolution this year will play a key role in how this winter shapes up.
Our Snowfall Forecast
The primary theme for this winter will be the return of the major Nor’Easter weather patterns. The past several years have not featured the potential of this one due to a persistent upper-level ridge over the Southeastern United States and a lack of sustained high latitude blocking.
The influences for this winter or drivers include the MJO and stratospheric warming. You’ll be hearing a lot about the Polar Vortex, low pressure jumps, blocking, and wintry mix change over timing.
Special thanks to the amazing team of meteorologists who helped contribute to this years Winter Forecast.