Winter Outlook 2000-2001
Posted: October 30-2:00PM
Winter 2000-2001 is just around the corner. Some areas in New England have already seen their first measurable snows thanks in part to a deep cut-off low which hung around for a few days in the Northwest Atlantic. Snow showers were even seen close to the coast in areas like Boston for instance.
Other recent notable weather events include the unusually dry conditions around the mid-Atlantic for the month of October. For example, Wilmington, DE has reported 0.08 inches of rain, the record in 0.06 inches back in October 1924. Pomona, NJ has reported 0.06 inches of rain in October, breking the old mark of 0.15 inches set back in 1963. Philadelphia reported 1.50 inches of rain, but this is also well-below the average for the month.
Another trend early this season has been the tendency for development of low pressure areas off the southeast coast. It's early to say if this is truly a trend, but several systems have developed in that area (east of the Bahamas) and trekked northward. For example, the system which affected Northern New England with early season snows on October 28 had originally developed in the aforementioned region. There were also a few late-summer tropical systems which developed in that same general area. On September 12, Hurricane Florence formed east of North Carolina. On October 6, Tropical Storm Leslie formed in the same area. Then, on October 17, Hurricane Michael formed in almost the same area! Perhaps this region is a hot spot that needs to be examined in this outlook as well.
There is a more important trend weatherwise the past few months which may actually have a larger impact on our weather this upcoming winter. That is the weakening of La Nina. La Nina weather patterns are usually progressive not allowing much room for a digging jet stream or buldging ridge. However, as we know, the patterns change periodically as we saw last year. Temps averaged above normal for the majority of the winter with one prolonged cold snap late in January thanks to a shift in the NAO from positive (trough in west/ridge in east) to negative (ridge in west/trough in east).
Many consider the collapse of La Nina a return to 'normal' winter weather for much of the country. But what 'is' normal winter weather? That depends who you ask and what part of the country you live in. For Philadelphia, see Climate for more information. In my own terms, normal winter weather for Philadelphia and surrounding suburbs is as follows: Colder air infiltrates region around Thanksgiving (highs in the thirties for a few days). First flurries arrive by mid December with a White Christmas, of course. Frigid temps in January and February with at least 2 minor snows (2-4") and one large storm (6-10"). March is never normal. We see blizzards and extreme warm spells variably. This is not my outlook for this year, just what we were used to seeing on average. The past few years have been above average in temperature and below average in snofall, respectively. With the demise of La Nina, things will be different this year.
That brings me to my outlook for the Winter of 2000-2001. One similarity that I notice fom last year is the arrival of a blue norther to the southern states early in October. I'm not sure if this is a yearly trend, or just coincidence, but it shows me that the northern branch of the jet didn't face much resistance by the southern jet in diving south. Also, similar to last year at this time, a ridge has set up across the south central US keeping temps mild across the midwest and southeast. However, the ridge is not quite as intense as the one last year reinforcing my point that the southern branch of the jet appers slightly weaker so far this year. This could be caused by the weakening of La Nina. Granted, we are still going to see remnants of La Nina as it too has a lag involved as does the change in season. It will take a while to get rid of the strong La Nina characteristics that have been present the past few years.
There are also hints of Greenland blocking trying to emerge as we head into November. One pattern this fall which has caught my attention is the tendency of a high pressure area to provide a Northeast flow across the northeast states as opposed to a high giving us a NW flow and going back into Canada. With high pressure aligned from southwest to northeast, this allows storms systems to be 'blocked' under it rather than pushed out into the Atlantic. We have seen this with the first snows in New England already as the system retrograded to the northwest (blocked by that high). Then, the high moves into Greenland while another takes it's place. This looks like a pattern setting up.
So, what's going to happen this year? Here are my thoughts:
The first two weeks in November will be normal as a ridge in the center of the nation starts moving eastward. It will not be unseasonably warm as last year, but temps will hang out in the mid to upper 50's for an average. Nice fall weather! By the middle of November, the pattern changes as the ridge exits the east coast. Snow will again be a possibility in New England as we head towards Thanksgiving. Philadelphia should see it's first hard freeze around this time. December will feature our first snows of the year with a White Christmas a strong possibility. We will see the famous "January Thaw" this year as temps push into the mid 50's for a brief period toward the middle of the month followed by an Arctic blast and winter "event" within the last 7-10 days of the month. February will be brutal this year, especially the second and third week. There will be another large "event" for the northeast around Valentines Day. The remainder of February will be normal with a small snow thrown in the last week. The first half of March will be seasonal with a wintry scenario predicted early in the month. By mid-March, we will be seeing our first signs of spring with temps reaching the 60's by the last week of the month.
How certain am I of this forecast? Better than half. It's difficult to pinpoint exactly when it will snow and how cold it will be and when, but trends over the last few years lead me to my final though . . . this winter will be colder overall than the past three with snowfall totals exceeding the average of the past three winters. For all the snowlovers out there and folks who just bought 4x4's, this will be an enjoyable winter.
