Long Range Pattern February 10th Onward:
While the first 9-10 days of February may be one of the warmest if
not the warmest on record, a mid month pattern change after
February 10th to a colder (seasonable or colder) and at least
somewhat active pattern is favored.
The passage of the aforementioned cold front toward the end of
next week will be the first signs of the impending pattern
change. Toward and after Valentine`s Day, mid and upper level
ridging will develop and establish itself near the west coast
and extend up to or just north of Alaska. The western ridging is
known as a +PNA (positive Pacific North American)
teleconnections pattern, and the ridging near Alaska is known as
a -EPO (negative East Pacific Oscillation). In response to the
upstream mid and upper level ridging (think a rise or bump in
the jet stream), downstream troughing (think of a dip or buckle
in the jet stream) will develop and establish over central and
eastern North America. Meanwhile, high latitude blocking in the
Arctic and North Atlantic (generally near Greenland) is expected
to develop, leading to a -AO (negative Arctic Oscillation) and
-NAO (negative North Atlantic Oscillation) teleconnections.
As troughing develops across the central and eastern US and
ridging manifests to the west and over Greenland, a seasonably
cold air mass from interior Canada should discharge into the
Midwest and potentially get "locked" in place. Meanwhile,
depending on the exact positioning and amplitude of western
ridging, an active El Nino subtropical jet (STJ) may continue to
cut underneath the ridging and feature associated disturbances
tracking eastward toward the Lower Great Lakes. Taken together,
the return of seasonably cold or colder air masses should bring
an attendant return of more regular occurrences of precipitation
to the general region, including the wintry variety, toward and
during the 2nd half of February. Stay tuned!
Castro