I continue to see indications that the mild pattern of the past
three weeks will soon begin to fade. Some high-latitude ridging looks
to develop across the Northwest Territories of Canada by early next
week and that will direct an initial blast of Arctic air into the
Great Lakes and Northeast for the Thanksgiving holiday. Until then,
we'll remain in a pattern dominated by Pacific and maritime tropical
air masses, and thus temperatures will continue 4 to 8 degrees above
normal through next Wednesday. Precipitation-wise, this morning's
drizzle will gradually develop into a steadier rain late today into
tonight. Sunny and mild conditions will then return Friday into
Saturday before a southern storm brushes by with a chance of rain
later Sunday into Monday.
The first step in the pattern evolution will come the middle of
next week as a strong trough digs across the Great Lakes on Wednesday
and to the East coast by Thanksgiving morning. A brief blast of
unseasonably cold air will drop in Thursday into Friday, so I expect
high temps to pull back into the 40s for the end of next week (upper
30s in the mountains) with wind chills in the 20s and 30s. Some lake
effect snow showers will likely fly across the mountains of
northwestern PA. Still, I don't see the cold locking in for the long
haul just yet--for that there has to be some downstream blocking over
Greenland (which I see no sign of yet). Consequently, I expect early
December to feature several progressive blasts of cold air passing
through with modest warm-ups between cold spells. This up-and-down
pattern can produce snow given just the right storm track; although I
don't see anything in the pipeline for southeastern PA just yet.
Monday's discussion:
I see no changes this morning to my story line from last week:
Arctic air is locked up in Alaska and Siberia, while jet stream
ridging continues over the southeast US; which means temperatures
here will remain at or above normal into late month. Weak passing
cold fronts can bring temporary "cool downs", however. For example,
Sunday's high of 71 degrees--which is pretty amazing for mid-
November--will be cut down a high near 60 degrees today and a high
in the mid 50s on Tuesday, due to a cold front that dropped through
last night. Still, average high/low temperatures for this week are
53/32, respectively, and I don't see us dropping below those levels
at all this week. In fact, another warming trend may develop by
Friday and Saturday with highs rising back to the upper 50s or low
60s.
Precipitation-wise, we'll continue with the relatively dry
pattern established this month. The first two weeks of November have
yielded less than a half-inch of rainfall, a dramatic change from
the October pattern that produced nearly 6 inches of rainfall. The
only threat of showers this week will come Thursday into Friday as
an upper-level system lifts slowly from the MS Valley into the Great
Lakes. High pressure should lead to improving conditions later
Friday into Saturday, before a more-moist southern storm perhaps
threatens late in the weekend.
Beyond that, the first half of next week looks to continue with the
mild pattern. However I do see the potential for a jet stream
rearrangement beginning the second half of next week. This could lead
to a turn to colder conditions in the day following Thanksgiving. So
enjoy the mild weather while it lasts!
