Big Temperature Swings Expected Over the Next Few Weeks


Coldest Air of the Season Likely to Arrive
Early Next Week...followed by a period of
Milder Weather...then...perhaps...another
Bitter Arctic Blast.

(this article updated 01/04/2014)

Expect sunshine and seasonably cool temperatures
in the Mid-State today. However, this tranquil day
will merely be the the calm before Sunday's
snowstorm and bitter cold outbreak. Already, a
winter weather advisory and winter storm watch
have been posted, with the expectation of anywhere
between one and four inches of snow between
noon Sunday and noon Monday.

Bitterly cold air will also come in with the snow,
and lows in the single digits are expected both Sunday
night and Monday
night...with some spots likely
to drop below zero Monday night! Lows
Tuesday night are forecast to be between 10
and 15 degrees.

The type of bitter cold doesn't happen very
often, and episodes like this only roll around about
every 7 to 10 years. Back on January 18, 2003
Nashville experienced a high of 14 degrees and a low
of 1 degree, for a daily average of 7.5. Prior to that, you
have to go back to February 4, 1996, when the high and
low at Nashville were 14 and -3, respectively (producing
a daily average of 5.5 degrees).  The current forecast for
Monday shows a high in Nashville of 8 and a low of 3;
yielding a daily average of 5.5 degrees.

However, this upcoming bitter cold, although intense, will
be relatively short-lived. Indeed, by next weekend, we will likely
see high temperatures pushing upwards of 50 degrees!

One of the predictors we've been watching closely
over the last couple weeks is called the Arctic
Oscillation Index (AOI). It provides clues to what type
of weather patterns might be expected to evolve over
the next several weeks.

When the AOI trends negative, it is generally associated
with the evolution of a cold weather pattern over the
eastern United States (including Middle Tennessee).
This is usually highlighted by a strong ridge of high
pressure in the upper atmosphere along the West Coast
and a deep area of low pressure over the Eastern United
States. This results in cold air masses being steered
southward out of Canada, down across the Great Plains,
the Midwest and the Tennessee Valley.

Below is the latest forecast graph of the AOI for the next week
(indicated by the red "spaghetti plot"). One of the first things

you will notice is that the trend is "down" for the next several
days, bottoming out near -2. However, by January 8th or
9th the AOI is forecast to make a decent recovery, with
most red forecast lines showing a movement into positive
territory. This indicates that our bitter cold snap of early next
week, though intense, will be shortlived. One of the interesting
things that is starting to show up, however, is the likelihood of
another precipitous drop in the AOI toward mid-January. This
would suggest that we might be looking at yet another surge of
bitter Arctic air roaring southward into our neck of the woods
in the not-too-distant future.

The Weather Prediction Center's (WPC) 3-day maximum temperature
forecast for next Tuesday shows Middle Tennessee still hanging in the
deep freeze for one final day, as highs are only forecast to be in the teens
and 20s. However, as with most things in life, it's all relative-- and compared
to highs in the single digits on Monday, we can actually consider highs in the
teens and 20s to be a modest warm-up!

Finally, if we look at the upper level flow pattern forecast for
the next 3 to 7 days (as issued by the National Weather Service's
Weather Prediction Center), we can cleary see the transition from
out deep and cold low pressure area over the Eastern United
States this Tuesday (January 7th), to a warmer southwesterly
flow pattern  by January 9-11th.) As mentioned earlier, by next
weekend (January 11-12), highs may very well rebound to
around 50 degrees! That's a 40 degree warm-up from the
bone-chilling highs in the single digits on Monday.

The air flow, in the graphic panels below, is parallel to the green lines. The
frames in the graphic are valid for the Jan. 7 through Jan. 11 period.

So, if we can suffer through the bitter cold during the
first half of next week, we should get at least a temporary
reprieve by the following weekend. However, as mentioned
earlier there are indications in the latest AOI forecast that
another blast of arctic air may be dropping down on us around
mid-January.  Stay tuned...




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