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You Say You're Getting Used to Warm Fridays?

A. Camden Walker @ 2:02 AM

Friday Forecast: Broken Record

Three layers today should include short sleeves underneath a sweater or two jackets! Lows this morning in the 40s will bounce up to around 63 degrees after 3pm. It will be dry all day, so there is no need for an umbrella.The clouds are always the hard part!!There will not be all too much water vapor ("humidity") in the air today, so it won't feel muggy or as perceptibly warm as last Friday. Sky conditions will vary between a mostly clear morning to an afternoon with batches of clouds moving into the area. Hopefully clouds will abate again as the sun sets.

A light, noticeable breeze out of the SW may cause National Airport temps to stay a little lower. But areas away from water should be warm. Can anyone buy a windbreaker for our airport weather station?

High Pressure off the coast is in charge today!
Click on above Current Surface map above for most current image of our pedestrian pattern of weather - Courtesy of The Weather Channel

Weather Patterns: The Atmosphere might work more than a 5-day week

Why must the fact that most of us work 5 out of 7 "week" days mean that Mother Nature can't have an 8-day workweek? Humans' concept of time--as divided into weeks and months on our calendar--isn't something Mother Nature necessarily adheres to. This makes it hard for meteorologists, even, to decipher repeating habits of The Atmosphere. Remember the Winter of 1996? Our season exuded the quintessential "Patterned" behavior that year. That pattern just so happened to include cold, wind, and snow.

Large-scale features and air masses can move in and out of a region in a pattern that encompasses more time than what we easily remember.  It is difficult for forecasters and short-term climatology offices to find patterns that repeat in the atmosphere outside of a one-week range.  Ever since the Industrial Revolution's convention of time and calendar-standardization, our minds have evolved to work strictly in 7-day terms.  It could be argued we're in a pattern that neatly fits into our calendar:  Fridays have been warm and/or windy, and then it rains!

A strong cold front could come through a region on a Friday, and then the next Sunday after that... and then the next Tuesday--9 days later--after the previous Sunday.  A nine-day "Weather Pattern" is very hard to grasp in our calendric confines.  But 2-10 day patterns often emanate in months when season-change is minimal in the Atmosphere.  When seasonal transition is not transpiring, Winter & Summer establish Jet Stream configurations that are not easily changed without the energy associated with Spring & Autumn dynamics (when hot and cold regimes fervently fight for control of the mid-latitudes).
Illustrative of our storm track off to our westOur entire nation has been under a patterned regime for about a month-- all of us stuck in regionally-similar weather.  Seattle has had unending rain.  Chicago has had bouts of snow and cold.  Texas has suffered drought and fires.  Yet as we approach this weekend: Seattle is finally drying out, Texas and Oklahoma will get rain, and Chicago may have its last swath of snow for a while.  Is DC going to stop playing its broken record of weather, too?

Temperatures and precipitation swaths will not always match up as a pattern exerts itself.  It can be difficult to predict temperature and precipitation a week away, even in an established pattern.  But it does help forecasters to sift through data that doesn't fit behaviors noted in analogous Jet Stream configurations of the past that match the current setup.  Similarly, it can  be seen that the pattern of the last month is not going to stay intact much longer.  And indications are the atmosphere will further degrade, or even "Shift," into a completely new pattern next month.  Since we are solidly in the middle of winter--despite temperatures recently averaging above the long-term 42 degree highs--Jet Stream behavior truly is key.  The season is not going anywhere, and Spring will not be fighting for control until March.

To make sense of temperature and weather patterns over a large area, meteorologists use the concepts of air masses and fronts.  Fronts are reflections of upper-level Jet Stream winds moving across the country and inside these Frontal "borders" are air masses associated with different sides of the Jet Stream.  When locked into a clear atmospheric pattern, looking upstream (usually to our West since our portion of the hemisphere has dominant west-to-east atmospheric motion) to see the air which will be over DC can be very helpful, and even accurate.  This involves looking at current conditions at other locations with the same relative position with respect to fronts and the pressure pattern as DC is forecast to have 24 hours later. After considering changes in temperature due to changing cloud cover, winds, or changes in elevation, a reasonably accurate forecast can be made.

Air masses and accompanying fronts do not remain stationary for long. But their average movements--while never exactly the same--can undergo broad simplification to aid in fine-tuning medium range forecasts up to two weeks away.  Information computers may print out could also be tweaked or fully ignored if it doesn't agree with an established reality currently illustrated by a locked-in Jet Stream configuration.  The Jet Stream, and the Fronts it drags along at the surface, truly drive our weather in predictable ways that aren't quite as chaotic when patterns are identified.

Currently, DC is under an established and easily-identifiable pattern.  See the graphic above.  Our region's storm track continues to be off to our west, and they track up into New England.  The Jet Stream is locked into a northerly track which translates into warm air and rain on the southeastern portions of these cyclones (yes, even in Winter!).  We won't experience winter weather unless the storm track slips over 400 miles south and east from its current position.  That would place DC back in a quadrant of these storms that would produce a snow swath, as being experienced by Chicago and Toronto this weekend.  To cash in more on snow, we would need the upper levels to cooperate.  The Jet Stream would have to move south of us--instead of its current position driving storms up and through the Ohio River Valley.

Even with brief spats of cold air behind some of these "warm" storms, temperatures rebound quickly.  This is because we aren't dealing with Arctic air, but rather cool air masses originating from the Pacific Ocean!  The Jet Stream is aligned almost coast to coast in one straight line lately.  This "zonal pattern" (as this coast-to-coast unamplified configuration is called) has ushered in air directly off the Pacific through the Rockies... and Great Plains... into our area thousands of miles away!  The Jet Stream has not had any chance to tap cold air up into Canada with its presence limited to the U.S.  and thus Canadian air masses have stayed in Canada.  Even the shallow troughs that bring us cold shots of air are not deep and are unable to access the coldest air locked-up to our far north.  There are signs that longer-lived Jet Stream troughs are in DC's future... more amplification (less straightness from coast to coast) and a general move to the South will allow colder air to seep in from the north perhaps starting next week.  We'll see if this current pattern truly is dead or just on brief hiatus.  We'll have to wait till the end of February's hindsight to assess!

Snow Lover's Crystal Ball

Next Chance of Snow: Monday, Jan. 23th
Probability: 15%
Potential Impact:
Commentary: Mainly N&W suburbs of DC and Baltimore - the potential changeover to light snow will occur during daytime hours, neutralizing chances of road accumulation.  Additionally, note Potential Impact reflects lighter precipitation than yesterday. There is decreasingly less moisture available to this small storm after the atmospheric conditions to DC's north and west become conducive for snow.  To reiterate, chances (15%) of accumulating snow developing after the initial rain Monday morning is substantially low.

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