Sunday, January 18, 2015

1/18: Clipper Train About to Take Off

1/18 6am
It looks like today will be the start of a train of northern stream disturbances to impact our area through the rest of the week.  The culprit will be a large, nearly-stationary upper level low that will spin and spin across northern Canada near the Hudson Bay.  Anti-clockwise flow around this low will force several weaker systems (or clippers) to pivot through the northern plains into the Great Lakes and Northeast.  Looking upstream, you can already see these beginning to line up.  
00z GFS 500 mb vorticity map 7am Sunday (Tropical TidBits)
There's no point in trying to pinpoint exact impacts from each of these this far out because that will in large part be determined by how the one in front of it behaves, but here's a few things worth noting:

  • The Wednesday clipper currently looks to be the most robust for our area.  This is largely in part due to: 1) The upper level energy digging south of our area (you usually need this for precipitation to make it across the mountains) and 2) the potential for the clipper surface low to strengthen pretty quickly once it reaches the coast.  These two things have been recent developments with the models so we'll have to watch to see if they hold going forward.
  • Towards the same time as our weekend clipper, models are insistent on the development of a southern stream system.  There's a timing issue here which is why it doesn't look like they'll team up to produce a big storm (we instead see the southern stream system slide out to sea).  This seems to fit the overall pattern as the Pacific jet continues to be fast and overpowering...not allowing troughs to truly dig into the east until too late.  There's still a slim chance we could "thread-the-needle"...but the better bet is for the southern system to miss all-together and leave us grazed by another minor clipper.
  • Looking ahead past next weekend...I think this clipper pattern will continue.  This isn't the best for snow lovers...but certainly not the worst either.
Taking each system one at a time, here's what I'm thinking for Sunday-Monday (upper level disturbance + coastal low).  My only change to yesterday's map was to "up" snow amounts a bit across the upslope areas of West Virginia due to current observations and short range models picking up on more available moisture.  I'll have updates on the ensuing clippers once we see how these first systems behave.  Follow me here:
Sunday-Monday Forecast
Shenandoah Valley Forecast
Today: Mostly cloudy with a stray sprinkle.  We will be sandwiched between heavier rains along and east of I-95 and rain changing to snow along the western facing slopes.  Highs: 47-50.

Tonight: Decreasing clouds in the Valley. Upslope snow will really start to get going across the favored higher elevations of WV and parts of far western VA.  Lows: 28-31.

Monday: Upslope snow showers coming to an end. Mostly sunny. Highs: 43-46.

Tuesday: Increasing clouds. A few rain/snow showers developing late.  Highs: 45-48.

Wednesday: Rain/snow shower mix.  Precipitation type and amounts will depend on eventual evolution of mid-week clipper.  Highs: 42-45

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