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Frail & Frisky Friday - Mild Between Unperfect Storms

A. Camden Walker @ 2:02 AM

Forecast: Sunshine Sandwich

Gorgeous Sunrise over Oakton, VA - by Kevin AmbrosePatchy showers & drizzle will end early this morning with temperatures in the 50s.  Damp conditions will be quickly eradicated with light Southwesterly breezes, becoming stronger out of the west later.  Between 4pm & 5pm, the 64 degree mark will be struck under brighter afternoon skies.

A weak downslope "Tuckahoe"(i.e. east of the Appalachians) wind component will augment our quick warming, plus continue our drying.  By sunset there will be high clouds visibly streaming into the area--in association with tomorrow's storm system.

Will SUN+DOWNSLOPING throw off the forecast?

Kevin Ambrose captures skies yesterday morning also demonstrative of today's midday sky.

Saturday Snow Stifled: The Incredulous Inland Stormtrack

You will notice has, once again, dropped its beloved Snow Lover's Crystal Ball. Saturday will be a rain event. Even if a couple flakes become visible as the precipitation ends mid-afternoon Saturday, there will be no accumulation inside the beltway or points east of I-95 (the "Fall Line"). Western Loudon & Fauquier--with points along the I-81 corridor as far south as Blacksburg--may see 15 minutes of snow flakes during midday. Surface temperatures are warm, and will continue through the storm. Winds will be from the west then south as skies brighten (and clearing even develops east of I-95) in the late afternoon.

  • Sat AM: Scattered showers overspread the area.
  • Sat midday: Light periods of rain persist in western suburbs as S&E of DC sees tapering precip (with 2 flakes of snow, maximum)
  • Sat mid-afternoon: Precipitation comes to an end from SE to NW.  Keep an eye out for clearing skies!

Archetypical Capital Snows: DC's Rare Ingredients Must Align

I. Strong Jet Streams must converge in the Southeast U.S.

Two distinct, fast-flowing Streams [Pacific & Sub-Tropical] jettison remnant storm energy over the Rocky Mountains from the Pacific to near the ArkLaTex region. This energy intersects the Polar Jet which has already plummeted out of Canada and "set up shop" over the warm waters of the northern Gulf of Mexico. A Low pressure is spawned off of the waters of Louisiana with this supplied upper-level energy in addition to a strong temperature gradient at the surface.

II. Cold air must already be in place from Canada

The aforementioned polar jet has already moved through the DC area prior to the Gulf Storm's formation. At least one "Alberta Clipper" has likely moved through.  At the surface, very cold, dry air with a perceptible northwesterly flow builds-in with an Arctic High Pressure behind a Clipper. The combined Gulf energy in the upper-levels draws the energized polar jet back towards our area--precariously aligning with the surface temperature gradient (cold continental land juxtaposed with warm waters) over the East Coast's Gulf Stream.

III. Potent surface High anchored to our North
A surface, arctic High Pressure maintains its position over eastern Quebec near the St. Laurence River. Very slowly it moves toward Maine during snow onset from the Gulf Low Pressure system. As the mid-Atlantic Low rapidly develops over the Outer Banks or coastal Hampton Roads, this High wedges cold air continuously down the eastern slopes of the Appalachians. It also indirectly aids in moisture delivery from the ocean and Bay, creating added orographic (upslope) lift in our area.

IV. Strong Low Pressure

Notice this weekend's stormtrack is too far *WEST* for an ideal trackA two-stage surface development must also take place, in addition to upper-level energy. The gulf low tracks up the piedmont areas of the Southeastern states, but weakens over land while transferring its energy to the coast. Cold air remains in place as the weaker gulf low sends moisture to overrun the dense, cold dome over DC. A new, second low develops between Cape Hatteras & Norfolk. As the air above the Gulf Stream remains relatively warm compared to the cold Canadian airmass just to the west, the new Low Pressure taps into an Upper-Level Low (over West Virginia). Energy transfers quickly into this strengthening Low, thus reinforcing NE winds in DC further entrenching the cold. As it marches up the coast toward New England, it continues to gather necessary warm air and moisture from the Atlantic.

From these complex, once-a-decade systems, Washington will typically get one-third of total snowstorm accumulation from the gulf low's moisture field, but then a burst of heavy snow from the exploding Hatteras low supplies our final two-thirds.

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