Early Evening Data Still Points To Heavy Snow

Data gathered from the 0z balloon launch is in (weather balloons are launched worldwide twice each day, at 0z, which is 7pm EST and 12z, which is 7am EST), and conditions still appear favorable for heavy snowfall around Baltimore Friday night and Saturday.  The balloon launched from the National Weather Service Forecast Office at Sterling, VA near Dulles Airport, revealed a thin deck of high level clouds over a deep layer of dry air.  That deep dry layer means the first snowflakes to form over us early Friday will dry up before they hit the ground.  That will take heat from the air and the temperature above ground level should cool even further.  See balloon sounding below.

Higher up in the atmosphere, around 30,000 feet above the ground, the balloons revealed two strong branches to the jet stream.  A jet streak embedded within the northern branch is racing along at up to 196 mph as it screams southeast out of Canada toward Boston.  This northern branch is positioned well to keep cold air locked into the mid Atlantic states.  The southern branch is zipping from south to north over Texas and Oklahoma with a jet streak embedded in the flow clocking winds up to 150 mph.  This branch of the jet is pumping sub-tropical moisture into the storm system.  Computer models are forecasting the two branches to interact with each other Friday night.  The entrance region to the northern jet streak is expected to combine with the exit region of the southern jet streak producing very strong upward motions in the atmosphere.  See map below.

The computer models are just beginning to ingest and process the rest of the balloon data, but the early evening run of the NAM and GFS continue to produce 1.5″ to 2.0″ of liquid precipitation over Maryland Friday and Saturday.  With the strong upward motion from the two jet streaks lifting the very moist air, we might see snow accumulations of more than an inch per hour for several hours Friday night and early Saturday morning…perhaps some thundersnow?

The one thing to watch, as far as snowfall accumulations go, is the possible intrusion of warm air in the mid levels of the atmosphere.  This would produce some sleet, especially south and east of the bay bridge, and cut down on snow totals in those areas.  Otherwise it still looks like most areas west of the bay will end up with 17-26″ of snow by Saturday evening, 8-16″ from Easton south to Cambridge and west of the bay in southern Maryland, and 4-7″ for most of the lower eastern shore around Salisbury.

Tom Tasselmyer

2 Responses

  1. Do you think the NWS will issue a “blizzard warning” sometime during the course of this storm?


  2. Interesting feature is the deep layering of the easterly flow ahead of the storm. Saw something similar to this back in 2003 — when that storm seemed to many to be wimping out, only to later watch a huge storm form off of the coast. The winds shifting around more from the east will be the first sign that this weekend’s storm is intensifying.

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