850 hPa Low Track

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850 hPa Low Track
Click here for current 850 mb data
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850 hPa Low (Blizzard of 2006)

• Heaviest snow band over the I-95 corridor at this
  time. Rates of 2 to 5 inches per hour. Phase 3
  of the storm (wrap around).

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850 hPa Low Strength and Track
The strength of the upper air low, the 850hPa
(mb) low, is one of the factors that aides in the
rapid development of a coastal low. Thus, an
intensifying 850 mb low, or an already strong 850
mb low, greatly aides in the development of heavy
snowfall near the Philadelphia region. This is
especially true in Miller B systems. For a
Miller B storm to be deemed a heavy snow event
for Philadelphia it is crucial that the 850 low
goes through a rapid intensification cycle.
However, even more important than strength is
track. The 850 hPa is best to the south of
Philadelphia, yet north the NC/VA border moving
in an easterly direction.
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850 Low and Snow (usedtobe on 01/31/2007)
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Table V HINTS FOR FORECASTING MODERATE TO HEAVY
SNOW (S)

• 850 mb
• About 1.5 degrees latitude to the left of the
  track of the low (60 to 240 nm)
• When cooling occurs in the rear quadrant of the
  low during early stages of development, heavy
  snow occurs
• Heavy snows occur more frequently with lows that
  generally move NE
• Heavy snows less rare with lows dropping south of
  east (e.g. Alberta Clipper or Manitoba Mauler,
  Saskatchewan Screamer)
• -5 C isotherm bisects the heavy snow
• -2C to -8 C for moderate snow
• gt5 C of WAA moving into area of interest
  (overrunning)

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Surface Low, 500mb Low, 850 Low, and 700 Low--
Merge
February 11-12, 2007