Transcript An analysis of Chesapeake Bay effect snow events from 1999

Bay Effect Snow from
the Chesapeake Bay
David F. Hamrick
WPC Meteorologist
College Park, Maryland
Presentation Overview
• Introduction to lake effect, ocean effect, and bay
•
•
•
•
•
•
•
effect snow
Requirements necessary for bay effect snow
November 30, 1999 event
December 25, 1999 event
January 15, 2006 event
January 24, 2013 event
October 18, 2015 mini bay-effect showers
Acknowledgments
What is Bay Effect Snow?
• Very similar to lake effect snow events
• Narrow band of snow oriented north to
south that affects southeast Virginia
• Does not happen as often as lake effect
• Similar processes occur downwind of
Delaware Bay, Long Island Sound, and the
Great Salt Lake in Utah
Bay Effect Criteria
• Occurs during strong cold air advection events when cold air
•
•
•
•
•
•
moves over a relatively warm body of water
Must have at least a 13 degree C difference between the water
surface temperature and the 850 mb temperature
Must have little directional wind shear and minimal speed shear
between the surface and about 900 mb
Must have a long and sustained wind fetch over the
Chesapeake Bay with an average wind direction between 340
and 10 degrees
Progressive synoptic scale patterns tend to limit or inhibit these
types of events
Land breeze convergence over the bay helps
Usually occurs from late November to January
29 November 1999 Event
• The surface water temperature of the Bay was
•
•
14C (57F) and a 850 mb temperature of -10C,
and this produced a temperature difference of
24C.
The wind at the Norfolk International Airport
was 350 degrees at 15 kts.
This resulted in a wind fetch down entire length
of the Bay and created a favorable environment
for bay effect snow.
11/30/99 12Z 850mb Temps
11/30/99 12Z ETA 500mb
Vorticity
11/30/99 1345Z Visible
Imagery
11/30/99 1347Z Radar
Imagery
11/30/99 1616Z Radar Imagery
Wallops Island Sounding Data from
the 30 November 1999 event
Radar Imagery at 13Z
25 December 1999
IR Satellite Imagery and
METARS at 16Z 25 Dec 1999
850mb Temperatures at 12Z
25 Dec 1999 event
Surface Analysis at 12 Z
25 December 1999
Surface Analysis at 15 Z
25 December 1999
Surface Analysis at 18 Z
25 December 1999
Wallops Island Sounding Data from
the 25 December 1999 event
January 15th, 2006
½” at ORF and 1-2” just east of ORF
Surface Analysis at 3Z
15 January 2006
Surface Analysis at 6Z
15 January 2006
Wallops Island Sounding Data
from the 15 January 2006 event
Photos from the 15 January 2006
event (Courtesy WFO AKQ)
Satellite and Radar Composite
during the 24 January 2013 event
Visible Satellite Imagery at 17Z
24 January 2013 with METARS
Surface Analysis and Satellite
Imagery 24 January, 2013
15Z Analysis
18Z Analysis
Wallops Island Sounding Data
from the 24 January 2013 event
WPC Winter Weather Forecast
prior to the 24 January 2013 event
Bay effect showers
18 October 2015
• Early season example that involves
showers instead of snow
• Strong cold air advection down the length
of the bay
• HRRR model captured these showers
several hours in advance, even though
they were very light
Visible Satellite image at 1430 Z
Radar Imagery at 1417 Z and
HRRR Model Guidance
Radar valid at 14:17 Z
HRRR model valid at 14Z
HRRR Depiction of 850mb
temperature and winds at 14 Z
-6
-3
0
In Conclusion
• Noteworthy events happen on average about every
•
•
•
•
•
5 years or so
It is necessary to have a steep lapse rate in the
boundary layer with a high to the west and a low to
the east
Can be high impact events if the band persists long
enough
Bay enhancement is also possible
High resolution model data, such as the HRRR, can
give indications to this within 24 hours of the event
WPC meteorologists are paying attention to these
types of events
Acknowledgments
• Brian Hurley – WPC lead forecaster
• Mike Rusnak – WFO Wakefield
• Mark Klein – WPC SOO