1. Cold Air Damming in the Appalachians Case Study Feb 13th 2008
Vanessa Przybylo

2. Where does the rain/snow line set up?
Motivation

3. Virtual Potential Temp used
CAD INDEX calculated hourly over nine years of data ( ) following Miller et al. 2014
KCRW
Charleston, WV
Buoy
KAHN Athens, GA
DX1 = km
DX2 = km
DY = km
Center Greensboro station had to be colder than surrounding stations
Index calculated by:
𝐴= Ѳ v KAHN − Ѳ v KGSO ∆Y
𝐵= Ѳ v KCRW − Ѳ v KGSO ∆𝑋1
𝐶= Ѳ v − Ѳ v KGSO ∆X2
CADINX=mean 𝐴, 𝐵, 𝐶 x 100
Averaged in all directions
KGSO Greensboro, NC
Virtual Potential Temp used
Virtual ~ ignores moisture and density differences
Potential ~ brought to 1000hPa (accounts for elevation)

4. Strongest event shown: CADINX = 5.77°C/100km
Cold air becomes entrenched along the eastern slope of the mountain range
Thermal trough present

5. Caused by H press in the Northeast (~>1030 hPa) Classical Case-strong CAA of stable air with minimal diabatic processes
High press system strengthens and moves east
More easterly onshore flow
Air blocked by mountain and decelerates
Coriolis decreases, PGF increases (balanced by friction)
Parcels turn to the left (to the south in this case)
Adiabatic cooling makes the air sink
More damming due to larger press/temp gradient
Lee trough amplifies
Warm, moist, gulf air pulled westward due to low pressure to the west
Increased cloudiness and precipitation results due to overrunning of warm air over cold dome

6. -Divergence in equatorward entrance region -Jet streak pushes high eastward 250 hPa, 0600Z 13 February 2008 Isotachs (shaded) and Geopotential Heights
Surface low press system near Gulf States with deep upper level trough lagging behind
Smaller upper level trough to the north (Great Lakes/Midwest region)
Large-scale confluence over New England
Surface cold front

7. Isallobaric Wind enhanced CAA
Pressure falling over 6 mb in 3 hrs across North Carolina enhancing ageostrophic northerly wind

8. Shallow layer of cold air with inversion above
NE flow at the sfc (barrier jet)
WAA with veering winds
strengthens the sfc inversion
Easterly wind above barrier jet due to onshore flow
W or SW flow at upper levels from trough swinging east
Saturation from surface throughout the cloud layer

9. 1800 UTC 500 hPa abs vorticity and geo heights ~ deep trough picks up moisture-lagging behind sfc
Still have differential vorticity advection

10. Satellite at 2015UTC – near end of event
Lingering stratus deck
with sharp cutoff
Most moisture
advected through
southern N.England
Parent high offshore
Weakening CAA
Baroclinic leaf moving offshore

11. Conclusion
Models usually exhibit a warm bias due to scouring the cold dome prematurely
Need high resolution with a package that includes diabatic processes
Along the coast, reverse bias where models do not forecast the warmth of the onshore flow

12. References
Bailey, C. M., Hartfield, G., Lackmann, G. M., Keeter, K., Sharp, S., 2003: An objective
Climatology, Classification Scheme, and Assessment of Sensible Weather Impacts for
Appalachian Cold-Air Damming. Weather and Forecasting, ,
doi:
Bell, G. D., Bosart, L. F., 1988: Appalachian Cold-Air Damming. Monthly Weather Review,
, doi:  
Miller, S., Hoffman, E., Kelsey, E., Cordeira, J, 2014: The New England Cold-Air Damming
Experiment (CADEX). 1-3
Plymouth State University weather maps retrieved from
Surface Analyses retrieved from /13/2008&selmap= &maptype=namussfc