Download The 22 December 2013 Cold Air Damming Event across the

The 22 December 2013 Cold Air
Damming Event across the Hudson
River Valley in East-Central New York
Ian Lee, Dr. Dave Fitzjarrald
NOAA/NWS Albany, NY
SUNY Atmospheric Sciences Research Center
NROW XVI
4 November 2015
Overview
• Cold air damming (CAD) occurred across portions of the Hudson
River Valley on 22 December 2013
▫ Produced an extended period of dense fog, intervals of drizzle, and nearfreezing temperatures in valley areas
▫ Above the boundary layer capping inversion, the sensible weather was
clear with overcast skies and warmer temperatures
▫ The strong inversion resulted in significant temperature differences
exceeding 15°C amongst elevation-dependent sites spaced less than 10
km apart
▫ A Sudden Warming Event occurred during the early afternoon resulting
in a period of enhanced turbulent mixing and fog dissipation
• So what made this event happen, and what clues can data mining
available datasets offer us?...
Areas of Interest
1
2
1. The Capital Region
(including the cities of
Albany, Schenectady,
Troy, and Saratoga
Springs)
2. The Helderberg
Escarpment/northern
Catskills
Geographic Information Systems (GIS) map
of Hudson Valley.
Quick Review
• Mechanisms that promote CAD events
▫
▫
▫
▫
▫
▫
▫
Terrain-blocking (typically on the east side)
Capping inversion
Low-level anticyclone to induce terrain-forced flow
Adiabatic and/or diabatic cooling
Cold air advection
Barrier jets (if CAD event is long duration)
Supportive boundary layer*
 What can be gleaned from an operational perspective?
Setting the Stage For This CAD Event…
Significant Nor’easter impacted much of the
ALY CWA ~1 week prior to event, with strong
high pressure building across the region
afterwards, locking in low-level cold air.
WPC surface analysis valid 1200 UTC 17 December 2013
GIS map of observed snowfall from 14-15 December 2013.
Many areas saw greater than 25.4 cm (10 in) of snow.
www.wpc.ncep.noaa.gov
Synoptic Overview – Upper Levels
•
•
•
Deep upper-level trough over central U.S.
Ridging aloft across New England
Upper-level jet structure promoted a slow-moving synoptic pattern,
with highest winds well downstream of trough axis
SPC 300 hPa analysis, valid 1200 UTC 22 December 2013
www.spc.noaa.gov
SPC 500 hPa analysis, valid 1200 UTC 22 December 2013
Synoptic Overview – Low-Levels and Surface
•
•
•
•
Strong low-level frontogentic forcing
Prominent high and low pressure centers at the surface
Low-level CAA favored adiabatic cooling prior to event
Overall synoptic setup promoted precipitation across upstate NY
SPC 925 hPa analysis, valid 1200 UTC 22 December 2013
www.spc.noaa.gov
www.wpc.ncep.noaa.gov
WPC surface analysis, valid 1200 UTC 22 December 2013
Regional Radar Mosaic
fffffffffffffffffffff
•
•
Diabatic cooling effects from precipitation
enhanced low-level cooling
-RA, -FZRA, -FZDZ reported at KALB
Loop valid 0000-1600 UTC 22 December 2013
Visible Satellite Loop
•
•
•
•
Mainly cloudy throughout most of day
Pockets of clearing just west of Capital Region
between 1545-1630 UTC and 1745-1815 UTC
Clearing likely caused by strong SW
downslope flow off northern Catskills
Helderberg Escarpment enhanced low-level
blocking flow with Froude Number (Fr) < 1
SPC 850 hPa analysis, valid 1200 UTC 22 December 2013
Valid 1500-1900 UTC 22 December 2013
www.aviationweather.gov, www.spc.noaa.gov
Infrared Satellite Loop
•
•
•
•
Cloud top temperatures < -20°C for much of the morning
Temperatures warm to -20°C and -10°C by the late morning
hours (revealing lower cloud deck)
Temperatures warm to > 0°C (surface skin temperatures)
between 1600-1700 UTC and 1745-1815 UTC coinciding
with pockets of clearing
Cloud tops cool to < -15°C after 1830 UTC
Valid 1000-2030 UTC 22 December 2013
www.aviationweather.gov
KALB Hourly METARs
•
•
•
•
www.ncdc.noaa.gov
Temperatures mainly in low/mid 30s most of day,
with dense fog and VLIFR ceilings/visibility
Temperatures spike into the low 50s, with period of
VFR ceilings and improved visibility in early
afternoon
Spike coincided with clearing in visible satellite
imagery and warming IR cloud tops
Dense fog re-forms after cloud cover is reestablished
KALB Surface Time Series
1
2
•
Sudden Warming Event during early
afternoon 12/22/13, along with spike
in moisture (1)
•
Surface remained moist until finally
mixing out ~00 UTC 12/24/13 (2)
•
Spike in surface wind coinciding with
sudden warming event, directional
change from NW to SW (3)
3
So what caused this sudden warming event and
period of fog dissipation?...
The Role of The Boundary Layer…
12/21/13 0000 UTC
Sounding Characteristics
•
•
•
•
•
Stable surface layer, with deep mixed layer above to ~1300 m
Moisture advection evident in specific humidity profile
Decoupling wind profile evident by 12 UTC 12/21/13
Cloud deck between 1000-1500 m with RH profile ~100%
No noticeable change in wind profile
12/21/13 1200 UTC
Prior to event, boundary layer
stratification increasing with time, as
decoupling wind infers trapping of
colder air near surface with lack of
turbulence and WAA in mixed layer
12/22/13 0000 UTC
Sounding Characteristics
Stratus deck
•
Continued WAA in mixed layer
•
Moisture advection continues in
specific humidity profile
•
Decreasing slope in wind profile
inferring decreasing momentum
transport through boundary layer
•
Cloud deck lowering with time with RH
near saturation ~500 m
•
Surface winds shift to northerly,
allowing more cold air to filter in near
the surface
•
Onset of Early-Evening Surface Layer
Transition (supportive for fog
formation), with spike in specific
humidity and decreasing RH profiles
just off the surface
12/22/13 1200 UTC
Sounding Characteristics
Fog layer
•
Continued WAA above 500 m with CAA
evident below 500 m
•
Fog layer established between surface
and 250 m (laminar, well-mixed
convective surface layer)
•
Strong stratification throughout rest of
boundary layer – limited momentum
transport
•
Entrainment processes occurring near
top of capping inversion ~1500 m, but
unable to mix down to surface
•
Inflection point in wind profile ~500 m
infers area of turbulent mixing*
•
What can be further gleaned regarding
boundary layer mixing?
12/22/13 1200 UTC – Turbulence Analysis
Turbulence Features
Turbulence analysis reveals
distinct stratification of
boundary layer, with layers of
horizontally-oriented eddies
limiting momentum transfer
5
•
Laminar flow in fog layer near the surface (1)
•
Spike in turbulence above fog layer, however, only
penetrated top of fog layer due to spike in gradient
Richardson Number (2)
•
Relative minimum in turbulence in mixed layer (3)
•
Spike in turbulence through capping inversion
entrainment zone (4)
•
•
Lack of turbulence in 850-700 hPa layer* (5)
So what does additional thermal heating do to the
entrainment zone?...
4
balloon
3
ωb
ωb = ωb + ωb’
2
Forces encountered by a rising balloon:
2
1
•
•
•
•
Upward force due to assumed constant
ascension rate over time
Downward force due to drag
Horizontal forces encountered while
ascending (ωb)
Averaging ωb through a layer can infer
turbulence encountered by the balloon
Role of Possible Kelvin-Helmholtz Instability
Critical
Ri = 0.25
Generally favorable turbulence profile
in ducting layer immediately above
boundary layer capping inversion
1200 UTC 22 December 2013 Sounding characteristics:
•
•
Steep 850-700 hPa lapse rates ducted between two stable layers
Parallel-sheared flow coinciding with steep lapse rates
Low and mid-level winds favored downslope trajectories off the
northern Catskills and Helderberg Escarpment. Combined with
adiabatic warming/drying and clearing pockets of sky cover,
enough heating may have promoted a period of breaking waves
that mixed out capping inversion.
12/24/13 0000 UTC
By 12/24/13 00 UTC,
boundary layer had fully
mixed out within dry, NW
flow regime
1
Sounding Features
•
Deeper and well-mixed CBL to ~1500 m
(1)
•
Sharp slope in wind profile, indicative of
strong momentum transport just above
the surface (2)
•
Vertically-oriented eddies allowed for
drier air to mix down to surface (3)
2
3
Surface Observations Valid
1500 UTC 22 December 2013
Possible meso-front
Rough approximation of
Helderberg Escarpment
www.mesowest.utah.edu
For most of the day,
temperatures within the
boundary layer (valley areas)
were only in the 30s, but
quickly jumped to the low 60s
across the higher terrain
above the capping inversion!
Photo overlooking the Hudson Valley from Thacher State Park. Thacher State Park is located along the
Helderberg Escarpment in Albany County, with elevations ranging from ~90 m (300 ft) to ~550 m (1800
ft). It was noted that temperatures in the fog layer were ~1°C (33°F) and ~13°C (55°F) near the top of
the escarpment – a nearly 10-15°C (20-25°F) across a ~460 m (1500 ft) elevation change!
Although difficult to see, presence of
ducting waves in layer of hypothesized
Kelvin-Helmholtz Instability
Notice the stratocumulus “lumpy-like”
appearance at the top of the fog layer
Photo courtesy of Dr. Jeff
Freedman, SUNY Atmospheric
Sciences Research Center
22
Conclusions
• Cold air damming (CAD) across portions of the Hudson Valley
on 22 December 2013 resulted in a period of extended dense
fog, along with extreme temperature differences exceeding 15°C
amongst elevation-dependent sites less than 10 km apart
• The event was aided by a strongly stable boundary layer, a
result in part of the local topography and blocking flow (Fr < 1)
• It is hypothesized that Kelvin-Helmholtz instability and
increased thermal heating (pockets of clearing) promoted a
period of breaking waves capable of mixing out the boundary
layer capping inversion
▫ Allowed for a period of enhanced turbulent mixing
• Data mining available datasets, such as the boundary layer, can
aid in the forecasting/understanding of these events
Acknowledgements
• SUNY Albany Atmospheric Sciences Research Center
▫ Dr. Jeff Freedman
• NOAA/NWS Eastern Region Scientific Services Division
▫ Brian Miretzky
• NROW XVI Steering Committee
▫
▫
▫
▫
▫
Warren Snyder
Tom Wasula
Neil Stuart
Vasil Koleci
Brian Frugis
This work is an unfunded component under CSTAR V, grant NA13NWS4680004.
Questions? Comments?
[email protected]