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Cold Air Outbreak Event Synoptic Patterns Associated with the 6-8 January 2017 South Texas Cold Air Outbreak Event WAYLON COLLINS NOAA/NWS/SR/WFO CORPUS CHRISTI 27 JANUARY 2018 Outline Eastern U.S. (east of Rockies) Cold Air Outbreak (CAO) events of short duration (≤ 5 days) precursor patterns Large Scale Meteorological Patterns (LSMP) associated with eastern CAO event onset Analysis of 6-8 January 2017 CAO event in context of precursor patterns and LSMP. 1-4 January 2018 CAO event and the Stratospheric Polar Vortex Cold Air Outbreak Definition and Development Cold Air Outbreak (CAO) Event Departure of cold air mass into a warmer region (Kolstad 2010) Typical North American wintertime CAO event development process Two stage process (Grotjahn et al. 2016) 1. Formation of an Arctic air mass/surface anticyclone over Canada 2. Rapid horizontal transport of the air mass to lower latitudes (enabled by a lower level circulation associated with a large scale meteorological pattern) Cold air partially offset by adiabatic warming in response to 100-300mb descent (Walsh et al 2001) Kolstad, E. W., Breiteig T., and A. A. Scaife, 2010: The association between stratospheric weak polar vortex events and cold air outbreaks in the Northern Hemisphere, Q. J. R. Meteorol. Soc., 136: 886-893. Grotjahn R., Black R., Leung, R. et al., 2016: North American extreme temperature events and related large scale meteorological patterns: a review of statistical methods, dynamics, modeling, and trends, Clim Dyn,. 46: 1151. Walsh, J. E., A. S. Philips, D. H. Portis, and W. L. Chapman, 2001: Extreme cold outbreaks in the United States and Europe, 1948–99. J. Climate, 14, 2642–2658 Eastern North American (NA) Cold Air Outbreak (CAO) Precursor Patterns Grotjahn (2016) Anomalously high MSLP coincident with polar air mass Negative Phase of the North Atlantic Oscillation Teleconnection Pattern Positive Phase of the Pacific North American Teleconnection Pattern Anomalously weak stratospheric polar vortex Teleconnection: Correlation between geopotential heights (on a specific pressure surface) at widely separated points on earth (Wallace and Gutzler, 1981) Grotjahn, R., Black, R., Leung, R. et al., 2016: North American extreme temperature events and related large scale meteorological patterns: a review of statistical methods, dynamics, modeling, and trends, Clim Dyn,. 46: 1151. Wallace, J. M., and D. S. Gutzler (1981), Teleconnections in the geopotential height field during the Northern Hemispheric winter, Mon. Weather Rev., 109, 784-812. Formation of Polar Air Mass over Western Canada The following formation process based on a composite study of 93 Northwest Canadian Arctic air mass formations by Turner and Gyakum (2011): First Stage: Snow falls into unsaturated layer in the lee of the Rockies Subliminal cooling/moistening subcloud layer Mid-tropospheric cooling via cloud-top radiation emissions Second Stage: Cessation of snow and associated drying of air column Clear sky surface radiation (augmented by high emissivity of fresh snow) Surface temperature falls rapidly (dataset maximum 18oC day-1) Third Stage: Near surface ice crystals and ice fog develops (when near surface temperature falls below the frost point.) Near end of formation: Cold air damming with cold pool/anticyclone at the lee of the Rockies, lower pressure over Gulf of Alaska, strong baroclinic zone oriented NW-SE along the Rockies. Turner J. K., and J. R. Gyakum, 2011: The Development of Arctic Air Masses in Northwest Canada and Their Behavior in a Warming Climate, Journal of Climate, 24: 4618-4633 Eastern N.A. CAO Precursor Patterns: Negative Phase of North Atlantic Oscillation North Atlantic Oscillation (NAO) “…meridional oscillation in atmospheric mass with centers of action near the Icelandic low and the Azores high…” (Hurrell and Van Loon, 1997) A measure of strength of the North Atlantic Oceanic westerlies within the 40oN- 60oN latitude belt (Greatbatch 2000) NAO Index: Normalized pressure difference between Stykkisholmur, Iceland and Lisbon, Portugal (Hurrell 1996) According to Hurrell (1996), the NAO accounted for 31% of variance in northern hemispheric (north of 20oN) surface temperatures in winter for the 1935-1994 period Greatbatch, R. J., 2000: The North Atlantic Oscillation, Stochastic Environ. Res. Risk Assess., 14(4), 213–242, doi:10.1007/s004770000047 Hurrell, J. W., 1996: Influence of variations in extratropical wintertime teleconnections on Northern Hemisphere temperature, Geophysical Research Letters, 23(6), 665-668 Hurrell, J. W., and H. van Loon, 1997: Decadal variations in climate associated with the North Atlantic Oscillation. Climate Change, 36, 301-326. Eastern N.A. CAO Precursor Patterns: Negative Phase of North Atlantic Oscillation Positive NAO: Stronger westerlies over North Atlantic Northward displacement of storm tracks Polar air more likely to remain over Canada/Fewer Cold Air Outbreaks Negative NAO: Weaker westerlies over North Atlantic Southward displacement of storm tracks Polar air less likely to remain over Canada/more Cold Air Outbreaks Woollings, T. J., A. Hannachi, B. Hoskins, and A. Turner, 2010b: A regime view of the North Atlantic Oscillation and its response anthropogenic forcing. J. Climate, 23, 1291–1307 Climate Prediction Center, 2005: North Atlantic Oscillation Correlation with Surface Temperature Departures, DOC/NOAA/NWS/NCEP/CPC. URL http://www.cpc.ncep.noaa.gov/data/teledoc/nao_tmap.shtml (accessed 17 November 2017) Eastern N.A. CAO Precursor Patterns: Positive Phase of Pacific North American Teleconnection Pattern Pacific North American Teleconnection Pattern (PNA) “…the strongest teleconnection pattern of low-frequency variability of the atmospheric circulation in winter in response to changes in the sea surface temperature” (AMS Glossary) A measure of the strength of the mid-latitude East Asian jet stream PNA Index: Combination of normalized 500-mb geopotential height anomalies at four locations (Wallace and Gutzler, 1981; Cellitti et al 2006): PNA = 0.25 [z(20oN, 160oW) – z(45oN, 165oW) + z(55oN, 155oW) – z(30oN, 85oW)] PNA = 0.25 [z(near Hawaii) – z(North Pacific Ocean) + z(Alberta) – z(U.S. Gulf Coast Region)] Cellitti, M. P., J. E. Walsh, R. M. Rauber, and D. H. Portis, 2006: Extreme cold air outbreaks over the United States, the polar vortex, and the large-scale circulation, J. Geophys. Res., 111, D02114, doi:10.1029/2005JD006273. Wallace, J. M., and D. S. Gutzler , 1981: Teleconnections in the geopotential height field during the Northern Hemispheric winter, Mon. Weather Rev., 109, 784-812. Eastern N.A. CAO Precursor Patterns: Positive Phase of Pacific/North American Climate Prediction Center, 2005: Pacific / North American Pattern, DOC/NOAA/NWS/NCEP/CPC. URL http://http://www.cpc.ncep.noaa.gov/data/teledoc/pna_map.shtml (accessed 24 January 2018) Ge, Y., G. Gong, and A. Frei, 2009: Physical mechanisms linking the winter Pacific–North American teleconnection pattern to spring North American snow depth. J. Climate, 22, 5135–5148 Eastern N.A. CAO Precursor Patterns: Anomalously weak stratospheric polar vortex/sudden stratospheric warming Sudden Stratospheric Warming (SSW) Definition (AMS Glossary): A rise in temperature of the stratosphere in the polar region in late winter resulting from enhanced propagation of energy from the troposphere by planetary- scale waves Definition (Charlton and Polvani, 2007): Zonal mean zonal winds at 60oN and 10-mb become easterly during the winter Process: 1. Persistent propagation of tropospheric planetary waves into the stratosphere 2. Wave breaking and subsequent drag exerted on stratospheric zonal flow 3. Geostrophic balance violation creating a poleward air mass movement 4. Convergence, sinking and adiabatic warming of air at high latitudes If wave-breaking is severe, stratospheric zonal flow reversal occurs resulting in sudden stratospheric warming (e.g. Kolstad et al 2010) Charlton, A. J., and L. M. Polvani, 2007: A new look at stratospheric sudden warmings. Part I: Climatology and modeling benchmarks. J. Climate, 20, 449–469 Kolstad EW, Breiteig T, Scaife AA, 2010: The association between stratospheric weak polar vortex events and cold air outbreaks in the Northern Hemisphere. Q. J. R. Meteorol. Soc., 136: 886-893. Eastern N.A. CAO Precursor Patterns: Anomalously weak stratospheric (not tropospheric) polar vortex/sudden stratospheric warming Waugh, D. W., Sobel, A. H., and L. M. Polvani, 2017: What is the Polar Vortex and how does it Influence Weather? Bull. Am. Meteorol. Soc., 98: 37-44. Eastern N.A. CAO Precursor Patterns: Anomalously weak stratospheric polar vortex/sudden stratospheric warming Butler,A., D. Seidel, S. Hardiman, N. Butchart, T. Birner, and A. Match, 2015: Defining sudden stratospheric warmings. Bull.Amer.Meteor.Soc., 96, 1913–1928 Eastern N.A. CAO Precursor Patterns: Anomalously weak stratospheric polar vortex/sudden stratospheric warming Statistically significant negative temperature anomalies over the Eastern CONUS Mitchell D. M., Gray L. J., Anstey J., Baldwin M. P., and Andrew J. Charlton-Perez, 2013: The Influence of Stratospheric Vortex Displacements and Splits on Surface Climate, Journal of Climate, 26: 2668-2682. Eastern NA Cold Air Outbreak (CAO) Large Scale Meteorological Patterns (LSMP) Eastern United States (east of the Rockies) Cold Air Outbreak Onset South/Southeastward advection of polar air mass in association with one or more of the following Large Scale Meteorological Pattern (LSMP) features (Grotjahn et al. 2016): 1. Southward extension (for CAO events affecting Texas)
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