What idiot is wasting our storm-chasing time talking about a winter storm? The New Year’s Day Storm in Central Minnesota Robert A. Weisman, Saint Cloud State University Amanda E. Brandt, NWS Forecast Office, Duluth, MN

22 March /1/05 Storm: 9th Northern Plains Convective Workshop2 Storm of 1 January 2005 Yes, there has been winter somewhere! Yes, there has been winter somewhere! cm ( in) of snow in northeastern Minnesota cm ( in) of snow in northeastern Minnesota Record 24 cm (9.5 in) snow at NWS Duluth Record 24 cm (9.5 in) snow at NWS Duluth –Hourly snowfall of 2.5 and 3.5 inches at KDLH in convective bands Snow Depth courtesy of MN State Climatology Office

22 March /1/05 Storm: 9th Northern Plains Convective Workshop3 Storm of 1 January 2005 Thundersleet in Saint Cloud at 20-22Z Thundersleet in Saint Cloud at 20-22Z –30 cloud-to-ground lightning strikes Thundersleet is frequent in cold sector (e.g., Gedzelman 1987) Thundersleet is frequent in cold sector (e.g., Gedzelman 1987) –Not “The Day Before The Day After Tomorrow” Sleet is significant because: Sleet is significant because: –Icing conditions –It hurts! Radar courtesy of UCAR Archive

22 March /1/05 Storm: 9th Northern Plains Convective Workshop4 Surface Set-up Rather Benign

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22 March /1/05 Storm: 9th Northern Plains Convective Workshop18 Role of Inverted Trough Inverted trough ahead case (Schumacher, Selzler, Frosig, et al., some century will get published?) Inverted trough ahead case (Schumacher, Selzler, Frosig, et al., some century will get published?) –Inverted trough at surface and in the lower troposphere is vertical IT is “limiting streamline” of warm-air advection IT is “limiting streamline” of warm-air advection Warm-air advection and lift downstream of IT position Warm-air advection and lift downstream of IT position Cold-air advection and sinking upstream of IT position Cold-air advection and sinking upstream of IT position –When the IT goes by, the precipitation ends

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22 March /1/05 Storm: 9th Northern Plains Convective Workshop29 Conclusions Large-scale Large-scale –Frontogenesis and warm-air advection to east of IT provided lift –Strong upper-level divergence added by right entrance region to anticyclonically curved jet streak Convection Convection –Formed just to east of IT near Sioux Falls in warm-air advection area Warm-air advection at 850 hPa accompanied by high T d s of 6-8 o C Warm-air advection at 850 hPa accompanied by high T d s of 6-8 o C Parcels lifted from both warm sector or 850 hPa above surface cold air were unstable until the upper troposphere Parcels lifted from both warm sector or 850 hPa above surface cold air were unstable until the upper troposphere

22 March /1/05 Storm: 9th Northern Plains Convective Workshop30 More Conclusions Microphysics Microphysics –Warm layer at hPa, reinforced by convection, kept precipitation as sleet or rain in central and southern Minnesota despite potential for evaporational cooling, cooling by lift –This layer was cold enough only in northeastern Minnesota, allowing heavy snowfall rates

22 March /1/05 Storm: 9th Northern Plains Convective Workshop31 References Moore, J. T., and G. E. VanKnowe, (Nov.) 1992: The effect of jet streak curvature on kinematic fields. Monthly Weather Review, 120, Moore, J. T., and G. E. VanKnowe, (Nov.) 1992: The effect of jet streak curvature on kinematic fields. Monthly Weather Review, 120, Plymouth State Weather Center Plymouth State Weather Center – Inverted trough references: Inverted trough references: –Webcast by Phil Schumacher: –Article Weisman, R. A., K. G. MacGregor, D. R. Novak, J. L. Selzler, M. L. Spinar, B. C. Thomas, and P. N. Schumacher, (Dec.) 2002: Precipitation regimes during cold-season Central U.S. inverted trough cases. Part I: synoptic climatology and composite study. Weather and Forecasting, 17, Weisman, R. A., K. G. MacGregor, D. R. Novak, J. L. Selzler, M. L. Spinar, B. C. Thomas, and P. N. Schumacher, (Dec.) 2002: Precipitation regimes during cold-season Central U.S. inverted trough cases. Part I: synoptic climatology and composite study. Weather and Forecasting, 17, –Co-authors on IT work: G. R. Frosig, J. L. Selzler, K. G. MacGregor, D. R. Novak, M. L. Spinar, B. C. Thomas

22 March /1/05 Storm: 9th Northern Plains Convective Workshop32 Acknowledgments More on the Storm: More on the Storm: –Amanda Brandt’s Winter Storm Summary at 1_2005.shtml 1_2005.shtml 1_2005.shtml –This talk will be posted in html at es/synguide/tsleet html es/synguide/tsleet html es/synguide/tsleet html

22 March /1/05 Storm: 9th Northern Plains Convective Workshop33 Acknowledgments Brad Nelson and Peggy Willenberg for their flaming s and interest both during and after the storm that inspired further investigation.