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Winter Weather Forecasting

Winter Weather Forecasting. An Empirical Approach to Winter Storm Forecasting for the National Weather Service Springfield, Missouri Forecast Area . Winter Weather Forecast Techniques. What in the world am I doing up here?

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Winter Weather Forecasting

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  1. Winter Weather Forecasting An Empirical Approach to Winter Storm Forecasting for the National Weather Service Springfield, Missouri Forecast Area

  2. Winter Weather Forecast Techniques • What in the world am I doing up here? • A quick review of moderate to heavy snow forecasting techniques & pattern recognition • Not discussing in great detail • Not looking at precipitation type • Not an in depth case study • Caveats • Every technique will not work in every situation • Every weather rule is meant to be broken

  3. Average Snowfall

  4. Average First Snow Date

  5. Observed Seasonal Snow

  6. 200 mb • S+ associated with stratospheric warming • S+ generally along and just north of 164 height

  7. 200 mb S+ associated with stratospheric warming Generally along and left of 164 height

  8. 200 mb Generally along and left of 164 height

  9. 300 mb • S+ along left front exit region and rear entrance region of jet max • S+ in area of coupled jet • S+ generally in area of strongest Q-vector convergence • S+ generally with deep with deepening long wave

  10. 300 mb S+ in right rear entrance and left front exit regions

  11. 300 mb Coupled jet

  12. 300 mb Strongest Q-vector convergence

  13. 500 mb • ~ 7 degrees latitude down stream from vort max • Slightly left of closed low or strong vort max • Slightly downstream from where the curvature changes from cyclonic and anticyclonic • Deepening low or trough • S+ between –20° and 25 ° • If storm warms at 50H then S+ left of 50H low. Otherwise S+ left of surface low track

  14. 500 mb • S+ begins at 50H ridge line and ends at trough axis. • S+ from the inflection pt. downstream from trough axis & to the south of the 50H speed max • S+ varies from 60 mi. left of vort max in open trough to 150 mi. left of vort max or closed low • If surface low is right of 50H height fall center track, S+ will lie parallel and left of height fall track • If surface low is to left of 50H height fall center track, S+ will lie parallel and left or either surface low or 50H low track

  15. 500 mb S+ begins at 50H ridge & ends at trough axis Subtle shortwaves ejecting NE

  16. 500 mb S+ from the inflection pt. downstream from trough axis & to the south of the 50H speed max

  17. 500 mb Slightly downstream from where curvature cyclonic to anticyclonic ~ 7 degrees lat. (360 nm) downstream of vort. max

  18. 500 mb ~ 60 to 150 nm left of vort max path. Closer in open system Deepening trough or upper low

  19. 500 mb

  20. 500 mb

  21. 500 mb S+ between -20° & -25°

  22. 500 mb

  23. 500 mb If surface low is of right height fall center, then S+ parallel and left of 50H height fall center track If surface low is left of height fall center, then S+ parallel and left of surface low or 50H low track

  24. 700 mb • Temperature -6 ° to -8 ° • South of -10 ° dew point • In axis of greatest 70H RH • S+ along path and just left of 70H low • Snow begins at 70H ridge and ends at trough • North of 70H closed center

  25. 700 mb Snow begins at ridge axis Track of maximum height falls

  26. 700 mb Temperature -6° to -8° Axis of strong frontogenesis

  27. 700 mb South of -10° dew point Strong moisture convergence

  28. 700 mb Strong WAA & Theta-e advection Well defined deformation axis

  29. 700 mb WAA & Theta-e axis wraps westward as the storm matures Just north of 70H low center

  30. 850 mb • About 1.5 degrees (60-240 nm) left of low track • Heavy snow occurs more frequently with lows that generally move NE • -5° isotherm bisects heavy snow • -2 ° to -8 ° for moderate snow • Dewpoints 0° to -4° • > 5 ° of WAA

  31. 850 mb Right of deformation axis Just north of strong WAA

  32. 850 mb Note axis of WAA as storm matures ~1.5 degrees lat (60-240 nm) left of low track

  33. 850 mb -2° to -8° for moderate snow -5° generally bisects heavy snow

  34. Surface • Surface low can be weak • 2-2.5 degrees lat. (150-240 nm) left of the low track • Surface low continues to deepen • Cold surface anti-cyclone to the N-NW and enhanced by confluent mid level flow • Optimum surface temperature 27° - 32 °

  35. Surface Surface low can be weak Cold surface high to the N-NW and enhanced by confluent mid level flow

  36. Surface Note position of surface ridge for onset of snow

  37. Surface S+ 2-2.5 degrees lat. (150-240 nm) left of low track Optimum temperature 27° - 32°

  38. November 2006 Storm • Track of surface, 850 mb and 700 mb lows • Well developed TROWAL • Strong 300 mb jet with jet coupling and strong upper divergence • Strong frontogenesis • Strong isentropic ascent / WAA regime followed by cold core system with strong Q-vector convergence • Strong moisture transport • Elevated instability • Track of 500 mb upper low, vort max, and height falls • Track of 200 mb low and warm air advection

  39. Winter Weather Forecast Techniques The End

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