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

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Presentation on theme: "Winter Weather Forecasting An Empirical Approach to Winter Storm Forecasting for the National Weather Service Springfield, Missouri Forecast Area."— Presentation transcript:

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

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7

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9 Review of techniques on December th Winter Storm

10 200 mb S+ associated with stratospheric warming S+ generally along and just north of 164 height

11 200 mb S+ associated with stratospheric warming Generally along and left of 164 height

12 200 mb Generally along and left of 164 height

13 300 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

14 300 mb S+ in right rear entrance and left front exit regions

15 300 mb Coupled jet

16 300 mb Strongest Q-vector convergence

17 500 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

18 500 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

19 500 mb S+ begins at 50H ridge & ends at trough axis Subtle shortwaves ejecting NE

20 500 mb S+ from the inflection pt. downstream from trough axis & to the south of the 50H speed max

21 500 mb Slightly downstream from where curvature cyclonic to anticyclonic ~ 7 degrees lat. (360 nm) downstream of vort. max

22 500 mb ~ 60 to 150 nm left of vort max path. Closer in open system Deepening trough or upper low

23 500 mb

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25 S+ between -20° & -25°

26 500 mb

27 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

28 700 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

29 700 mb Snow begins at ridge axis Track of maximum height falls

30 700 mb Temperature -6° to -8° Axis of strong frontogenesis

31 700 mb South of -10° dew point Strong moisture convergence

32 700 mb Strong WAA & Theta-e advection Well defined deformation axis

33 700 mb WAA & Theta-e axis wraps westward as the storm matures Just north of 70H low center

34 850 mb About 1.5 degrees ( 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

35 850 mb Right of deformation axis Just north of strong WAA

36 850 mb Note axis of WAA as storm matures ~1.5 degrees lat ( nm) left of low track

37 850 mb -2° to -8° for moderate snow -5° generally bisects heavy snow

38 SurfaceSurface Surface low can be weak degrees lat. ( 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 °

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

40 SurfaceSurface Note position of surface ridge for onset of snow

41 SurfaceSurface S degrees lat. ( nm) left of low track Optimum temperature 27° - 32°

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43 November 2006 Storm 1. Track of surface, 850 mb and 700 mb lows 2. Well developed TROWAL 3. Strong 300 mb jet with jet coupling and strong upper divergence 4. Strong frontogenesis 5. Strong isentropic ascent / WAA regime followed by cold core system with strong Q-vector convergence 6. Strong moisture transport 7. Elevated instability 8. Track of 500 mb upper low, vort max, and height falls 9. Track of 200 mb low and warm air advection

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45 Winter Weather Forecast Techniques The End


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