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? 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

Average Snowfall

Average First Snow Date

Observed Seasonal Snow

Review of techniques on December th Winter Storm

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

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

200 mb Generally along and left of 164 height

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

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

300 mb Coupled jet

300 mb Strongest Q-vector convergence

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

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

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

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

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

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

500 mb

S+ between -20° & -25°

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

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

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

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

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

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

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

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

850 mb Right of deformation axis Just north of strong WAA

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

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

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 °

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

SurfaceSurface Note position of surface ridge for onset of snow

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

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

Winter Weather Forecast Techniques The End