1. WINTER WEATHER FORECAST PROBLEMS INCLUDE: –SNOW –ICE –STRONG WINDS

2. WINTER WEATHER SNOW CLIMATOLOGY

3. WINTER WEATHER SNOW CLIMATOLOGY

4. WINTER WEATHER SNOW CLIMATOLOGY

5. WINTER WEATHER SNOW CLIMATOLOGY

6. WINTER WEATHER TYPES OF SNOW STORMS –SYNOPTIC-SCALE Classic Cold Conveyor (i.e. Nor’easter) Overrunning (Strong cyclone, Alberta Clipper) Jet streak –MESO-SCALE Lake-effect Orographic Convective

7. WINTER WEATHER The “Classic” Cold Conveyor Snowstorm

8. WINTER WEATHER ->>> Northwest of sfc/850mb low The “Classic” Cold Conveyor Snowstorm About 150 miles NW of surface low About 50 miles NW of 850mb low

9. WINTER WEATHER Often yields widespread/ heavy snow The “Classic” Cold Conveyor Snowstorm Snow banding - model bias: underdoes amounts - model bias: not far enough to NW Duration

10. WINTER WEATHER The “Classic” Cold Conveyor Snowstorm Narrower FZRA/PL zone In Cold conveyor area

11. SNOW STORMS: TYPES Classic Cold Conveyor –Northwest of sfc/850mb low –Often yields widespread/ heavy snow These are the 1 to 3’ storms –Impressive snowfall rates Often have 1-3”/hr rates –Narrow FZRA/PL zone –Can yield blizzards

12. SNOW STORMS: TYPES Overrunning –Less accumulation Typically 2-6”, can be more –Shorter-lived snows –Snowfall rates can be impressive Can reach 1-3”/hr rates –Followed by PL/FZRA/RN (Large cyclones)

13. WINTER WEATHER Overrunning snowstorm (Strong cyclone)

14. WINTER WEATHER Overrunning snowstorm (Alberta Clipper)

15. WINTER WEATHER FORECASTING AMOUNTS: –THREE FACTORS QPF … How much liquid will fall? Temperature … Will it be cold enough to snow? What will the liquid-to-solid ratio be?

16. WINTER WEATHER FORECASTING AMOUNTS: –QPF: Consider snow bands if ‘rip roaring’ cyclone If max VV occurs where T near -15C … expect higher QPF –Temperature: When its precipitating hard, models likely too warm For coastal cities, model low-level T’s too slow to transition to colder values when surface flow turns offshore (after being onshore) –Ratios: Temperature dependent Cold conveyor: 8:1 to 20:1 Warm advection (strong cyclone): 7:1 to 15:1 Warm advection (Alberta clipper): 15:1 to 25:1

17. WINTER WEATHER