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

9. WINTER WEATHER The “Classic” Cold Conveyor Snowstorm Often yields widespread/ heavy snow 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