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

WINTER WEATHER SNOW CLIMATOLOGY

WINTER WEATHER SNOW CLIMATOLOGY

WINTER WEATHER SNOW CLIMATOLOGY

WINTER WEATHER SNOW CLIMATOLOGY

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

WINTER WEATHER The “Classic” Cold Conveyor Snowstorm

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

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

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

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

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)

WINTER WEATHER Overrunning snowstorm (Strong cyclone)

WINTER WEATHER Overrunning snowstorm (Alberta Clipper)

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?

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

WINTER WEATHER