WINTER WEATHER

• FORECAST PROBLEMS INCLUDE:– SNOW– ICE– STRONG WINDS

WINTER WEATHERSNOW CLIMATOLOGY

WINTER WEATHERSNOW CLIMATOLOGY

WINTER WEATHERSNOW CLIMATOLOGY

WINTER WEATHERSNOW 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 NWDuration

WINTER WEATHERThe “Classic” Cold Conveyor Snowstorm

Narrower FZRA/PL zoneIn 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 WEATHEROverrunning 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