WINTER WEATHER

WINTER WEATHER

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

Scenes from a massive pile-up

Scenes from a massive pile-up

Deaths, injuries …

Destruction

Blame it on the ….…

01-07-04

The number of people dead in a massive pileup of more than 50 cars on Interstate 80 rose to six Wednesday as police and rescue crews finished combing through about 3,000 feet of wreckage. The accident -- involving at least 50 vehicles, 30 of which were tractor-trailers -- happened around 11 a.m. Tuesday. A snow squall caused a whiteout on I-80 near the Milesburg exit, just east of Bald Eagle Creek.

At least six people were killed and dozens injured Friday in a massive pileup snarling miles of I-80 during a heavy snow squall.State police at Lamar said the accident occurred shortly before 1 p.m. when whiteout conditions apparently caused more than 50 vehicles to rear-end one another in the westbound lanes at mile marker 186 near Loganton."You couldn't see in front of you, it was a whole mess of cars," Frank Valley of Massachusetts, who was involved in the wreck here, told the Williamsport Sun-Gazette. "You couldn't avoid it, you just had to get into the pile."

12-29-01

WINTER WEATHERSNOW CLIMATOLOGY

WINTER WEATHERSNOW CLIMATOLOGY

WINTER WEATHERSNOW CLIMATOLOGY

TERRAIN AND PRECIPITATION

80” 60”

40”20”

WINTER WEATHERSNOW CLIMATOLOGY

WINTER WEATHER

• TYPES OF SNOW STORMS– SYNOPTIC-SCALE

• Classic Cold Conveyor (i.e. ‘Noreaster)• Overrunning (Strong cyclone, Alberta clipper)• Jet streak

– MESO-SCALE• Lake-effect• Oragraphic• 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

CSI banding - model bias: underdoes amounts - model bias: not far enough to NWDuration

WINTER WEATHERThe “Classic” Cold Conveyor Snowstorm

Narrower FZRA/PE 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/PE 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 PE/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?

– Critical thickness … 850 0C … soundings

• What will the liquid-to-solid ratio be?

COOL WX website

EWALL

WINTER WEATHER

• FORECASTING AMOUNTS:– QPF:

• Consider CSI 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