winter weather forecast problems include: –snow –ice –strong winds
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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