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<br />PRE-FRONTAL
<br />
<br />TRANSITIONAL
<br />
<br />Clouds
<br />
<br />Layered
<br />from
<br />surface
<br />to 30,000
<br />feet with
<br />clear
<br />layers.
<br />
<br />Layered
<br />to 18,000
<br />feet with
<br />embedded
<br />cumulus.
<br />
<br />Crystal Types
<br />
<br />Often water saturated
<br />crystals at temperatures
<br />< -20oC (usually above
<br />18,000 feet) e.g., hollow
<br />bullets, side planes, hollow
<br />columns, radiating assemblage
<br />of plates" sectors and
<br />dendri tes, also solid columns
<br />and solid bullets,
<br />combinations of bullets.
<br />Usually sub-water saturated
<br />at temperatures > -20oC
<br />(usually below about 18,000
<br />feet) e.g. plates, some
<br />crystals with broad branches
<br />and sector---like branches and
<br />warm region columns" thick
<br />plates.
<br />
<br />Water saturated crystal types
<br />at all levels, e.g. hollow
<br />bullets, 5 ide planes, hollow
<br />colunms., combinations of
<br />bullets, dendrites" stellars
<br />some crystals with sector-
<br />like branches and broad
<br />branches., only a few plates
<br />many sheaths and needles,
<br />some warm columns.
<br />
<br />POST-FRONTAL Convective
<br />wi th tops
<br />to 15,000
<br />feet.
<br />
<br />1-
<br />
<br />!-
<br />
<br />\-
<br />
<br />Few crystals generally
<br />dendrites, a few plates and
<br />some needles and sheaths.
<br />
<br />I"
<br />
<br />1-
<br />
<br />TABLE ".1
<br />
<br />SUMMARY OF MICROPHYSICAL AND SYNOPTIC DIFFERENCES BETWEEN PRE-FRONTAL, TRANSITIONAL, AND
<br />
<br />POST-FRONTAL PORTIONS OF PACIFIC NORTHWEST STORMS OVER THE CASCADE MOUNTAINS
<br />
<br />Relative I Relative
<br />Concentrations Concentration
<br />of Ice of Water
<br />Parti cles Droplets
<br />
<br />Western slopes Western slopes
<br />of Cascades: of Cascades:
<br />1000 to 15,000 250 to 10,000.
<br />Eastern slopes Eastern slopes
<br />of Cascades :of Cascades:
<br />250 to 5,000. 100 to 5,000.
<br />Puget Sound puget Sound
<br />Basin: 500 to Basin: 200 to
<br />10,000. 7,500.
<br />
<br />Western slopes
<br />of Cascades:
<br />o to 100,000
<br />Eastern slopes
<br />of Cascades:
<br />o to 15,000.
<br />Puget Sormd
<br />Basin: 0 to
<br />50,000.
<br />
<br />Western slopes
<br />of Cas cades :
<br />o to 10,000.
<br />Eastern slopes
<br />of Cascades
<br />o to 1000.
<br />Puget Sormd
<br />Basin: 0 to
<br />2500.
<br />
<br />-
<br />
<br />Western slopes
<br />of Cascades:
<br />20,000 to
<br />350,000.
<br />Eastern slopes
<br />of Cascades:
<br />5,000 to
<br />80,000.
<br />Puget Sound
<br />Basin: 10,000
<br />to 200,000.
<br />
<br />Western slopes
<br />35,000 to
<br />300,000 (many
<br />small droplets
<br />average 10 ~rn
<br />in diameter).
<br />Eastern slopes
<br />100 to 10,000.
<br />Puget Sormd
<br />IBasin: 0 to
<br />15,000.
<br />
<br />1-
<br />
<br />,-
<br />
<br />Liquid
<br />Water
<br />Content:
<br />(g m-3)
<br />
<br />o to 0.5.
<br />Some increase
<br />on western
<br />slopes of
<br />Cascades.
<br />Liquid water
<br />concentration
<br />near zero for
<br />temperatures
<br />< -lOoC
<br />(higher than
<br />about 13,000
<br />feet).
<br />
<br />Up to about
<br />17,000 feet
<br />(about -200C)
<br />0.5 to 2.0
<br />
<br />0.1 to l.0
<br />
<br />\-
<br />
<br />Turbulence
<br />
<br />Relati ve
<br />Concentration
<br />of Aggregated
<br />Ice Particles
<br />
<br />o to light.
<br />Some
<br />increase on
<br />western
<br />slopes of
<br />Cascades.
<br />
<br />Moderate to 0 to 2,000
<br />severe..
<br />S.trong
<br />increase
<br />on western
<br />slopes of
<br />Cascades.
<br />
<br />Moderate to O. to 10
<br />severe.
<br />Strong
<br />increase on
<br />western
<br />slopes of
<br />Cascades.
<br />
<br />I
<br />
<br />..
<br />I
<br />
<br />~
<br />
<br />Riming
<br />
<br />10 to 100
<br />
<br />Very little
<br />except near
<br />the surface
<br />in the
<br />Cas cades.
<br />More riming
<br />over east
<br />slopes of
<br />Cascades
<br />than west.
<br />
<br />Quite common,
<br />particularly
<br />for warm
<br />region
<br />crystals
<br />e.g.
<br />needles
<br />and sheaths.
<br />
<br />Heavy
<br />riming on
<br />the few ice
<br />particles
<br />present.
<br />
<br />I
<br />I
<br />
<br />I
<br />
<br />'..'
<br />I
<br />
<br />Precipi tation
<br />Rate -1
<br />(inch hr )
<br />
<br />Orographic
<br />Effect
<br />of Cascade
<br />Mountains
<br />
<br />Steady between Increase in
<br />0.05 to 0.10 water saturated
<br />crystals such as
<br />dendri tes,
<br />needles and
<br />sheaths. Increase
<br />in concentrations
<br />of aggregates on
<br />wes tern slopes.
<br />Decrease in
<br />concentrations of
<br />ice crys tals on
<br />the eastern
<br />slopes. Higher"
<br />precipi tation
<br />~ate on. western
<br />than eas tern
<br />slopes.
<br />
<br />Showery .
<br />o to 0.30.
<br />
<br />Showery .
<br />Nearly 0 on
<br />eastern slope
<br />to 0.20 on
<br />western slopes
<br />
<br />i.
<br />I
<br />
<br />..)
<br />I
<br />
<br />Heavy showers on
<br />western slopes,
<br />often rapid
<br />clearing on
<br />eastern slopes.
<br />More riming on
<br />western than on
<br />eastern slopes,
<br />also more graupel
<br />and frozen drops
<br />on western slopes
<br />
<br />Scattered heavy
<br />orographic
<br />showers on
<br />w€s tern slopes.
<br />
<br />~
<br />
<br />Special Features
<br />
<br />Concentration of cloud
<br />particles quite uniform-
<br />over large horizontal
<br />distances. Cold . region
<br />crystals very common.
<br />Riming at low altitudes
<br />over Cascades and on
<br />eastern slopes.
<br />
<br />I
<br /><0
<br />en
<br />I
<br />
<br />Graupel and frozen
<br />drops common.
<br />Concentration of
<br />crystals variable.
<br />Heavy riming,
<br />particularly on western
<br />slopes of Cascades near
<br />surface.
<br />
<br />Graupel, . aggregates
<br />and frozen droplets
<br />common particularly on
<br />western slopes of
<br />Cas cades .
<br />
<br />'.
<br />r
<br />
<br />~
<br />
<br />~
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<br />-
<br />I
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