WEF Flashcards
Drizzle
Always a warm process
Must be 2000ft thick
~(-5C)
Showery Precipitation
Clouds need to be at least 8,000-10,000ft thick
Tops (-12C) - (-20C)
Single Freezing Levels (rain, snow, mixed)
Rain: >1200ft
Snow: <600ft
Mixed: 600-1200ft
Freezing Rain
Top cold layer
Thick warm layer where ice completely melts
Cold layer with supercooled droplets
Surface 0C or less
Eastern side of US
Ahead of warm front and behind cold front
Poleward side of stationary front
Ice Pellets
Cold top layer
Warm shallow layer where droplets partially melt
Cold bottom layer
Slower accumulation rate
Snow
Freezing level is cold throughout
Heaviest snow will have temperatures closest to the freezing level
Heaviest snow fall
Surface low: 0C w/ 0 to(-5C) dew point, N and downstream of Low
700mb: -6C w/ -6 to (-10C) dew point, passage of ridge snow begins
500mb: -35/-25C, heaviest snow after 500 ridge and ends after 500 trof
Vorticity: -24 to -37C
Baroclinic Deep Occluding Low: Blizzard, >40kts/<20F, >50kts/<10F, 1-2 inches lasting 20 hrs
Insulation/Radiation factors
Latitude, seasons, diurnal changes, lapse rate and inversions
Ways to forecast MAX temp
Climatology, Advection upstream, Skew T, CCL, Persistence, Numerical Guidance
How to forecast MIN temperature
Climatology, Skew T, Dew point method, Numerical Guidance
Cold/Heat wave setup
Cold: Trof to E, Ridge to W
Heat: Trof to W, Ridge to E
PA/DA
PA: the altitude which corresponds to a given standard atmospheric pressure
DA: the altitude is the altitude in the standard atmosphere characterized by known air density in the existing atmosphere. Warmer temps - less dense, colder temps - more dense (higher take off speed).
Fog Formation
Stability, cooling, moistures and light mixing
Fog Dissipation
Instability, Heating, Drying out and Increased mixing (winds)
Radiation Fog
Nocturnal event
After rain event (36hrs)
Calm winds, Cool dew points, Clear skies
Does not form over snow
If there is a lack of moisture can be ~2ft
Extremely vulnerable to conditions
Advection Fog
Cold surface/ Warm air (maritime air)
3-9kt winds, deep fog
can extend 150-250nm
Sea fog: Warm moist air over cold water. Can still exists in strong winds if water is 30-40F
Upslope Fog
Air cools adiabatically as it rises upslope at a rate of 5.3F per 1,000ft
Begins as stratus
Great Plains, Appalachians and Rockies
Steam Fog
Unstable, Cold/Warm
2-3ft thigh
Fall, early winter
Frontal Fog
Pre-frontal: Associated with the warm front, cP air mass (warm/cold)
Post-frontal: Associated with a cold front, caused by precip, 150-200nm behind cold front, passes with 850mb frontal trof
Ice Fog
Human made
-20C
>50 latitude
Valley Fog
Increased moisture can allow fog to form @ night
Most common in early morning
Air cools as it rises up the mountain and condenses to saturation
Advection Radiation Fog
Land advection fog that stays inland and undergoes radiational nighttime cooling
Onshore winds (fog)
~3kts even coastal fog
~10 uneven (fog in headlands/convex)
Offshore winds (fog)
Lighter winds keeps fog confined to bays
With stronger winds fog gets pushed offshore (cold/warm)
Forecasting Fog tools
CCL
Fog formation graphic
Convective Turbulence
Thermally: SFC to boundary layer (10,000ft), Warm summer afternoons with clear skies and light winds.
Thunderstorm induced: MOD-EXT, 10,000-15,000ft or 5,000 of freezing level
Mechanical Turbulence
Low-level: caused by terrain, pressure gradient or frontal shear (less likely at nighttime)
High level: mountain wave turbulence. Can extend up to 70,000ft and can extended 300nm downstream. 35kts or greater, 45 perpendicular and stable layer at mountain top.
Clear Air Turbulence (CAT)
Not associated with turbulence or thermally induced
- trof present and moving >20kts
- Horizontal wind shear of >35kts/120nm
- Wind >55kts perpendicular to CAA
- Wind shift >75 degrees in CAA
U/L ridge, SFC cyclogenesis, Confluent jets, U/L lows, Diffluent winds, shearing Trof
Turbulence Chart
Light - Hor (<25kt/90nm) Vert (3-5kts/1000ft)
Mod - Hor (25-49kt/90nm) Vert (6-9kts/1000ft)
Sev - Hor (50-89kt/90nm) Vert (10-15kts/1000ft)
Ext -Hor (>90kt/90nm) Vert (>15kts/1000ft)
Turbulence effects on aircraft
Fixed wing: Increase speed, increase turb/ increase wt, decrease turb
Rotary wing: increase speed or arc, increase turb/ wt or lift velocity, decrease turb
Clear icing
0 to -8C
Increase WV and droplets
Cumulus cloud
Rime icing
< 0C Stable stratus (0 to -15C) and cumulus (-15C)
Mixed icing
-9 to -15 cumulus
Or stratus w/ embedded convection
Frost
<0C surface or descending w/ increased humidity
Stratiform clouds (icing)
Horizontal hazard
Mid-low levels
3,000-4,000 ft
Time most common
Cumuliform clouds (icing)
Vert hazard
All types of icing
Trace icing
0 to -40C
0 to -7 with DP of < 2 / -8 to -15 with DP < 3, with weak CAA
Light
0 to -22C
0 to -7 with DP of < 2 / -8 to -15 with DP < 3, with strong CAA
Occasional use of deicing equipment
Moderate icing
0 to -15C
Continuous use of deicing equipment
Severe Icing
Deicing no longer useful
Can occur in all thunderstorms
Icing intensity (dew point depression)
Light: 3 to >2C
Mod: 2 to 0C
Severe: OC
Levante
Winds from NE/W through the Strait of Gibraltar
Azores High over Spain
12-25kts
Mistral
NW/NE offshore winds
A and B are Blocking ridges. C is series of depressions.
40-100kts
Sirocco
SE or SW winds originates over N Africa
SE (cloudiness and drizzle)
SW (blowing dust)
Bora
Cold katabatibc wind
High pressure over Yugoslavia region
70-110kts
Gregale
Similar to Bora but central Mediterranean with NE winds
