Does QPF utilize MOS or raw data?bothWill raw data produce a QPF?yesWhat time of day best shows QPF?all day eventsWhat is the first step in making a precipitation forecast?look at the surface chart:
- airmass type
- thermal advection
- cloud cover
- high and low pressure
- fronts
- moisture (dew point)What is the second step in making a precipitation forecast?verify model data
- verify model data with radar, specifically for precipitationWhat is the third step in making a precipitation forecast?determine when rain should be expected based on current conditions and forecasted conditionsWhat percent of relative humidity and what dew point temperature is needed to produce overcast conditions?70%, 5 degrees Celsius or lessWhat percent of relative humidity (from surface to 500 mb) and what UVV values contribute to the chance of precipitation being nearly 100%?90%, -3 mb/s or lessWhat is step 4 in making a precipitation forecast?look at MOS dataWhat is step 5 in making a precipitation forecast?make the forecastWhat does the general precipitation forecast contain?- probability of precipitation or descriptive words
- QPF
- timingWhat is step 6 in making a precipitation forecast?check your forecastIn the southeast, is snow usually dry or wet?wetThis precipitation is composed of white or translucent ice crystals, chiefly in complex branch hexagonal form and often agglomerated into snowflakessnowWhat type of snowflakes are most common?dendritesWhat are the dendritic growth zone values?-12 to -18 degrees CelsiusWhat thresholds does snow exist in the atmosphere? (height and temperature)Height: 1500 ft - 4000 ft
Temperature: 1 degree Celsius to 3/4 degree CelsiusThe _____ (higher or lower) the snow growth region, this leads to a _______ (higher or lower) snow to liquid ratiohigher; lowerThis precipitation type is light snow falling for short durations; no accumulation or light dusting is all that is expectedsnow flurriesThis precipitation type is snow falling at varying intensities for brief periods of time; some accumulation is possiblesnow showersThis precipitation type is brief intense snow showers accompanied by strong, gusty winds; accumulation may be significant; best known in the Great Lakes regionsnow squallsThis precipitation type is wind-driven snow that educes visibility and causes significant drifting; may be snow that is falling and/or loose snow on the ground picked up by the windblowing snowThis type of precipitation is when winds are over 35 mph with snow and blowing snow, reducing visibility to 1/4 mile or less for at least 3 hoursblizzardsThis precipitation type is used to describe an observation of snow at the surface that occurs with lightning and thunderthundersnowThis precipitation type may be spherical, irregular, or conical in shape; partially melted snowflake that refreezes before reaching the ground; gone through an elevated melting layersleetThis precipitation type is rain that falls in liquid form but freezes upon impact to form a coating of glaze upon the ground and on exposed objects; rain isn supercooledfreezing rainWhat are the 3 ways that freezing rain forms?- entire sounding is above freezing except the surface
- total melting of a snowflake that freezes on contact at the Earth's surface
- entire sounding is below freezing but the minimum temperature does not get cold enough to support ice crystal formation (not cold enough to reach dendritic growth zone)This precipitation type is soft, small pellets formed when supercooled water droplets (at a temperature below 32 degrees Fahrenheit) freeze onto a snow crystal, a processed called riminggraupel (looks like dip n dots)What are temperatures at the surface and aloft for sleet?- below freezing at the surface and warm air aloftWhat are temperatures at the surface and aloft for graupel?- above freezing at the surface and cold air aloftTrue or False: Rain drops do easily freeze in the air without the presence of a nuclei ( partially melted snowflake)FalseDo snowflakes form when temperatures reach freezing?NoAt what temperature do ice crystals activate onto a nuclei?-10 degrees CelsiusAt the 1000-500 mb thickness, what should it be used for in making a winter weather forecast?First guest for the rain/snow lineWhy is the freezing line used?Taking an average and freezing line occursWhat thickness level is a better indicator of the rain/snow line?1000-700 mbTrue or False: Thickness values should replace hourly sounding analysisFalseAt what temperature does pure water freeze (no nuclei present)?-40 degrees CelsiusAt what temperature does supercooled water freeze?Before reaching -20 degrees CelsiusDoes the amount of ice crystal activation increase or decrease with relative humidity.IncreasesIs deposition a warming or cooling process?WarmingWhat is deposition?gas to solidDoes ice have a high or low saturation vapor pressure?low saturation vapor pressureDoes water have a high or low saturation vapor pressure?high saturation vapor pressureWhat is accretion/ riming?Ice crystals grow through collision- coalescence with supercooled waterAt what temperature does riming occur?-10 to 0 degrees CelsiusWhat is aggregation?Ice crystals stick togetherAt what temperature does aggregation occur?-5 to 0 degrees CelsiusWhat is the Bergeron process?- creating precipitation is ideal when ice crystals and supercooled water droplets coexist
- since the air is supersaturated, with respect to the limited ice crystals, water molecules begin to collect on the ice crystals
- since deposition is occurring, relative humidity decreases and surrounding water droplets begin to evaporate to replenish lost water vaporWhat phase of water is associated with high vapor pressure?waterWhat phase of water is associated with low vapor pressure?iceWhat are the steps of the Bergeron process? (4)- growth of ice crystals is dependent on evaporation and shrinkage of the liquid droplets
- ice crystals become large and begin to fall due to gravity
- some ice crystals will break apart as they fall through the air where fragments create new freezing nuclei
- this chain reaction creates many ice crystals which grow into snowflakesWhat is the top down approach when looking at soundings for winter weather? (4)- is any part of the cloud cold enough to support ice crystal formation (DGZ)
- is any portion of the sounding above freezing?
- where is the melting layer found
- is the layer below the melting layer below freezingThe process by which ice crystals form from liquid water molecules as the molecules collect and freeze onto foreign particles, such as dust is considered what?heterogeneous nucleationTrue or false: Snowflakes do form when temperatures reach freezingfalseWhat temperature does ice crystal activation onto nuclei occur?-10 degrees CelsiusWhat happens if the maximum temperature of the elevated melting layer is less than 1 degree Celsius?Minimal melting will occur and snow will retain identityWhat happens if the maximum temperature of the elevated melting layer is greater than 3 or 4 degrees Celsius?Complete melting will occur and no snow will occurWhat happens if the maximum temperature of the elevated melting layer is between 1 and 3/4 degrees Celsius?partial melting will occur and no snow will occur; ice crystal in the middle is preservedWhat happens if the thickness of the elevated melting layer is between 1500 - 4000 ft?partial melting will occur and no snow will occur; ice crystal in the middle is preservedWhat happens if the thickness of the melting layer is greater than 4000 ft?total melting will likely occur regardless of the max temperatureWhat happens if the freezing level is below 900 ft above the surface?limited melting will occur; snow will survive and remain its appearanceWhat happens if the freezing level is higher than 1200 ft?total melting will occurAt what temperature does unmixed precipitation occur (sleet)?-5 degrees Celsius or colderAt what temperature does mixed precipitation (sleet and freezing rain) occur?-2.5 to -5 degrees CelsiusAt what temperature does unmixed precipitation occur (freezing rain)?-2.5 to 0 degrees CelsiusIf complete melting of the snowflake has occurred how can sleet still occur?If the minimum temperature of the sub-freezing layer below the elevated melting layer is -8 degrees Celsius or colder and the depth of the sub-freezing layer is at least 3,000 ftStudy different skew-Ts for type of winter weather occuringWhat are the steps to determine the snow-to-liquid ratio?1. determine precipitation type
2. take into consideration the cross-section between omega and DGZ and relative humidity within and below the DGZ
3. forecast QPF
4. determine snow to liquid ratiosIf dry air (less than 70%) exists below the DGZ, what atmospheric process will occur?evaporation/ sublimation; limiting snow at the groundWhat are the omega values for the NAM that suggest heavy snowfall rates?-16 microbars/s or lessWhat are the omega values for the GFS that suggest heavy snowfall rates?-5 microbars/s or lessWhat are the omega values for the HRRR that suggest heavy snowfall rates?-90 microbars/s or lessPure water freezes at what temperature?-40 degrees Fahrenheit/ CelsiusWhat are the two characteristics that snow to liquid ratio depend on?- cloud physics
- vertical temperature profileThe closer to 0 degrees Celsius, the __________ (more/less) supercooled water is going to freeze.less likelyAdding moisture to a snowflake will ___________ (increase/decrease) the snow to liquid ratio and being close to 0 degrees Celsius.decreaseDecreasing moisture will _________ (increase/ decrease) snow to liquid ratio and be further from 0 degrees Celsius.increaseThe vertical temperature profile for winter weather can change during an event due to? (6)- sublimation/ evaporation (wet-bulb temperature)
- melting or freezing
- thermal advection
- vertical motion
- convection
- solar radiation (especially during spring)What factors influence the snow to liquid ratio? (5)- height of the bottom of the snow growth region
- temperature profile below the bottom of the snow growth region
- depth of any isothermal layers near 0 degrees Celsius
- surface and ground temperatures
- wind speedWhat is needed to have a high snow to liquid ratio? (2)- DGZ close to the surface
- temperature profile closer to -10 degrees CelsiusWhat is needed to have a low snow to liquid ratio? (2)- DGZ further from the surface
- temperature profile closer to 0 degrees Celsius
- isothermal layer close to 0 degrees CelsiusWhat is the average snow to liquid ratio?10:1What is considered a wet snow to liquid ratio?10:1 or lessWhat is considered a moderate wet snow to liquid ratio?12 - 18:1What is considered a dry snow to liquid ratio?20:1 or greater
