midterm Flashcards
What are some important reasons that we forecast the weather?
- What to wear
- Protect lives
- Large storm events
- Agriculture
- Transportaion
- a lot
What are the 3 main forecasting sectors?
- Broadcast
- Government
- Private
What are the major roles of the 3 main forecasting sectors, and how do they differ?
Government: Issues hazardous weather events with watches/warnings, short- and long-range forecasts, weather briefings/discussions. Dissemination through NOAA Weather Radios, Internet, smartphone apps
Broadcast: Share weather forecasts and related stories, as well as NWS advisories, watches and warnings
Radio, TV, Internet, Apps
Private: Forecast for businesses:
Utility companies
Renewable Energy Agencies
Insurance Companies
Agricultural Corporations
Could be its own forecasting business!
WeatherBug
AccuWeather
Weather Underground
How does Confidence change over time
You typically get less and less confident the farther out you attempt to forecast
What are the 4 forecasting methods?
- Trends
- Climatology
- Analog
- Numerical Weather Prediction (Consensus)
Which two forecasting methods are most useful, and during which type of scenarios are they most useful?
- Analog –> forecasting precip type and synoptic scale patterns
Lake Effect Snow
Pineapple Express
Severe Weather Outbreaks - Consensus –> Probability of Precipitation (PoP) forecasts
What does NWP stand for?
Numerical Weather Prediction
What is NWP?
A forecast model is a set (huge, thousands) of mathematical equations that describe how pressure, temperature, moisture, air density, and wind will change over time.
What are two major factors that influence the accuracy of a model?
- Quality of equations to predict atmospheric chaos
- Quality of observations
What are the 3 main American forecast models?
- NAM (North American Mesoscale)
- RAP (Rapid Refresh Model)
- GFS (Global Forecast System)
What are the characteristics and the strengths/ weaknesses of the NAM?
- Forecasts out 84 hours.
Run 4 times per day (00Z, 06Z, 12Z, 18Z).
12x12 km grid spacing.
Better for mesoscale analysis!
Takes about 2.5 hours to run.
What are the characteristics and the strengths/ weaknesses of the RAP?
Very similar to NAM. Uses different governing equations.
Forecasts out 18 hours.
Runs hourly! (Takes in new data every hour!)
13x13km grid spacing.
Takes a little over one hour to run.
Another version of RAP, known as the HRRR, also exists.
Generates data down to a 3-km grid for smaller regions of interest!
What are the characteristics and the strengths/ weaknesses of the GFS?
Observations/Forecasts on the global scale (Hemispheric/Synoptic).
Forecasts out 384 hours (16 days).
Run 4 times per day (00Z, 06Z, 12Z, 18Z).
13x13 km grid spacing.
Takes about 4 hours to run.
Great for synoptic weather pattern and long-term forecasting!
What does MOS stand for?
Model output statistics
What is MOS?
Aa statistical model that combines the NWP data with other local variables andruns through a set of regression equations.
Statistical blend of model output, climatological information, and past weather observations
Made for a specific observation station, not 3-D
Differences and similarities between MOS and NWP?
- NWP simplifies the upper-air analysis and synoptic features while MOS offers more surface features
- Large cities/ airports are the only places with MOS data
Be able to fully decode a MOS forecast from top to bottom.
do it dummy
Be able to prepare a basic technical Discussion based on given map analysis and NWP tools.
growls u know the drill buckaroo
What is the forecast funnel?
A breakdown of where to forecasting?!?1 girl idk
Describe each of the different scales within the funnel, and what observations are taken with each
Planetary Scale: Look at hemispheric patterns and how they will affect your forecast; WIND
Synoptic Scale: Looking more nationally, what systems may affect your forecast. “What is the problem of the day?; HOW WIND IS AFFECTING NATIONAL SCALE LIKE TROUGHS N RIDGES
Mesoscale: Regionally, what features are going to effect the overall processes?; TOPOGRAPHIC FEATURES, CONVECTION SHIT LIKE THAT
Local Scale: How will terrain and other features influence my forecast?; YER
Why is the forecast funnel useful for forecasting?
Using the knowledge of the scales of the atmosphere helps a better understanding of how to forecast for a local area. If you notice a rapidly developing mid-latitude cyclone on a synoptic level, it’ll help you prepare for possible severe weather in your forecasting area
What type of Lake Effect Snow bands are there?
- Wind Parallel Bands: occur across the shorter width of the lake. Generally associated with strong surface winds and shear.
- LLAP (Long-Lake axis parallel) Bands: occur in the middle of the lake and stretch it’s length to the leeward shore. Usually associated with the strongest LES events.
What ingredients are needed for Lake Effect Snow
- High/steep vertical temperature gradient
- Temp gradient between lake and 850 mb greater than 13ºC (23ºF).
The larger the gradient, the greater chance for intense snow bands
Increased instability! - Unfrozen Lake
- Large Fetch
- Fetch - The distance traveled by wind or waves across open water.
- Typically need a fetch length greater than 160 km (~100 miles)
What type of soundings produce rain/freezing rain/sleet/snow?
-Rain: Temperature is above freezing
- Freezing rain: top of sounding is below freezing –> large dip above freezing –> shallow surface freezing layer
- Sleet: Shallow freezing layer aloft –> deep freezing layer at surface
- Snow: Continuously below freezing
What synoptic parameters can we look at to predict rain vs. snow?
The 540 line
-The 1000-500mb thickness!
540 gpm line evaluated at 500 mb
Thickness is proportional to average virtual temperature between two levels of the atmosphere.
- Warmer air = thicker column
- Colder air = shallow column
So what is the height at 500 mb?
- Greater than 5,400 gpm = rain
- Less than 5,400 gpm = snow
Where on the 500 mb chart does the 540 line fall.
- North of the line: snow
- South of the line: rain
What are the typical characteristics with the upper levels of the atmosphere?
The Planetary Scale:
- Examine changes in the hemispheric pattern over past 3-5 days:
- Look at progression of Rossby waves (i.e. troughs and ridges) at 300 and 500 mb.
- Are there blocking patterns?
- Is the flow mostly zonal or are there waves?
Synoptic Pattern:
- Warm and cold air advection
- Frontal systems
- Jet streaks
- Rossby waves (i.e. troughs/ridges)
- Cyclones/anticyclones
Mesoscale Processes:
- Convection
- Topographic/geographic effects (i.e. upslope, mountain-valley circulation, urban heat island, land/sea breeze circulation, cold air pooling in low area)
- Remnant outflow boundaries or mesoscale convective vortices (low pressure generated from convection) from previous convection
- Lake effect snow (often poorly resolved in models!)
How are these observations taken? What products are useful in this analysis?
Radiosondes/Rawinsondes (wind speed and direction)/Soundings (weather balloons)
What are the 5 standard levels of analysis?
Surface
850 mb (1500 gpm)
700 mb (3100 gpm)
500 mb (5500 gpm)
250/300 mb (9300 gpm)
(250/300 mb) What is the Jet Stream? What are its characteristics?
- High velocity river of air that flows “completely” around the Earth at mid latitudes.
- Very well defined at 200 mb in the summer (300 mb in the winter).
What can the Jet Stream provide in regards to our forecasts?
- Strength dependent upon the temperature difference between the two air masses.
- The jet stream is strongest during the winter, when the temperature difference is greatest. (More equatorward)
- The jet stream is weakest during the summer because the temperature difference is smaller. (More poleward)
What is Geostrophic flow? How does it relate to the Jet Stream?
- Flow is assumed to be parallel to the height contours (Isohypses)
- Steers major weather features at all levels of the atmosphere!
What are the 2 main types of flow and their characteristics?
- Subgeostrophi: occurs when the centrifugal force counters the PGF via the geostrophic balance model. Winds are expected to be slower than geostrophic speed (Troughs)
- Supergeostrophic: occurs when the centrifugal force enhances the PGF. Winds are expected to be faster than geostropic speed (Ridges)
Be prepared to discuss the different types of trough Orientation
okay pookie!
What is a Jet Streak?
- Characterized by areas of strong convergence and divergence
Be able to fill in/label the Jet Streak Schematic
slide 15 in the 250/300/500 mb ppt :smork:
What can Jet Streaks signify in regards to a forecast?
- Typically the primary weather makers in a trough
- Capable of amplifying/weakening troughs and ridges
(500 mb) What is Vorticity?
Vorticity (Relative):the clockwise or counter-clockwise spin of the atmosphere inrelation to a vertical axis
What two types of vorticity do we observe? What do they mean for surface features?
In Northern Hemisphere:
-AV (NVA)= anticyclonic= negative vorticity; sinking air and increasing geopotential heights
-CV (PVA)= cyclonic= positive vorticity; rising air and falling geopotential heights
Vorticity (Absolute):= Relative vorticity + Coriolis Force (lat.)
- Abs vorticity is what’s plotted on the 500mb constant pressure chart
- Almost always + because planet vorticity is greater than relative vorticity
How does vorticity relate to the Jet Stream Schematic?
- Cyclonic vorticity in areas of DIV, positive vorticity with Lows
- Anticyclonic vorticity in areas of CON, negative vorticity with Highs
(700 mb) Shortwave vs Longwave features
Longwave Flow Pattern:
- Typically >1000 km
= Warmer under ridges, cooler under troughs
- Standard trough/ridge size we are used to
- Pay attention to the axis of orientation (mostly for troughs)
If the trough is tilted from NW to SE (negative), it means the low pressure has reached its “maturity” and is usually unstable (clouds/precip/storms).
- Also be aware of how tight the Isohypses are together (gradient). This helps you understand how the longwave pattern is going to progress over time.
Tighter gradient, faster progress. Typically W→E
Shortwave:
- A “kink” in the height contours is typically indicative of a shortwave flow pattern.
Like a small bump within the longwave flow pattern.
- With these shortwave patterns, it is important to determine if it is Barotropic or Baroclinic:
Barotropic: A region of uniform temperature distribution; a lack of fronts. Weather features remain fairly static (typically with ridges/zonal flow)
Baroclinic: A region with a distinct difference in air masses (a separation of warm/cold air) Surface frontal boundaries usually present (typically with troughs and developed low pressure systems). Will likely amplify the ridge/trough. - Usually great areas of temperature advection (especially with troughs/fronts)
Cold air to the left of the shortwave trough axis, warm air to the right
(700 mb) Vertical Velocities
Negative = Sinking Motion
Regions of surface CAA, negative vorticity adv.
Positive = Upward Motion
Regions of surface WAA, low level convergence, positive vorticity adv.
Correlates with jet streaks and vorticity advection similar to upper levels
(700 mb) Dewpoint Depressions
The difference between the air temperature and dew point of an area. The smaller the value, the greater the RH.
Can be indicative of instability
More moisture (higher RH), more unstable
Saturation of mid-levels (detects if vertical motion is resulting in clouds/precip)
Very helpful in forecasting clouds, depending on the direction of motion
Upward vertical motion + high RH (low DPD) = cumulus clouds
Horizontal motion (limited vertical motion) + high RH (low DPD) = stratus clouds
(850 mb) Be prepared to discuss temperature advection and how it affects surface features.
Regions where isotherms cut across isohypses
- Baroclinic environments
These help dictate how highs and lows strengthen or weaken
(850 mb) Be prepared to identify and discuss Low Level Jets and their role in Low Pressure development.
A channel of increased winds near the surface located in the warm sector of a mid-latitude cyclone (Between a SE High and a NW low)
Typically synoptically driven by MLCs
Forms due to the PGF between high and low pressure which is turned to the right by the Coriolis Force
Can happen pretty much anywhere a MLC exists.
Efficient in transporting warm, moist air northward (may also increase severe wx %)
