Reminders:

1
Reminders

• 1. Assignment 4 handed out today due Thursday
  December 4th.

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Exam 2
Bubble answers
Short answers
Exam 2 curved to make median 80 curve 2
points
F D- D D C- D C B- B B A- A
F D- D D C- D C B- B B A- A
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Exam 2 short answer questions

• Zonal flow is E-W or W-E, parallel to lines of
  latitude. Meridional flow is N-S or S-N,
  parallel to meridians.
• ITCZ affects regional weather, e.g. where rains
  do and do not occur in the Sahael region of
  Africa. As the ITCZ migrates north-south with the
  seasons, so does the region receiving (no) rain.
  OTHER EXAMPLES Subpolar jet can bring storms and
  cold, arctic air down to the lower 48. The
  strength of the jet is stronger in the winter
  than in the summer.
• There would be a trough dipping down so
  somewhere south of the Great Plains, and a ridge
  north of the east coast. The magnitude of the
  wave would be large.
• Major wind systems Monsoons, foehn (chinook,
  Santa Ana), katabatic, sea and land breeze,
  valley and mountain breeze.
• Must include why they develop e.g. low pressure
  over Asia creates the monsoons high pressure
  over the Great Basin moves air from E to W, over
  mountains, and air warms adiabatically as it
  descends into S. CA. Katabatic winds develop
  where cold air collects, and then descends
  because it is dense.

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Exam 1 short answer questions

• 75.
• a. Conditionally unstable
• b. 200 m
• California current off coast is cold, preventing
  warm front from developing AND high pressure cell
  sits off the coast in the winter and summer .
• Warm belt, originates at the surface
• Cold belt, originates at the surface
• Dry belt, originates in the upper atmosphere

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Exam 2 short answer questions

• A waterspout is a tornado that moves or occurs
  over water. It differs from a tornado in that is
  it usually smaller and has lower winds. It does
  not pick up water from the ocean.
• No, hurricanes do not cross the equator. For one
  thing, they require a Coriolis force, which is 0
  at the equator.
• Current conditions neutral, or very mild La
  Nina, ENSO near 0 or slightly positive
• (a) Neutral conditions few SST anomalies cold
  water from upwelling off the western coast of
  South America, warm waters in the western
  tropical Pacific.
• (b) Negative ENSO El Nino warm water in
  eastern tropical Pacific
• (c) Positive ENSO La Nina larger area of
  cold water in the eastern tropical Pacific
• EC1 Mount Baker Lodge, Washington, 1998-1999
  season, 95 feet (1140 inches)
• EC2 Super Typhoon Tip, (October) 1979, 2200 km
  diameter.

6
Weather Forecasting and Analysis

• Forecasting methods
• Forecast types
• Assessing forecasts
• Forecast procedures

http//www.cpc.noaa.gov/products/forecasts/
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Forecasting Methods

• What do you need to consider when forecasting?
• Water vapor distribution
• Clouds type, thickness
• Precipitation amount and form
• Winds speed and direction
• ALL X 3 DIMENSIONS!!!

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Forecasting Methods

• 1. Climatological forecasts
• predict the climatology for a region
• e.g., Thanksgiving in Bozeman? http//www.weather.
  gov/climate/xmacis.php?wfotfx

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Forecasting Methods
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Forecasting Methods

• 2. Persistence forecast
• Predict current conditions
• E.g. http//www.wrh.noaa.gov/mesowest/getobext.php
  ?wfotfxsidKBZNnum168raw0dbnm

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Forecasting Methods

• 3. Analog approach
• Find similar situations from the past and predict
  similar outcome
• E.g., It always snows on homecoming
• E.g., It snows more during La Nina years

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Forecasting Methods

• 4. Numerical weather forecasting
• Simulate actual behavior of the atmosphere
• Explicitly compute the evolution of wind,
  pressure, temperature, etc.
• Obtain a depiction of the 3-D state of the
  atmosphere for a moment in the future

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Types of Forecasts

• Quantitative
• high of 54F
• 2 inches of snow
• Qualitative
• Provides categorical information
• rain vs. no rain
• partly cloudy
• above normal
• Probability Forecasts
• Chance that some event will occur within the
  forecast area at some point over the forecast
  period.
• E.g., http//www.wrh.noaa.gov/tfx/main.php?wfotfx
  sidtfxpilzfp

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Assessing Forecasts

• Forecast value
• usefulness of a forecast
• Forecast quality
• Agreement between forecast and observations
• Accuracy
• Precision

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Assessing Forecasts

• Forecast bias
• Over or under prediction
• Forecast skill
• How much better is the forecast as compared to an
  uninformed prediction?
• E.g., forecast vs. climatology, forecast vs.
  persistence, etc.

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Data Acquisition and Dissemination

• World Meteorological Organization (WMO)
• Oversees collection of weather data across the
  globe, from 179 nations
• 10,000 land observation stations
• 7000 ship stations
• 300 ocean buoys
• Weather satellites
• Upper air-data from 1000 weather balloon sites 2x
  daily
• LOTS OF DATA sent to World Meteorological
  Centers Washington, DC Moscow, Russia
  Melbourne Australia

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Data Acquisition and Dissemination
Textbook Fig. 13-4
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Forecasts Procedures

3. Post-processing Phase

Gridded fields 3-D data of a particular variable

Extract useful data from the model simulations,
e.g.

Sea-level pressure maps

500 mb heights

Precipitation amounts

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Forecasts Procedures Textbook Fig. 13-5
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Forecasts Procedures

3. Post-processing Phase

Gridded fields 3-D data of a particular variable

Extract useful data from the model simulations,
e.g.

Sea-level pressure maps

500 mb heights

Precipitation amounts

Model output statistics (MOS) secondary
variables (e.g. min/max T, dew point, wind, PoP)
based on statistical relationships between model
output and observation in the past.

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Forecasts Procedures

MOS vs. humans

Textbook Fig. 13-8
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Forecasts Procedures MRF

• Medium Range Forecasts (MRF)
• 72 hours 7-10 days
• model results can be very sensitive to staring
  conditions!
• Ensemble forecasting
• Uses a number of different runs for the same
  forecast period, with slightly different starting
  conditions.
• Evaluate variability between runs, or use mean of
  all runs for your prediction (e.g. Global Climate
  Models as well see)

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Forecasts Procedures MRF

• 10-day ensemble for 500 mb layer

Textbook Fig. 13-9
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Forecasts Procedures LRF

• Long-range forecasts
• 1 week to the limits of the models
• Climate Prediction Center (CPC)
• http//www.cpc.noaa.gov/products/forecasts/
• Methods
• Climatology
• Statistics
• Numerical models
• Subjective judgment

Textbook Fig. 13-9
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Weather Maps and Images

• Go over tutorial on class CD.