1. WX-352 Weather Forecasting

2. PG-13 Weather Joke
This had most of the state of Michigan laughing for 2 days and a very embarrassed female news anchor who will, in the future, likely think before she speaks. What happens when you predict snow but don't get any. A true story... A female news anchor that, the day after it was supposed to have snowed and didn't, turned to the weatherman and asked: "So Bob, where's that 8 inches you promised me last night?"
Not only did HE have to leave the set, but half the crew did too they were laughing so hard!

3. TV Weatherman in Serious Need of Medication

5. Four Forecasting Steps:
1) Assess the present state, called the analysis, by plotting 6 hourly surface and 12 hourly sounding data
2) Predict a future state by running a computer model of weather changes…
3) Interpret the model results, called a prognostic chart, given forecasting experience…apply ROTs
4) Translate forecast into something that is useful

6. Persistence Forecast Method
The persistence method works well when weather patterns change very little and features on the weather maps move very slowly. It also works well in places like southern California, where summertime weather conditions vary little from day to day.

7. Trend Forecast Method
Determining motion of systems, and projecting that motion into the future
Frontal and air mass movement

8. Analogue Forecast Method
Figure 14.7

9. Forecast Using Climatology
Using long-term average weather to predict future conditions
Most useful for long-range forecasting
Includes probability forecast methods

10. Climatology--Winds

11. Forecasting Using Probability
Figure 14.6
- Climate records can be used to generate probability forecasts for a given event.
-- Florida has less than a 5% chance of snow on December 25th, while northern Minnesota has had snow on that date for each of the past 30 years.

12. Numerical Weather Prediction (NWP)
At 00Z and 12Z each day, data is collected and NWP models are run
NWP is the 2nd largest user of super computers in the world

13. NWP--Limitations
While NWP has greatly improved the accuracy of weather forecasts, it still haves significant limitations
Usually the best method for forecasting weather 12 hours to 5 days in the future

14. When Forecast Models “Go Bad”…

15. Ensemble Modeling
Numerical weather models are run multiple times with small changes in the initial conditions
Gives forecaster a good estimate of the possible range of weather conditions at a future times
“Spaghetti Chart” helps forecaster to know where/when to rely on the NWP model, and where/when to ignore the NWP model

16. Weekly and Monthly Forecasts
30-90 day outlook of weather conditions
Doesn’t give a specific forecast
Warmer or cooler (wetter/dryer) than normal
Uses ensemble modeling and analogue methods
Slightly better than climatology alone
These 90 day outlooks were downloaded after Christmas, How accurate do you think they were?
Figure 14.8A
Figure 14.8B

17. Forecast Periods Nowcasting (less than 6 hours)
Mainly surface observations, weather satellite and radar, and persistence or trend forecasts
Short-range (<3 days)
Trend and analogue methods, weather charts and numerical weather forecast products
Medium range (3-8 days)
Analogue forecasts, numerical weather forecast products, climatology
Long-range (>8 days)
Climatology; NWP Ensembles

18. Accuracy and Skill
How good are weather forecasts??
0-24 hours: very good
2-5 days: fairly good
Beyond 7 days: slightly more accurate than persistence
Accuracy—what is considered “right”?
If the TAF called for rain, and it rains in FWB (but not at HRT), the forecast is wrong
Skill—how complicated/hard is the forecast
Southern California in summer…easy or difficult?
Exactly where and when a tornado will touch down…easy or difficult?
Where they are likely to form--not difficult 3 days in advance
Precise area struck--fairly easy a few minutes in advance
Forecast skill is determined by comparing our forecast against either persistence or climatology
If we’re no better than persistence or climatology—why bother?

19. NWS Probability of Precipitation
Probability of Precipitation (PoP) describes the chance of an event occurring at any point in the forecast area, over a certain period of time (usually 12 hours).
PoP is defined as: PoP = Pa x Pc, where:
Pa =the probability that precipitation will occur somewhere in the forecast area during the forecast period and           
Pc =the percent of the area that will receive measurable precipitation, if it does occur

20. Forecast Product Accuracy

21. Forecast Practice
Scenarios

22. Forecasting with Surface Charts
This simplified 6 AM Tuesday surface weather map is useful for short time interval predictions of fronts and associated weather.

23. Surface Chart Predictions
- 3-hour pressure tendencies plotted on isallobar maps help predict the movement of highs and lows
Lows tend to move toward the region of greatest pressure fall, while highs move toward the region of greatest rise.

24. Upper Level Charts
Figure 14.11
Upper level winds guide the path of surface pressure systems.

25. Observed Movement of Fronts
Surface weather observations from 6 PM Tuesday and 6 AM Wednesday show how the fronts, pressure systems, and precipitation have moved as predicted.

26. Forecast
Using both trend and persistence forecast techniques, what is your forecast for 24 hours from now in:
Denver? Dallas? Chicago? Memphis?
Washington? Augusta?
Tues 6am
Wed 6am

27. Observed Weather for 6 AM Wednesday

28. Another Scenario: Forecast for central CA coast for tomorrow
Slowly falling barometer and increasing high clouds
Weak low pressure in Pacific.....
Will it rain, or not??

29. Surface Weather for 4 PM Sunday
Look at 500mb chart for clues:

30. 500 mb Chart for 4 PM Sunday
564 line across the area (local ROT); Omega High present…but cold advection and shortwave may change the stagnant upper pattern; upper-level divergence??

31. 12, 24, & 36 hour Progs
Forecaster has access to several forecast models
-Which one is best?
-- Choice is based on initialization and experience….

32. Surface Weather Map for 4 AM Sunday

33. 500 mb Chart for 4 AM Monday

34. IR Satellite for 6:45 AM Monday

35. Surface Weather Map for 4 AM Monday

36. Visible Satellite for 9 AM Tuesday

37. Forecast Applications

38. Weather Impacts on Aviation Mishaps
88% of all weather-related aircraft mishaps occurred under IMC (Instrument Meteorological Conditions)
83% of fatal crashes involved FAR Part 91 (General Aviation) aircraft

39. Weather Impacts on National Airspace System

40. Wx Impacts on Flight Operations

41. < VFR Conditions ceiling (broken or overcast cloud bases) are more than 1,000 feet above the ground, and the visibility is three miles or more, the weather is VFR.

42. Types of Flight Weather Briefings
Briefings and Advisories: All pilots must obtain a formal weather briefing during preflight. Based upon the following pilot's information a briefing is given:
Type of flight (VFR or IFR), aircraft type, departure and destination airport, flight route, flight altitudes, estimated time of departure (ETD), estimated time of arrival (ETA)
There are three types of briefings that are offered to pilots by "pilot weather briefers" who have been certificated by the National Weather Service, and work at local Flight Service Stations and Weather Service Offices.
Pilots need to know which weather briefing to request:
The Standard Briefing
The Abbreviated Briefing
The Outlook Briefing

43. Types of Flight Weather Briefings
1. Standard Briefing is the most complete weather briefing and for the pilot who does not have an opportunity to gather any other weather data. Includes:
Adverse weather conditions expected
VFR (visual flight rules) flight not recommended
Synopsis
Current conditions
En route forecast
Destination forecast
Winds aloft
Notices to airmen (NOTAM)
ATC (air traffic control) delays
2. Abbreviated Briefing is for pilots who need to update previous weather data they have gathered, or who only need a few bits of weather data to complete their weather picture.
3. Outlook Briefing is requested by pilots whose departure time is 6 or more hours away. The briefer then gives forecast information appropriate to the proposed flight route. This will assist the pilot in making an initial decision about the feasibility of such a flight.