The Forecast Process

The Forecast Process• Step 1: What is climatology for the

location in question? What are the record and average maxima and minima? You

always need very good reasons to equal or break records.

• Step 2: Acquaint yourself with the weather evolution of the past several days. How has the circulation evolved? Why did past forecasts go wrong or right?

• Step 3: The Forecast Funnel. Start with the synoptic scale and then downscale to the meso and local scales. Major steps:I. Synoptic Model EvaluationWhich synoptic models have been the most skillful during the past season and last few days? Has there been a trend in model solutions? Have they been stable? Are all the model solutions on the same page? If so, you can more confidence in your forecast.Evaluate synoptic ensemble forecasts. Are there large or small spread of the solutions?Which model appears to most skillful today based on initializations and short-term (6-12h forecasts)?

Satellite imagery and surface data are crucial for this latter step

II. Decide on the synoptic evolution you believe to be most probable. Attempt to compensate for apparent flaws in the best model.

III: Downscaling to the mesoscale. What mesoscale evolution will accompany the most probable synoptic evolution?

This done in a variety of ways:

a. Subjective rules and experience: e.g., the PSCZ occurs when the winds on the WA coast are from the W to NW? Onshore push occurs when HQM-SEA gets to 3.5 mb. Knowledge of these rules is a major component of forecast experience.

Typical diurnal wind fields in the summer.

b. High resolution mesoscale modeling: e.g., WRF, NMMB.

Clearly becoming more and more important

c. Model Output Statistics (MOS, for some fields)

IV. Downscaling to the microscale for point forecasts.

Subjective approach using knowledge of terrain and other local characteristics.

For subjective forecasts remember the approach: It is nearly impossible to forecast a parameter value from first principles--so consider what has changed.

STEP 4. The Homestretch• Combine the most probable synoptic, mesoscale, and

microscale evolution in your mind to produce a predicted scenario

• Attempt to qualify the uncertainty in the forecast. Synoptic and mesoscale (SREF) ensemble systems are becoming increasingly important for this task.

• Ask yourself: am a missing something? Am I being objective? Overcompensating for a previous error? Check forecast discussions from other forecasters to insure you are not missing something.

The Future Role of Human Forecasters

• Humans will still play crucial roles:– Short-term forecasts is where our imagery

interpretation abilities are critical.– For communicating and interacting with

growing user communities.– For producing watches and warnings – For watching over automated systems– To continue local research.