Interpreting Four-Panel Progs: Taking the Next Step in Your Forecasting Apprenticeship
Please don't be intimidated by the four-panel prog we just showed you (we show it again below for convenience). Yes, there are a lot of lines and a lot of colors, but we believe you will be able to interpret these charts by the end of this chapter, and thereby be in a position to access current progs on the Web and gain a sense for the short-term forecast at any place in the country.
Your first step as an apprentice forecaster is to master the time codes listed below each panel. After all, if you don’t know the time when the model was initialized and the forecast time when the prog is valid, you might apply the guidance to the wrong future time, causing your forecast to “bust.”
Let's get up close and personal with initialization and forecast times by zooming into the code below the upper-left panel (see image below). First of all, the "WRF-NMM" indicates that we've accessed the WRF model (in case you're wondering, the "NMM" stands for "Nonhydrostatic Mesoscale Model").
Okay, back to the business at hand. Following a fundamental rule of forecasting, you must first determine when the model was initialized so that you're sure you're looking at the most current computer guidance. Focus your attention on the bottom entry, INITIAL TIME = 090211/1200F006. The first two digits represent the year (2009), the middle two digits correspond to the month (February), and the last two digits represent the day (the 11th). The 1200 indicates that the WRF was initialized at 12Z on this date(0000 would indicate 00Z as the initialization time). Putting it all together, the WRF run for this specific prog was initialized on February 11, 2009, at 12Z. Finally, F006 means that this WRF prog was the six-hour forecast ("F" stands for "forecast").
It's not rocket science to deduce that this prog should be valid six hours after the initialization time...at 18Z on February 11, 2009. The top line of time code, 090211/1800V006, verifies our simple deduction. Keeping in mind that the "V" stands for "Valid", 090211/1800V006 translates to: "This six-hour forecast is valid at 18Z on February 11, 2009." So we were correct!
Although it might seem a bit tedious to you, always remember to check the time and date that a specific prog is valid before you use it to make your forecast. There's nothing more embarrassing to a forecaster than using the wrong computer guidance!
Okay, let's get down to brass tacks and learn how to interpret the four panels on a standard prog.