I have been attempting to develop a severe weather probability formula that will be good for a baseline in severe weather outlooks for combined threat probabilities to get a better idea of whether or not we're looking at a Slight Risk, etc. So far it is still in its "rough draft" stages but the results have been decent so far so I thought I'd put it out and see how it does for awhile.

prob of svr = (S/40) * P * [(Ö(C) - 2*|L|) + (D-60)]

S is deep layer shear, P is the probability that thunderstorms in general will occur, C is effective CAPE, L is effective LI, and D is surface dewpoint in degrees Fahrenheit. Negative values indicate a probability of effectively 0. Because nothing is a certainty, as a general rule make values less than 1 equal to 1 and greater than 99 equal to 99. Probabilities are for the occurance of severe weather within 25 miles of a point for the time that you calculated, +/- 30 minutes.

In order to make the probability more accurate, you need to multiply your final answer by a time coefficient. Severe weather occurs more frequently at certain times of the day on average and thus this will lead to a better overall degree of confidence. If you were forecasting similar squall lines in similar situations, one at night and one during the day, you would generally expect the squall line in the day to have a better inherent threat of severe weather.

According to the National Oceanic and Atmospheric Association (NOAA), the new Enhanced Fujita Scale will be implemented operationally in February of 2007. No worries though! F5 damage in the past will still be F5-type damage now, and so on, so forth. The only change is the wind speed. Winds at the surface, based on engineering/wind-tunnel tests, are much lower than previously estimated on the Fujita Scale. In addition there are now 28 damage indicators to base the damage assessment on, while the previous Fujita Scale only had standardized house assessments.

Operational EF Scale (Feb 2007)