Rain is on the Way.

Since the next 48 hours will see the best chance of rain we have had around here in quite awhile, thought an explanation of the probability of precipitation (PoP) or the chance of rain that you see on the forecast graphics may be in order. Strictly speaking, the percentages you will see on weather forecasts are an attempt to express the uncertainty of a weather event (precipitation) occurring at any location within the forecast area and during the designated time frame. It is actually the product of two separate percentages. One is the percentage chance that any measurable precipitation will occur at all within the forecast area and the other is the percentage of the forecast area that may receive measurable precipitation given that precipitation occurs and during the specified time period.

That may seem a little confusing, so let me give a couple of examples. For tonight, rain is expected to be moving into NE OK and by morning the entire forecast area is expected to have received measurable amounts of rainfall. So, the chances of it raining at all are 100% and the areal coverage is 100%, so the product of those two is a 100% chance that any one location will receive measurable rainfall during the night. Notice I did not say that it would rain all night long, just that there is a 100% chance that measurable rainfall will occur at some time during the night.

Another example would be a Spring-time event in which there is an 80% chance that rain will occur at all, but if it does rain, only 40% of the forecast area would be expected to receive measurable rainfall. In that example, the chances of any one location receiving measurable rainfall during the forecast time would be the product of those two percentages or 32% which is rounded to 30%. In terms of how those two individual determinations are made, that is where some sophisticated statistical techniques are employed and I sure don't want to get into that.

Don't know if that helps or not, but perhaps it provides a little better insight into what the technical definition of PoP is. As mentioned, rain is expected tonight and should be moving into the metro area by around 11 or 12. The rain will be widespread for the rest of the night with some breaks possible by afternoon and tapering off from west to east late in the day. A few showers may linger into the day Thursday followed by some afternoon sunshine.

Temperatures will drop into the 40s when it starts raining and pretty much stay there through Wednesday. We should see a rebound into the 50s for Thu and Fri before another cold front arrives Friday evening or night. There is even a slight chance of some flurries along the OK/KS state line Friday night followed by a cold, breezy Saturday. Sunday and early next week will see a quick rebound in temperatures though.

So, stay tuned and check back for updates.

Dick Faurot