I May Be Stirring Up Something But...

[wx247]

I remember a previous discussion in here about the NWS POP (prob. of precip) and I believe it was Tom (forgive me if it was someone else) that said the NWS uses that as a general wash. For example, if your forecast says a 20% chance of rain, it meant that 20% of the County Warning Area would receive.

If I misunderstood the point I am sorry, but if I didn't then when I was on the NWS web page this morning this point was brought up to me. In different parts of the Springfield CWA, there are different percentages of pops... for example, Monett has a 30% chance on Wed. while Joplin has a 40%. They are both under the same jurisdiction so wouldn't that mean that POPs would be the chance of rain in any given area?

I have thoroughly confused you by now probably, but hopefully someone will be able to coorespond and clarify my dilemma.

THANKS!

[therock1811]

Oh that's ok Garrett. It was actually my question.
That's an excellent point, however this would be an example of probability in a given area.

[wx247]

Yes... it would probability of precip. @ my house vs. what someone else said the definition was. They said that it meant the probability of precip. anywhere in the CWA. If that was so, there would be a blanket pop for the whole area wouldn't there?

[therock1811]

It probably would. However most NWS offices separate their CWA's into more "manageable" pieces.

[David]

Well, the reason why the NWS has diff pops on different cities is because of Zone Forecasts, when you click on a county. Something like TWC or your local news station still has pops for all the county area.

[Aslkahuna]

are just that-probability of precipitation. Depending upon the forecast product used, it could be the probability that measureable rain would occur somewhere in a general area or at a specific location. Most WSFOs forecast for zones and different zones (and those localities within the zones) might easily have different POPs-such, for example would be the general rule here in AZ for winter storms where usually the POPs are highest in northern AZ, the Rim and Whites, around Phoenix and western AZ tapering off to low values in the SE corner of the State (unless we have a situation that doesn't follow the general pattern for winter storms) while POPs work the other way during the monsoon being highest in the eastern part of the State and Mountains dropping off into the SW corner of the State.

Steve

[Guest]

Alot of it depends on as well as to where the reporting stations are located............Like lets say for example Philly...............There for example twc has two reporting stations for Philadelphia one is at the Philly INT which is located in South Philly and then they have one that is located on the otherside of the city in NE Philly at a smaller airport.........In such circumstances like this you will get two different forcast at times with precip pops..........Meaning the southern location may have a 40% chance of showers while the one up to the ne may have a 30% this is where reporting stations come in...............This is the case in larger towns and cities that have more then one reporting station.................Like here for example the city of Columbus has like 4 reporting stations and many of times in the winter they all didnt exactly match up..................So this precip pops thing depends alot on the closet reporting station to your location and who you get your forecast from.........Here where i am at its done by county with the nws meaning when they say we have a 30% chance of precip it goes for the whole county and not just my town.....................I hope this helps some..........

[ColdFront77]

Yes, Garrett... I brought up the issue and then Jeremy brought up a question on the issue.

[wx247]

Yeah... I know it was done by county. I was just trying to figure it all out. It is a confusing issue which mets don't even tend to agree on. Thanks for your info. everyone!