Before I get into today's rain threat...I did want to take a moment to explain "rain chances". We use that % a lot on TV, but on days when we have 10 or 20% rain chances in the forecast..and storms hit..some get upset saying "ummm looks more like 100% to me". Well in a way, they would be correct and yet wrong.
Let me explain.
Below is the "official" explanation of what a rain chance is. We call them POPS in the meteorology world. Which stands for Probability of Precipitation. Below is the defintion that the NWS in Atlanta put out not long ago:
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What does this "40 percent" mean? ...will it rain 40 percent of of the time? ...will it rain over 40 percent of the area?
The "Probability of Precipitation" (PoP) describes the chance of precipitation occurring at any point you select in the area.
How do forecasters arrive at this value?
Mathematically, PoP is defined as follows:
So... in the case of the forecast above, if the forecaster knows precipitation is sure to occur ( confidence is 100% ), he/she is expressing how much of the area will receive measurable rain. ( PoP = "C" x "A" or "1" times ".4" which equals .4 or 40%.)
But, most of the time, the forecaster is expressing a combination of degree of confidence and areal coverage. If the forecaster is only 50% sure that precipitation will occur, and expects that, if it does occur, it will produce measurable rain over about 80 percent of the area, the PoP (chance of rain) is 40%. ( PoP = .5 x .8 which equals .4 or 40%. )
In either event, the correct way to interpret the forecast is: there is a 40 percent chance that rain will occur at any given point in the area.
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Okay, so...'coverage area' and 'chance of a given point' are both used. NWS likes the "given point" idea, I personally think you, the viewer, understand "coverage area" better. So that is how I put together chances for rain each day.
I think most understand that if the chance is 30%, then 30% of our viewing area will see rain that day. Pretty simple.
Today's chance: 60% is where I am leaning right now.
We certainly do not want a repeat of yesterday....here is the rain estimates from the radar out of INDY (Lou reset their radar this morning back to 0").
Some reports of 4-6" in Henry County were received. Amazingly, the west end of Jefferson County (not to mention most areas west of I 65) did not see one drop.
Today, the wind fields are a bit stronger. This means the storms at least will have movement to them. While heavy rain/flash flooding can't be ruled out---6" rain totals are not expected.
The downside to the slightly higher wind field today is that the thunderstorms can tap into that wind and push it toward the ground. That could lead to severe thunderstorm warnings as well as gusts up to 60 mph would be possible.
SPC OUTLOOK: we are in the "see text" area...which is below SLIGHT RISK
Tornado Threat (east) Hail threat (not outlooked) Wind threat (5%)
Storms are approaching as I type...and the latest RUC has a good handle on this.
Late morning-- pretty much how the radar looks now. Storms moving in from the west
Early afternoon- that line arrives, but new development in advance of it takes place
Late afternoon-- storm threat shifts mainly to the KY side of the Ohio River.
We will watch the radar carefully. When it is not raining---it will be quite warm with highs near 90.
MONDAY: storm threat should be mainly east of I 65. Kept 10% rain chance in for now. Highs likely to cross 90.
The heat will be the big story this week. Highs will vary as areas that see/saw no rain this weekend---likley to push 94/95 degrees. If you saw rain, shave about 2-3 degrees off that. And given how spotty the rain was---forecasting highs this week won't be fun :)
The hottest day looks to be Thursday...look at how the heat shown here on the EURO surges all the way to Canada!
There is a front slated for next weekend...Fri/Sat. But the models have backed off on the intensity of this front. If that is the case, the heat may last through the weekend into the next week. There are signs of a cool down for the last few days of June. We'll let ya know.
Tropics wise:
Models still do not know what to do with the energy in the Gulf of Mexico. It will be slow moving ...that appears likely. So we will have time to track anything that does develop.
CMC models takes it close to LA next week.
GFS drifts it into Central America.
Again, do not adjust vacation plans along the Gulf/SE coast as the models have not locked in on development and the track of such. We will keep you posted.
NOTES TO PASS ALONG:
We are close to 30,000 likes on facebook!!
Please "share" this link with your friends/family to get the latest updates on our weather. When you click the "share" button...it will post to your wall. Thanks in advance!
And finally, this will be my last post for awhile. I am taking a vacation----so I will see you before the month ends.
Take care everyone :)
Great post this a.m.; loved the information! Have a super goode vacation & we'll try to hold down the fort for you. LOL
Posted by: Troy Carter | June 17, 2012 at 01:29 PM