Author Topic: Microclimates  (Read 1558 times)

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Offline SLOweather

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Microclimates
« on: April 02, 2012, 10:38:24 AM »

Offline Farmtalk

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Re: Microclimates
« Reply #1 on: April 04, 2012, 09:25:43 AM »
Our highest peak in West Virginia is Spruce Knob...At the base (2,500 ft) it will be in the middle 70s during the summertime, but at the top of the peak its rare to hit 55!

Thats a great comic! :lol:
Joe Fitzwater
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Offline Lefty

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Re: Microclimates
« Reply #2 on: April 05, 2012, 11:44:55 AM »
That's exactly why I got my weather station. We can have clear skies and calm winds up here where I live, while 10 miles down the road in town it will be raining cats-and-dogs. I got tired of hearing that my house just lived through an apocalypse to come home and find out that it was a perfectly nice (if hot) day.

In my 20 years in AZ, I've learned one thing: when the forecast calls for 10% chance of rain, it isn't that everyone has a 10% chance of getting some rain, it means that somewhere in the metro area 10% of the city will have a 100% chance of rain, while everyone else will have a 0% chance.
-Steve- Peoria, AZ
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Offline ocala

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Re: Microclimates
« Reply #3 on: April 05, 2012, 01:45:07 PM »
That's exactly why I got my weather station. We can have clear skies and calm winds up here where I live, while 10 miles down the road in town it will be raining cats-and-dogs. I got tired of hearing that my house just lived through an apocalypse to come home and find out that it was a perfectly nice (if hot) day.

In my 20 years in AZ, I've learned one thing: when the forecast calls for 10% chance of rain, it isn't that everyone has a 10% chance of getting some rain, it means that somewhere in the metro area 10% of the city will have a 100% chance of rain, while everyone else will have a 0% chance.
Very good way of stating that Lefty. =D>
The blues had a baby and they named it Rock & Roll

Offline Farmtalk

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Re: Microclimates
« Reply #4 on: April 07, 2012, 01:49:50 PM »
That's exactly why I got my weather station. We can have clear skies and calm winds up here where I live, while 10 miles down the road in town it will be raining cats-and-dogs. I got tired of hearing that my house just lived through an apocalypse to come home and find out that it was a perfectly nice (if hot) day.

In my 20 years in AZ, I've learned one thing: when the forecast calls for 10% chance of rain, it isn't that everyone has a 10% chance of getting some rain, it means that somewhere in the metro area 10% of the city will have a 100% chance of rain, while everyone else will have a 0% chance.

Bravo! That IS a great way of stating that. I always considered a 10% chance of rain as saying that 10% of the viewing area is likely to receive rain and the other 90% stay dry
Joe Fitzwater
Chief Meteorologist for WVNS-TV 59 in Beckley, WV

Work Page on Facebook -> www.facebook.com/meteojoe
Work Page on Twitter -> https://twitter.com/meteojoe
Waterfalls -> www.wvfalls.com

Offline neondesert

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Re: Microclimates
« Reply #5 on: April 07, 2012, 08:50:57 PM »
Here's the way the NWS defines it:

Quote
Forecasts issued by the National Weather Service routinely include a "PoP" (probability of precipitation) statement, which is often expressed as the "chance of rain" or "chance of precipitation".

EXAMPLE
ZONE FORECASTS FOR NORTH AND CENTRAL GEORGIA
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
119 PM EDT THU MAY 8 2008

GAZ021-022-032034-044046-055-057-090815-
CHEROKEE-CLAYTON-COBB-DEKALB-FORSYTH-GWINNETT-HENRY-NORTH FULTON-
ROCKDALE-SOUTH FULTON-
INCLUDING THE CITIES OF...ATLANTA...CONYERS...DECATUR...
EAST POINT...LAWRENCEVILLE...MARIETTA
119 PM EDT THU MAY x 2008

.THIS AFTERNOON...MOSTLY CLOUDY WITH A 40 PERCENT CHANCE OF
SHOWERS AND THUNDERSTORMS. WINDY. HIGHS IN THE LOWER 80S. NEAR
STEADY TEMPERATURE IN THE LOWER 80S. SOUTH WINDS 15 TO 25 MPH.
.TONIGHT...MOSTLY CLOUDY WITH A CHANCE OF SHOWERS AND
THUNDERSTORMS IN THE EVENING...THEN A SLIGHT CHANCE OF SHOWERS
AND THUNDERSTORMS AFTER MIDNIGHT. LOWS IN THE MID 60S. SOUTHWEST
WINDS 5 TO 15 MPH. CHANCE OF RAIN 40 PERCENT.

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:
PoP = C x A where "C" = the confidence that precipitation will occur somewhere in the forecast area, and where "A" = the percent of the area that will receive measureable precipitation, if it occurs at all.

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.

http://www.srh.noaa.gov/ffc/?n=pop
Larry
"But it's a DRY Heat!"


Offline Farmtalk

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Re: Microclimates
« Reply #6 on: April 08, 2012, 12:52:15 AM »
I guess it can be interpreted in different ways, but of course the NWS is the right way of interpretation. Thanks for sharing that Larry! And that formula they use is interesting. Never thought there was actual math used in determining the probability.
Joe Fitzwater
Chief Meteorologist for WVNS-TV 59 in Beckley, WV

Work Page on Facebook -> www.facebook.com/meteojoe
Work Page on Twitter -> https://twitter.com/meteojoe
Waterfalls -> www.wvfalls.com