Weather Probabilities

General Weather Discussions and Analysis

Weather Probabilities

Postby petertohen » Fri Aug 04, 2017 9:57 am

http://www.khou.com/news/local/local-ar ... /462393777
Wonder what is the probability that Houston sees snow, single digit temperatures, and hurricanes. I know nature does not care for probabilities and statistics. However, if spread out, it can give us a good idea how often it happens. Let's start with snow in Houston, which is on everyone's mind. Mind, this goes back to 1895 up to 2010.

Any Snowfall
1 Snowfall=Every 3 years
2 Snowfall=Every 9 years
3 Snowfall=Every 27 years
4 Snowfall=Every 81 years

>0.01 Snowfall
1 Snowfall=Every 5 years
2 Snowfall=Every 25 years
3 Snowfall=Every 125 years
4 Snowfall=Every 625 years

The last winter to see more than one snowfall event (trace to +1") was in 1985. One snowfall had 1 inch and the other had 0.3 inches.

>1 Inch Snowfall
1 >1" Snowfall=Every 8.2 years
2 >1" Snowfall=Every 67.2 years
3 >1" Snowfall=Every 551.4 years
4 >1" Snowfall=Every 4,521.2 years

>2 Inch Snowfall
1 >2" Snowfall=Every 19.2 years
2 >2" Snowfall=Every 368.6 years
3 >2" Snowfall=Every 7,077.9 years
4 >2" Snowfall=Every 135,895.5 years

The only winter in Houston were there were more than one +1" snowfall was the winter of 1973. Houston sees +2" snowfall event about every 19.2 years As for a 1895 snow event, my guess it probably happens every 150 to 300 years. It is only a guess. It is very likely Houston has been hit by a huge snow event prior to 1895.

Single digit (Fahrenheit) temperature <10 is very rare in Houston. So rare, it has only happened four times going back to 1895 to 2010.

Single Digit Temperature
1 <10 Temperature=Every 28.75 years
2 <10 Temperature=Every 826.6 years
3 <10 Temperature=Every 23,763.7 years
4 <10 Temperature=Every 683,205.6 years

The only winter/year with more than one instance of single digit temperature was in February of 1899, which was the Great February 1899 Freeze. It hit single digits in cloudy weather two nights in a row! The other instance of that is in January of 1930 (Hit an all time low of 5!) and December of 1989 (Hit 7).

To put this statistic in perspective, a tropical cyclone (tropical storm and hurricane) hits the Upper Texas Coast every (1.9) year. Hurricanes come every 3.6 years, while major hurricanes come every 10.8 years. This going back to 1870 to 2010.

Probability For Landfall on Upper Texas Coast
1 Tropical Cyclone=Every 1.9 years
1 Hurricane=Every 3.6 years
1 Major Hurricane=Every 10.8 years

2 Tropical Cyclones=Every 3.6 years
2 Hurricanes=Every 13 years
2 Major Hurricanes=Every 117 years

3 Tropical Cyclones=Every 6.9 years
3 Hurricanes=Every 46.7 years
3 Major Hurricanes=Every 1,260 years

4 Tropical Cyclones=Every 13 years
4 Hurricanes=Every 168 years
4 Major Hurricanes=Every 13,605 years

Probability by months for the Upper Texas Coast. It is from 1870 to 2010. Tropical cyclones that made landfall as tropical depressions count as tropical cyclones and are included (Ivan in 2004 and Erin in 2007).

June (14/6/0)
Tropical Cyclone=Every 10 years
Hurricane=Every 23.3 years
Major Hurricane=None Recorded (Hurricane Audrey was not a major hurricane.)

July (12/5/1)
Tropical Cyclone=Every 11.7 years
Hurricane=Every 28 years
Major Hurricane=Every 140 years (Some hurricanes that made landfall on Texas could get reclassified as major hurricanes.)

August (21/7/6)
Tropical Cyclone=Every 6.7 years
Hurricane=Every 20 years
Major Hurricane=Every 23.3 years

September (22/6/5)
Tropical Cyclone=Every 6.4 years
Hurricane=Every 23.3 years
Major Hurricane=Every 28 years

October (5/2/1)
Tropical Cyclone=Every 28 years
Hurricane=Every 70 years
Major Hurricane=Every 140 years (Only one documented major hurricane made landfall in October. It is probable that there have been major hurricanes that made landfall on the Upper Texas coast in October.)

November
None. However, it could be possible that some tropical cyclones have had made landfall on the Upper Texas Coast, but went unrecorded prior to 1851.

To put that in perspective, Houston area has a much better chance of getting +1" snow event or major hurricane making landfall than hitting single digit in the winter. Upper Texas Coast has a better chance of getting hit by two major hurricanes in one season than getting three +1" snowfall events in one winter.

Now, is it probable that the Upper Texas Coast has been hit by more than one major hurricane, more than likely yes. Is it also probable that there were single digit temperatures, more than likely yes.
Last edited by petertohen on Mon Aug 07, 2017 12:36 am, edited 2 times in total.
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Re: Weather Probabilities

Postby Texaspirate11 » Fri Aug 04, 2017 5:48 pm

Peter - this is great!
I once did research on comparison of when it snowed and when we got hit with storms.
Seems the times it did snow 1 inch or more, we got some kind of storm from the GOM...
but your research is far more intricate than mine....great! thanks!
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Re: Weather Probabilities

Postby DoctorMu » Mon Aug 14, 2017 8:27 pm

Wow - very interesting stats. Tropical cyclone frequency is a case in point why we can't be complacent about tropical systems this time of year.


The last great Houston snowfall was December 24, 2004, the only recorded snowfall on Christmas Eve. Unforgettable. The kids and I drove down from College Station for a peek as the storm hopped from the Hill Country. The storm created beautiful slice of white along the coast. Victoria had 13 inches of snow as the area saw the largest snowfall since 1895.

The snowflakes were big and wet...as we caught the first flakes on Hwy 290. About two inches of snow were on the ground and beginning to stick to the streets, when just 3 blocks from my wife's brother's him the thermostat in the radiator system stuck and the van overheated...in freezing temps and now heavy snow! Blew out the #1 cylinder. A Christmas that will never be forgotten around our home.

Image

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We all know what happened the following summer in the GOM!
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