flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

Strange TAF...curious As To What You All Think

Wed Feb 04, 2004 3:53 pm

Doing my nightly TAF reading, I came across this...

KCOS 040530Z 040606 10007KT 3SM -SHSN BR SCT006 BKN020
TEMPO 0608 1SM -SN BR OVC006
FM0800 VRB05KT 5SM -SN BR OVC015
TEMPO 0812 1SM -SN BR OVC008
FM1200 VRB05KT P6SM OVC025
TEMPO 1216 3SM -SN BKN015
FM1600 02006KT P6SM OVC025
TEMPO 1620 3SM -SHSN BKN015
FM2000 04008KT P6SM OVC025
TEMPO 2024 3SM -SHSN BKN015
FM0000 02010KT P6SM OVC025
TEMPO 0004 3SM -SHSN BKN015
FM0400 02010KT P6SM OVC025
TEMPO 0406 3SM -SHSN BKN015=

At 12, 16, 20, 00, and 04, it is predicting P6SM OVC025. But, for 12-16, 16-20, 20-24, 00-04, 04-06, it is predicting snow with much lower ceilings. Whats the deal? I could understand it if the times were spread out, but for example, 12-16 and 16-20 is snow, while 16 on the dot is much better weather.
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Strange TAF...curious As To What You All Think

Wed Feb 04, 2004 10:41 pm

I'll have to wait until later to chart this one out, but at a glance it appears to me that they have kind of a baseline forecast going all day long but with the consecutive TEMPOs for lower. That sort of looks like they maybe should have used a PROB instead.

Like the weather is going to be P6SM and OVC025 but from time to time during the day snow showers are going to make it lower - they just don't know when.

Just hedging, or so it looks.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
CFIcraigAPA
Posts: 223
Joined: Mon Jan 12, 2004 10:20 pm

RE: Strange TAF...curious As To What You All Think

Wed Feb 04, 2004 10:52 pm

I'd agree. Looks like they know it's going to be variable, but there is no certainty as to when it is going to happen. I don't have am AIM in front of me, but there may be an implied probability percentage when the TEMPO term is used. Interesting catch, F15.
Prior Proper Preparation Prevents Piss-Poor Performance
 
Air1727
Posts: 318
Joined: Mon Aug 25, 2003 10:57 am

RE: Strange TAF...curious As To What You All Think

Thu Feb 05, 2004 4:26 am

Folks, a TEMPO is to be looked at as a fluctuation in predominant conditions. TEMPOs are usually expected to last less than an hour at a time and over all less that half the period indicated.

So from the example above from Colorado Springs, you would look at it like this:

FM1600 02006KT P6SM OVC025
TEMPO 1620 3SM -SHSN BKN015

The predominant conditions from 1600-on are vis greater than 6 statute miles with ceiling overcast at 2500feet; but between the hours of 1600 and 2000, vis of 3 statute miles ceiling broken at 1500ft with light snow showers will exist for periods of less than one hour.

So essentially, from a forecast point of view the visibility and ceilings stay constant, however there are bands of snow showers moving through the area in intervals.

Hope this makes sense. If not, let me know.
In the Alaska bush I'd rather have a two hour bladder and three hours of gas than vice versa.
 
flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

RE: Strange TAF...curious As To What You All Think

Thu Feb 05, 2004 5:23 am

Air1727, ah! I'm ashamed that I did not remember that.

 Big thumbs up
 
Air1727
Posts: 318
Joined: Mon Aug 25, 2003 10:57 am

RE: Strange TAF...curious As To What You All Think

Thu Feb 05, 2004 8:43 am

Ashamed? Don't be crazy. That is one of those little stipulations in non-graphic weather that is easily forgotten.
In the Alaska bush I'd rather have a two hour bladder and three hours of gas than vice versa.

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