WX Phenoms.

[The Natural]

Flew into Colorado Springs for cheap gas about a month ago, and there was a microburst alert "All quadrants" +/- 40knots as reported by a controller that lasted for 1 hour, on a day with blue skies extremely CAVU. Maybe microburst detection equipment cant tell the difference from windshear, maybe it depends on the system. Always read the disclaimer in WX books that microburst are generally associated with T-storms, (typically 5-15 min) But this was the first time I saw it w/o precip. or did? Is this typical phenomenon close to the rockies????

 

[chperplt]

Microbursts come in two flavors.. Wet and Dry.

The wet form as you noted come from T-storms. The dry form comes when the temp/dew point spread gets very large. If my memory serves me correctly, 40 degrees difference and you may start to see some nasty winds.

 

[Vector4fun]

If they are using Weather System Processor, (WSP), http://www.faa.gov/and/and400/and420/wsp/main.htm

The system is limited because it's run off the WX channel of an ASR-9 ATC Terminal radar system. There's no way to measure the actual height of the phenomina because the antenna tilt is fixed and optimized for ATC, not WX. We get windshear alerts and gust front warnings because of winds 6000' or more above airport elevation. It's just a "poor man's" Doppler Radar. The WSP may have been sensing all sorts of weird winds at 10,000 or 14,000', that never got close to the ground. But the tower still has to issue the warning anyway.

That's just a guess....

 

[91100 100 set]

Wouldn't a "Weather Phenom" be one of the babes on the weather channel,or am I spelling that incorrectly? I seem to remember a thread afew months back about this very thing, but I'm too lazy to go searchingfor it.

 

[PropsForward]

Seems there was a 121 operator that lost a plane a few years back due to this. It was so nice that they were calling visibiltiy as 100 miles.

will look on the NTSB for this...

 

[EagleRJ]

If they are using Weather System Processor, (WSP), http://www.faa.gov/and/and400/and420/wsp/main.htm

The system is limited because it's run off the WX channel of an ASR-9 ATC Terminal radar system. There's no way to measure the actual height of the phenomina because the antenna tilt is fixed and optimized for ATC, not WX. We get windshear alerts and gust front warnings because of winds 6000' or more above airport elevation. It's just a "poor man's" Doppler Radar. The WSP may have been sensing all sorts of weird winds at 10,000 or 14,000', that never got close to the ground. But the tower still has to issue the warning anyway.

That's just a guess....

I thought windshear alerts were only generated by the grid of microburst stations (anemometer on a pole) around an airport. Is terminal radar used for that too? I knew strong fronts could be seen on radar, but I didn't know they had wind velocity capability outside of precip drift.

There's a new doppler radar that looks straight up. It's supposed to be used for mapping wind speeds at different altitudes. I don't know if it's officially entered service yet, but it is supposed to be able to give very accurate wind readings.

 

[Vector4fun]

I thought windshear alerts were only generated by the grid of microburst stations (anemometer on a pole) around an airport. Is terminal radar used for that too? I knew strong fronts could be seen on radar, but I didn't know they had wind velocity capability outside of precip drift.

Nope, we had the LLWAS system when we opened ABIA, and the towers are still there, but all the windshear and microburst warnings now come from a computer that's running WX channel data through a Doppler-like program. There's still a lot of LLWAS systems out there, but the FAA bought something like 40-60 of these WSP systems, and we and ABQ were test sites. It actually works pretty good most of the time, I like it. But there's times we get warnings when nothing's really happening at the surface, yet you can look up and see the clouds churning pretty good 5000' above...

 

[SkyWestCRJPilot]

I was in COS that day. We sat at the end of the runway waiting for about an hour for the winds to calm down but the tower kept issuing windshear alerts and then the even worse microburst alerts. Like you said it was a nice day with hardly any clouds. The problem I believe is that the winds coming off of the front range were about 50 knots at 2000 feet AGL creating the windshear at the surface with 20 knot winds coming from all different directions at different places on the field. It was news to me that you could get a microburst alert without a thunderstorm but I think the equipment on the field only measures wind velocities and changes in direction over a given area. When they hit a preset level it goes from just a windshear alert to a microburst alert. Our LAX roundtrip ended up getting cancelled due to the microburst alerts.

 

[The Natural]

That was the day. I heard the warning, then approx. 10 min later a citation landed and reported nothing speacial on his ride. I came in about 40 knots faster due to the warning +/-40knots, (not hard to do in a Pilatus) 3-4min later and experienced one shot of severe turbulence about 700ft agl that sent one of my passengers to hit his head on the ceiling so hard he broke a walkway flood light.
I told them to strap on tight and put their shoulder harnesses on, which they didnt, but do now! even though its not as comfortable. Anyways operations continued an MU-2 landed right after me, another citatation etc, etc. uneventfully.