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bedellympian

Better PNW weather forecasting

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I've been aware of UW's time-height forecasting system for a while but really started using it this year. There have been several days where NOAA pt predicts clouds or high winds but the time-height shows its calm and clear above 5-6k' and its right on. 

Reading them takes some getting used to, they are definitely not the most user friendly, but once you've practiced a bit it's easy enough. Time goes from R-L on the x-axis in UTC (date/hour, 00=4pm PST day before and 12=4am day of), elevation is on the y-axis in mbar pressure (800 is aprox 6k', 700 = 10k'). Green = clouds/precip, arrows = wind (more fletchings = more wind, they point in the compass direction), temp is deg C shown in red lines ("0" line is the freezing level). 

Here is the link to a map of the time-heights. Click on the location down wind of where you want to go. Look for white above 800mbar with small wind arrows, there's your window.

https://a.atmos.washington.edu/mm5rt/rt/timeheights_d3.cgi?GFS+current_gfs+

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I haven't used those yet off the atmos site.  I will have to spend more time with your x axis description.  So.....it is for a 36 hour window?

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Just now, JasonG said:

I haven't used those yet off the atmos site.  What is the x axis time format?  Seems hard to decipher.

x-axis starts on the R and goes back L (counter intuitive right?) and is in xx/yy format. xx is the date. yy is the hour in UTC (8 hours ahead of us in winter and 7 in summer so 00=4pm PST and 12=4am PST). basically you just look for the date and the 12 which is about when you'd be heading up with an alpine start most days. If its white (clear) above and to the L of that then its clear skies.

 

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3 hours ago, JasonG said:

I haven't used those yet off the atmos site.  I will have to spend more time with your x axis description.  So.....it is for a 36 hour window?

Every xx/00 to xx/12 is 12 hours, it covers 84 hrs.

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Wow thanks for sharing!  That is some really cool stuff.  Do you know what the green lines mean?  It seems to have higher numbers for where the green shaded areas are....maybe dealing in chance of precip or sky coverage??  Also it looks like all of this is based on the GFS models but there is a 12km, 4km and 4/3km.  What is difference between them?

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Thanks @bedellympian!!  This looks to be another good tool.  Right now I am just using the loops of column integrated cloud water and the 1 hr. precip on the 4km grids

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18 hours ago, mthorman said:

 Do you know what the green lines mean? Also it looks like all of this is based on the GFS models but there is a 12km, 4km and 4/3km.  What is difference between them?

Green lines (I'm pretty sure) are relative humidity as a %, so yes cloud cover/precip in essence. I always use the 4km to be honest and don't understand the difference between the 12 and 4. The 4/3 looks like a shorter time frame than the 12 and 4, and the 12 looks like it has a little less detail than the 4km. I know TMG uses the 4km at Troutdale for all their guiding on Hood.  

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Yeah, 12, 4, and 4/3 refer to the grid cell size (how long on a side the squares for model output).  So you hit it right, less detail as you increase grid size.  And yes, for whatever reason, they don't run the 4/3 as far out, maybe due to computing limitations?

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This past Friday on Hood was a perfect example of how Time-Heights are better... 

NOAA pt called for 80% chance of snow and high winds out of the W. The Time-Height showed that while there would be clouds and precip it would be clear above 6,000ft and the winds would actually be out of the NW at that elevation. We went for it and poked out of the clouds at the top of Palmer, while there were high winds in places we were mostly sheltered by the mountain. We were the ONLY climbers or skiers on the entire upper peak that day and climbed Reid Headwall in beautiful conditions under perfect blue sky. We encountered strong winds at Illumination Saddle and on the summit ridge but otherwise it was just a little breezy. We had to start and finish skiing in the cloud layer in what looked pretty terrible from the parking lot, but persistence and confidence in the forecast paid off. 

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Awesome story!  I will have to get better at reading those. 

I guess I was thinking that the clouds would ride up over the summit if there was strong wind and precip?  Do you have a good sense for when that happens, or what a time-eight would look like when it would?  Or does the time-height accurately predict how high the moisture will be allowed to be pushed (before condensing and dropping out) over terrain?

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In my experience, if the Time-Height is white at summit altitude, then it will be clear. There MIGHT be a summit cloud capping it, but it won't be anything major.

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I found out what the units for the wind vane fletchings are...

They are in knots (nautical mph) cause everyone knows knots! :crosseye: 1 knot = 1.15 mph

A half line = 5 knots

A full line = 10 knots

A triangle = 50 knots

So a wind vane arrow pointing from L to R at 700mbar with a triangle, a line, and a half line coming off its side means wind out of the West at 10,000ft with an average speed of 50+10+5=65 knots or ~75mph (so stay the F%$# home!)

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Would like to thank @bedellympian for this excellent resource. Was able to get in a summit on Hood Sunday before the weather rolled in thanks to knowing when exactly we had to be off and heading down. Seemed everyone else was scared off by the forecast they got from other resources, or they got their fill in on Saturday.

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On 1/13/2021 at 5:53 PM, bedellympian said:

I've been aware of UW's time-height forecasting system for a while but really started using it this year. There have been several days where NOAA pt predicts clouds or high winds but the time-height shows its calm and clear above 5-6k' and its right on. 

Reading them takes some getting used to, they are definitely not the most user friendly, but once you've practiced a bit it's easy enough. Time goes from R-L on the x-axis in UTC (date/hour, 00=4pm PST day before and 12=4am day of), elevation is on the y-axis in mbar pressure (800 is aprox 6k', 700 = 10k'). Green = clouds/precip, arrows = wind (more fletchings = more wind, they point in the compass direction), temp is deg C shown in red lines ("0" line is the freezing level). 

Here is the link to a map of the time-heights. Click on the location down wind of where you want to go. Look for white above 800mbar with small wind arrows, there's your window.

https://a.atmos.washington.edu/mm5rt/rt/timeheights_d3.cgi?GFS+current_gfs+

Thanks for the heads up

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