1000km Alert - Mojave Desert to Reno & SW Nevada - for Sunday 07/13/2014

[WaltWX[_2_]]

Ladies and gentlemen,

A great summer soaring pattern for long cross country and triangle flights is developing late this weekend. Sunday looks fantastic with just a taste of scattered cu 15500 to 18000 and light E-SE low to mid level flow for early thermal starts.

Monday will be too late... as monsoon moisture sweeps into the Mojave and Southern Sierras Mon afternoon with mid cloud cover and thunderstorms.

A strong 500mb high will build over Nevada between Ely and Reno Sunday. Circulation around the high brings drier airmass in a northerly flow over Utah, turning to E-SE over the Mojave Deserts and Southern Sierra. This is my "classic" 1000km triangle pattern because the flow sweeps in steep lapse rates to the Western edge of the Mojave Desert (Tehachapi for example) for early starts (say 1030am Double Mtn). Late finishes up to 7 or 8pm looks reasonable as the low level westerlies will be shallow and only favor triggering of convergence zone 25-40 miles out of Tehachapi. Easterly flow around the high will begin bringing monsoon moisture to the Eastern Mojave and lower deserts late afternoon and evening perhaps triggering scattered thunderstorms Barstow-Daggett Big Bear area. More cloud cover, moisture and showers should spread into the lower deserts 9pm to after midnight.

For Sunday XCSkies is showing high cloud cu bases on the Sierras around 17.5-19.0 msl, with somewhat lower bases say 16.5 over the Inyos and 15.5 Barstow region.

My plans were to fly out of Inyokern with the Southern Sierra group, but because of the large number of private owners turning up, I might change to Tehachapi if there is a 2nd tow plane available. A 750km triangle is my goal.... unless it looks spectacular... then I might go for a 1000km triangle.

More to follow tonight or Saturday morning... with graphics and illustrations.

Walt Rogers WX

PS - Jane... what's the likelihood of a 2nd tow plane for Sunday?

[WaltWX[_2_]]

1000km Alert - Mojave Desert to Reno & SW Nevada - for Sunday - Graphics/Maps and my Analysis

Here's a rather technical look at how I'm analyzing soaring weather these days. Browse some weather maps depicting soaring weather forecasts for Sat, Sun and Mon July 12-14, 2014:


https://www.dropbox.com/sh/sl1h0m3m5mkot7d/AAB5hWw4YFtId1BGMq-26Rt6a

The 500mb charts depict winds and Relative Humidity at 18k msl for 2pm on Sat, Sun and Mon. Note the developing high center Sat night in Central Nevada. Monsoon moisture from Arizona and NW Mexico gets swept into the SE Deserts of Southern CA late Sunday, then up over all the Mojave, Sierra and Central CA area Monday.

The XCSkies graphic shows cloud bases at 5pm Sunday. Just enough cu cloud cover (at least I hope it's only Scatter cu... and now mid layer altocumulus). Bases Mt Whitney north to Bridgeport are 17.5-18.5msl. Inyo Mtns eastward and to the south bases 15-16msl. Barstow will probably have an active area of thunderstorms propagating toward the west late afternoon Sun toward Four Corner near sunset.

The time series graphs are a little hard to read and understand, but show hourly soundings with winds aloft. Times along x-axis are GMT (18Z =11am; 21Z =2pm etc). Heights msl give thermal altitudes (MIXING HEIGHT) in red; LCL Lifted Condensation Level or cu cloud bases in dark green; Surface temp DegC in light green; Surface winds kts bold black; 1km agl winds kts thin black line.

Concentrate on the file names with 2014071200 in the prefix. This represents the NAM numerical model initialized on July 12 at 00Z (5pm Friday).

KMHV = Mojave
NID = China Lake
KDAG = Barstow-Daggett
EDW = Edwards AFB
C01 = Point in high Sierras west of Bishop

The colored graphics have the same line plots, but add relative humidity.

Looking at the KMHV time series plot, note how the MIXING HEIGHT (thermal height) goes up steadily from Sat to Sun to Mon. But, the LCL (cloud bases) goes down from about 15.5msl to 14.5 msl on Monday. Barstow Daggett shows a big drop in cloud bases with showers/TS and high RH on Monday.

From this explanation, once can gather quite a bit of soaring weather information for the next three days. These time series hourly sounding plots are now one of my key tools.

Walt Rogers WX

[WaltWX[_2_]]

UPDATE AND ANALYSIS OF THE DAY...

Well,

The Great 1000km triangle day was a let down.

My forecast analyses relied heavily on thermal heights and cu cloud coverage with high bases. What I noticed during my flight was weaker than expected climb rates once I reached the southern Sierras NE of Kernville... only 4-5kts average and lots of circle tries to center things (cloud bases 15500.... 17500 later in day). With the SE flow aloft, there was no convergence zone along the Sierra crest, so cu were concentrated only over heated terrain well west in the Sierras.

Perhaps, not having the SW flow aloft (climatological normal over the Sierras during summer) and light E-SE low level flow just east of the Sierra crest was the key. My experience shows in the "normal" situation is to find strong lift along the Sierra crest with 7-12kt climbs.... almost completely absent on Sunday 07/13.

For my 1000km flight, the first leg was slow and then blue and low until I turned around just short of Lake Crowley (near Mammoth). From my fellow glider pilots, it sounds like the Inyos and Whites were quite good with isolated cu. Not sure how things were further east on my second and third leg toward Las Vegas and return.

[Brad Alston]

;886037']UPDATE AND ANALYSIS OF THE DAY...

Well,

The Great 1000km triangle day was a let down.



Sorry to hear it didn't turn out as expected...this time. We'll be waiting to hear the details of the time when things fall into place for you with the 1,000k try! :)

Keep up the good work...and persistence with your goals!

Brad.