Using BLIPMAPs and other forecast tools at Hollister.
October 15, 2002

Everyone talks about the weather, yet nothing is done about it.
– Mark Twain

In the interest of spreading weather knowledge, I plan to write about the forecasting tools I use and my experience with the results.  This may turn into a regular column, depending on whether others find it useful, and I invite other BASA members to write about their own experiences trying to forecast soaring conditions.

Forecasting Tools.  If you are not already using the Dr. Jack weather products, you need to be.  These represent a huge leap ahead in forecasting of thermal soaring conditions.  Go to www.drjack.net to access the BLIPMAPs, BLIPs and TIPs.  You can also sign up on the Soar Hollister website to have the Hollister TIP forecast automatically e-mailed to you every morning.  “Dr. Jack” is Jack Glendening, a local soaring pilot and research meteorologist.  Jack described the BLIPMAPs and related tools in the July, 2002 issue of Soaring magazine.  There are further explanations on the drjack website.  Here is a summary of what these products tell you, and how I use them:

The BLIPMAPs and BLIPs result from taking numerical meteorological model outputs produced by the NOAA, downloading them to Jack’s computer and reprocessing the numbers to get forecast parameters relevant to soaring pilots.  BLIPMAPs and BLIPs for each day are usually available beginning about 6:30 PM PDT the evening before.  Updated forecasts are produced periodically through the night and morning, so it is worth checking the BLIPMAPs and BLIPs again in the morning.

Both the BLIPMAPs and BLIPs use the same methodology, but present the results in different formats.  BLIPMAPs are color-coded maps showing forecast conditions over all of California and Nevada (with other maps for other regions of the US), at a single time (21:00 Zulu time for the California – Nevada maps).  BLIPs are forecasts of the same parameters, but for specific locations, and for different times over the course of the day.  We are fortunate that Jack flies at Hollister, because his website includes daily BLIP forecasts for Hollister, Quien Sabe, Panoche, Hernandez, Black Mountain (the high ridge west of Avenal), and Avenal.  In the mountains, BLIPs are produced for Truckee, Minden and Mount Patterson.

For me, the most important parameters in the BLIPMAPs and BLIPs are the “BL Top” and “Hcrit” numbers.  “Hcrit” represents the highest predicted thermaling height over flat terrain.  The “BL Top” is a good estimate of the highest thermaling height over mountains and ridges.  The correlation has been remarkable between the forecast BL Top for Panoche and Hernandez and the actual thermaling heights at the Panoche and Hernandez “elevators”.  More often than not, the forecast  BL Top is within 1,000 feet of the actual thermaling heights achieved.  These forecasts do not take into account the effects of cumulus clouds, so on days that clouds are present the actual thermaling height may be lower (because cloudbase is lower), or higher (because condensation releases heat, propelling the thermal higher). 

There is a lot of other information in the BLIPs, including a forecast of winds aloft at increments of approximately 200 feet.  For flights to Panoche and back, these usually confirm that the summer seabreeze doesn’t extend above a few thousand feet.

The Hollister BLIP is less reliable than those for other locations, probably because of the marine influence.  As we get into winter and get more post-frontal days, the BLIP and BLIPMAP will probably do a better job of forecasting local conditions at Hollister.  The Quien Sabe BLIP does a pretty good job of forecasting conditions over the east ridge of the Quien Sabe valley, and reported thermal heights there the last two months were often between the forecast Hcrit and BL Top heights.

TIPs are much less accurate than BLIPs and BLIPMAPs, but they include forecasts for the current day and the next two days.  I use TIPs mainly for trend analysis – i.e., will conditions improve or worsen over the next few days?

Other resources are available on the National Weather Service websites.  My starting point is usually the forecast page of the Monterey office, at http://www.wrh.noaa.gov/Monterey/forecast.html.  The Zone Forecast gives you the basic weather forecast over the next five to seven days, while the Forecast Discussion gives the reasoning behind the forecasts.  It takes some time to get used to the jargon used in the Forecast Discussion, but it is worthwhile to read these regularly.  There is a link on the main forecast page to a glossary of terms used.  The Forecast Discussion is the place to find out whether a ridge or trough is forecast to move in aloft, when an offshore flow is predicted, and other general trends.

I also like the NWS aviation weather page, at http://www.wrh.noaa.gov/Monterey/aviation.html.  This has links to METARs for current conditions, Winds Aloft forecasts, and TAF and TWEB forecasts.  The Salinas TAF gives the closest aviation forecast to Hollister.  During post-frontal conditions in the winter and spring, it is often a good forecast of the cloudbase at Hollister, allowing that the Hollister cloudbase may be 500 feet or so higher than the Salinas cloudbase.  The TWEB en-route forecast for San Jose to Bakersfield (#421) gives the forecast cloudbase over the east hills and the Panoche area.

To see how the forecasts match with reality, I regularly consult the satellite photos at http://www.wrh.noaa.gov/satellite/1km/Monterey/VIS1MTR.GIF and http://www.wrh.noaa.gov/satellite/1km/Reno/VIS1RNO.GIF.  In the winter, you can watch wave clouds forming over Hollister on a stormy day, and then marching south to Avenal and beyond as the front moves through.  In the spring, the photos show cloudstreets forming over the Panoche / Hernandez area, and in the summer you can see the thunderstorms building over the Sierra and into Nevada.

Recent Soaring Conditions at Hollister.  September and early October provided many good days of soaring in the hills east of Hollister, as well as south into the Panoche and Hernandez area.  I noticed three kinds of days with good conditions:

1.         The best cross-country days were generally when the Forecast Discussion predicted a strong high-pressure ridge building aloft over a period of several days.  Temperatures at King City, Los Banos and Coalinga were forecast to climb into the 90s or even low 100s, but an afternoon seabreeze was still forecast for the coast.  These days provided the usual strong blue thermals at Panoche, but the seabreeze washed out any local thermals at Hollister.  There were often good conditions over the hills around Henrietta and on the east side of the Quien Sabe Valley, however, allowing long-duration flights within gliding distance of Hollister.

2.         As we got into late September and early October, the high-pressure events were accompanied by an offshore flow reaching all the way to the coast.  Temperatures inland were not as hot as before, and temperatures on the coast were almost as hot as those inland.  The flow aloft was forecast to come out of the northeast, and no seabreeze was predicted.  These days had usable thermals right at Hollister.  Strong thermals were found in the hills, but not at the usual locations, the best lift generally being further west than normal.

3.         In between the high-pressure events, upper-level troughs would swing through, bringing in cooler air aloft.  Some of these troughs were completely dry, but others had enough moisture that partly-cloudy conditions were forecast.  The best of these troughs came through in early September, and resulted in a lovely cloud street stretching from north of Panoche to south of Hernandez, which Tom Hubbard was able to follow for a 300 km flight.

So, read the Forecast Discussions regularly to see what is coming a few days out.  In the late spring and early fall, a forecast of a ridge building aloft usually means strong blue thermals over the hills east and south of Hollister.  As we get into the rainy season, the Forecast Discussion will help you predict when fronts will pass, and whether they will produce strong winds for wave conditions.

Harry Fox

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