Soaring Forecasts and Current Weather


The RASP forecasts are the most refined and accurate soaring forecasts available for regional areas.  We are lucky to have two RASP enthusiasts that build and maintain systems to provide pretty detailed forecasts up to 4 days out.

These tools will save you many gallons of gas and hours of frustration if you learn which parameters to pay attention to and when.  Mid winter wave, summer convergence, spring Post-frontal cu, all are accurately predicted sometimes days in advance.

Key Values to be aware of are covered below.

Val's RASP

Valentin Mayamsin created a RASP for both the coastal range in California and the Sierras. This Rasp covers further south than Bart's RASP and forecasts out 7 days, further than any other soaring model.

Bart's RASP

Bart's Avenal RASP

Focused primarily on the Temblor range and up to Panoche, Bart's RASP is generally very accurate.  BL Max Up/Down is a fantastic tool for predicting the convergence on any particular day.

Bart's Sierra RASP

Alex's RASP

With Bart providing a fairly tight view of things, Alex's RASP provides a larger picture and includes some of the Southern Sierra for those of us keen on crossing the valley and getting into the Sierra.

Alex's Super RASP

In December 2012 Alex created a super RASP covering much of the western region.  Should be an interesting experiment.

Key Values to look at on the RASP:

BL Top - The Boundary Layer Top.  This indicates the top of the convective layer predicted.  Typically this would be higher than you can thermal.  In our mountainous terrain and with the influence of the convergence this often provides an accurate assessment of how high the thermals will go in the mountains or in the convergence.

HCrit - This is the height of Critical Updraft Strength.  Typically the max you'll routinely be able to thermal to.  This is generally pretty accurate for the valley and flat land areas.

BL Max Up/Down - This is the magical Convergence predictor.  Looking at this for warm colors will typically show you where to expect the convergence.

Vertical Velocity -  850 and 700mb vertical velocity will often show wave bars when we have wind events.  Avenal experiences wave from SW and N/NE winds.  Typically SW wave sets up straight over the field.

Precipitation at Avenal... How Wet is Too Wet 

Observation over the years has shown me that if the field is dry, as in a week or more without rain, then less than .3" the day before will usually be absorbed and dry enough for operations.  This depends on wind and cloud coverage as well.  

There are two "failure modes" that happen at Avenal.  The first is from short, but intense rain.  Even .10" will nearly immediately produce a saturated layer of soil that is grease like and sticks to everything.  But that layer is also very thin, so it separates from the dry soil underneath.  If you walk across the field, you will get gradually taller as each step yanks a pancake of wet soil that adds to the bottom of your shoe.  This is typically a problem if we have a cell come through on an unstable day and drop a bunch of rain while gliders are still out and need to be put away.  It becomes a slippery, sticky mess.  But the scars are not very deep into the runway.  1/4" or so.

The second failure mode is when the soil is much more saturated, but the surface is relatively dry.  After .5" or more over a period of time.  Then the ground gets spongy, no longer sticky.  But if you drive a vehicle across the field it will create tire marks as deep as 1" or more.  Typically you can walk onto the runway and feel a little give to the surface.  If you feel that, it's not ok to drive on.

Also worth noting is that there are several low spots on the runway near the takeoff area for 30.  Particularly around where the towplane lines up and just ahead of that. The edges of the runway might be perfectly fine, but those low spots that captured runoff will not be ok and need to be avoided.  That can mean a usable runway with a couple of 30ft circles to avoid during takeoff.

The main thing is to avoid the airfield surface with vehicles when ruts will be created.  They can linger for months and even driving down the side of the airfield can create a rut right in the assembly area of gliders.  Enough to give wing riggers a fit.  Any time after a rain, walk any suspect areas first and feel for the spongy soil.

The field dries pretty quickly, especially after intermittent small rain events.  Even a few hours of sun and a breeze can do wonders.

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