1300 PST 4km forecasts are available around 1900Z (12:00AM PDT)
For Panoche: 1km 1300 PST forecasts are also available around 3 hours later
The 4km forecasts result from model initializations with 12Z
data. Update times for non-1300 PST times are spaced roughly 45-60
minutes for each 3hr increment.
Each update simply overwrites
the previous forecast, so while the model is still running two different
forecast times can have different dates -
please check the forecast
dates at the top of each plot for currency !
### use colspan=3 to produce a wide column - expect to always have at least 3 grid2 columns
RASP News:
(Latest 5 news items)
Dec 10:
Change plot "frame":
RASP plots contain a dashed line "frame" indicating an outer zone of
decreased confidence resulting from mismatches between the coarse and
fine nested grids near the boundary. A recent WRF model
alteration doubled the width of the smoothed zone near the boundary so
the "frame" border has been increased to reflect that change.
Nov 6:
Cloud Parameter Changes:
I've altered the cloud parameters by removing the previous
"OvercastDevelopment" parameters and replacing them with forecasts for
"Extensive CloudBase" and "BL Cloud Cover". "Extensive
CloudBase" is a replacement for "OvercastDevelopment", based on a
model-predicted cloud water prediction. "BL Cloud Cover" is
based upon the relative humidity in the BL and while overly simplistic
can still be useful.
Nov 2:
World-wide accuracy improvement:
Finally - after beating my head against mysteries with few clues for
the past three days, I figured how to to uncompress the new "GRIB2"
files produced by NCEP's GFS (Global Forecast System), allowing use of
GFS predictions at 0.5x0.5 degree resolution (about 50km) to
initialize the non-US forecasts (I've been using GRIB1 files with
100km resolution). So I've now changed to their use for the
SW_SOUTHAFRICA and GREATBRITAIN runs, which should result in improved
accuracy of larger-scale (non-terrain-generated) features such as the
position/movement of fronts and upper-level clouds.
Oct 30:
Meteorological model updated:
Today I upgraded my WRF meteorological model to the latest version
available, which has several bug fixes and in particular should reduce
boundary matching problems (which are occasionally apparent in the
region between the domain boundary and the dashed-line "frame").
After correcting some problems I believe I now have it working
properly, but will keep an closer-than-usual eye on the processing for
the next day.
Oct 12:
New viewer:
As an alternative to selecting forecast BLIPMAPs from the "index
page", a RASP
UniViewer is now available. Some will find this more
convenient to use and it can display forecasts for multiple times
during the day, but it does assume basic BLIPMAP knowledge provided on
the index page so is intended for experienced RASP users. On startup
it displays the current forecast for the parameters utilized for the
last forecast viewed.
View ALL recent news items here
ARCHIVE of
older news items which have now lost much relevance
I only look at the webpages and maps that I use personally or that I
suspect might contain an error. If you notice a consistent
problem with a webpage or map, please post a message on the
RASP Forum.
Links to Further Information:
RASP UniViewer
- displays BLIPMAPs for the current day at multiple times
RASP Archive Viewer
- displays BLIPMAPs for the current and previous days (one time per day only)
Parameter descriptions
BASIC thermal forecast parameters
- a short and simple list of the parameters most important for thermal soaring
July 2002 SOARING magazine BLIPMAP article - a descriptive "first thing to read" for potential BLIPMAP users, giving an
overview of BLIPMAP predictions
Additional information
but intended for users
of my traditional RUC and ETA BLIPMAPs, not these RASP BLIPMAPs, so
allowances must be made
Overview
These forecasts are intended to help the
meteorology-minded pilot better evaluate soaring conditions. The
maps are particulalry useful to cross-country soaring pilots, since
they allow evaluation of conditions away from the home field.
Utilizing the forecasts can require some self-education (though that
can't be too hard since over 2000 US pilots actively use BLIPMAPs in
the US) as individualized assistance is not provided. At first
glance the website can seem intimidating since so many parameters are
forecast - but most are "supplemental" forecasts to be used as needed
and many users normally look only at the three or four they have found to be
most useful, such as the expected lift strength or the maximum (dry)
thermalling height or cloud potential/height forecasts, looking at
additional parameters only under special conditions.
How are RASP forecasts produced ?
RUC and ETA BLIPMAP forecasts are obtained by
post-processing forecast files output from NCEP prognostic models, so
horizontal and vertical resolutions are determined by those used in
those models. But here I am running a prognostic model myself,
so am able to specify the vertical/horizontal grid (though of course
subject to limits of practicality). A WRF (Weather Research and
Forecasting) model is being initialized and marched forward in time at
30 second time intervals to produce forecasts at 3 hr
increments. Initial and boundary conditions come from the
larger-scale models run by NCEP. To increase accuracy, forecasts are produced for both a
larger-domain coarse grid (12 km) and a smaller-domain fine grid (4
km) nested inside it, but only results for the latter are
displayed. To produce a 1300 PST 1km forecast, after the preceding forecasts are complete, the model
is re-initialized from the 1000 PST 4km forecasts and a 4km/1.3km nested-grid
forecast run for 3 hours. BTW, the
data needed to make such runs is available globally, so in theory
such forecasts can be made for anywhere in the world !
Rationale and Accuracy
A higher resolution model is expected to better
predict those phenomenon which are "locally forced" and influenced by
terrain. But forecasts of higher accuracy than the RUC/ETA
BLIPMAPs are not guaranteed since: (1) all else is not equal, as the
RUC/ETA model uses different algorithms which might be more correct
than those used by the WRF, (2) the RUC/ETA models use a more refined
initialization procedure, and (3) any limited-area model is subject to
"boundary condition" errors, which for a large-area model such as
RUC/ETA are very far away and of little importance but here are much
closer and may have a significant influence. The question of
which model forecast is more accurate may depend upon what parameter
is being evaluated and can only be assessed through comparison to
actual conditions.
Of course one advantage of running a model is
that one has full control over it and can change its behavior.
The WRF has many, many parameters which can be adjusted. And one
of it's claims to fame is that is is modular, allowing use of
different routines, written by different people/groups, to make the
calculations which determine, say, cloud formation - so alternate
modules can be utilized to improve model accuracy. But on the
other hand one could spend a lifetime evaluating and changing things
to improve accuracy - this is what meteorologists at weather
prediction centers do, but I don't plan to do that myself!
BTW, the WRF model is considered to be the "model
of the future" for many operational weather predictions centers and is
a candidate to replace the ETA model at NCEP within the next few
years.
Notes and Caveats:
() One is not supposed to believe all the details of these
forecasts, particularly since the small-scale structure is constantly
changing yet one a few snapshots at different times are shown.
Rather, one should be looking for patterns.
() Forecasts for points close to the boundary will be less
accurate than for those located nearer the center of the domain, due
to inevitable mis-matchings between the coarse and fine grids.
In particular, predictions of max/min BL vertical velocity are very
noisy and inaccurate near the boundary (particularly where boundary
condition problems exist). To remind users of this, a dotted
line marks the "frame" outside of which coarse-fine boundary
interaction problems are most prevalent.
() The "Explicit CloudWater Cloudbase" estimates are based on
cloud water predicted from model equations and problematical since there
is no simple criterion for differentiating "mist" concentrations from "cloud" concentrations.
The criterion presently used is a first guess.
() The "Cu Potential" and "Sfc. LCL" predictions are based on a simple formula which considers
only water vapor at the surface
() This model does not ingest as much observational data as do the institutional models
such as RUC and ETA, hence some effects are not included: for example, soil moisture
is neglected
() While many pilots are accustomed to using the 20km-RUC BL top
to estimate a maximum soaring height in terrain, that likely works
because 20km-RUC terrain heights are usually significantly lower than
actual ones. With better defined terrain on the 4 and 1 km
resolution grid, Hcrit is likely to become the more relevant
parameter. I suggest also looking at the BL depth and BL max/min
Upward Motion parameters as indicators for where maximum lift is
likely to occur.
() The present simulation is only a first cut, since to get
things running quickly many decisions have been on the basis of whatever
was easiest. Many choices must be re-examined in light
of experience gained with the present parameters. In particular,
I expect at some later time to alter the horizontal domain to reduce
some obvious boundary problems and to alter the vertical grid such
that a larger proportion of points occurs nearer the surface.
() The fact that these forecasts are only a snapshot in time of
a fairly noisy field should be particularly emphasized for the 1 km
resolution forecasts, as forecasts for, say, 30 minutes before or
after 1300 PST would look different. At this point it's difficult to
figure whether they will really add anything, but one never knows til
one tries.
() The "Vert. Velocity at 850mb" (and 700mb and 500mb) and
"Vert. Velocity Slice at Vert.Vel.Max" parameters attempt to forecast
mt. wave events, although strong vertical velocities resulting from
deep BL convergence can also be found in the plots. The first
parameter gives a plan view of vertical velocity at the 850mb level, a
height of roughly 5000 ft MSL and thus often above the BL top.
The second parameter is a vertical slice taken at a point of maximum
vertical velocity (as found at a height of around 5000 ft AGL within a
horizontal box which excludes the outmost edge of the domain) and
oriented parallel to the wind at that point, as indicated by a dotted
line on the plot of the first parameter (with left-right on the slice
always being left-right on the plan view). A label above the
plots gives the location and magnitude of the found maximum
value. Mt. wave predictions are best made using resultions no
larger than 4km, since a coarser grid generally does not resolve the
waves accurately. A key indicator of a mt. wave is its upwind
tilt with height, which is usually evident in the vertical
slice. For examples of mt. wave forecasts (at 1km resolution),
see these predictions of vertical velocity at 18,000 ft (500mb)
and in a vertical
slice.
() Because the intrinsic short-term time variability of the
atmosphere at scales as small as 1 km makes evaluations based on a
single-time forecast uncertain, I have added loops of parameter
forcasts for times near 1300 PST to aid assessment of short-term forecast
variations with time. A limitation of the present implementaion
is that colors can represent slightly different values at different
times, but the relative maxima are readily apparent.
Timeliness Issues
The forecasts are not as timely as I would
like. In particular, it woulld be best for launching pilots to
have viewed forecasts initialized from the early morning sounding data
of that day since otherwise the models depend upon soundings taken the
previous evening and are thus less accurate. But at present the
1300 PST forecasts from that data are not available until
after 8 AM PST (which will be 9 in the summer), later than I would
like.
The reason, of course, is that it takes time for
sounding data to be obtained and sent to NCEP, time for NCEP to
process it and run their model and produce output files, and time for
me to download those files and run my model and plot the output
produced. NCEP model output becomes available a bit over 2 hours
after sounding release time and downloading takes around 10 mins - I
have no control over things up to that point. My model run time
depends on many factors, notably the speed of the computer CPU and the
size of the domain modelled. At present the run time is around 2
hours to produce forecasts at 1300 PST plus another 5 minutes for
plotting. This is slower than it might be because I have chosen
to produce forecasts for two different locations instead of just a single
one, which increases the run time by about 50%, and because the
computer I am using (2.4Ghz dual Xeon) is not the fastest
available. On a faster computer running only a single location the
1300 PST forecasts could be made available around 40-60 minutes
earlier. But since the RASP forecasts have not yet been shown to
be useful, for now I consider forecast timeliness a secondary
issue.
And a yet-to-be-resolved conundrum is that
several changes I would like to make to improve forecast accuracy
would also significantly increase the run time and hence make the
forecasts less timely. In particular, in the interest of
providing more timely forecasts I have used a larger time step than is
desirable, which decreases forecast accuracy. The crux of the
matter is that at present these forecasts are at the edge of what is
possible and practical - the good news is that as computer power
increases in the next years the timeliness and accuracy of the
forecasts will improve.
The Future ?
If these forecasts prove useful, I would plan to
make the code public so that others might produce high-resolution
soaring forecasts for their own local regions. Such a
"distributed computing" concept is much more practical than trying to
have a centralized computational effort (whereas the RUC/ETA BLIPMAP
processing is only practical when done centrally since for them the
very large "native grid" files must be downloaded, vice the much
smaller files tha RASP downloads). What is required is a DSL
connection, a reasonably powerful Linux computer, and time and energy
and commitment. The forecast images could be uploaded to either
a club's webpages or to a special section of the DrJack website for
viewing by others.
However, I will be spending much time simply
creating the system and can't afford to spend additional time
shepherding people through the somewhat involved build procedure - so
people would have understand that the code comes with no support from
me other than to fix something that is found to be broken. My
present thought is that I would work with some volunteer to build a
forecast for his location and in the process create detailed
instructions describing the process. There would also be the
understanding that he would assist at least one other person with the
same process, who would in turn make the same commitment to assist one
other person, etc. - in this way the knowledge and work required
could be spread over many. Such users could also interact and
help each other using the RASP forum. But those are only my
present thoughts and the time for such an endeavor has not yet
arrived.
