Blip

For several years now "Dr. Jack" Glendening, a West-coast meteorologist, has arranged an on-line soaring-specific forecast based on National Weather Service data. Although that data is available elsewhere, putting it all together into a forecast of the day's thermal height and strength (and cloudiness) is a chore better left to a computer program. His setup also generates color-coded maps that neatly show the wider geographical patterns. But for local, or even short-range cross-country flying, you can't beat his one-page textual summary for a specific location, known as "BLIPspot". The closest BLIPspots to us were in Mass. and Ontario, and for years I've wanted one in our area.

So now I've gone ahead and asked Dr. Jack to make one for us, located at the Montpelier airport. Why there? It is not a soaring base per se, but the 3 soaring operations in Northern Vermont are within 20 miles around it. It does not boast elevation as high as nearby hills, but is 500 feet higher than the valleys, and represents the relatively lower ground between the mountains where some thermals are needed in order to soar cross-country in our area. We can then expect lift to be better in the mountains. If we were to base a BLIPspot on Spruce Mountain instead, for example, the forecast may be good for the mountains, but would be overly optimistic for most of the XC area. Also, this airport is a TAF, METAR and ASOS spot, and thus one can compare the actual temperature and dewpoint, reported hourly, with the forecast and adjust one's expectations accordingly.

BLIPspots are freely accessible to anybody, although you need to "register" with Dr. Jack's site. But the sponsor of a BLIPspot needs to pay an annual fee to create and maintain it. If you find the BLIPspot useful, consider helping me with the payment, this year or in the future.

The new BLIPspot can be accessed either via the main BLIPSPOT page, or directly at this link.

The location of the new BLIPSPOT is shown on the regional "grid orientation" map - it can be accessed via an "Identified Locations" map for the NE region.

Important message from Dr. Jack:

PLEASE PASS ALONG THE FOLLOWING INFORMATION TO ANY WHO WILL WANT TO ACCESS THIS BLIPSPOT:

This BLIPSPOT is available for viewing by anyone via the internet, but access to the "current day" forecasts (which everyone will want) does require that each user individually "register" (which is free) at this link. I require individual registration, rather than group registration, because knowing the number of individual users of each forecast product is important to me.

Registration also allows access to the other "free" DrJack forecasts, which includes "Thermal Updraft Velocity" BLIPMAPs, "Buoyancy/Shear Ratio" BLIPMAPs, all "Previous Day" BLIPMAPs, and all BLIPSPOTs. "Subscription" (which is not free) is required to gain access to the other DrJack BLIPMAP forecasts. Normally registered/subscribed access occurs through use of a DrJack registration "cookie", for which one's browser must accept cookies from the "drjack.info" domain. (In lieu of accepting cookies, more complex "cookieless" access methods are available.) For further information on DrJack registration, see this link.

Notes from Moshe:

* I use cookieless access by embedding my registered ID in the URL thusly:

http://www.drjack.info/BLIP/RUC/SPOT/FCST/montpelier_vt.txt?id=user&pw=password

* For BLIPMAPs go here.

* More details on the BLIPMAP and BLIPSPOT parameters can be found here - I've written up some interpretive text (shorter than the page linked above, longer than the brief definitions in the bottom of the BLIPspot page itself):

The BLIPspot includes forecasts for several times of day, the important ones for us would be: 15Z (11 am EDT), 18Z (2 pm), and 21Z (5 pm) - spanning the possible soaring hours. Note that the time dimension is only available in BLIPSPOTs, not in the BLIPMAPs.

Temp@2m is the forecast ground temperature (actually 2 meters above ground), on which the predicted thermals are based, and can be compared with actual temperature (as measured or reported in METARs, e.g. at 11am) to judge whether the BLIPspot forecast is working out.

BL throughout stands for "boundary layer", the part of the lower atmosphere mixed by the thermals.

BL Depth shows how high the thermals will reach AGL.

BL Top shows the altitude MSL at the top of the thermals.

Hcrit: the very tops of the thermals are too weak to use, "Hcrit" shows the expected top of the usable part of the thermals [ftMSL] (assuming blue thermals, otherwise cloudbase caps the usable top).

Hgt.Variab. shows the uncertainty or variability of the BL depth, it will be this much higher over hot spots (4 degrees hotter - or effectively so, via higher ground elevation). This variability is influenced by the temperature profile of the atmosphere: if there is a sharp inversion capping the thermals, for example, then this variability will be small. On the other hand, if the lapse rate is still high at the tops, the thermals will be significantly higher over hot spots (or lower, if the ground temperature turns out lower than forecast).

W* is the Thermal Updraft Velocity (in fpm - subtract glider sink rate (typically about 150 fpm) to get climb rate).

B/S = Buoyancy/Shear Ratio. This compares the upward buoyancy of the thermals to the horizontal shear due to the change in wind speed or direction with altitude. Thermals may be unworkable if B/S is 5 or less.

BL Wind = Wind Speed averaged through BL [kt] - keep in mind that wind speed may change quite a bit with altitude - look at the wind profile at the bottom of the BLIPSPOT.

Direction = Wind Direction averaged through BL [degTrue] - keep in mind that wind direction may change quite a bit with altitude - look at the wind profile at the bottom of the BLIPSPOT.

CLOUDpotent predicts the potential for the thermals to condense into cumulus clouds. Expect clouds if this is positive. If this is large then the clouds will be thick. (This number is the height difference between the top of the thermals (if they were blue) and the expected cloudbase (due to moisture).

sfcLCL = Base of Lowest Clouds, if CLOUDpotent>0 (LCL = Lifting Condensation Level based upon sfc. humidity) [ftMSL]. If that's higher than Hcrit then the prediction is that cloudbase will be unreachable.

ODpotential is the potential for "overdevelopment" - expect extensive clouds if positive. (This number is the difference between H(TI=0) & blCL) [ft].

bLCL = Base of Extensive Clouds, if ODpotential>0 (bl CL = Condensation Level based upon BL humidity) [ftMSL] - the difference between this and sfcLCL is that this is based on the moisture of the humidity of the whole BL, while sfcLCL is based on the humidity near the surface - if the air aloft is fairly dry, then there will not be "overdevelopment" and the condensation of the moisture brought up from near the surface will result in only limited cu.

CAPE = Convective Available Potential Energy [J/kg] - if this is high then the condensation in clouds will release a lot of additional "latent" heat and the cu will get thick and there may be thunderstorms.

DewPt@2m = Dew Point Temp. at 2m AGL [F] - this is the basis for the forecast of cloudbase (sfcLCL), and can be compared with actual dewpoint (as reported in METARs) to judge whether the BLIPspot forecast is working out.

As you can see, there is a lot of good info at-a-glance in the BLIPspot: not just how strong the thermals will be, but also their workable height, change during the day, and the potential for overdevelopment.

Additionally, the BLIPspot lists the predicted wind profile (speed and direction) at different altitudes at several times. The asterisks in this table bracket the BL top altitude.

One thing the BLIPspot does NOT offer is a sense of how things will be different in different places. If planning a long XC, one should also look at the BLIPmaps, which roughly describe many of the same parameters via color coding on a map. BLIPmaps for thermal strength and B/S ratio are available free (as are BLIPspots, once sponsored), while the other BLIPmaps are available by paid subscription.

- Moshe