STORM2K

As y'all know, I've been interested in the weather since I was about 4 yrs old......it has ALWAYS been a fasanation to me, as well as most of us here are, there's only ONE little problem for me..........I don't quite know how to read a doppler radar image, I know.....I should BUT......

During the Kinishba Fire, we learned a LOT from DJ about doppler as well as DJ learning a lot about fire behavior from Michelle. Anyways.....any infor would be appreciated. The info I'm looking for has to do with the color code on the left hand side of NOAA'S/NWS Flag doppler site......how can you tell the exact impact an area is going to have, I know the darker reds and oranges means heavy rain and hail.....right???

Thanks for not laughing TOOOOOOOOO loud "LOL!"

Dennis

BTW......the reason for this question, take a look at the NWS/FLAG doppler, we've got a pretty intense cell moving in...........in fact, "I'M OUTTA HERE, don't want to toast my box!"

Dennis

azsnowman wrote:As y'all know, I've been interested in the weather since I was about 4 yrs old......it has ALWAYS been a fasanation to me, as well as most of us here are, there's only ONE little problem for me..........I don't quite know how to read a doppler radar image, I know.....I should BUT......

During the Kinishba Fire, we learned a LOT from DJ about doppler as well as DJ learning a lot about fire behavior from Michelle. Anyways.....any infor would be appreciated. The info I'm looking for has to do with the color code on the left hand side of NOAA'S/NWS Flag doppler site......how can you tell the exact impact an area is going to have, I know the darker reds and oranges means heavy rain and hail.....right???

Thanks for not laughing TOOOOOOOOO loud "LOL!"


Dennis

That's right Dennis, the more orange and red, it means the colder the cloud tops and heavier precipitation.

Dennis, that's actually a good question and does require some interpretation as well to decipher the color codes ... including VIL (which determines what the DBZ or decibel reading in which hail is being read by the Doppler) ... Base Reflectivity detects the lower levels of the atmosphere while the composite shows the maximum DBZ in the entire cross-section of a storm and can be used to detect the core (or hail) of a storm ... the composite reflectivity will be higher and more widespread than the base reflectivity.

Below is a link to RadarInfo for anyone interested in reading.
http://www.crh.noaa.gov/radar/radinfo/radinfo.html

The Charleston, SC Storm Spotter Newsletter contains information regarding the VIL (Vertically Integrated Liquid) determines the freezing level and Dbz reflectivity threshold of hail on a given day based on many factors in a given storm situation.

Scroll down a little to find the Topic (Detecting Hail with the VIL product)
http://wchs.csc.noaa.gov/SC2003/spring/page2.html
It's continued on page 3 as well.

Thanks for all that info, SF...I really appreciate it! I could learn some of that stuff, too...

Ditto SF! Very good explanation of the different graphs and radars!

Help page from NWS

http://www.srh.noaa.gov/radar/radinfo/radinfo.html

These links should help

http://www.theweatherprediction.com/radared/index.html

More advanced:
http://www.srh.noaa.gov/shv/Techniques_for_Warnings.htm

http://okfirst.ocs.ou.edu/train/materials/radar.html

http://www.crh.noaa.gov/pah/science/emrdr3/

Another point to consider Dennis, is that radar reflectivity is a mathematical calculation and as such, it can be set to be "more sensitive or less sensitive." Seasonal changes in the Midwest for example, require "finetuning" of the radar sensitivity levels to better pick up snow rather than thunderstorms.

Just some more complications to add to the mix.

include determining at what level the radar beam intercepts the storm (contrary to popular opinion, radar does not propagate in a straight line but on a path with a radius of curvature of 3/2 Earth's radius due to atmospheric refraction), the widening of the beam with distance, side lobes in the antenna pattern, and non standard (or anomalous) propagation within the atmosphere-most often due to temperature or moisture inversions.

Steve

Aslkahuna wrote:include determining at what level the radar beam intercepts the storm (contrary to popular opinion, radar does not propagate in a straight line but on a path with a radius of curvature of 3/2 Earth's radius due to atmospheric refraction), the widening of the beam with distance, side lobes in the antenna pattern, and non standard (or anomalous) propagation within the atmosphere-most often due to temperature or moisture inversions.

Steve

It depends on whether 'Clear Air Mode'updated every 10-12min vs 'Precip
Mode' ...more senstitive to 240km to Base Reflectivity and ultimately 'Composite Storm Reflectivity'with apparent 'Virga' to flatlanders
hitting upper elevations.
Note...the latter is faster by 40%..on avg...and each rad is calibrated per MSL or mean sea level.
Wanna talk Doppler?I'm here anytime.BTW..DB=Decibels or sound relflex
Z=Intensity of the RA or particulates to hail+ backup
There are two setiings..
the 50-60-70 DBz for Summer Storms
The lower set for winter..as snow does not refect as intensely as RA
However..the Color Scale remains intact for both.\
See 'NOAA Products' for a further explaination.

would not affect the physical aspects of the propagation of the radar beam as determined by the atmospheric conditions or the antenna pattern. The transmission mode is a function primarily of pulse power, pulse length, and PRF. the latter too also being a determining factor is resolution. The old CPS-9 had a short pulse/high PRF setting which could be used in short range and which gave great resolution which is how I got some great photos in April 1964. It was a 3.2 cm radar which tends to be attenuated by heavy rain. Another thing not affected by the transmission mode will be the altitude at which the beam intercepts the storm which is determined by the geometry of the situation. This is why spotters are still need since rotation detected by Doppler at 100 miles (160km) out will not be in the lower levels of the storm which is where tornado initation occurs. This is because the curvature of the propagation path of the radar has a greater radius than the Earth so the low levels of the storm will be below the radar horizon. Additionally, you lose reolution further out as the beam spreads out. Reflectivity or dBZ is an old term-I remember reading about in Louis Battan's book on Radar Meteorology and Air Force training materials during my in house training on Radar at my first assignment in 1962. At the Met Team at FHU we had direct access to a Doppler Radar in 1988 and I do know what a TVS looks like-having seen one up close on that Doppler.

Steve

Kahuna,
Allow me to explain my basis.I am speaking of the Precip(that being a faster load time vs Clear Air on 88-D).This is why a Clr Mode on the PHX 88-D is such a pain in the azz.So much ground clutter..it's tough to determine a flock of inbound Geese Canadien vs local virga or just Urban heat Island Clutter off the base Reflectivity.
Moreover..I should have emphasised that indeed I did not mention the 'Toggle' feature on 88-D as they correspond.For instance..a KEMX Base Ref to a Toggle to YUM or SAN has Elevation issues each unique that Build-10 Software does a nice job of handling.
Also..not in the 88-D Purest realm..I have used Raytheon systems for Marine/Aviation sweeps that are calibrated with algorithisms unique to the system.The Marine systems that were carried over to Gen Aviation use a similar set,however,the speed of the Aircraft to 190kt to 22.5K Ft asl needs a wider beam as opposed to the Marine/used for max 55kt water speed AT asl.The software used was good,however somewhat tricky to calibrate.They are aslo mucho bucks.

boils down to the guy at the console-tonight was a perfect example. I called NWS TUS with a report that a severe boomer was about to hit SV. The guy at the other end said that his radar reading didn't indicate a severe storm-meanwhile, I'm watching outflow clouds zipping along at a good 60-70 mph. The problem is that the storm was partially in the terrain shadow of the Whetstones at the time. So instead of getting a lead on the warning he got it out after the winds at the Airport hit 56kt which means that the storm had swept across most of SV at the time. Visually, anyone who saw the storm knew it was a severe storm.

Steve

Thought I'd add a few things...

The Z/R relationship on the WSR-88D radars is changed depending on the type of precipitation and time of year. This is the way the radar's software calculates precipitation estimates vs actual reflectivity measurements.

The relationships and rain rate can be found on this page:
http://www.roc.noaa.gov/ops/z2r_osf5.asp

The tropical relationship is very important when being involved with landfalling tropical cyclones. I received 5.10" of rain with Isidore last September. Based on radar reflectivities and the duration of the event, I'd normally expect only about half of that amount (differences in raindrop size cause differences in radar reflectivity). I can recall that our old WSR-57 and WSR-74 radars would often only depict D/VIP 3 to 4 at the most with tropical cyclones (up to 45 dBZ), which wouldn't signal high rain rates with most extratropical systems. This is probably attributed to less powerful radar units and beamwidth (2 degrees of the '57 vs .95 degrees of the 88D).

Light precipitation (drizzle and light snow) may or may not be detected by the 88D. My experience shows that drizzle may be detected at ranges up to 50 nm at times, usually at dBZ levels of less than 10. Sometimes this may show up on Clear Air Mode, but that may also be embedded within ground clutter and other non-precipitating echoes. Radar operators often use Clear Air Mode during times of no precipitation, or during snowy situations (at least around here). Some providers that create 'mosaics' of many radars, do not always provide the full 15 color spectrum of the data. TWC doesn't display the 5-15 dBZ data on their images, so light precipitation is often missing from their products.

Notes on severe weather detection with the WSR-88D...

While the radar can detect precipitation out to 248 nm, the algorithms that create the data and severe weather detection do not.

Within 124 nm of the radar (assuming no terrain shadows) at 0.5 degree elevation...the radar can use the velocity products (which include the TVS and MESO algorithms), as well as precipitation estimates and HAIL detection (size and probability). At the edge of the 124 nm circle, the radar's beam will average 14,700 feet ( 2.5 miles) AGL (above ground level), assuming no terrain or temperature influences.

Between 124 and 186 nm, only the reflectivity algorithms work. The radar's beam is approximately 30,300 feet AGL (3.7 miles) at the edge of this circle. Shallow precipitation events will not be detected at this range.

Between 186 and 248 nm, only reflectivity shapes can be seen on the radar display. At this point, the radar beam is approx 50,500 feet AGL (5 miles) at the edge of this circle. Only the tallest thunderstorms will be scanned at this altitude.

Currently, the WSR-88D standard scanning proceedures limit the lowest elevation angle of the antenna to 0.5 degrees. The radar's hardware can scan down to 0 degrees (-1 degree limitation). Our older radars (the '57 and '74s sometimes scanned down to zero degrees).

All of the 88D radars have standard scanning proceedures that they follow. These include two pulse lengths in Clear Air Mode (mode B 31 and 32) and two precipitation mode pulse lengths (mode A 21 for standard and A 11 for severe weather rapid scan). Scanning proceedures can be found here:
http://weather.noaa.gov/radar/radinfo/radinfo.html

with the KEMX 88D is that although it's located on top of a hill (Empirita Mountain) at 5319 ft, there are mountains up to 7k not far SE of it and to 10k to the SW and we get some really bad shadowing at 0.5 deg elevation.
So happens that the shadow to the SE covers part of the area where the severe storms that hit SV undergo rapid intensification.

Steve

It must be aggravating being a meteorologist in the western United States. The Rocky Mountains shadow the snowfall on the radar. It makes it difficult to follow the current weather and to nowcast properly.

is the sparseness of the population in the West plus the fact that all of that varied terain makes for some very interesting local effects. In the longer term, the models do not have good resolution of the terrain (most of them miss the Huachucas for example) so terrain effects are poorly modeled except by the hi-res ones.

Steve