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<br />astimuta is increased by observaUon of certal' doad features -- such
<br />as overshooting topS, merging, or ~tatlo~ary stO~~5. Good results have
<br />been i1dicated io some tests, but the tnethod has <lot been perfeCtEd [or
<br />certa1n stor~ types. The NattonRl Environmeatal Satellite Service ia
<br />Cam~ Spri"g~, 'lArylaod, ""kes s3te1lite ratnhll ~sti"ate' "" request
<br />framl/SPO'.. There is nor,....lly a tt"", delay of 1 1/2hoursurlllore
<br />from the r~quest time to the ti~ users receive dat~.(9) Sateltite
<br />iO>aSes are usdul ",he" II storm Brst .tarts, but "s clouds spread, 1t
<br />becomes difficult to pick out the core of a sror~ to locate heavy
<br />rainfall. (Telephone conver3aUon '~ith :lr. Morry Paun, Denver Weather
<br />Service Forecs.tOfftce,7 lloveraber 1979).
<br />
<br />occurrio;\or is forecast ",tthin the r..nge of the Cheyenne radar, or at
<br />the r~quest of the D~nver ~SfO. The Cheyenne radar shoutd detect most
<br />stor", conditions. (interview ",ith Mr. nth Burton, D~nver '~~ath~r
<br />S~rvice Forecast Office, 20 Dec~",ber 1979).
<br />
<br />Another us~ of satellites is to moni~or rain or stream gaSe" "'hich
<br />have telemetry equi?,.e:1.t. The ~'~5 has <l li'lllt~d nllI.b~r of such Auto-
<br />mated Hydrological Observing Station (AH05) site. in Colorado. Most of
<br />these r~port on a 6-hour tiOle $ch~dule.
<br />
<br />Rainfall rate" are theoretic~lly reiated to the intensity of the
<br />radar echo or rdlecti~1ty frolll th~ raio-producing cloud. In thh
<br />region, however, low-level dry air may Cause precipitation to evaporat~
<br />0" rhe way to the ground. Other factor~ such as hail may distort the
<br />expe"ted relationship between rainfall end radar reflectivtty. Ground
<br />obse-rvationor "groundtrurhn is needed to verify rainfallinten.ity
<br />lev~ls gho",n on th~ radar screen.
<br />
<br />11;adar. N\,'S wcather rdd"u .ue located at Li:tO:1. and Cheyenn~. -~
<br />coi"r radar receiver ia ""'''ed by the local ",.ather consultant ret.~ined
<br />hy Larimer ~ounty. The effective ra"-g~ ef ra~u <"r ""king reliable
<br />~stlm"tes of rainfall i3 abo"t 70 ,"-il~s. The C"ch~ 18 PO\ldre River
<br />"a<lin:l$ fanher than de3irab1e from tl1e L10l0n rad.n bur is -~ell
<br />situated :Of the Cheyean~ radar. ~he ti~Qn radar i~ a ~SR-S7 1etwork
<br />radar and is 'O:'lOnitored 24 hours a d"y. The Cheyenne rad~r Is ~ I,'S~-HC
<br />100,,1 ",,,rning rada.r and is aottvated "'~"neVH pred~lt,,~lon I.
<br />
<br />In 1979, ~he D~nver ",etropol1tan area flash flood situation wa.
<br />~onitored by the ~~S and a ~rivate met~orological consuttant, both
<br />using color radar im&ge~ from Limon and Ch~yenne. The ?robabllity of
<br />detection of flash flood pot~nt1al dllY', that is, days in ",hich large
<br />~hunderstorms produced 1/2 inch or more of rain, ~a' 94 percent, ",ith a
<br />6 percent fa15~ alarm rate. Actusl flooding w"s predicted in five of
<br />seven ev~nts, for a 71 percent probability of det~ction, and th..re "'as
<br />a 38 percent false aiarlll r<lte. The radar recdver. were available for
<br />only hate of the flood se<l.on and only 00 a dial-l1p dc13yd basis.
<br />With dedicated pnon~ data 1tn~. to tne radar receiwns anJ OIOre
<br />experience, tne prediction rate is ex~ect~d to improve. (H)
<br />
<br />The U.S. G~otogical Sl1rvey haa awarded a contract ~o test the
<br />feasibillryofsatellitellKlnitoringofhydraul1cdata. 5rre"mg,'lgea
<br />are to be queriEd every 15 minutes with a~. addittonal t5 rdnute$ to
<br />provide data to the u>ler. Abo<.lt 75 sites will be selectad in ,,~ven
<br />state.. ..a sites aN located in t':1o Cnche la PO'ld~~ 'Uver >,,,.in. Th1"
<br />progrs'" 'Jeg~n in A.ugust 1980.
<br />
<br />OL\e po..ibte alternative for flash flood d"'tection would be fo,
<br />local interesU to purchase their 0010 wcather n.Jar. A ~".'S-ty~e radat
<br />~oul~ co,: fro~ $125,000 to "25n,000; mainten.nne ",ou1d cost several
<br />thousand dollau a year and a qualified operator would be requIred.
<br />This rad,lt would have to be iocated n'~I1Y fro" the "-o\Jntaias "0 the hea"
<br />could clear the foothills ~"d sweep over tho mou<1tatn ~re... ihis '..'''uld
<br />,,~ es"~nr1ally .-. ,lu~lteHion of the Cheyenne r~d<lr.
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