FVXX20 KWBC 211630
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VOLCANIC ASH ADVISORY STATEMENT
ISSUED 1630 UTC 21 JULY 1999 BY THE WASHINGTON VAAC 
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SOUFRIERE HILLS 99-185    WEST INDIES 16.7N 62.2W
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BACKGROUND:    SOUFRIERE HILLS MONTSERRAT (1600-05)
               SUMMIT HEIGHT 3000 FT (915M)
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SOURCES OF INFORMATION: GOES-8 VISIBLE AND MULTISPECTRAL IMAGERY
THROUGH 21/1215 UTC.  21/1200 UTC PRINSES JULIANA RADIOSONDE. 
ROOSEVELT ROADS NAS, PUERTO RICO.  SAN JUAN FLIGHT SERVICE CENTER.

ERUPTION DETAILS:  ERUPTION OCCURRED AT ABOUT 20/0910 UTC.
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DETAILS OF ASH CLOUD: PILOT REPORTS AND SERFACE OBSERVATIONS SUGGEST
THAT THE TOPS OF THE ASH CLOUD ARE SIGNIFICANTLY LOWER THAN PREVIOUSLY
ESTIMATED.  ONE PILOT REPORT INDICATED THIN ASH AND HAZE AT FL100 25
NMI EAST OF ST. CROIX AT 1402 UTC WHILE ANOTHER PILOT REPORT INDICATED
A BROWN THICK LAYER OF HAZE AT FL070 50 NMI EAST OF ST CROIX AT 1340
UTC. THE MOST RECENT PILOT REPORT FROM 1508 UTC INDICATED A LINE OF
VOLCANIC ASH TOPS OF UNKNOWN HEIGHT OVER ST. CROIX.  SURFACE
OBSERVATIONS FROM ROOSEVELT ROADS NAS IN EASTERN PUERTO RICO INDICATED
SCATTERED ASH WITH A BASE OF FL140 AT 1500 UTC AND 1600 UTC.  THIS
INFORMATION IN CONJUNCTION WITH BACK TRAJECTORY ANALYSES SUGGEST THE
ASH TOPS ARE LIKELY BELOW FL170.  ASH IS NOT DISCERNIBLE IN EITHER
INFRARED OR MULTISPECTRAL SATELLITE IMAGERY AND HAS BECOME
INCREASINGLY FAINT AND DIFFICULT TO DISCERN IN VISIBLE IMAGERY.  AT
1532 UTC ASH AND HAZE WAS LOCATED WITHIN 23 KM (12 NMI) EITHER SIDE OF
A LINE FROM 18.0N68.6W TO 18.1N66.2W TO 19.0N65.0W.  THE HAZE BEING
REPORTED IN SOME PILOT REPORTS MAY ALSO BE DUST WHICH HAS BEEN TRACKED
FROM AFRICA.  SO LONG AFTER THE INITIAL ERUPTION IT IS IMPOSSIBLE TO
DISTINGUISH BETWEEN DUST AND VOLCANIC ASH IN SATELLITE IMAGERY.
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TRAJECTORY: TOWARD THE NORTHWEST AROUND 10 KNOTS.
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REAL TIME SATELLITE IMAGERY ALONG WITH THIS AND OTHER VOLCANIC ASH
ADVISORY STATEMENTS OFTEN ACCOMPANIED BY A MAP DEPICTING ASH LOCATION
ARE AVAILABLE AT INTERNET URL ADDRESS
www.ssd.noaa.gov/VAAC/washington.html
(all lower case except /VAAC/)
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OUTLOOK:  SEE LATEST SIGMETS AND VAFTAD.
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THE NEXT MESSAGE WILL BE ISSUED BY 21/2230 UTC.
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PLEASE REFER TO SIGMETS FOR CURRENT WARNINGS.
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NNNN
"Attached Graphic Map Depicting Ash" 

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