FVXX21 KWBC 310900 . VOLCANIC ASH ADVISORY STATEMENT ISSUED 0900 UTC 31 MAR 1999 BY THE WASHINGTON VAAC . POPOCATEPETL 99-055 MEXICO 19.02N 98.62W . BACKGROUND: POPOCATEPETL MEXICO (1401-09) SUMMIT HEIGHT 17930 FT (5465 M) . SOURCES OF INFORMATION: SIGMET FROM MEXICO CITY METEOROLOGICAL WATCH OFFICE. GOES8 INFRARED AND MULTISPECTRAL IMAGERY. 0000Z UTC MEXICO CITY UPPER AIR SOUNDING . ERUPTION DETAILS: ERUPTED AT APPROXIMATELY 31/0158 UTC . DETAILS OF ASH CLOUD: THROUGH 04 UTC ASH COULD BE SEEN IN SATELLITE IMAGERY AS IT RAPIDLY MOVED TOWARD THE EAST AND EASTSOUTHEAST. BY 04 UTC ASH COULD BE OBSERVED AS FAR AS 150 KM (80 NMI) EAST OF THE VOLCANO. HOWEVER MORE RECENTLY ASH HAS BECOME TOO DIFFUSE TO SEE IN MULTISPECTRAL OR INFRARED SATELLITE IMAGERY THROUGH 0830 UTC. . TRAJECTORY: THE 0000Z UTC UPPER AIR SOUNDING SUGGESTS THAT ANY ASH BETWEEN FL180 AND FL250 WOULD MOVE TO THE EAST OR EAST SOUTHEAST AT ABOUT 35 KNOTS. . 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/messages.html (all lower case except /VAAC/) . OUTLOOK: SEE SIGMETS AND VAFTAD. . THE NEXT MESSAGE WILL BE ISSUED BY 31/1500 UTC. . PLEASE REFER TO SIGMETS FOR CURRENT WARNINGS. . NNNN