FVXX21 KWBC 181900 . VOLCANIC ASH ADVISORY STATEMENT ISSUED 1900 UTC 18 MAR 1999 BY THE WASHINGTON VAAC . POPOCATEPETL 99-025 MEXICO 19.02N 98.62W . BACKGROUND: POPOCATEPETL MEXICO (1401-09) SUMMIT HEIGHT 17930 FT (5465 M) . SOURCES OF INFORMATION: GOES-8 VISIBLE INFRARED AND MULTISPECTRAL IMAGERY. MEXICO CITY UPPER AIR SOUNDING. . ERUPTION DETAILS: ERUPTION OCCURRED AROUND 18/1130 UTC . DETAILS OF ASH CLOUD: GOES 8 IMAGERY THROUGH 1815 UTC SHOWS THAT THE ASH PLUME HAS BECOME VERY DIFUSE AND HARD TO DISTINGUISH FROM METEOROLOGICAL CLOUDS. THE PLUME WAS LAST CLEARLY VISIBLE IN THE 1615 UTC IMAGE NEAR 22.1N 93.4W. BY FOLLOWING THE CLOUD MOTION SIGNATURES AND USING EXTRAPOLATION THE POSITION OF THE ASH PLUME AT 1815 IS NEAR 22.8N 91.8W. . TRAJECTORY: 1200 UTC MEXICO CITY SOUNDING SUGGESTS ASH BETWEEN FL350 AND FL400 WOULD MOVE TOWARD THE NORTHEAST AT ABOUT 65 KTS. . 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 AT 19/0100 UTC. . PLEASE REFER TO SIGMETS FOR CURRENT WARNINGS. . NNNN