MESOSCALE PRECIPITATION DISCUSSION 0425
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
155 PM EDT MON JUL 09 2018

AREAS AFFECTED...SOUTHWEST NEW MEXICO...SOUTHERN ARIZONA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 091754Z - 092350Z

SUMMARY...SCATTERED THUNDERSTORMS WILL BEGIN TO DEVELOP IN SW NEW
MEXICO AND SE ARIZONA AROUND MIDDAY AND THEN BECOME MORE NUMEROUS
AND SPREAD WEST INTO SRN ARIZONA DURING THE AFTERNOON. THESE
STORMS MAY HAVE RAIN RATES OF 1-2 IN/HR WHICH COULD LEAD TO FLASH
FLOODING...ESPECIALLY IN URBAN AREAS OR NEAR TERRAIN GRADIENTS.

DISCUSSION...REGIONAL RADARS AND GOES-15 VISIBLE SATELLITE SHOWED
CONVECTION BEGINNING TO INITIATE IN PORTIONS OF THE DESERT
SOUTHWEST... PRIMARILY IN CLOSE PROXIMITY TO THE SLIGHTLY COOLER
AIR ALOFT ASSOCIATED WITH AN UPPER LEVEL LOW DRIFTING WEST OVER
NEW MEXICO. THIS SAME REGION (THE SOUTHERN NM-AZ BORDER AREA) WAS
ALSO IN THE LEFT EXIT REGION OF A 30-50 KNOT UPPER LEVEL
JET...EVIDENT IN WATER VAPOR IMAGERY AS A POCKET OF DRIER (HIGH
PV) AIR CURLING AROUND THE NW PERIPHERY OF THE UPPER LEVEL LOW.
THUS THE AREA IS ALSO IN A FAVORED PLACE FOR UPPER LEVEL
DIVERGENCE...AND THE LARGE SCALE SETUP ALOFT FAVORS VERTICAL
MOTION INTO THE AFTERNOON INTO THE SOUTHERN TIER OF ARIZONA AS THE
LOW CONTINUES TO DRIFT WEST. THEREFORE...CONVECTION IS ALSO
EXPECTED TO DEVELOP AND/OR SPREAD WEST INTO SRN
ARIZONA...PARTICULARLY AS A COUPLE MORE HOURS OF INSOLATION ERODES
REMAINING CINH AND MID-LEVEL LAPSE RATES GET A LITTLE STEEPER WITH
THE APPROACH OF THE UPPER LEVEL LOW. AS CONVECTION REACHES
ARIZONA...IT SHOULD ENCOUNTER BOTH STRONGER INSTABILITY AND HIGHER
PWS (OVER 1.5 INCHES). THIS WILL SUPPORT MORE VIGOROUS CONVECTION
CAPABLE OF SUSTAINING 1+ IN/HR RAIN RATES FOR LONGER PERIODS OF
TIME.

THEREFORE...SPORADIC AND LOCALIZED HEAVY RAINFALL WILL BE POSSIBLE
CLOSE TO THE UPPER LEVEL LOW IN SW NEW MEXICO (GENERALLY PRIOR TO
21Z) AND COULD LEAD TO VERY LOCALIZED FLASH FLOOD ISSUES.
HOWEVER...THE THREAT OF FLASH FLOODING SHOULD INCREASE IN THE
21-00Z TIME FRAME IN SOUTHERN ARIZONA AS CONVECTION BEGINS TO
ENCOUNTER A MORE FAVORABLE ENVIRONMENT. 1-2 IN/HR RAIN RATES COULD
LEAD TO AREAS OF FLASH FLOODING...PARTICULARLY IN SMALL BASINS
AROUND TERRAIN GRADIENTS AND IN URBAN AREAS SUCH AS THE PHOENIX OR
TUCSON METRO AREAS.

LAMERS

ATTN...WFO...ABQ...EPZ...FGZ...PSR...TWC...

ATTN...RFC...CBRFC...WGRFC...

LAT...LON   34510869 34100695 32790650 31590757 31050865
            31071097 31941329 32861319 33791145