MESOSCALE PRECIPITATION DISCUSSION 0589
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
116 AM EDT MON OCT 19 2015
 
AREAS AFFECTED...SOUTHERN UT...NORTHWEST AZ 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 190510Z - 190945Z
 
SUMMARY...INTENSE BAND OF SHOWERS AND THUNDERSTORMS LIFTING
THROUGH NORTHWEST AZ WILL BEGIN TO IMPACT SOUTHERN UT OVER THE
NEXT FEW HOURS. FLASH FLOODING IS LIKELY GIVEN RAINFALL RATES OF
UP TO 2 INCHES/HOUR.

DISCUSSION...A BAND OF STRONG CONVECTION CONTINUES TO IMPACT
PORTIONS OF NORTHWEST AZ IN RESPONSE TO A WELL-DEFINED SHORTWAVE
IMPULSE ROUNDING THE BASE OF THE BROADER UPPER LEVEL TROUGH OVER
CA/NV. THE ENERGY WHICH IS CROSSING INTO EXTREME WESTERN AZ AS
DEPICTED IN THE LATEST IR/WV SATELLITE IMAGERY IS FOCUSING A
CONCENTRATED AREA OF ENHANCED VERTICAL ASCENT OVER NORTHWEST
AZ...AND IS INTERACTING WITH A LINGERING SOUTH/NORTH ORIENTED FEED
OF MODEST INSTABILITY THAT EXTENDS AHEAD OF THE SHORTWAVE FROM
NORTHERN MEXICO UP ACROSS AZ AND INTO FAR SOUTHERN UT.

MEANWHILE...PWATS CONTINUE TO BE RATHER ANOMALOUS AHEAD OF THE
ENERGY WITH VALUES RUNNING LOCALLY 2 TO 3 SIGMAS ABOVE THE MEAN.
AN EXPECTED INTRUSION OF MID LEVEL DRY AIR WILL ALLOW THESE
ANOMALIES TO BEGIN TO DECREASE WITH TIME...BUT THE PRESENCE OF
STEEP MID LEVEL LAPSE RATES AND BROADER LARGE SCALE ASCENT WITH
THE SHORTWAVE WILL MAINTAIN THE THREAT FOR RELATIVELY STRONG AND
ORGANIZED CONVECTION FOR A FEW MORE HOURS.

THE HIRES GUIDANCE FAVORS THE CONVECTION LIFTING NORTHEAST IN
ALIGNMENT WITH THE DEEPER LAYER MEAN FLOW...AND THIS WILL FAVOR AN
ADDITIONAL RISK FOR TRAINING CELLS AS THE HEAVY SHOWERS AND
THUNDERSTORMS CONTINUE TO LIFT ACROSS NORTHWEST AZ AND GRADUALLY
MOVING INTO SOUTHERN UT.

THE 00Z ARW AND 00Z NMMB APPEAR TO BE UNDERDONE WITH THEIR
RESPECTIVE QPF OUTPUT...AND BASED ON RECENT SURFACE
OBSERVATIONS...IT IS EXPECTED THAT INTENSE RAINFALL RATES OF 1 TO
2 INCHES/HR WILL OCCUR. ADDITIONAL STORM TOTAL AMOUNTS OF 2 TO 4
INCHES WILL BE POSSIBLE LOCALLY OVERNIGHT...AND THIS WILL LIKELY
RESULT IN FLASH FLOODING. THIS WILL PARTICULARLY BE THE CASE IN
LOW LAND DRY WASHES/ARROYOS AND ALSO OVER ELEVATED TERRAIN WITH
EMBEDDED CANYON CHANNELS. WILL CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...FGZ...GJT...SLC...VEF...

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

LAT...LON   38851161 38791087 38041031 36871052 35311191 
            34871322 35481402 36351399 37381358 38161280