MESOSCALE PRECIPITATION DISCUSSION 0168
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
723 PM EDT FRI MAY 18 2018

AREAS AFFECTED...SE WY...ERN CO...FAR WRN NE

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

VALID 182322Z - 190222Z

SUMMARY...THERE IS A CONDITIONAL THREAT OF FLASH FLOODING BASED ON
SUPERCELL MOTION AND CELL MERGERS. THE CONVECTIVE ENVIRONMENT IS
GENERALLY FAVORABLE WITH DIFLUENT UPPER FLOW ATOP MOIST
POST-FRONTAL UPSLOPE.

DISCUSSION...AT 23Z A FEW CELLS HAD EXHIBITED VERY SLOW MOTION IN
BOULDER CO...AND ALSO UP ALONG THE CHEYENNE RIDGE. EARLIER CELLS
HAD PROMPTED FLASH FLOOD WARNINGS NEAR COLORADO SPRINGS...BUT HAD
SINCE BECOME OUTFLOW DOMINATED.

THE SYNOPTIC ENVIRONMENT IS FAVORABLE FOR CONTINUED SCATTERED
THUNDERSTORM ACTIVITY THROUGH THIS EVENING...WITH DIFLUENCE ALOFT
AND MOIST EASTERLY UPSLOPE IN THE LOW LEVELS. PRECIPITABLE WATER
VALUES AROUND 0.6 TO 0.8 INCHES ARE SOMEWHAT ANOMALOUS...AND MORE
ANOMALOUS WITH EASTWARD EXTENT AWAY FROM THE FRONT RANGE.
RELATIVELY SLOW DEEP LAYER FLOW ALSO FAVORS SLOW MOVEMENT...AND
ANY ROTATING STORMS WILL TAKE ON EVEN SLOWER MOVEMENT...TO NEAR
ZERO TO 5 KNOTS OVER NORTHEAST CO AND SOUTHWEST WY.

CELLS MAY NOT BE ABLE TO MAINTAIN THEMSELVES IN AN OVERLY
ORGANIZED FASHION...HOWEVER...AS HAD BEEN OBSERVED IN RADAR
TRENDS...GIVEN VERY WEAK FLOW AROUND 700 MB...AND GENERALLY
UNFOCUSED DEEP LAYER ASCENT. THE RISK OF FLASH FLOODING WILL BE
MORE CONDITIONAL AS TO WHERE INDIVIDUAL UPDRAFTS CAN BECOME
ORGANIZED FOR A PERIOD OF TIME BEFORE GUSTING OUT. CELL MERGERS
COULD ALSO LEAD TO BRIEFLY ENHANCED RAINFALL AMOUNTS. WFO BOU
NOTED AN OBSERVATION OF MORE THAN 2 INCHES OF RAIN AT THE NCAR
FOOTHILLS LAB PER NWS CHAT. ISOLATED 1 TO 2 INCH DOWNPOURS WILL
PROBABLY BE MORE COMMON THIS EVENING...AND MAY LEAD TO ADDITIONAL
FLASH FLOODING. THE OUTLINED AREA WAS DETERMINED BY OBSERVATIONAL
TRENDS BUT ALSO THE 12Z WRF-NMMB AND GEM REGIONAL QPF.

BURKE

ATTN...WFO...BOU...CYS...GLD...PUB...

ATTN...RFC...ABRFC...MBRFC...

LAT...LON   42210427 41810323 40460269 38450342 37920529
            38460521 38940478 39990521 40780535 41760596