MESOSCALE PRECIPITATION DISCUSSION 0693
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
635 PM EDT FRI SEP 23 2016
 
AREAS AFFECTED...EASTERN WY...FAR WESTERN NE...WESTERN SD 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 232235Z - 240235Z
 
SUMMARY...CONVECTION FORMING IN A STRONG UNIDIRECTIONAL FLOW COULD
RESULT IN TRAINING...LEADING TO A FLASH FLOOD THREAT INTO THE
EARLY EVENING HOURS. 

DISCUSSION...REGIONAL RADARS HAVE SHOWN A SLOW INCREASE IN
CONVECTION DEVELOPING OVER PORTIONS OF SOUTHEAST CO AND THE NEARBY
WESTERN NE PANHANDLE. THE CONVECTION IS FORMING IN AN AREA OF
500-1000 J/KG MLCAPE...AS SOME OF THE EARLIER LOW LEVEL CIN HAS
BEEN ERASED BY HEATING. PRECIPITABLE WATER VALUES HAVE ALSO BEEN
SLOWLY INCREASING...WITH THE CONVECTION DEVELOPING IN A
PRECIPITABLE
WATER GRADIENT LYING ACROSS SOUTHEAST WY INTO WESTERN NE. 

THE KCYS RADAR INDICATED HOURLY RAINFALL RATES NEAR 1.25 INCHES
OVER SOUTHERN ALBANY COUNTY IN WY. HOWEVER...RAP SOUNDINGS IN THIS
AREA SHOWED A FAIR AMOUNT OF DRY AIR IN THE MID LEVELS... WHICH
SUGGEST THAT THE AIRMASS CURRENTLY IS BETTER PRIMED FOR HAIL THAN
HEAVY RAINFALL (AND THIS IS BORNE OUT BY THE HCA PRODUCE FROM THE
CYS RADAR...WHICH INDICATED HAIL).

HOWEVER...RAP SOUNDINGS ACROSS EASTERN WY...FAR WESTERN NE AND
WESTERN SD SHOWED THE COLUMN MOISTENING WITH TIME...AS A SHORT
WAVE APPROACHES FROM SOUTHWEST CO. AHEAD OF THE SHORT WAVE...THE
MID AND UPPER LEVEL FLOW BECOMES INCREASINGLY DIFFLUENT...WITH THE
BEST LIFT EXPECTED BETWEEN 23Z AND 03Z. DURING THAT TIME... THE
RAP INDICATED THAT MUCAPE VALUES BETWEEN 500-1000 J/GK SHOULD BE
IN PLACE...AS PRECIPITABLE WATER VALUES INCREASE TO NEAR 1.25
INCHES.

THE MOISTURE AND INSTABILITY SHOULD BE SUFFICIENT TO SUPPORT AT
LEAST SCATTERED CONVECTION INTO THE EARLY EVENING HOURS. A STRONG
UNIDIRECTIONAL FLOW AHEAD OF THE SHORT WAVE COULD PROMOTE TRAINING
OF THE CONVECTION...ESPECIALLY ACROSS FAR WESTERN WY INTO
SOUTHWEST SD. THE LATEST HRRR/EXPERIMENTAL HRRR INDICATED THE
POTENTIAL FOR 2.00 INCH RAINFALL TOTALS IN AREAS WHERE THREE HOUR
FLASH FLOOD GUIDANCE VALUES ARE AS LOW AS 1.00 TO 1.50 INCHES
(LOWEST OVER NORTHEAST WY AND SOUTHWEST SD). THE POTENTIAL FOR
TRAINING INCREASES THE FLASH FLOOD THREAT IN THESE AREAS. IT IS
POSSIBLE THAT CONVECTIVE COVERAGE COULD A LIMITING FACTOR FOR
FLASH FLOODING...SO AT THIS TIME FLASH FLOODING IS CONSIDERED
POSSIBLE.

HAYES

ATTN...WFO...BYZ...CYS...LBF...UNR...

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

LAT...LON   45730281 45190237 41820289 41350432 41960514 
            43380515 45060418