MESOSCALE PRECIPITATION DISCUSSION 0560
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
834 AM EDT TUE JUL 25 2017

AREAS AFFECTED...SOUTHEAST NV...NORTHWEST AZ...UT...NORTHWEST CO

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 251230Z - 251830Z

SUMMARY...SLOW-MOVING SHOWERS AND THUNDERSTORMS WITH VERY HEAVY
RAINFALL WILL CONTINUE THROUGH THE MORNING HOURS. FLASH FLOODING
IS LIKELY.

DISCUSSION...THE LATEST EXPERIMENTAL GOES-16 10.3 MICRON/IR DATA
SHOWS A RATHER CONCENTRATED AND PERSISTENT AREA OF COLD-TOPPED
CONVECTION OVER ESPECIALLY SOUTHEAST NV...FAR NORTHWEST AZ AND
SOUTHWEST UT IN ASSOCIATION WITH A CLASSIC MONSOON SET-UP FOR
HEAVY RAINFALL. MORE SCATTERED AND DISORGANIZED CONVECTION IS
NOTED FARTHER OFF TO THE NORTHEAST ACROSS ADJACENT AREAS OF
CENTRAL/EASTERN UT AND INTO FAR NORTHWEST CO. THE CONVECTION IS
FOCUSING IN VICINITY OF A 700 MB TROUGH AXIS WHICH IS ENHANCING
CONVERGENT FLOW WITHIN A MODESTLY UNSTABLE AND VERY MOIST COLUMN.

PWATS THIS MORNING REMAIN HIGHLY ANOMALOUS ACROSS THE
REGION...WITH VALUES OVER SOUTHEAST NV...NORTHWEST AZ AND
SOUTHWEST UT OF 1.7 TO 2.0 INCHES. THESE ARE AGAIN A SOLID 3+
STANDARD DEVIATIONS ABOVE NORMAL AND THE DEPTH OF THE MOIST COLUMN
IS CONFIRMED BY A 09Z CIRA-LPW DATA PLOT WHICH SHOWS A SUBSTANTIAL
AMOUNT OF TROPICAL MOISTURE GETTING PULLED NORTH IN BETWEEN AN
UPPER LOW/TROUGH OVER CENTRAL/NORTHERN CA AND THE WESTERN
PERIPHERY OF THE SUBTROPICAL RIDGE OVER THE SOUTHERN HIGH PLAINS.
THE RESULT CONTINUES TO BE CONVECTIVE ELEMENTS IN AN ENVIRONMENT
CONDUCIVE TO EXTREMELY HEAVY RAINFALL RATES...AND ESPECIALLY WITH
LOCALIZED OROGRAPHICS/UPSLOPE FLOW OVER THE HIGH TERRAIN.

THE SW/NE ORIENTED LOW TO MID LEVEL TROUGH AXIS IS FORECAST TO
GRADUALLY SHIFT EAST THROUGH MIDDAY...WHICH MAY ALLOW FOR THE
CONVECTION OVER SOUTHEAST NV AND NORTHWEST AZ TO SHIFT A BIT
FARTHER EAST AND PERHAPS SOUTHEAST WHERE SOMEWHAT BETTER
INSTABILITY IS EXPECTED TO BE FOCUSED.

ADDITIONAL RAINFALL AMOUNTS THROUGH 18Z OF 2 TO 3 INCHES...WITH
ISOLATED AMOUNTS PERHAPS UP TO 4 INCHES WILL BE POSSIBLE OVER FAR
SOUTHEAST NV...NORTHWEST AZ AND FAR SOUTHWEST UT.
HOWEVER...POCKETS OF HEAVY RAINFALL WITH AS MUCH AS 1 TO 3 INCHES
WILL BE EXPECTED FARTHER NORTHEAST UP ALONG THE TROUGH AXIS ACROSS
AREAS OF CENTRAL/EASTERN NM AND NORTHWEST CO. GIVEN THE RECENT
HEAVY RAINFALL AND THE ADDITIONAL AMOUNTS FORECAST THIS
MORNING...FLASH FLOODING IS LIKELY.

ORRISON

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

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

LAT...LON   40990940 40980876 40840804 40470772 39690787
            39000861 38720889 37700974 37081064 36231196
            35561333 35271464 35951565 36931569 37521539
            38141473 38711300 39441170 40541058