MESOSCALE PRECIPITATION DISCUSSION 0637
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
638 PM EDT SUN AUG 06 2017

AREAS AFFECTED...SIERRA-NEVADA...SHASTA/SISKIYOU
RANGES...NORTHWEST TO CENTRAL/EASTERN NV

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

VALID 062235Z - 070400Z

SUMMARY...SLOW-MOVING SHOWERS AND THUNDERSTORMS WILL CONTINUE INTO
THE EVENING HOURS. THE THREAT FOR FLASH FLOODING WILL CONTINUE
OVER THE NEXT SEVERAL HOURS.

DISCUSSION...MID-AFTERNOON NON-OPERATIONAL GOES-16 0.64 MICRON/VIS
IMAGERY ALONG WITH RADAR OBSERVATIONS CONTINUES TO SHOW CLUSTERS
OF SLOW-MOVING SHOWERS AND THUNDERSTORMS UP ALONG WITH THE SPINE
OF THE SIERRA-NEVADA AND ADJACENT FOOTHILLS. MEANWHILE...SCATTERED
CLUSTERS OF CONVECTION ARE ALSO SEEN FARTHER EAST OVER CENTRAL NV
SLOWLY MOVING EASTWARD.

ALL OF THE ACTIVITY IS IN ASSOCIATION WITH AN UPPER LOW MOVING
GRADUALLY EAST ACROSS NORTHERN CA WITH A RATHER WELL DEFINED
TROUGH AXIS AND DEFORMATION ZONE EXTENDING EAST-SOUTHEAST ACROSS
THE GREAT BASIN. DESPITE THE INTRUSION OF DRY AIR IN THE 500/300MB
LAYER AND A GENERAL LOWERING OF PWATS...THERE IS PLENTY OF
INSTABILITY IN PLACE AND SUFFICIENT MID LEVEL MOISTURE FOR THE
ONGOING CONVECTIVE ACTIVITY TO PRODUCE SOME HEAVY RAINFALL
RATES...WITH SOME HOURLY ACCUMULATIONS APPROACHING 1 INCH.

THE STRONGEST FORCING OVER THE LAST COUPLE OF HOURS HAS BEEN UP
OVER THE NORTHERN SIERRA-NEVADA AND ADJACENT RANGES INVOLVING THE
SHASTA/SISKIYOU REGION. THIS IS WHERE SOME OF THE COLDEST CLOUD
TOPS HAVE BEEN AND WHERE THE MOST IMPRESSIVE VISIBLE IMAGERY
PRESENTATION HAS BEEN SEEN. MOST LIKELY THIS IS WHERE THE HEAVIEST
RAINFALL RATES HAVE BEEN OVER THE LAST HOUR.

GIVEN THE SLOW MOVEMENT OF THE CELL ACTIVITY AND INTERACTION OF
DEEPER LAYER FORCING WITH THE HIGHER TERRAIN...SOME RAINFALL
TOTALS OF 1 TO 2 INCHES ARE EXPECTED...AND THIS MAY LEAD TO SOME
FLASH FLOODING CONCERNS AND ESPECIALLY NEAR ANY BURN SCAR AREAS.

ORRISON

ATTN...WFO...EKA...HNX...LKN...MFR...REV...SLC...STO...VEF...

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

LAT...LON   42032103 41881989 41101885 40191746 39891626
            39541485 38971412 38301404 37881434 37451544
            37061637 36601669 35911723 35861757 36111819
            36821869 37711928 38271965 38832006 39432042
            39872074 40202128 40502159 40952191 40972242
            40682276 40302278 39572266 39612291 39902318
            40452336 40992341 41652312 42002236