MESOSCALE PRECIPITATION DISCUSSION 0688
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
855 AM EDT THU SEP 22 2016
 
AREAS AFFECTED...NORTHEAST NV...NORTHWEST UT...SOUTH CENTRAL ID 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 221300Z - 221830Z
 
SUMMARY...TRAINING SHALLOW CONVECTION OVER COMPACTED SOILS/AREAS
OF LOW FLASH FLOOD GUIDANCE MAY LEAD TO ISOLATED FLASH FLOODING
THOUGH 18Z. 

DISCUSSION...GOES-WEST WV LOOP INDICATES DEEP UPPER LEVEL LOW
DROPPING SOUTH WHILE DEEPENING INTO NW NV WITH A SHORTWAVE SPOKE
LIFTING ACROSS THE SNAKE RIVER BASIN WHILE ANOTHER WAVE ROUNDS THE
BASE OUT OF CENTRAL CA INTO NV.  THIS ALIGNMENT HAS SUPPORTED
STRONG JET STREAK AND HIGHLY DIFFLUENT PATTERN ACROSS NE NV INTO
ID/MT...SUPPORTING A LARGE WEDGE OF MID-LEVEL CLOUD SHIELD WITH
NICELY PRESENTED TRANSVERSE WAVES LIFTING NORTHEAST THROUGH IT. 
GIVEN THE STRONG DPVA WITH THE SHORTWAVE LIFTING NORTH EAST...THE
SURFACE PATTER INDICATES A DEEPENING LOW IN CENTRAL NV WITH FAIRLY
STRONG FRONTOGENETIC FORCING/WAA IN THE 700MB LAYER ACROSS E AND
NE NV LEAKING INTO EXT W UT.  THIS DEEPENING FLOW ALSO SUPPORTED
THE LOW LEVEL FLOW REGIME TO DRAW SOME TROPICALLY CONNECTED AIR
MASS ACROSS E NV/W UT.  TPW ANALYSIS SHOWS A BROADENING AREA OF 1"
TPWS UP TO THE NV/UT BORDER BUT AT LEAST .75" BACK TO THE SURFACE
LOW AND ATTENDANT WARM FRONT.  WITH THE CAA/STEEPENING LAPSE RATES
ALOFT AND THE WARMER LOW LEVEL FLOW...MODERATE INSTABILITY EXISTS
ACROSS CENTRAL AND EASTERN NV UP TO 500 J/KG MLCAPES PER THE RAP.
ISENTROPIC/FRONTOGENETIC ASCENT OVER THE WARM FRONT HAS BEEN
SUFFICIENT TO SUPPORT CONVECTIVE DEVELOPMENT ALONG THE SW PORTION
OF THE CLOUD SHIELD WEDGE EXTENDING FROM SE LANDER COUNTY ENE INTO
N WHITE PINE COUNTY.  RAIN RATES UP TO .75-1"/HR WITH ONE HOUR
TOTALS AROUND .5" ARE EXPECTED VERY CLOSE TO 1HR FLASH FLOOD
GUIDANCE VALUES SUGGESTING FLASH FLOODING IS POSSIBLE IN THE SHORT
TERM. 

ANALYSIS AND HI-RES CAMS SUCH AS THE 11Z HRRR/ARW AND NMMB SUGGEST
CELLS WILL CONTINUE TO REMAIN ANCHORED ALONG THE WARM FRONT WITH
PROGRESSION THAT SUPPORTS SOME ISOLATED REPEAT CORES IN THE SHORT
TERM GIVEN VERY SLOW/STATIONARY NATURE OF THE WARM FRONT. 
EVENTUALLY BY 14-15Z...HEIGHT FALLS FROM SHORTWAVE WILL EJECT
EASTWARD SHIFTING THE SURFACE LOW EAST EXPANDING THE BAROCLINIC
SHIELD NORTHWARD INTO NE NV AND INTO NW UT THOUGH 18Z EXPANDING
THE FLASH FLOOD THREAT FURTHER EAST WITH TIME. 

GALLINA

ATTN...WFO...BOI...LKN...PIH...SLC...

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

LAT...LON   42691396 42381290 41321282 40701334 39931497 
            39201617 39551664 40981564 42371494 
a