MESOSCALE PRECIPITATION DISCUSSION 0665
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
323 PM EST SUN DEC 06 2015
 
AREAS AFFECTED...NW WASHINGTON... CENT COASTAL OREGON 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 062030Z - 070300Z
 
SUMMARY...HIGHLY DYNAMIC S/W WITH STRONG ASCENT CAPABLE OF .5"/HR
FOR A FEW HOURS LEADING TO 2-3" TOTALS OVER NEXT 6HRS COMPOUNDING
YESTERDAY'S TOTALS.  FOCUS SHIFTING TOWARD CENTRAL OREGON COAST
FOR PERSISTENT VERY MST PERPENDICULAR ONSHORE FLOW STARTING AOA
02-03Z.  

DISCUSSION...A VERY SHARP...NEGATIVE TILT EXTENSION OF ENERGY FROM
ALEUTIAN LOW CONTINUES TO SHIFT NORTHEAST WHILE BECOMING
INCREASINGLY OCCLUDED.  89GHZ LOOP SHOWS HIGHLY CYCLONIC CURVED
COLD FRONT WITH STRONG SURGE OF DEEP MOISTURE AT THE NOSE OF THE
WARM CONVEYOR BELT NEAR 46N128.5W...COINCIDENT WITH ENHANCING IR
TOPS AT THE APEX OF THE 100-120 KT (PER SATELLITE DERIVED WINDS). 
STRONG DIVERGENCE ALOFT FROM THE LEFT EXIT OF JET AND DPVA FROM
THE ATTENDANT S/W CONTINUE TO PROVIDE MODERATE UVVS THAT CURRENTLY
SUPPORT NEAR .25"/HR CURRENTLY.  CURRENT TRACKING APPEARS TO BRING
THESE RATES ASHORE ACROSS SW WA INTO THE OLYMPICS BY 22-23Z IN
LINE WITH HIGH-RES GUIDANCE PARTICULARLY THE ARW/NMMB AND RECENT
HRRR RUNS.  THOUGH THE TRACK DOES APPEAR TO BE A BIT FURTHER SOUTH
FOCUSING IN ON OLYMPICS RATHER THAN FURTHER NORTH ON VANCOUVER
ISLAND AS SUGGESTED BY THE CAMS. 
EXPECTATIONS OF INCREASED OROGRAPHIC ASCENT WITH 60-70 KT 85-7H
SWLY FLOW LIKELY TO SUPPORT RATES AROUND .5"/HR WITH POTENTIALLY
HIGHER RATES AT TIMES. ON A POSITIVE NOTE IS THAT THE WRAPPING
BACK WEST OF THE WARM CONVEYOR WILL LEAD TO SHORT DURATION OF
THESE RATES BEFORE THE COLD FRONT/OCCLUSION PRESSES THROUGH LIKELY
02-03Z LEAVING LINGERING LIGHT SCATTERED SHOWERS.  POTENTIAL FOR
UP TO 2" TOTALS SEEMS LIKELY WITH SLIGHTLY HIGHER AMOUNTS POSSIBLE
IN MOST EXTREME OROGRAPHY.  TYPICALLY THIS WOULD BE LESS OF A
CONCERN OVER THIS SHORT DURATION OF TIME...BUT ANTECEDENT
CONDITIONS FROM YESTERDAY'S 4-6" TOTALS COULD POSE ADDITIONAL
COMPOUNDING ISSUES PARTICULARLY WITH ANY DEBRIS FLOWS THAT WOULD
SLOW RUNOFF PROCESS.

CENTRAL OREGON COAST...TOWARD 02-03Z FOCUS OF HEAVY RAINFALL WILL
SHIFT DOWN COAST AS COLD FRONT PRESSES EASTWARD.  A SECONDARY WAVE
FURTHER UPSTREAM AND SHORTWAVE RIDGING WILL ALLOW SOUTHWARD
PROGRESS TO STALL AND ORIENT ONSHORE FLOW NEARLY PERPENDICULAR TO
THE CENTRAL COASTAL RANGE...LIKELY TO FOCUS IN LINCOLN AND LANE
COUNTIES.  TPWS IN EXCESS OF 1.5" WILL BE ADVECTED THROUGH A
NARROW CORRIDOR AND COULD POTENTIALLY HAVE SIGNIFICANT RAINFALL
TOTALS THROUGHOUT MONDAY MORNING. WILL CONTINUE TO MONITOR ON
MESOSCALE DETAILS THIS EVENING.     

GALLINA

ATTN...WFO...MFR...PQR...SEW...

ATTN...RFC...NWRFC...

LAT...LON   48362460 48192299 47822270 47182303 46022324 
            44342344 43432375 43402444 44382462 46202436 
            47402479 48232489