MESOSCALE PRECIPITATION DISCUSSION 0010
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
218 AM EST MON JAN 29 2018

AREAS AFFECTED...OLYMPIC PENINSULA OF WA

CONCERNING...HEAVY RAINFALL

VALID 290718Z - 291918Z

SUMMARY...AN ATMOSPHERIC RIVER IS EXPECTED TO SLOWLY MOVE THROUGH
THE OLYMPIC PENINSULA WITH TIME.  HOURLY RAIN TOTALS COULD
APPROACH 0.5" WHILE LOCAL AMOUNTS OF 4" ARE POSSIBLE THROUGH 19Z.

DISCUSSION...WATER VAPOR IMAGERY SHOWS A DEEP LAYER CYCLONE NEAR
50N 144.5W AND A WARM CONVEYOR BELT OF MOISTURE OFF TO ITS SOUTH
AND EAST, ORIGINATING TO THE EAST OF HAWAI'I.  THE IVT ALGORITHM
SUGGESTS THAT THE MOISTURE PLUME QUALIFIES AS AN ATMOSPHERIC
RIVER, AND IS BEGINNING TO MOVE INTO THE OLYMPIC PENINSULA OF WA. 
QUILLAYUTE REPORTED 0.25" OF RAIN BETWEEN 05-06Z.  PRECIPITABLE
WATER VALUES OF 0.7-1.1" HAVE BEEN INDICATED BY GPS IN NORTHWEST
WA.  INFLOW AT 850 HPA IS 25 KTS FROM THE SOUTH-SOUTHWEST PER THE
SEATTLE VAD WIND PROFILE.  THE 00Z SOUNDING FROM QUILLAYUTE WAS
MOIST, SHOWING A WET BULB ZERO HEIGHT NEAR 8,000 FEET.  SINCE
PRECIPITATION HAS BEEN DOUBLE NORMAL OVER THE PAST COUPLE WEEKS,
SOILS COULD BE SATURATED.

AN UPSTREAM SHORTWAVE NEAR 39N 140W IS STREAKING NORTHEASTWARD AND
SHOULD LEAD TO AN ENHANCEMENT OF RAIN RATES MONDAY MORNING.  MODEL
GUIDANCE SHOWS 850 HPA INFLOW INCREASING TO 50-60 KTS OUT OF THE
SOUTHWEST AND A BAND OF BOUNDARY LAYER MOISTURE CONVERGENCE (COLD
FRONT) MOVING ACROSS THE REGION FROM 15Z ONWARD.  THE MESOSCALE
GUIDANCE SHOW 0.25"+ HOURLY TOTALS THROUGH THE MORNING ACROSS THE
AREA, WITH LOCAL AMOUNTS OF 4" POSSIBLE THROUGH 19Z.  SHOULD ANY
POCKETS OF MINIMAL MUCAPE (50-100 J/KG) MATERIALIZE, HOURLY RAIN
TOTALS OF 0.5" WOULD BE ACHIEVABLE GIVEN THE WET BULB ZERO HEIGHT
AND DEGREE OF LOW LEVEL INFLOW.

ROTH

ATTN...WFO...SEW...

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

LAT...LON   48452473 48182359 48292255 47562270 47052313
            46922362 47032420 47612449 48072477