MESOSCALE PRECIPITATION DISCUSSION 0669
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1240 PM EST TUE DEC 08 2015
 
AREAS AFFECTED...W WASHINGTON...NW OREGON 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 081800Z - 090000Z
 
SUMMARY...INCREASING FORCING AHEAD OF NEXT WAVE NEAR 140W WILL
FOCUS HIGH MST FLUX ASHORE CAPABLE OF UP TO 2-3" OVER THE NEXT
6HRS...WITH LOCALLY HIGHER AMOUNTS IN SW FAVORED TERRAIN OF W
WA/NW OR COASTAL RANGE AND WA CASCADE RANGE.

DISCUSSION...1241Z 89GHZ AMSU PASS INDICATES DEEP SURFACE LOW IN
VICINITY OF 53N148W WITH AN OCCLUDED FRONT ARCING FROM IT SE ALONG
THE BC COAST.  A WARM FRONT SEEN NEAR/HUGGING COAST AND IS CLEARLY
WELL ASHORE ATTM...THIS OPENS UP THE DEEPLY MOIST NEARLY
UNIDIRECTIONAL FLOW ALONG THE WARM CONVEYOR BELT AHEAD OF THE COLD
FRONT ORIENTED SW TO NE DIRECTLY AT W WA.  WITHIN THE PLUME HIGHLY
ANOMALOUS MOISTURE WITH TPWS OF 1.3-1.4" OBSERVED IN BLTPW PRODUCT
WHICH IS WELL OVER 200% OF NORMAL AND NEARING DECEMBER RECORD
VALUES. IR LOOP INDICATES LARGE SUBTROPICAL SHIELD CONTINUES TO
COOL UNDER INCREASED DIVERGENCE ALOFT AT THE APEX OF 150-160KT UL
JET WHICH WILL PERSIST THROUGH THE DISCUSSION AREA FOCUSING
THROUGH THE OLYMPICS AND WA CASCADES TO ABOUT 00-01Z WHEN WEAK
INFLECTION IN THE STREAM CURRENTLY SEEN ALONG 140W COMES ASHORE
PROVIDING STRONG ASCENT. 

A WEAK 7H TROF HAS RECENTLY PRESSED WEST TO EAST THROUGH W WA
ABOUT 1 HR AGO LEADING TO A SHORT LULL.  THIS SHOULD ALSO ALLOW
THE FRONTAL ZONE TO SINK SOUTHWARD SLOWLY PRIOR TO THE NEXT
WAVE...LIKELY TO STALL NEAR THE MOUTH OF THE COLUMBIA RIVER BEFORE
PROGRESSING SOUTHWARD AGAIN AFTER 00Z. 7H WINDS SHOULD BEGIN TO
BACK A BIT SHORTLY AND INCREASE WITH 60KT-70KT WSWLY FLOW (50-60KT
AT 85H) WITHIN THIS DEEP MOISTURE PLUME TO PRODUCE .1-.3"/HR RATES
ALONG THE COAST AS SEEN IN RECENT AMSU PASS UPSTREAM...BUT
INCREASING TO .5-.6"/HR IN OROGRAPHY AND AT TIMES POTENTIALLY
HIGHER LOCALLY. ORIENTATION OF THE BEST ASCENT/MOISTURE FLUX PER
SATELLITE TRENDS POINTS TO FOCUS THE MOUTH OF THE COLUMBIA RIVER
THROUGH TO MOUNT ST. HELENS/MT. ADAMS VICINITY OF THE CASCADES
WITH 6HR TOTALS OF 1-1.5" IN LOW COUNTRY AND 2-3" IN HIGHER SW
ORIENTED TERRAIN IN LINE WITH RECENT HRRR RUNS/12Z ARW/NMMB AND
00Z NSSL-WRF

GALLINA/HANNA

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

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

LAT...LON   49062195 48982153 47752155 45932186 45722273 
            45372311 45102369 45432404 45992404 46992431 
            47612439 48002423 48062365 47462278 48542273 
            48192271 48692271 49042273