905
AWUS01 KWNH 130456
FFGMPD
CAZ000-ORZ000-WAZ000-131200-
MESOSCALE PRECIPITATION DISCUSSION 0009
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1156 PM EST TUE JAN 12 2021
AREAS AFFECTED...PACIFIC NORTHWEST
CONCERNING...HEAVY RAINFALL
VALID 130500Z - 131200Z
SUMMARY... ONE FINAL ROUND OF HEAVY RAINFALL IS IN STORE FOR THE
PACIFIC NORTHWEST BEFORE A COLD FRONT PASSES THROUGH THE REGION
LATER TONIGHT. SOAKING RAINFALL ATOP OVERLY SATURATED GROUND MAY
LEAD TO ADDITIONAL FLOODING AND EXACERBATE ONGOING AREAS OF
FLOODING.
DISCUSSION... SURFACE ANALYSIS AROUND 04Z INDICATED A SURFACE LOW
NEAR VANCOUVER ISLAND WAS TRACKING NORTHEAST WHILE ITS ASSOCIATED
COLD FRONT WAS RACING TOWARDS THE WESTERN WASHINGTON COAST. A
500MB SHORTWAVE TROUGH IS INDUCING PVA ALOFT ALONG WITH LINGERING
850-700MB WAA AHEAD OF THE COLD FRONT. IN ADDITION, THERE IS A
STRONG 850MB JET EXPECTED TO PEAK AS HIGH AS 80 KNOTS OVER WESTERN
OF OREGON BETWEEN 05-07Z THAT WOULD HELP TO PROMOTE HEAVIER
RAINFALL RATES VIA STRONG UPSLOPE FLOW. THERE ALSO REMAINS NO
SHORTAGE OF RICH PACIFIC MOISTURE AS PWS REMAIN 2.5-3 STDS ABOVE
NORMAL THROUGHOUT THE REGION. IN FACT, VIA THE 00Z SLE SOUNDING,
THE MEASURED PW VALUE WAS 1.19" IS MORE THAN DOUBLE THE AVERAGE PW
VALUE FOR THIS TIME OF YEAR.
THESE INGREDIENTS CONTINUE TO SUPPORT A SOAKING RAINFALL FOR MUCH
OF THE WATER-LOGGED AREAS OF WESTERN WASHINGTON, WESTERN OREGON,
AND FAR NORTHWESTERN CALIFORNIA. RAINFALL RATES OF 0.4-0.75" PER
HOUR ARE LIKELY WITH THE HIGHEST RATES TO BE OBSERVED ALONG THE
WINDWARD SIDES OF THE COASTAL RANGE AND CASCADES OF WESTERN OREGON
AND SOUTHWEST WASHINGTON. THESE RAINFALL RATES COULD TRIGGER
ADDITIONAL AREAS OF URBAN AND RIVER FLOODING. THERE IS ALSO
ONGOING CONCERNS FOR MUDSLIDES GIVEN THE OVERLY SATURATED AND
UNSTABLE SOIL.
THE COLD FRONT SWINGS THROUGH THE OLYMPICS AND PUGET SOUND FIRST
SOMETIME BETWEEN 06-08Z. ONCE THE COLD FRONT HAS PASSED THROUGH,
DRIER WESTERLIES ALOFT SHOULD QUICKLY REDUCE RAINFALL RATES,
ALTHOUGH LINGERING UPSLOPE SHOWERS ARE STILL LIKELY TO OCCUR ALONG
THE CASCADES INTO THE EARLY MORNING HOURS. COLD AIR ADVECTION
ALOFT WILL FORCE SNOW LEVELS TO CRASH LATER TONIGHT AND FORCE
PRECIPITATION AT LOWER ELEVATIONS TO CHANGE OVER TO SNOW. THE COLD
FRONT THEN CROSSES THROUGH WESTERN OREGON BETWEEN 08-10Z, LEADING
TO THE SAME RESULTS THE NEIGHBORS FARTHER NORTH WITNESS. BY 12Z,
THE COLD FRONT IS LIKELY TO HAVE REACHED FAR NORTHWESTERN CA AND
DRIER CONDITIONS RETURN AS HIGH PRESSURE BUILDS IN FROM THE WEST.
MULLINAX
..PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT
ATTN...WFO...EKA...MFR...PDT...PQR...SEW...
ATTN...RFC...CNRFC...NWRFC...NWC...
LAT...LON 49312233 48812158 47652137 45192173 43122299
42092316 41102408 42322472 44472458 46062432
47482476 48462490 48582453 48572401 48782345
49152300
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page