Quantitative Precipitation Forecast
Issued by NWS

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807
FOUS30 KWBC 180008
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
808 PM EDT FRI MAR 17 2017

...VALID 01Z SAT MAR 18 2017 - 12Z SAT MAR 18 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NW S47 25 NW AST 10 SSE HQM 15 W OLM 15 SSE OLM 25 SE TCM
50 E TDO 35 NNE CZK CZK 10 N TTD 15 SE KLS KLS 25 WSW KLS
20 E S47 20 W SLE 15 NE ONP 15 NNW ONP 25 NW S47.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NNE MQY 40 E MQY 45 SE MQY 15 N MDQ 35 NW MSL 25 E OLV
30 WNW M97 M19 20 WNW BYH 50 NE MKL 10 NNE MQY.


...NE AR/WRN AND CNTL TN...

INTRODUCED A MARGINAL RISK AREA FOR PORTIONS OF THE ABOVE AREA IN
RESPONSE TO CONVECTION INCREASING WITHIN AN AXIS OF 1000 TO 1500
MUCAPES EXTENDING EWD FROM NRN ARKANSAS INTO NRN TN.  DECENT LOW
LEVEL THETAE ADVECTION WITH 85H WINDS OF 30-40 KTS OUT OF THE WSW
WILL GRADUALLY VEER MORE WLY THIS EVENING WITH SHARPENING OF NRN
STREAM UPR TROF ACRS THE UPR MIDWEST.  THIS COULD ALLOW STORMS TO
BECOME MORE E/W ALIGNED LEADING TO SOME BRIEF TRAINING BEFORE LINE
GAINS A MID MORE SWD MOMENTUM LATER TONIGHT.  MDTLY HEAVY RAINFALL
RATES ARE PSBL WITH PWS AOA 1.25 INCHES AHEAD OF A COLD FRONT WITH
RECENT HRRR TRENDS SUGGESTING SOME LOCAL 3 HR AMOUNTS OF 1.5
INCHES WILL BE PSBL.  THESE AMOUNTS ARE LOWER THAN SOME OF THE 12Z
WRF RUNS AS WELL AS THE CANADIAN GEM WHICH INDICATE LOCAL AMOUNTS
COULD APCH 2.5 TO 3 INCHES IN SOME SPOTS.  WHILE THE HRRR RUN
AMOUNTS ARE DRIER AND BELOW FFG VALUES..GIVEN THAT THE HRRR RUNS
APPEAR A LITTLE SLOW TO DVLP CONVECTION THIS EVENING THEY COULD BE
A LITTLE ON THE DRY SIDE AND THUS FEEL A MARGINAL RISK OF
EXCESSIVE RAINS IS WARRANTED.


...WESTERN OREGON AND WASHINGTON...

SOILS REMAIN UNUSUALLY SATURATED THROUGHOUT THIS REGION OWING TO
SNOW MELT AND CONTINUED ADDITIONAL RAINFALL. A DEEP LAYER...FULL
LATITUDE TROUGH WILL MIGRATE INLAND TODAY AND TONIGHT...BRINGING
STRONG SOUTHWESTERLY FLOW AND MODESTLY ANOMALOUS MOISTURE
FLUX...PRECIPITABLE WATER VALUES RISING TO JUST ABOVE 1.00 INCH AT
THE COAST AND WEST OF THE CASCADES. THOUGH THE SITUATION IS
PRIMARILY ONE OF LONGER TERM...LARGER SCALE FLOOD CONCERNS...THERE
IS SOME POTENTIAL FOR RAINFALL-INDUCED LANDSLIDES PER INFORMATION
FROM WFO SEATTLE. HOURLY RAIN RATES FROM THE HI-RES MODELS DO NOT
QUITE REACH 0.50 INCHES LATER TODAY...BUT THREE-HOURLY AND LONGER
DURATION ACCUMULATIONS ARE ON THE HEAVY SIDE...WITH 1.00 TO 2.5
INCHES OF NEW RAINFALL EXPECTED THROUGH SATURDAY MORNING. WE HAVE
INTRODUCED A MARGINAL RISK OF EXCESSIVE RAINFALL TO ACKNOWLEDGE
THE UNUSUAL SENSITIVITY OF THE SOILS TO THIS ADDITIONAL RAINFALL.

BURKE/SULLIVAN
$$





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