Quantitative Precipitation Forecast
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FOUS30 KWBC 201501
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1000 AM EST MON FEB 20 2017

...VALID 15Z MON FEB 20 2017 - 12Z TUE FEB 21 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
140 W ACV 95 W CEC 70 NW CEC 40 SSW OTH 35 SSE OTH 15 W SXT
35 SSW SXT 30 ESE CEC 25 ESE ACV 20 WSW O54 15 ESE O54
20 NNW RDD 15 NNE RDD 10 ESE RDD 15 ENE RBL 30 NNE CIC 40 NE CIC
50 NE CIC 45 NNW BLU 10 NNW BLU 30 W TVL 40 SSW TVL 50 WNW MMH
30 ENE FAT 20 NE VIS 15 NE VIS 20 SE FAT 15 N FAT 15 NE MCE
15 ESE MOD 15 SSW MOD 30 ENE WVI 25 ESE SNS 25 NE 87Q 20 NE 87Q
15 S 87Q 75 SW 87Q 135 SW 87Q 195 WSW 87Q.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SSE KBBF PKV 25 SSW LHB 25 WSW TYR OSA 30 NE GGG 35 ENE OCH
JAS 40 SE ESF 25 N 7R3 35 SSE P92 KEIR 15 ENE 3B6.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
145 WSW STS 110 SW UKI 85 SW UKI 65 SW UKI 35 WSW UKI UKI
35 E UKI 15 NNW VCB 15 WSW MYV MYV OVE 15 NNE OVE 20 ENE CIC
25 ENE CIC 35 E CIC 25 NW BLU BLU 20 S BLU 30 SW TVL 50 SSW TVL
50 NE MCE 45 NNE MAE 30 NNE FAT 20 ENE FAT 15 E FAT 20 N FAT
25 NNE MAE 30 NNE MAE 35 NE MCE 35 ENE MOD 25 NE MOD 10 SE SCK
25 WSW MOD 20 ENE WVI SNS 20 N 87Q 15 N 87Q 20 WSW 87Q 40 SW 87Q
65 WSW 87Q 110 WSW 87Q 130 WSW 87Q.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSE KGVX 10 S LBX CXO 40 WSW JAS 25 N BPT 10 WSW KVBS
40 WSW KCRH.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
65 W SFO 35 SW STS STS 15 N APC 10 WSW SAC MHR AUN 20 NNE BAB
20 NE OVE 25 ENE OVE 20 WNW BLU 15 E AUN 40 SW TVL 50 SSW TVL
45 NE MOD 40 NNE MOD 25 NE SCK 10 NNE SCK 15 WSW SCK 15 E RHV
SNS 35 NNW 87Q 25 NW 87Q 30 WNW 87Q 40 W 87Q 70 W 87Q.


...N-CENTRAL CA...

A MAJOR PCPN EVENT THREAT REMAINS ON TAP. LATEST SATELLITE IMAGERY
AND MODELS STILL STRONGLY INDICATE THAT A STORM SYSTEM WILL TRACK
ENEWD TOWARD THE PAC NW WITH A TRIPLE POINT LOW STILL EXPECTED TO
REACH THE OREGON COAST BY MON MRNG. AHEAD/UNDERNEATH OF THIS
FEATURE...YET ANOTHER WELL DEFINED AND LONG FETCH ATMOSPHERIC
RIVER PLUME WITH ORIGINS WELL PAST HAWAII INTO THE
SUBTROPICAL-CENTRAL PACIFIC WILL BE DIRECTED WITH MAIN FOCUS INTO
THE CA COAST INVOF SFO BAY REGION INTO THE SANTA CRUZ MOUNTAINS
WITH INITIAL WARM FRONTAL BNDRY AS 85H WINDS INCREASE TO OVER
40KTS WITH PWS NEAR 1.25+ INCHES FOCUS INTO THE AREA MON MRNG.
AMSU MICROWAVE DATA OFFERS SOME EMBEDDED .3"/HR RATES THAT COULD
LATER DOUBLE INLAND AIDED BY TERRAIN LIFT. AS THE INITIAL WAVE
MOVES INLAND ACRS THE PAC NW MON MRNG...THE TRAILING COLD
FRONT/BAROCLINIC BNDRY IS EXPECTED TO HANG UP INVOF THE SFO BAY
REGION IN RESPONSE TO AN UPSTREAM DVLPG LOW PRES SYSTEM THAT IS
EXPECTED TO DEEPEN SEVERAL HUNDRED MILES OFF THE NRN CA COAST BY
LATE MON AFTN AND MAIN EFFECTS SLAM INLAND MONDAY NIGHT INTO TUE.
THE PROLONGED AND FOCUSED ATMOSPHERIC RIVER PLUME IS EXPECTED TO
LEAD TO VERY HEAVY RAINS OVER W/SW OR AND ESPECIALLY N-CENTRAL CA.
THIS INCLUDES A FOCUS FROM THE SFO BAY REGION EWD THROUGH THE
SACRAMENTO VALLEY INTO THE SIERRA RANGE WITH DEEP LAYERED SWLY
FLOW PROVIDING VERY FAVORABLE UPSLOPE COMPONENT TO THE SW FACING
MTN RANGE. DYNAMIC FORCING AND IMPRESSIVE MSTR PROFILES WILL BE
QUITE FAVORABLE IN SUPPORT FOR SOME OF THE HEAVIER RAINFALL TOTALS
SUGGESTED BY A CONSENSUS OF HI RES GUIDANCE HERE THAT SPOTS COULD
REACH UPWARDS OF 6-9" LIQUID LOCALLY THIS PERIOD OVER MOST FAVORED
TERRAIN. MAIN MODEL DIFFERENCES HAVE REVOLVED AROUND SMALL N/S
DIFFERENCES IN WHERE THE MAIN QPF AXIS WILL SET UP ACRS THE BAY
REGION...BUT SPREAD CONTINUES TO DECREASE APPROACHING THE EVENT.
THESE HEAVY RAINS WILL LEAD TO INCREASING RUNOFF ISSUES ACRS A
RATHER BROAD AREA OF CNTL/NRN CA GIVEN THE RECENT HEAVY RAINS.

...SE/ERN TX INTO SRN LA...

1500 UTC UPDATE...

MADE A FEW RELATIVELY MINOR CHANGES TO THE PREVIOUS
OUTLOOK...BASED ON THE SATELLITE AND COMPOSITE RADAR TRENDS. THE
MESOSCALE (CAM) GUIDANCE CONTINUES TO STRUGGLE WITH THE CONVECTIVE
FEEDBACK (DEGREE OF OUTFLOW CONTRIBUTION AND FORWARD PROPAGATION).
THE HRRR AND ARW...AMONG OTHERS...CONTINUE TO BE TOO FAST WITH THE
EASTWARD PROGRESSION OF THE COMPLEX...WHILE THE EXPERIMENTAL HRRR
SEEMS TO BE DOING A MUCH BETTER JOB.

PREVIOUS DISCUSSION BELOW...


STRONG TO SEVERE CONVECTION HAS ERUPTED OVER THE SRN PLAINS IN A
LOADED AIRMASS IN RESPONSE TO EJECTING SW UPR TROF INTERCEPTING
DEEPENING RETURN FLOW FROM FROM THE WRN GULF THROUGH THE SRN
PLAINS. THERE IS ALSO A MID LEVEL MOISTURE CONNECTION ALOFT FROM
THE SUBTROPICAL ERN PACIFIC EVIDENT IN LATEST BLENDED SATELLITE
LOOPS. WAVES INDUCED ALONG THE BANDED CONVECTION ARE FEEDING ON
THE DEEPENED MOISTURE AND INSTABILITY/UPPER DIFFLUENCE AND
ENHANCED JET SUPPORT. SOME OF THIS WIDESPREAD ACTIVITY WILL LINGER
INTO MORNING IN A WEAKENING STATE AS THE AREA SHIFTS SLOWLY EWD AS
PER ADVENT OF STEADY HEIGHT FALLS AND CONVECTIVE GRADIENTS. EXPECT
WEAKENING ACTIVITY TOWARD THE UPPER TX COAST AND INCREASINGLY
OFFSHORE INTO LATER MON AS THE SRN PORTION OF UPR TROF UNDERGOES
TRANSITION TO A CLOSED LOW...BUT LINGERING SUPPORT AND MOISTURE
SHOULD COMBINE TO SUPPORT THE THREAT FOR HEAVY RAINFALL OVER ERN
TX/OK AND ESPECIALLY SERN TX INTO LA LATER MON WITH HEATING THAT
MAY PRODUCE SOME RUNOFF PROBLEMS WITH AMOUNTS UPWARDS OF 2-3"
POSSIBLE/SEVERAL HRS WITH TRAINING IN DEEP FLOW CONSIDERING STILL
ENHANCED PRECIPITABLE WATER VALUES. OPTED FOR A SLOWER PROGRESSION
THAN MOST OF THE MESO MODELS GIVEN THE CLOSING NATURE OF THE SRN
END OF THE MAIN MID-UPPER LEVEL TROUGH.

SCHICHTEL/HURLEY
$$





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