Quantitative Precipitation Forecast
Issued by NWS

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057
FOUS30 KWBC 060829
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
428 AM EDT FRI MAY 06 2016

...VALID 12Z FRI MAY 06 2016 - 12Z SAT MAY 07 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 SE BIL SHR 25 N GCC 20 WSW IKA 35 SSE BFU 20 E SIB BRX
30 ENE ARL 25 SE PAT 15 W PAT 35 W PAT 20 N CTD 35 SSW RWL
35 NW CAG 25 NNE VEL 20 S FIR 25 W LGU 25 NNE BYI 10 NE SUN
50 SE LLJ 35 NW IDA 40 S JAC 35 ENE JAC 15 NNE P60 15 SE LVM
45 ESE LVM 35 N COD 25 W WRL 10 SSE WRL 20 NNE WRL 30 NNW GEY
45 SE BIL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 NW WMC 60 NNW RNO 15 E TVL 45 W MMH 20 N MCE 15 ENE BAB
30 NNW RDD 15 SE SIY 20 W LKV 35 SW BNO 50 WSW EUL 10 NW MUO
50 S MUO 45 WNW AWH 40 NW WMC.


...WESTERN U.S...

AN ANOMALOUS UPPER LOW...BETWEEN 2-2.5 STANDARD DEVIATIONS BELOW
CLIMATOLOGY AT 500 MB...WILL SPIN SLOWLY ACROSS SOUTHERN CA AND
THE SOUTHWEST-LOWER GREAT BASIN DURING DAY 1.

ACROSS CALIFORNIA...PERSISTENT DEEP-LAYER CYCLONIC FLOW AND
ANOMALOUS MOISTURE (PWATS 0.75-1.00"+ OR 2-3 STANDARD DEVIATIONS
ABOVE NORMAL)... ALONG WITH MODERATELY STEEP MID LEVEL LAPSE RATES
(7-7.5 C/KM BETWEEN 700-500 MB)...WILL CONTINUE TO GENERATE
SCATTERED TO AT TIMES NUMEROUS SHOWERS AND THUNDERSTORMS TODAY.
ANY DIMINISHMENT IN THE CONVECTION LATER THIS MORNING (AS THE THE
FAVORABLE REGION OF UPPER LEVEL DIFFLUENCE AND DIVERGENCE SHIFTS
E-NE) WILL BE OFFSET SOMEWHAT BY THE INCREASED DIURNAL
INSTABILITY...ESPECIALLY IN THE VALLEYS WHERE MIXED-LAYER CAPES
COULD APPROACH OR EXCEED 1000 J/KG. IN TERMS OF THE QPF...WPC
CONTINUED TO LEAN TOWARD THE HIGHER-RESOLUTION
GUIDANCE...ESPECIALLY THE RECENT HRRR RUNS...00Z NSSL-WRF...AND
(TAKING OUT THE HIGH BIAS) THE 00Z SPC-WRF EARLY ON...ALL OF WHICH
SEEMED TO HAVE A GOOD HANDLE ON THE CURRENT CONVECTION LATE THU
EVENING. DURING THE DAY 1 PERIOD (12Z FRI - 12Z SAT)...
AREAL-AVERAGE AMOUNTS BETWEEN 0.10-0.25" OVER SOUTHERN CA AND
0.25-0.75" OVER THE NORTHERN HALF ARE EXPECTED. HOWEVER...AS
IMPLICATED BY THE HIGH-RES GUIDANCE...THERE WILL BE QUITE A
VARIANCE FROM THE MEAN WITH LOCALIZED HIGHER AMOUNTS BETWEEN 1-2+
INCHES...PARTICULARLY ACROSS THE MOUNTAINS IN NORTHERN CA.

OVER SOUTHEAST OR-EASTERN ID EASTWARD INTO WY...A RIBBON OF ROBUST
UPPER LEVEL DYNAMICS WILL RESULT IN APPRECIABLY HIGHER
AREAL-AVERAGE PCPN TOTALS (PARTICULARLY ACROSS WY). THIS AS THE
AXIS OF FAVORABLE UPPER DIFFLUENCE...INITIALLY ORIENTED
SE-NW...PIVOTS MORE E-W AS THE CLOSED LOW PASSES TO THE SOUTH.
MEANWHILE... AS THE NORTHERN STREAM SHORTWAVE DROPS ACROSS
SOUTH-CENTRAL CA AND INTO THE FAR UPPER MS VALLEY BY THE END OF
THE PERIOD...STRENGTHENING UPPER LEVEL CONFLUENCE OVER THE
NORTHERN PLAINS-UPPER MS VALLEY WILL INDUCE A 90-100 KT JET STREAK
AT 250 MB. IT IS WITHIN THE RIGHT ENTRANCE REGION OF THIS JET THAT
WILL ENHANCE THE UPPER DIVERGENCE ACROSS WY...WHICH WILL COUPLE
WITH THE STRONG FORCING NORTHEAST OF THE UPPER LOW. THE MODELS
CONTINUE TO PICK UP ON THIS SIGNAL...WITH ONCE AGAIN A SOLID
CONSENSUS FOR HEAVY RAINFALL AND HIGH ELEVATION (8000+ FT)
SNOWFALL ACROSS MUCH OF WY INTO EASTERN ID AND FAR NORTHEASTERN UT
DURING THE DAY 1 PERIOD. WPC DID SHIFT THE AXIS OF HEAVIEST QPF A
LITTLE SOUTH FROM CONTINUITY (PREVIOUS FORECAST)... ALIGNING WITH
THE BETTER DEEP-LAYER INSTABILITY THIS AFTERNOON INTO FRI NIGHT
WITH MUCAPES GENERALLY 500-1000 J/KG. WPC NOTED A FAIRLY
WIDESPREAD SWATH OF 1-2+ INCH AREAL-AVERAGE AMOUNTS...HIGHEST
(2-2.5") ALONG THE EASTERN SLOPES OF THE WIND RIVER RANGES. THE
HIGH RESOLUTION GUIDANCE CONTINUES TO SHOW CLUSTERING OF LOCALLY
HIGHER AMOUNTS (3-4+ INCHES) OVER THIS SAME AREA...WHICH GIVEN THE
RELATIVELY LOW 3-6 HOURLY FFG...WILL MAKE FOR AN INCREASED RISK
FOR EXCESSIVE RAINFALL AND RUNOFF ISSUES IN THE SHORT TERM.

HURLEY
$$





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