Quantitative Precipitation Forecast
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000
FOUS30 KWBC 221455
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1055 AM EDT THU SEP 22 2016

...VALID 15Z THU SEP 22 2016 - 12Z FRI SEP 23 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 ENE CZMJ 40 NW ISN 10 N GDV 35 WSW BHK 60 NE SHR 10 NNW DHS
25 NW TMH 30 ENE BVR 35 SE BIT 40 WNW EEO 25 NNW GJT 30 W MTJ
25 NNW CPW 25 ESE CPW 10 ESE E33 20 W E33 10 W DRO 20 SSE 4BL
20 ESE PGA 40G 10 SSE 40G 10 NNW DVT 35 WNW LUF 30 SSE IGM
60 N IGM 15 NW CDC 20 N CDC 25 N MLF 50 SW DPG 15 N ELY 30 S P68
25 WSW P68 20 SW EKO 20 WSW AWH 45 SSW MUO 25 E MUO 20 S MYL
35 SW P69 45 NNE P69 25 SSW 3DU 15 E BTM 30 SSE HLN 10 E HLN
45 W GTF 25 S CWGM 25 SW CNPK 10 E CYYC.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
FBL 15 WNW CMY 10 WSW CLI 10 SE SBM 10 E DKB GBG 25 NNW IRK
10 NW ICL 15 W TQE 25 NW SHL 20 SSW RWF FBL.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 ESE HXD 15 SSW CHS 30 ESE SSC POB 10 N GWW 15 ENE EWN
90 SE MRH.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NW SUN 30 E MYL 35 SE P69 60 NNW SMN 35 NE SMN 30 SSE DLN
15 SW P60 60 NW RIW 20 S LND 15 SSE BIT 25 ENE VEL 35 S VEL
40 NE CNY 20 E U28 20 W U28 40 ENE BCE 45 WSW PGA 30 WNW GCN
60 W GCN 20 E SGU 20 E MLF 15 ENE U24 DPG 25 ESE ENV 25 SSW ENV
25 E P68 25 N P68 15 E EKO 25 ENE AWH 20 WNW BYI 25 NW SUN.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 W DVN 15 NW OTM 15 NNE HNR 20 WNW FOD 15 N CCY 15 W DLL
10 NNE FEP 15 W DVN.


...15Z UPDATE...

PREVIOUS OUTLOOK WAS WELL PLACED...AND THERE IS LITTLE CHANGE IN
THINKING AT THIS TIME. WE ADJUSTED THE ORIENTATION OF THE SLIGHT
RISK IN IOWA SOMEWHAT...AND EXPANDED IT SOUTHEASTWARD. ROBUST
THUNDERSTORMS SHOULD REFORM THIS AFTERNOON ALONG THE STALLING
OUTFLOW BOUNDARY...SUPPORTED BY WARM ADVECTION INTO THE BACK SIDE
OF AN EXITING MID LEVEL SHORTWAVE TROUGH. FORCING SHOULD DECREASE
DURING THE USUALLY FAVORABLE EVENING HOURS...HOWEVER...AS THE
SHORTWAVE DISTANCES ITSELF FROM THE POOL OF STRONGER INSTABILITY
BUILT UP OVER SOUTHERN IOWA. EXPECTATIONS FOR EVENT DURATION AND
INTENSITY ARE THEREFORE SOMEWHAT LIMITED...BUT THERE WILL BE A
SEVERAL HOUR PERIOD LATE TODAY IN WHICH LOCAL HEAVY RAINFALL MAY
OCCUR NEAR THE OUTFLOW BOUNDARY. -BURKE

...PREVIOUS DISCUSSION...

...UPPER MIDWEST...

STRONG...SOMEWHAT PERSISTENT RIGHT ENTRANCE REGION FORCING VIA THE
BROAD W-E UPPER JET STREAK JUST NORTH OF THE US-CANADIAN BORDER
WILL FINALLY TAPER AS THE CLOSED UPPER LOW DROPS INTO THE GREAT
BASIN AND (IN TURN) AMPLIFIES THE DOWNSTREAM RIDGE ACROSS THE
NORTHERN PLAINS AND UPPER MS VALLEY. THE DISSIPATION OF
BROAD-SCALE DIVERGENCE ALOFT AND DEEP-LAYER FRONTOGENETIC FORCING
WITH THE ENSUING HEIGHT RISES UPSTREAM WILL RESULT MUCH LESS
COVERAGE OF ADDITIONAL MOD-HEAVY RAINFALL DURING THE DAY 1 PERIOD
(12Z THU-12Z FRI)...HOWEVER...EVEN WITH THE TRANSITION ALOFT A
RENEWED FOCUS ACROSS IOWA (SOUTH OF THE QUASI-STATIONARY SURFACE
FRONT) IS NOTED PER CONSENSUS OF MUCH OF THE GUIDANCE (GLOBAL AND
HIGH-RES). WPC QPF WAS INITIALIZED FROM CONTINUITY (PREVIOUS
FCST)...ADJUSTED PER THE 00Z GFS AND ECMWF TRENDS...THEN
INCORPORATED THE WRF-ARW WHICH APPEARED TO HAVE THE BEST HANDLE ON
THE AXIS OF HEAVIEST RAINFALL A SHADE SOUTH OF THE GLOBAL GUIDANCE
CONSENSUS (I.E. FARTHER INTO THE INSTABILITY GRADIENT WHERE
MUCAPES AVERAGE 1000-2000 J/KG). THE RESULT WAS MAX AREAL-AVERAGE
AMOUNTS BETWEEN 1.5-3.0 INCHES ACROSS CENTRAL AND NORTH-CENTRAL
IA. GIVEN THE DEGREE OF AVAILABLE DEEP-LAYER INSTABILITY ALONG AND
SOUTH OF THE FRONTAL BOUNDARY...IN ADDITION TO PW ANOMALIES
BETWEEN 2-2.5 STANDARD DEVIATIONS ABOVE NORMAL...LOCALLY HIGHER
AMOUNTS BETWEEN 4-7+ INCHES ARE ANTICIPATED ANYWHERE WITHIN THE
SLIGHT RISK AREA PER THE HIGH-RES GUIDANCE.


...WESTERN U.S...

IMPRESSIVE GREAT BASIN / NORTHERN ROCKIES STORM TAKING
SHAPE...WITH EXTENSION OF THE PRIMARY PRECIPITATION AXIS INTO
WESTERN AND NORTHERN ARIZONA. NEGATIVE HEIGHT ANOMALIES AT 500 MB
DIP TO 3 STANDARD DEVIATIONS AS A LOW BEGINS TO CLOSE OFF AND
SLIDES TOWARD NEVADA TONIGHT AND THURSDAY. COUPLE THIS WITH
ANOMALOUS MOISTURE AHEAD OF THE SURFACE FRONTAL SYSTEM...SOME OF
WHICH WAS TRANSPORTED INTO THE REGION AHEAD OF THE RECENT TROPICAL
SYSTEM IN THE EASTERN PACIFIC...AND THE STAGE IS SET FOR
WIDESPREAD HEALTHY AMOUNTS OF PRECIPITATION...PARTICULARLY IN A
STRIPE FROM NORTHERN AZ THROUGH MUCH OF UTAH AND INTO THE NORTHERN
ROCKIES...INCLUDING SOME UPSLOPE ENHANCEMENT OVER MONTANA. WPC QPF
BEGAN WITH A 40/30/30 BLEND OF THE PREVIOUS FORECAST...00Z
WRF-ARW.....AND 00Z BIAS-CORRECTED ENSEMBLE. OVERALL THIS REALLY
PRESERVED THE LARGE SCALE SHAPE AND INTENSITY OF THE FORECAST
PRECIPITATION...ALTHOUGH SPOT TOTALS WILL HAVE CHANGED THROUGH USE
OF THE NEW BLEND AND THROUGH DOWNSCALING (LOWER AREAL-AVERAGE
AMOUNTS WITHIN THE VALLEYS AND SOME ENHANCEMENT ACROSS THE
WASATCH-UINTAS AND EASTERN SLOPES OF THE NORTHERN ROCKIES). AREAL
AVERAGE 24-HOUR AMOUNTS ARE FORECAST TO EXCEED 2 INCHES IN A FEW
SPOTS OF FAVORED TERRAIN IN UTAH...WITH SOME MODELS (PARTICULARLY
HIGH-RES CAMS) SUGGESTING 3 INCH TOTALS. THIS APPEARS PLAUSIBLE
GIVEN THE STRENGTHENING UPPER-LEVEL DIVERGENCE AND DIFFLUENCE AND
DEEP-LAYER UNIDIRECTIONAL FLOW THAT WILL DEVELOP AS THE LOW CLOSES.


...EASTERN CAROLINAS...

THE CLOSED LOW INITIALLY ALONG THE COASTAL NC/SC BORDER IS
EXPECTED TO BECOME INCREASINGLY SHEARED THIS PERIOD.  THIS SHOULD
RESULT IN WEAKENING OF THE ONSHORE EASTERLY FLOW TO ITS NORTH
WHICH HAS BEEN FOCUSING PERSISTENT MODERATE TO HEAVY RAINS OVER
NORTHEAST NC INTO SOUTHEAST VIRGINIA. DESPITE THE DIMINISHING
UPPER SUPPORT (WEAKENING LOW-MID LEVEL DEFORMATION AND
FGEN)...CONTINUED CYCLONIC ONSHORE FLOW ALONG WITH PWS REMAINING
AOA 1.75" WILL SUPPORT ADDITIONAL MODERATE/LOCALLY HEAVY RAINS
ACROSS THE EASTERN CAROLINAS. MAXIMUM AREAL-AVERAGE TOTALS WILL
RANGE BETWEEN 0.50-1.0"...HOWEVER PER THE HIGH-RES CAM GUIDANCE
ISOLATED AMOUNTS BETWEEN 2-4 INCHES CAN BE EXPECTED WITHIN THE
MARGINAL RISK AREA.

HURLEY
$$





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