Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 231857
QPFERD

EXCESSIVE RAINFALL DISCUSSION...CORRECTED.
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 PM EDT SAT AUG 23 2014

...VALID 18Z SAT AUG 23 2014 - 00Z MON AUG 25 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 NNW COD 30 N WYS 25 NNE BTM 55 WNW GTF 25 ENE CWOE
40 ESE CWIK 40 NE BDE 10 SE CQM 15 WSW LXL PQN 10 S MHE
20 SW PIR 30 SE 2WX 50 WSW 2WX 15 NNE DHS 25 ENE GEY 45 NNW COD.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 SSE CWEH 30 E CYEN 15 NW KD55 25 SE DVL 45 NE K7L2
40 ENE HEI 30 SW DIK 10 NNW BHK 65 NE SHR 35 NNW SHR 25 NE BIL
45 NNE BZN 30 NE GFA 40 SSE CWEH.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 SE HVR 55 SSW CWVN 30 WSW GGW 15 NW JDN 20 WSW JDN
55 WSW JDN 40 ESE LWT 25 NNE LWT 50 SE HVR.


...EASTERN FOOTHILLS OF THE NORTHERN ROCKIES INTO THE NORTHERN
PLAINS AND UPPER MISSISSIPPI VALLEY...

THE EARLY STAGES OF A SIGNIFICANT RAINFALL EVENT IS CURRENTLY
TAKING SHAPE ACROSS THE EASTERN FOOTHILLS OF THE NORTHERN ROCKIES
EASTWARD INTO THE NORTHERN PLAINS. BASED ON THE CURRENT GUIDANCE
AND RADAR TRENDS...HAVE MADE ONLY CHANGES TO THE PREVIOUS (15Z)
EXCESSIVE RAINFALL OUTLOOK...WHICH INCLUDES CONFINING THE MODERATE
RISK AREA NORTH OF SD WHILE EXPANDING A LITTLE FARTHER EASTWARD
INTO EASTERN ND...AND ALSO EXPANDING THE SLIGHT RISK AREA A BIT
FARTHER EAST THROUGH THE NW HALF OF MN.

EVOLVING DIFFLUENT UPPER LEVEL FLOW AND STRENGTHENING POCKET OF
UPPER LEVEL DIVERGENCE AHEAD OF THE VORT MAX CURRENTLY LIFTING
N/NNE ACROSS WRN NE AND SWRN SD IS GENERATING A SEPARATE
WIDESPREAD AREA OF GENERALLY MODERATE RAINFALL ACROSS WRN SD AND
WRN ND. DRY AIR ALOFT (STEEPENING THETA-E LAPSE RATES) NORTH OF
THE AFOREMENTIONED VORT MAX WILL LIKELY ENHANCE CONVECTION AHEAD
OF THIS VORT MAX AS IT LIFTS N/NNE THIS AFTERNOON. MEANWHILE...THE
MORE EXPANSIVE AREA OF MOD-HVY RAINFALL CONTINUES OVER MUCH OF
MT...WITHIN THE LAYER OF BROAD UPPER LEVEL DIFFLUENCE...GOOD UPPER
DIVERGENCE...AND ANOMALOUS LOW-MID LAYER MOISTURE/THETA-E POOLING
FROM THE E/SE VIA THE WESTERN EXPANSION OF THE TROWAL ZONE. OVER
TIME...THE THERMODYNAMIC PROFILES OVER EASTERN AREAS OF THE
OUTLOOK AREA (EASTERN DAKOTAS INTO MN) WILL BECOME INCREASINGLY
FAVORABLE FOR MORE OF A CONVECTIVE CONTRIBUTION AND THUS AN
ENHANCED EXCESSIVE RAINFALL THREAT...ALONG THE N/NW PERIPHERY OF
THE INSTABILITY AXIS (MUCAPES CLIMBING BTWN 1000-2000 J/KG PER THE
ARW WITH PWATS RISING TO AROUND 1.75 INCHES. PWATS THROUGHOUT THE
OUTLOOK AREA ARE OR SHORTLY WILL BE AROUND 3 STD DEVIATIONS ABOVE
NORMAL...OR AOA THE 99TH PERCENTILE FOR THE AREA THIS TIME OF
YEAR. MEANWHILE...THE NEGATIVE U-WIND COMPONENT OR EASTERLY FLOW
ANOMALIES AT 850-700 ARE AT 5+ STANDARD DEVIATIONS PER THE GEFS
AND ECENS.

AS A RESULT OF THE ANOMALOUS COMBINATION OF FAVORABLE COOL-SEASON
DYNAMICAL FORCING ALONG WITH THE FAVORABLE THERMODYNAMIC (DEEP
MOIST) PROFILES...THE MODEL GUIDANCE...BOTH GLOBAL AND HIGH
RES...CONTINUE TO SHOW A STRONG SIGNAL FOR A SIGNIFICANT RAINFALL
EVENT ACROSS THE EASTERN FOOTHILLS OF THE NRN ROCKIES INTO THE NRN
PLAINS AND AT LEAST WRN PTNS OF THE UPPER MS VLY...WITH THE LATEST
SSEO MEAN PROBABILITIES OF EXCEEDING 3 AND 6 HOURLY FFG OVER 70
PERCENT IN THE HIGH RISK AREA ACROSS PORTIONS OF CENTRAL MT ALONG
THE WESTERN PERIPHERY OF THE TROWAL ZONE. 24 HOUR AREAL-AVERAGE
QPF WITHIN THE HIGH RISK AREA PER THE GLOBAL MODEL CONSENSUS
RANGES FROM 2.5 TO 5 INCHES...WHICH IS SUPPORTED BY THE SREF AND
GEFS PROBABILITIES OF 50% OR GREATER OF RECEIVING MORE THAN 3
INCHES IN 24 HOURS. AT THE SAME TIME...VIRTUALLY ALL OF THE HIGHER
RES GUIDANCE SHOW LOCALLY HIGHER AMOUNTS OF 6+ INCHES. FARTHER
EAST INTO THE DAKOTAS AND WRN MN...THE TOTAL RAINFALL IS EXPECTED
TO AVERAGE CLOSER TO 1-3 INCHES...HOWEVER GIVEN THE GREATER
INSTABILITY TO FEED OFF OF (ESPECIALLY IN THE EASTERN DAKOTAS AND
WRN MN)...THERE WILL MORE DEVIATION FROM THE MEAN WITH LOCALLY
HEAVIER...POTENTIALLY EXCESSIVE AREAS OF RAINFALL...SUPPORTED BY
THE ISOLATED 4-6+ INCH BANDS PER THE LATEST 4KM NAM CONEST... NSSL
WRF...AND WRF-ARW.

FOR FURTHER DETAILS REGARDING ANY ACTIVE MESOSCALE PRECIPITATION
DISCUSSIONS (MPD) WITHIN THE EXCESSIVE RAINFALL OUTLOOK AREA...
PLEASE REFER TO THE LINK FROM THE WPC HOME PAGE ABOVE THE TOP NEWS
OF THE DAY... OR GO DIRECTLY TO THE MPD PAGE:
WWW.WPC.NCEP.NOAA.GOV/METWATCH/METWATCH_MPD.PHP.

HURLEY
$$




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