Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 301409
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1008 AM EDT SAT JUL 30 2016

...VALID 15Z SAT JUL 30 2016 - 12Z SUN JUL 31 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NW AOH 20 NW SBN 10 E MKG 15 NE PTK 15 SSE CXPT 10 NNW ERI
15 N PEO 30 WNW MSV 15 SSW 12N PHL ADW OFP EDE 30 ESE OCW
10 SSE OCW 15 WSW RZZ 35 SSW SHD 10 E MGW HLG 15 NW AOH.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 NW GBN 35 ESE EED 40 NNW IFP 35 NW SGU 25 S MLF 10 NNW BCE
45 NNW GCN 20 WNW INW 35 NW SJN 30 WSW RQE 25 NNW RQE 25 WNW GNT
65 NW TCS 35 N SVC 35 WSW SVC 45 E DUG 30 SE DUG 45 W OLS
30 SSW GBN 45 NW GBN.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 W TOP 30 ENE CNU 30 ESE CFV BVO 15 NNW RSL 35 S HDE HSI
25 SSW BIE 15 W TOP.


1500 UTC UPDATE

CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE
TO PUSH THE SLIGHT RISK AREA OVER THE SOUTHWEST FARTHER TO THE
WEST INTO FAR SOUTHERN NV AND EASTERN CA.  THIS WAS TO ACCOUNT FOR
CONVECTIVE POTENTIAL IN THE AXIS OF MUCH ABOVE AVERAGE PW VALUES
THAT ARE FORECAST TO EXTEND INTO THESE AREAS.  CONVECTION ALREADY
HAS FIRED EARLY THIS MORNING INTO FAR EASTERN CALIFORNIA. WHILE
THIS ACTIVITY IS WEAKENING RAPIDLY---ADDITIONAL ACTIVITY POSSIBLE
IN THIS HIGH PW AXIS THROUGH THE REMAINDER OF THE FORECAST PERIOD.

OVER THE CENTRAL PLAINS---THE SLIGHT RISK AREA WAS EXTENDED
NORTHWARD INTO SOUTH CENTRAL NE TO ACCOUNT OF FOR CURRENT
ORGANIZED CONVECTION DROPPING SOUTHEASTWARD.  PLEASE SEE WPC`S
MESOSCALE PRECIPITATION DISCUSSION #0505 FOR ADDITIONAL SHORT TERM
INFORMATION ACROSS THIS AREA.

OVER THE MID ATLANTIC---A SLIGHT EASTWARD EXPANSION TO THE SLIGHT
RISK AREA WAS DRAWN TO COVER THE LOWER FFG VALUES FROM NJ---INTO
DE AND EASTERN VA.

ORAVEC


...MID ATLANTIC CENTERING ON PENNSYLVANIA AND STRETCHING BACK TO
LOWER MICHIGAN...

LOOKING AT THE BIG PICTURE IN THIS REGION...GREATEST CONCERN IS
OVER PENNSYLVANIA...WHERE MODELS HAVE A UNANIMOUS HEAVY RAIN
SIGNAL...BUT THAT SAME QPF SIGNAL IS NOT ESPECIALLY FOCUSED. THE
CONCERN IS THAT CONVECTION MAY HAVE A TENDENCY TO WEAKEN UPON
MOVING OFF THE CAPE GRADIENT...AND THEN REFORM BACK TO THE WEST.
THIS SETUP COULD YIELD A MORE FOCUSED FLASH FLOOD THREAT ACROSS
SOUTHERN / CENTRAL PA AS OUTFLOWS BECOME ESTABLISHED AGAINST
INCREASED SOUTHWESTERLY INFLOW SPEEDS. IN DISCUSSION WITH WFO
CTP...MUCH OF THE RAIN WILL BE WELCOME...AND FLASH FLOOD GUIDANCE
VALUES ARE ON THE HIGH SIDE...BUT INTENSE SHORT DURATION RAINFALL
COULD LEAD TO FLASH FLOODING...ESPECIALLY IF IT OCCURS IN
SOUTH-CENTRAL PA AS INDICATED BY THE MAJORITY OF 00Z HI-RES
GUIDANCE.

THE HEAVY RAIN THREAT SHOULD MATERIALIZE AS VERY MOIST
SOUTHWESTERLY FLOW ALOFT AND SOUTHERLY FLOW AT SURFACE WILL
QUICKLY RETURN INTO THE MID ATLANTIC TODAY AHEAD OF A
SEMI-PERMANENT UPPER TROUGH OVER THE GREAT LAKES AND OHIO VALLEY.
MODEL QPFS ARE RELATIVELY HEAVY AND ARE SPATIALLY SIMILAR. THE QPF
IS SUPPORTED BY THE FORCING MECHANISMS WHICH WOULD SEEM TO FAVOR
LOCAL MAXIMA IN SOUTH CENTRAL PA WHERE JET-FORCED ASCENT WILL
COINCIDE WITH THE GREATEST AMOUNT OF LOW LEVEL INFLOW AND MODEST
CAPE...AND THEN ALSO ALONG THE SLOWLY LIFTING WARM FRONT IN
SOUTHERN VA AND NORTHERN NC. THE FLASH FLOOD RISK IN BETWEEN THESE
AREAS IS MORE CONDITIONAL...AS CONFIDENCE IN AREAL COVERAGE IS NOT
AS GREAT OVER NORTHERN VA AND ADJACENT DC/MD GIVEN NEUTRAL HEIGHT
CHANGE. HEATING SHOULD PROVE SUFFICIENT...HOWEVER...FOR SCATTERED
INITIATION IN THE HIGHER TERRAIN...WITH THAT ACTIVITY THEN
RELATIVELY LIKELY TO MAKE SOME EASTWARD PROGRESS GIVEN INCREASING
DEEP LAYER MOISTURE.

THE MODEL QPF SIGNAL IS ALSO INCREASING BACK WESTWARD ALONG WHAT
COULD BE CONSIDERED A WEAK OCCLUSION ACROSS NORTHWEST PA INTO
NORTHERN OH AND LOWER MI. LIGHT MEAN WINDS IN THE CLOUD LAYER
ALONG THIS AXIS WILL MAKE FOR SLOW CELL MOTIONS...SIMILAR TO THE
ENVIRONMENT THAT PRODUCED A FEW 3-PLUS INCH RAINFALL EVENTS AND
OBSERVED FLASH FLOODING IN ILLINOIS / INDIANA THE PREVIOUS DAY.


...ARIZONA / NEW MEXICO / FAR SOUTHWEST UTAH...

THE MONSOON HAD SLOWLY STRENGTHENED IN RECENT DAYS...AND WAS MORE
PRODUCTIVE ACROSS ARIZONA ON FRIDAY WITH SEVERAL MESONET STATIONS
REPORTING MORE THAN AN INCH OF RAIN. ENHANCED EASTERLY FLOW AROUND
THE UPPER HIGH WILL CONTINUE TO FAVOR WESTERN NM INTO
CENTRAL/SOUTHERN/WESTERN ARIZONA FOR ORGANIZED CONVECTION AND
LOCALLY HEAVY RAINFALL...FOLLOWING THE TYPICAL DIURNAL PATTERN FOR
TIMING. PRECIPITABLE WATER IS HIGHEST NEAR THE MOGOLLON RIM AND
MOUNTAINS OF SOUTHEAST AZ EXTENDING WESTWARD INTO THE DESERT
AREAS. STEEP LAPSE RATES ARE ALSO FORECAST TO PERSIST...RESULTING
IN MUCAPE VALUES APPROACHING 2000 J/KG BY EARLY AFTERNOON. THESE
PARAMETERS FAVOR INTENSE LOCAL RAIN RATES...ESPECIALLY IN THE
EARLY FORMATIVE STAGES AND DURING EARLY CELL MERGERS PRIOR TO
UPSCALE GROWTH AND FORWARD PROPAGATION.


...EASTERN KANSAS AND ADJACENT SOUTHERN NEBRASKA / NORTHEAST
OKLAHOMA...

A LOOSELY ORGANIZED CLUSTER OF CONVECTION OR MCS MAY BRIEFLY RAISE
THE POSSIBILITY OF FLASH FLOODING THIS MORNING IN SOUTHERN
KS/NORTHERN OK ALONG THE SAME PATH OF SEVERAL RECENT CONVECTIVE
EVENTS. BEYOND THIS...IT APPEARS THE NEXT OPPORTUNITY FOR LARGER
SCALE AND MORE ROBUST ACTIVITY WILL COME SATURDAY NIGHT AS
SHORTWAVE RIDGING PROVIDES AN OPPORTUNITY FOR THE PLAINS LOW LEVEL
JET TO STRENGTHEN AND SET UP
FARTHER NORTH AND EAST. MOST GUIDANCE PRODUCES A SWATH OF SOMEWHAT
HEAVY PRECIPITATION ACROSS EASTERN KANSAS AND PERHAPS EXTENDING
INTO ADJACENT NE/MO/OK. THOUGH PLACING THESE SWATHS IN ADVANCE CAN
BE DIFFICULT...IT IS LIKELY THAT SOME OF THE HEAVIER RAINFALL WILL
OVERLAP WITH LOWER FLASH FLOOD GUIDANCE VALUES AS PARTS OF EASTERN
KS AND ADJACENT OK HAVE SEEN ABOVE NORMAL RAINFALL OVER THE PAST
WEEK.


...ARLATEX TOWARD THE MID/LOWER MISSISSIPPI VALLEY...

DOWNSTREAM OF THE PLAINS ENVIRONMENT...THE PRECIPITATION
DISTRIBUTION IS SOMEWHAT MORE CHAOTIC...BUT MODELS GENERALLY
INDICATE A BETTER CHANCE OF MEANINGFUL RAINFALL FROM THE ARKLATEX
INTO WESTERN TN/MS...AIDED AT TIMES BY OUTFLOWS ARRIVING FROM THE
WEST...AND THEN ALSO IN THE UPSLOPE REGIONS DOWNSTREAM OF THE
UPPER TROUGH AXIS INTO EASTERN KENTUCKY AND ADJACENT AREAS TO THE
EAST. ISOLATED FLASH FLOODING CANNOT BE RULED OUT.

BURKE
$$





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