Quantitative Precipitation Forecast
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634
FOUS30 KWBC 190059
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
858 PM EDT TUE JUL 18 2017

...VALID 01Z WED JUL 19 2017 - 12Z WED JUL 19 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSW CBE 20 ENE CBE 25 W CXY 30 SSW AVP MSV BAF 20 ESE BOS
15 W SFZ 10 W OXC UKT 10 WSW GAI CJR FVX 10 W RZZ CTZ 20 WNW MYR
30 SSE SSC CAE 30 SSW UZA 10 ENE JQF 15 WNW INT 10 WNW HLX
20 SW LWB 15 SSW CBE.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 W CWNL GOV 35 ESE SBM 10 ESE JVL SQI 15 WNW PIA 15 N IJX
25 S MQB 10 E MUT CID 15 W CID 10 WNW TNU 10 SSW CSQ 25 SSE SDA
20 S AFK MLE 30 E SUX 15 NNW AXA 15 SSE OWA 15 N RST 30 NE ONA
CMY 30 SSW PCZ 10 SE ATW 15 E SUE 25 SW SJX 15 ENE SJX ANJ
15 NE ANJ.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 N MMHO 50 N MMHO 50 WSW OLS 75 W OLS 55 SE YUM 10 ENE IPL
30 SSE TRM 30 NNE CZZ 20 E CZZ 45 SE CZZ 60 S CZZ 45 S CZZ
10 NE RNM RAL 10 NNE BUR 15 W WJF EDW 30 ENE EDW 45 NNE NID
55 NNW DRA 75 E TPH 75 S ELY 65 SSE ELY 30 SE U24 45 NW 4HV
30 SSW 4HV 40 NE PGA 40 ENE PGA 65 SSW 4BL 35 WSW CEZ 40 NE 4BL
30 NE MTJ 15 SW MYP 20 SSW MYP 35 NW VTP 25 W RTN 20 NW LVS
25 WSW LVS 50 NNE TCS 15 WNW DMN 80 SSW DMN 120 NW MMCU.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 N SGU CDC 30 NW BCE 15 ENE BCE 15 NE PGA 70 NNE INW
30 NNW SJN 55 SSE SJN 40 ENE SAD 50 NE DUG 25 ESE DUG 35 SW DUG
15 SSW OLS 70 WSW TUS 15 S GBN 25 WSW GYR 40 NW LUF 60 WSW PRC
25 ESE EED 30 E NXP 30 ENE DAG 30 SSE DRA 15 N SGU.


01 UTC UPDATE...

MADE ADJUSTMENTS TO THE EARLIER ISSUED 18 UTC SPECIAL WPC
EXCESSIVE RAINFALL OUTLOOK BASED ON THE LATEST SATELLITE AND RADAR
TRENDS...AS WELL AS THE LATEST RUNS OF THE HRRR. THIS MANIFESTED
IN THE REDUCTION OF THE NWRN PERIPHERY OF THE UPPER MIDWEST THREAT
AREAS DUE TO CELL PROPAGATION AND GENERAL REDUCTION OF COVERAGE
AND COMBINATION OF THE THREAT AREAS PREVIOUSLY OVER THE ERN US
INTO THE EVENING HOURS. OTHERWISE...THE PREVIOUS OUTLOOKS OVER THE
SWRN US REMAIN LARGELY UNCHANGED EXCEPT FOR AN
EXPANSION/COMBINATION OF THE SLIGHT RISK AREAS TO BETTER MATCH
MORE WIDESPREAD CONVECTIVE DEVELOPMENT. THIS BLENDS WELL WITH
THOUGHTS ON OUR EARLIER COORDINATION CALL WITH EFFECTED WFOS AND
LATEST WPC MESOSCALE PRECIPITATION DISCUSSIONS NOW IN EFFECT.


18 UTC UPDATE...

A SLIGHT RISK WAS ADDED TO PORTIONS OF SOUTHEASTERN AZ...WHERE AN
MCV APPROACHING FROM SOUTHEASTERN NEW MEXICO INTERACTING WITH VERY
ANOMALOUS MOISTURE IS EXPECTED TO SUPPORT HEAVY AMOUNTS DURING THE
AFTERNOON INTO THE EVENING HOURS.  REFER TO WPC MPD #505 FOR
FURTHER INFO ON THE SHORT-TERM HEAVY RAINFALL THREAT ACROSS THE
REGION.


15 UTC UPDATE...

BASED ON THE LATEST SATELLITE AND RADAR TRENDS...AS WELL AS THE
LATEST RUNS OF THE HRRR...MADE A SLIGHT NORTHWESTWARD ADJUSTMENT
TO THE OUTLOOK AREAS ACROSS ACROSS THE UPPER MIDWEST.
OTHERWISE...THE PREVIOUS OUTLOOK REMAINS LARGELY UNCHANGED.

PREVIOUS DISCUSSIONS...

...EASTERN CAROLINAS...

A MARGINAL RISK HAS BEEN ADDED FOR PORTIONS OF THE EASTERN
CAROLINAS WHERE DEEP MOISTURE TO THE EAST OF A SLOW MOVING
MID-UPPER LEVEL TROUGH AND ALONG A REMNANT FRONTAL BOUNDARY HAS
LED TO THE DEVELOPMENT OF SLOW-MOVING CONVECTION PRODUCING LOCALLY
HEAVY ACCUMULATIONS ACROSS PORTIONS OF SOUTHEASTERN NC AND THE PEE
DEE REGION OF SC.  IN ADDITION...EXPECT DAYTIME HEATING TO SUPPORT
SCATTERED CONVECTION AND LOCALLY HEAVY AMOUNTS FURTHER TO THE
SOUTH ALONG THE SOUTHERN COASTAL REGIONS OF SC.

...SOUTHWEST U.S...

SUBTLE MOVEMENT OF UPPER AIR FEATURES HAD PUSHED THE GREATER PW
AXIS...VALUES ABOVE 1.5 INCHES...OUT INTO THE DESERTS AND FARTHER
INTO SOUTHERN CALIFORNIA. THE BETTER OVERLAP FOR HIGH TERRAIN AND
CELL INITIATION WITHIN THE PW PLUME SHOULD BE CENTERED AROUND THE
COLORADO RIVER BASIN FROM NORTHWEST AZ INTO SAN BERNADINO COUNTY
CA...AND UP THROUGH THE LAS VEGAS AREA TOWARD SOUTHWEST UTAH.
UPPER LEVEL FEATURES ARE RATHER BENIGN...BUT THERE IS SOME
ENHANCED SOUTHERLY LOW LEVEL FLOW EXPECTED...WITH ASSOCIATED
MOISTURE TRANSPORT UP THROUGH THE COLORADO RIVER BASIN. THIS COULD
LEAD TO MORE SUSTAINED...REGENERATIVE ACTIVITY HERE COMPARED TO
ELSEWHERE...OFFERING GREATER ODDS OF TRAINING OR MERGING CELLS TO
BOOST LOCAL RAIN TOTALS. A SLIGHT RISK OF EXCESSIVE RAINFALL WAS
DRAWN FOR PARTS OF AZ/CA/NV/UT IN COORDINATION WITH LOCAL OFFICES.

FARTHER WEST...ISOLATED CONVECTIVE INITIATION IS ALSO SIGNALED BY
THE GLOBAL MODELS AND A FEW HI-RES MODELS INTO THE SOUTHERN
CALIFORNIA MOUNTAINS. COVERAGE MAY BE SPARSE...BUT ANY CONVECTIVE
RAINS HERE WILL POSE A RISK OF FLASH FLOODING.

SIMILARLY A MARGINAL RISK BLANKETS THE MONSOONAL ACTIVITY IN
SOUTHEAST ARIZONA AND UP THROUGH WESTERN NM/CO. ALTHOUGH COVERAGE
WILL REMAIN RATHER HIGH...CELLS SHOULD BE LESS ORGANIZED COMPARED
TO RECENT DAYS...WITH GREATER INHIBITION TOWARD REDEVELOPMENT
ALONG OUTFLOWS.


...UPPER MIDWEST / WESTERN GREAT LAKES...

AN ELONGATED UPPER TROUGH SWIPES ACROSS THE NORTHERN PLAINS AND
UPPER MIDWEST TODAY. AN ASSOCIATED JET STREAK WILL SUPPORT
CONVECTION INTO THE DAYTIME HOURS FROM WISCONSIN INTO AREAS OF
MICHIGAN BORDERING LAKE MICHIGAN. MEANWHILE ENERGETIC WEST TO
NORTHWEST FLOW WILL LEAD TO ORGANIZED STORM MODES FOR DIURNAL /
AFTERNOON STORMS FORMING BACK ALONG THE COLD FRONT IN THE
FOUR-STATE AREA NEAR SIOUX FALLS. THE UPPER RIDGE POSITION INVITES
SOME DIFLUENT MID LEVEL FLOW IN THIS AREA...WITH LIKELY SUFFICIENT
INSTABILITY AND INFLOW TO SUPPORT SOME PROPAGATION OF OUTFLOWS
WELL INTO NORTHERN IOWA. THE EVENT IS NOT ESPECIALLY WELL
FOCUSED...AND IT WILL TAKE SOME MOISTENING OF THE ENVIRONMENT
THROUGH CONVECTION TO PUSH PRECIPITABLE WATER VALUES INTO MORE
ANOMALOUS RANGE. MODEL QPFS ARE FAIRLY HEAVY...HOWEVER...WITH
AREAL AVERAGE OF 1.50 INCHES EXPECTED IN THE CONFLUENT REGION TO
THE REAR OF THE GREAT LAKES JET STREAK...AND ALSO IN THE EARLY
STAGES OF NEW DEVELOPMENT NEAR/EAST OF SIOUX FALLS. WIND PROFILES
WILL FAVOR SOME TRAINING WHICH MAY RESULT IN LOCAL AMOUNTS 3-PLUS
INCHES...CAPABLE OF EXCEEDING FLASH FLOOD GUIDANCE.


...EAST COAST...

THE UPPER TROUGH IN THE EAST WILL BREAK APART...WITH ONE VORT MAX
MOVING OFFSHORE OF NEW ENGLAND AND ANOTHER LAZY CIRCULATION
FORMING OVER VA/NC. PROBABLY MORE IMPORTANTLY...THOUGH...THE LOW
LEVELS WILL CHANGE VERY LITTLE...WITH SUFFICIENT MOISTURE DEPTH
AND STRONG HEATING TO ALLOW FOR SCATTERED CONVECTIVE DEVELOPMENT
ALONG THE PIEDMONT AREAS IN VA/MD...AND UP THROUGH SOUTHERN NEW
ENGLAND. THE MODELS OFTEN DO A POOR JOB OF PROPAGATING THIS
ACTIVITY TOWARD THE COAST AS REFLECTED IN THEIR QPF...SO WE TOOK A
MORE GENEROUS APPROACH...AND PUSHED THE CONVECTION EASTWARD
THROUGH THE CAPE AXIS...PARTICULARLY THE NAM CAPE. WE BOOSTED THE
AREAL AVERAGE PRECIPITATION A LITTLE BIT...BUT IT STILL LOOKS
RATHER TAME GIVEN THE DISORGANIZED STORM MODES THAT ARE EXPECTED.
STILL...WITH WEAK STEERING FLOW THERE MAY BE ISOLATED VERY HEAVY
DOWNPOURS AND AN ASSOCIATED LOW PROBABILITY RISK OF FLASH
FLOODING.

PEREIRA/BURKE
$$





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