Quantitative Precipitation Forecast
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FOUS30 KWBC 180831
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
431 AM EDT TUE JUL 18 2017

...VALID 12Z TUE JUL 18 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
75 SW OLS 100 S GBN 40 SSE GBN 10 SW CGZ 10 WNW DVT 45 NW GBN
30 ESE BLH 20 WSW BLH 25 SE TRM 30 NNE CZZ 20 E CZZ 45 SSW NJK
50 SSE CZZ 10 E MMTJ 10 N RNM 10 SW RIV 10 NNE BUR 15 W WJF EDW
25 WNW DAG 25 NNW DRA 65 SSE ELY 30 SE U24 45 NW 4HV 30 SSW 4HV
35 NE PGA 40 ESE PGA 75 NNW RQE 25 WSW CEZ 40 W MTJ 15 WSW GUC
15 SW ALS 30 NNE SAF 40 S ABQ 10 S SVC 55 SW DMN 80 ESE DUG
100 SSE DUG 80 NE MMHO.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSW CBE 15 SSW MSV CON 25 E BVY 15 ENE BLM 10 WSW RIC
20 NNW SOP 10 ESE IPJ AND 30 N GVL 40 NNE 1A5 15 NNW GEV
15 SSW CBE.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 NNW CWBE 15 E PZQ 20 NW LDM 20 E VTI RDK 15 ENE BIE
10 NNW HJH 20 ESE BBW 30 SE 9V9 25 NE PHP 35 E D07 15 NNW 8D3
20 SSW ASX 55 SW CWXZ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SE PRC 30 SSE EED 45 E NXP 30 ENE DAG 30 ENE DRA 35 WNW CDC
25 NNW BCE 40 WSW PGA 55 N INW 35 NNW SJN 35 WNW SOW 25 SE PRC.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNW LNR 15 NW MIW 15 WSW DNS 15 WSW PQN LJF 10 SW ARV
40 ENE SAW 15 E ISQ 10 NNE GRB 20 NNW LNR.


...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 INITITATION 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.

BURKE
$$





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