Quantitative Precipitation Forecast
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FOUS30 KWBC 181824
QPFERD

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

...VALID 1823Z 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
20 N MMHO 50 N MMHO 50 WSW OLS 90 W OLS 40 SSE GBN 25 N GBN
35 SE BLH BLH 25 SE TRM 30 NNE CZZ 20 E CZZ 45 SE CZZ 60 S CZZ
MMTJ 15 NW 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 35 SW CEZ 40 NE 4BL 30 NE MTJ 15 SW MYP
20 SE ALS 25 WSW LVS 50 NNE TCS 15 WNW DMN 80 SSW DMN
120 NW MMCU.

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
45 SE SUT 40 S MYR 15 ESE NBC 10 SSW OGB 15 SSE JNX 25 ESE FFA
130 E FFA.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 NNW CWBE 10 E SLH 35 ENE MTW 20 SE MSN 15 SSE DBQ 10 NNE PEA
30 SSE ICL 10 W FNB 25 W AFK 15 SE ORC 15 ENE FSD 15 ENE HON
45 NNE PIR 25 ENE MBG FFM 20 SE BFW 55 NNW CYLD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 SSW PRC 25 ESE EED 30 E NXP 30 ENE DAG 30 SSE DRA 20 NNE SGU
35 NW BCE 20 ENE BCE 30 SSW PGA 35 NE INW 25 NE SJN 55 SSE SJN
50 N SAD 60 NE SDL 40 SSW PRC.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
MNM 25 SSE ISW 10 NW DEH 10 E CAV 25 SE SPW 15 S MML 15 SSW ATY
ETH 15 W ASX 30 SE P59 40 N ISQ MNM.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 NNE MMHO 30 SSW OLS 20 ESE DMA 45 NE DMA 10 SSE SAD
25 NE DUG 50 ESE DUG 105 SSE DUG.


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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