Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
109
FOUS30 KWBC 160017
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
817 PM EDT SAT JUL 15 2017

...VALID 01Z SUN JUL 16 2017 - 12Z SUN JUL 16 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
180 WNW MMHO 85 SE YUM 55 W GBN 55 WNW LUF 20 N LUF 25 ENE SDL
55 NNE DMA 30 NNW SVC 25 N SVC 20 SW TCS 30 W ROW 30 SSE CNM
50 SSW MRF 125 E MMCU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
105 SE CHS 25 E NBC 20 NNE SAV 20 S LSF 20 SW TOI 15 NNW GZH
35 W PIB 25 SSW TVR 30 NE JAN 15 NNW NMM 15 SE 1M4 30 NNE GVL
30 ESE GSP 20 W TTA 15 NNW PGV 30 E HSE 95 SSE HSE.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 ENE RAC 10 WNW ORD 25 NW DVN 10 NNW OLZ 20 NE OVS 35 SSW PCZ
10 SE CLI 25 SSW SUE 25 ESE MTW 30 ENE MKE 30 ENE RAC.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE GLD 35 N DDC 20 WNW END 25 SSE JWG 10 W PYX 20 SE CAO
45 NNW TCC 35 N LVS 10 NNW TAD 20 ENE COS 25 SW AKO 20 NNE GLD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
ITR 35 W GCK 20 NE EHA 30 SSW SPD 45 W SPD 25 ESE LIC ITR.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 ENE LBT 10 WNW EWN 10 SSW NKT SUT 40 NE CHS 35 N NBC
25 SSE AGS AGS 15 ENE LBT.


16/01Z UPDATE...

CHANGES TO PREVIOUS EXCESSIVE RAINFALL GENERALLY REFLECT REDUCTION
OF MARGINAL AND SLIGHT RISK AREAS WHERE LOSS OF DAYTIME HEATING
AND OVERTURNING OF INSTABILITY FROM EARLIER CONVECTION HAS REDUCED
RISK OF FLASH FLOODING.

FROM SE NC SWWD INTO MS...STILL LOOKING LIKE SMALL WINDOW OF
OPPORTUNITY FOR EXCESSIVE RAINS PRIMARILY FROM MERGING OUTFLOWS
BNDRIES AND CONVECTIVE CELLS THROUGH THE EARLY OVERNIGHT WITH
SOMEWHAT CONFLUENT LOW/MID FLOW THROUGH THE ERN SC INTO SERN NC
NEAR AND SOUTH OF WEAK COLD FRONT PSBLY SUPPORTING SOME SLOW
MOVING HEAVIER RAIN CLUSTERS OR LINES THAT COULD BRIEFLY SUPPORT
SOME TRAINING.

ACRS ERN CO...SLOW CELL MOTION AROUND WEAK AND NEARLY STATIONARY
UPPER LOW COMBINED WITH MERGING OUTFLOWS ESPECIALLY OVER UNTAPPED
INSTABILITY COULD LEAD TO LOCALLY HEAVY TO PSBLY EXCESSIVE
RAINS..PARTICULARLY OVER PARTS OF ERN/SE CO INTO WRN KS.   RECENT
HRRR RUNS HAVE SHOWN DECENT RUN TO RUN CONTINUITY SUPPORTING AN
AREAL OF 1 TO LOCALLY 3" RAINS ACRS THIS REGION OVERNIGHT.

ACRS SRN AZ/SRN NM INTO WRN TX...MAIN CHANGE HERE WAS TO REMOVE
SLIGHT RISK ACRS WRN TX IN SRN NM GIVEN RATHER LARGE CLOUD
COVER/REDUCED INSTABILITY THERE..BUT CONDITIONS ELSEWHERE WILL
CONTINUE TO SUPPORT LOCALLY HEAVY CONVECTIVE CELLS THROUGH AT
LEAST THE EARLY OVERNIGHT.  CELLS ACRS AZ SHOULD REMAIN FAIRLY
PROGRESSIVE TO THE SW THIS EVENING BUT WILL BE RUNNING INTO
PROGRESSIVELY HIER PWS SUGGESTING POTNL FOR SOME BRIEF BUT FAIRLY
INTENSE RAIN RATES THAT COULD LEAD TO ISOLD RUNOFF ISSUES.

ACRS THE UPPER MIDWEST...REDUCED THE MARGINAL RISK AREA TO COVER
AREAS THAT HAVE LOW FFG VALUES..MAINLY FROM SRN WI INTO NRN IL AND
ADJACENT AREAS OF ERN IA.  THIS LOOKS PRIMARILY A SEVERE THREAT
GIVEN CAPE VALUES OF 2 TO 4 THSD J/KG..BUT PWS HAVE INCREASED TO
OVER 1.25 INCHES FROM IA INTO PARTS OF SW IA SO COULD NOT RULE OUT
SOME BRIEF BUT INTENSE RAIN RATES IN SOME OF THE STGR TSTMS
OVERNIGHT AS ACTIVITY GENLY TRACKS SEWD ACRS THE REGION.  SULLIVAN
  PREVIOUS DISCUSSIONS FOLLOW...



...15Z UPDATE...

WPC WENT AHEAD AND MADE SOME MODIFICATIONS FROM THE EARLIER 09Z
ISSUANCE, IN COMBINING THE TWO MARGINAL THREATS ACROSS THE
SOUTHERN TIER OF THE COUNTRY ALONG WITH COMBINING TWO SLIGHT AREAS
FROM THE SOUTHERN TN VALLEY TO THE EASTERN CAROLINAS. WPC ALSO
ENLARGED THE SLIGHT RISK OVER CO EXTENDING SOUTH AND EAST TO THE
OK PANHANDLE AND INTRODUCED A MARGINAL THREAT ACROSS THE UPPER MS
VALLEY.

BASED ON ONGOING CONVECTIVE HEAVY RAINFALL INVOF BNA AND 12Z NAM
CONEST/00Z HREF MEAN SUGGESTING HEAVY RAINFALL POTENTIAL
CONTINUING ACROSS EAST CENTRAL TN TOWARD THE SOUTHERN APPALACHIANS
AND PERHAPS EXTENDING TOWARD THE EASTERN CAROLINAS FOR LATER THIS
AFTERNOON INTO THE EVENING, WPC WENT AHEAD COMBINED THE TWO AREAS
INTO A LARGE SLIGHT RISK WITH WEAK WAVE OF LOW PRESSURE RIDING
ALONG WELL DEFINED QUASI-STATIONARY FRONT WITH DEEP TROPICAL
MOISTURE REMAINING ENTRENCHED FROM THE TN VALLEY INTO THE
SOUTH/SOUTHEAST. 12Z RAOBS SUGGESTING 850 MB FLOW BEING 10 KTS OR
LESS ACROSS THE AREA, MEANING SLOW MOVING CONVECTIVE RAINS AND
LOCALIZED RUNOFF ISSUES.

BASED ON HI-RES SUITE FROM OVERNIGHT AND MORNING SCATTERED
CONVECTION OVER EASTERN OK INTO NORTHERN TX, EXPECT THIS NORTHERN
ACTIVITY TO POSSIBLE INTERACT WITH EXPECTED SEA BREEZE ACTIVITY
ACROSS SERN TX FOR LOCALIZED HEAVY RAINFALL AND AN INTRODUCTION TO
A MARGINAL THREAT.

ALSO EXPANDED THE SLIGHT RISK OF EXCESSIVE FROM CO TO WESTERN OK
BASED ON HI-RES GUIDANCE AND NICE CONVERGENCE AXIS SETTING UP FROM
THE SMALL CONVECTIVE CLUSTER EAST OF APX TO LBL AND GAG.

FINALLY INTRODUCED A MARGINAL THREAT IN CONJUNCTION WITH SPCS
SLIGHT RISK OF SEVERE ACROSS THE UPPER MS VALLEY. FLASH FLOOD
GUIDANCE REMAINS RELATIVELY LOW ACROSS THIS AREA FROM HEAVY RAINS
EARLIER IN THE WEEK. DESPITE THE STRONG SYNOPTIC SCALE FORCING AND
LIKELY INSTABILITY LATER TODAY, MOISTURE CONTENT WILL BE SOMEWHAT
LIMITED AND NARROW FOR WIDESPREAD HEAVY RAINS. HOWEVER LOCALIZED
ISSUES WILL BE POSSIBLE FROM CONVECTIVE ELEMENTS TRACKING NW TO SE
ACROSS THE UPPER MS VALLEY.

MUSHER



...MID SOUTH / ALABAMA / MISSISSIPPI...

WE ARE STUCK IN A REPEATING PATTERN IN WHICH DIURNAL THUNDERSTORMS
FORM ALONG THE GULF COAST SEA BREEZE AND SEPARATELY ALONG A WAVY
FRONTAL BOUNDARY IN THE LOWER MS / TN VALLEY BEFORE MEETING IN THE
MIDDLE. USING MOISTURE IN THE 700-500 MB LAYER TO TRACE THE
GREATER COVERAGE OF CONVECTIVE RAINFALL POINTS US TOWARD A
SATURDAY FORECAST THAT FAVORS THE 00Z GFS AND NSSL WRF...WITH THE
18-21Z MAXIMUM IN LAYER RELATIVE HUMIDITY ORIENTED FROM SOUTHWEST
MISSISSIPPI TO NORTHERN
ALABAMA / FAR NORTHWEST GEORGIA. COLLISION OF OUTFLOWS WITHIN A
SEASONABLY MOIST AND UNSTABLE ENVIRONMENT WILL SUPPORT ISOLATED
HEAVY RAINFALL TOTALS AND A RISK OF FLASH FLOODING...ESPECIALLY
OVER PARTS OF MS/AL WHERE THE WPC MANUAL AREAL AVERAGE QPF IS
MAXIMIZED.


...CAROLINAS...

SIMILAR TO THE GULF COAST STATES...CONVECTION IS LIKELY TO FORM
BOTH ALONG SEA BREEZES AND IN THE ELEVATED TERRAIN FARTHER
INLAND...AND THEN MEET. THERE IS A BIT MORE WESTERLY MID LEVEL
FLOW AND STRONGER SOUTHWESTERLY LOW LEVEL INFLOW HERE...WHICH MAY
GIVE COLLIDING THE TRAINING THUNDERSTORMS MORE STAYING POWER /
LONGEVITY...ALLOWING FOR SOME EXCESSIVE LOCAL RAINFALL TOTALS.
MODELS SHOW A CONSISTENT HEAVY RAINFALL SIGNAL FROM MYRTLE BEACH
UP THROUGH THE OUTER BANKS...AND GENERALLY EAST OF I-95.


...SOUTHWEST U.S. / SOUTHWEST TEXAS...

THERE IS A MULTI-MODEL SIGNAL FOR HEAVY RAIN IN THE EL PASO AREA
PERHAPS AS EARLY AS THE MORNING HOURS. THE CIRA LAYER PW SATELLITE
PRODUCT FOR 700-500 MB SHOWS A SLUG OF MOISTURE MIGRATING INTO
THAT REGION ALONG THE CONVERGENT EASTERN PERIPHERY OF A BROAD
EASTERLY WAVE MIGRATING THROUGH NORTHERN MEXICO. ONCE
THUNDERSTORMS FORM THEY WILL EXPERIENCE SOME ENHANCED
SOUTHEASTERLY INFLOW AT 850-700 MB TO SUPPORT REGENERATION AND
SMALL SCALE TRAINING ALONG OUTFLOWS...RESULTING IN A RISK OF HEAVY
RAINFALL AND FLASH FLOODING. THE DISTRIBUTION OF MOISTURE WILL
ALSO CONTINUE TO FAVOR SOUTHERN
ARIZONA FOR RELATIVELY ORGANIZED CONVECTION AND RISK OF FLASH
FLOODING ASSOCIATED MORE WITH THE SHORT TERM RAIN RATE AND QUICK
RESPONDING TERRAIN. WIND PROFILES ARE MORE FAVORABLE FOR TRAINING
AND PERHAPS MORE EXCEPTIONAL EVENT TOTAL RAINFALL AMOUNTS OVER
SOUTHERN NEW MEXICO AND SOUTHWEST TEXAS.


...COLORADO / KANSAS / NEW MEXICO / OKLAHOMA...

NOCTURNAL VEERING OF LOW LEVEL WINDS...THEN INDUCING WEAK WARM
ADVECTION...COULD LEAD TO INITIATION OF ELEVATED THUNDERSTORMS
OVER EASTERN OKLAHOMA THIS MORNING. IF THIS OCCURS STORMS WILL BE
SLOW MOVING AND A CAPABLE OF HEAVY RAIN...ALTHOUGH THE WIND SPEEDS
/ FORCING WILL BE VERY WEAK AND THE HRRR WAS TENDING TO KEEP THE
AREA DRY.

OF MORE CONCERN IS EASTERN COLORADO AND WESTERN KANSAS. WE WILL
HAVE TO WATCH THIS AREA DILIGENTLY FOR HEAVY RAINFALL. THERE ARE
SEVERAL FAVORABLE INGREDIENTS IN PLACE WITH AMPLE SUMMERTIME
MOISTURE COINCIDENT BENEATH A PERSISTENT UPPER LOW / SHEAR AXIS.
THE DEEP LAYER WIND SPEEDS...HOWEVER...WERE SO WEAK THAT THE
DIURNAL THUNDERSTORM ACTIVITY IN RECENT DAYS HAD TENDED TO BE VERY
SMALL SCALE AND NOT SUPPORTED MUCH AFTER DARK. ALL IT WOULD TAKE
IS A TIMELY ARRIVAL OF GREATER UPPER DIVERGENCE TO ENHANCE THIS
SMALL WEATHER SYSTEM AND ITS RAINFALL PRODUCTION. ALTHOUGH SUCH AN
OCCURRENCE IS NOT EXPECTED ON THE SYNOPTIC SCALE...THE HI-RES
MODELS ARE EVEN MORE EMPHATIC IN PRODUCING ORGANIZED HEAVY RAIN
OVER THE REGION SATURDAY AND SATURDAY EVENING. THE MODELS HAVE
BEEN STRUGGLING...OVER-FORECASTING THE QPF PROBABLY BECAUSE OF THE
SMALL SCALE OF THE INDIVIDUAL THUNDERSTORMS. WPC QPF MAY STILL BE
A LITTLE ON THE HEAVY SIDE OVERALL...BUT THERE IS POTENTIAL FOR
LOCALLY VERY HEAVY RAINFALL WHEREVER THE MORE PERSISTENT CELLS ARE
ABLE TO FORM...WITHIN SOUTHERN/EASTERN CO AND WESTERN KS. MARGINAL
RISK EXTENDS AROUND THE SOUTHERN PERIPHERY OF THE UPPER LOW...INTO
NEW MEXICO WHERE HEAVY SHORT TERM RAINFALL IS POSSIBLE...THOUGH
WIND PROFILES WILL BE LESS FAVORABLE FOR TRAINING HERE COMPARED TO
AREAS EAST OF THE COLORADO FRONT RANGE.


...SOUTHEAST TEXAS / LOUISIANA...

ALTHOUGH THE FRONTAL BOUNDARY IN THE SOUTHERN PLAINS WILL MOVE
VERY LITTLE...NORTHERLY DEEP LAYER FLOW IS EXPECTED TO INCREASE IN
STRENGTH AS AN INVERTED TROUGH / EASTERLY WAVE CONTINUES TO
MIGRATE WESTWARD ALONG THE GULF COAST. THIS SHOULD PROMOTE
THUNDERSTORMS PROGRESSING SOUTHWARD AND PRODUCING ANOTHER RELATIVE
MAXIMUM SWATH OF RAINFALL OVER EAST TX AND WESTERN LA. AS IN OTHER
PARTS OF THE SOUTH...SOME COLLISIONS OR FOCUS ALONG THE SEA BREEZE
COULD LEAD TO HEAVIER LOCAL TOTALS...ESPECIALLY THE UPPER TX COAST
AND SOUTHWEST LOUISIANA.

BURKE
$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.