665
FOUS30 KWBC 160106
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
906 PM EDT MON OCT 15 2018
DAY 1
VALID 01Z TUE OCT 16 2018 - 12Z TUE OCT 16 2018
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER CENTRAL AND
NORTHEAST TEXAS...
0100Z UPDATE: FOR THE FINAL ISSUANCE OF THE EXCESSIVE
PRECIPITATION OUTLOOK...MODERATE RISK AREAS WERE ADDED OVER
PORTIONS OF CENTRAL TO NORTHEAST TEXAS WHERE FFG VALUES HAVE
LOWERED FROM RECENT RAINS. ADDITIONAL MODERATE TO HEAVY RAINS
LIKELY THROUGH THE REMAINDER OF THIS FORECAST PERIOD. HOURLY
RAINFALL RATES OF .50-1"+ POSSIBLE...WITH THESE VALUES POSSIBLY
EXCEEDING THE LOWERED FFG VALUES. SEE WPC'S MESOSCALE
PRECIPITATION DISCUSSION # 0982 VALID UNTIL 0500 UTC OCT 16 FOR
ADDITIONAL INFORMATION IN THE VICINITY OF THE TX HILL COUNTRY.
ORAVEC
..EARLIER DISCUSSION
..CENTRAL TEXAS TO THE ARKLATEX
HERE WE CONFINED SLIGHT RISK TO AREAS WHERE THE GREATEST 3 TO
6-HOUR RAIN RATES OVERLAP WITH LOWER FLASH FLOOD GUIDANCE VALUES.
MOST RAINFALL WILL BE ELEVATED / ROOTED IN THE MID LEVELS AND
LOCATED WELL NORTH OF A FRONTAL BOUNDARY. THIS WILL PLACE A LIMIT
ON AVAILABLE INSTABILITY AND SHORT TERM RAIN RATES, WITH MOST OF
THE HEAVIER CONVECTION OCCURRING IN A PROGRESSIVE FASHION CLOSER
TO THE GULF COAST. STILL, GENERALLY SATURATED SOILS ALONG WITH
CONTINUED RAINFALL AND OCCASIONALLY EMBEDDED, CONVECTIVELY
ENHANCED RAIN RATES, WILL SUPPORT MARGINAL AND SLIGHT RISK AREAS
FROM CENTRAL AND SOUTHWEST TEXAS UP THROUGH THE ARKLATEX. SOME OF
THE HEAVIER RAIN RATES ARE EXPECTED LATER IN THE DAY 1 PERIOD,
MAINLY MONDAY NIGHT.
..TEXAS COAST
A COLD FRONT WILL ENCOUNTER INCREASINGLY UNSTABLE AIR AS IT DROPS
TOWARD THE COAST THIS MORNING. COVERAGE OF THUNDERSTORMS IS
EXPECTED TO INCREASE, ESPECIALLY BETWEEN 12 AND 15Z. MODERATE CAPE
VALUES AND HIGH PW VALUES - ANOMALOUSLY HIGH EVEN FOR SOUTH TEXAS
- WILL SUPPORT INTENSE SHORT TERM RAIN RATES. A RELATIVE ABSENCE
OF MID AND UPPER LEVEL SUPPORT, HOWEVER, SHOULD GIVE THIS
CONVECTION A RELATIVELY DISORGANIZED CHARACTER. HI-RES MODELS
SUGGEST OUTFLOWS AND ADVANCEMENT OF THE FRONTAL ZONE WILL PUSH THE
STORMS ALONG TO THE SOUTH AND EAST, OFFSHORE, BY LATE MORNING TO
EARLY AFTERNOON. ISOLATED INSTANCES OF FLASH FLOODING ARE
POSSIBLE, MAINLY IN URBAN, POORLY DRAINED AREAS, AND ANY
PARTICULARLY SENSITIVE BASINS.
..EAST COAST OF THE U.S
A STRONG SHORTWAVE TROUGH WILL PASS THROUGH THE NORTHEAST AND
MID-ATLANTIC STATES THIS AFTERNOON/EVENING. THE TROUGH IS MARKED
BY GREATER THAN 200 METER 12-HOUR HEIGHT FALLS OVER SOUTHERN
QUEBEC, WITH MODERATELY STRONG HEIGHT FALLS EXTENDING TO THE
LATITUDE OF MARYLAND / NEW JERSEY. MOISTURE RETURN WILL RUSH UP TO
MEET THE ASSOCIATED COLD FRONT, AND HI-RES MODELS DEPICT A
STRONGLY FORCED LINE OF CONVECTION FORMING OVER COASTAL SECTIONS
OF SOUTHERN NEW ENGLAND THE THE MID ATLANTIC. RAPID MOVEMENT WILL
KEEP EVENT RAINFALL TOTALS CONTAINED, BUT WITH PW VALUES OF 1.50
INCHES IN A STRONGLY FORCED CONVECTIVE REGIME, WE WOULD EXPECT
RAPID ACCUMULATION OF A HALF TO ONE INCH, WHICH SUPPORTS
INTRODUCTION OF MARGINAL RISK FOR THIS HIGHLY POPULATED CORRIDOR.
..SOUTHERN ARIZONA
THERE IS A SMALL ZONE IN WHICH SOME THUNDERSTORMS CARRYING HEAVY
RAIN MAY OCCUR THIS AFTERNOON, FROM PHOENIX DOWN TO JUST WEST OF
TUCSON. A SQUEEZE PLAY WILL TAKE PLACE AS A COLD FRONT DROPS DOWN
FROM THE NORTH AND COOLER, DRIER AIR PUSHES WEST THROUGH THE
MOUNTAIN GAPS IN NEW MEXICO. THERE IS POTENTIAL, HOWEVER, FOR A
FEW ORGANIZED THUNDERSTORMS EAST OF AN UPPER LOW CENTER IN
SOUTHERN ARIZONA, WITHIN A NARROW ZONE WHERE AFTERNOON DEWPOINTS
ARE FORECAST TO HANG IN THE 50S, WITH A FEW HUNDRED J/KG OF CAPE.
SHEAR IS SUFFICIENT FOR ORGANIZED UPDRAFTS AND SOME REDEVELOPMENT
ALONG FLANKS WHICH COULD BOOST LOCAL RAIN TOTALS. THE PW
ENVIRONMENT IS MARGINAL AT AROUND 0.65 INCHES, BUT WITH DECENT QPF
SIGNAL FROM THE GFS AND THE UNIVERSITY OF ARIZONA WRF, WE
INTRODUCED A VERY SMALL MARGINAL RISK AREA.
BURKE
DAY 2
VALID 12Z TUE OCT 16 2018 - 12Z WED OCT 17 2018
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NORTH CENTRAL TEXAS...
..SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY
LOCALLY HEAVY RAIN IS EXPECTED TO BE ONGOING AT THE START OF THE
DAY 2 OUTLOOK PERIOD (12Z/16) WITH STRONG 850-700 MB FRONTOGENESIS
IN PLACE FROM NEAR DEL RIO TO NORTHEASTERN TX. PRECIPITABLE WATER
VALUES OF 1.25-1.75 INCHES SHOULD BE IN PLACE OVER CENTRAL AND
NORTHERN TX WITH EVEN HIGHER VALUES NEAR THE COAST. REMNANT
ISENTROPIC LIFT WILL HELP SQUEEZE OUT MOISTURE ACROSS
CENTRAL/NORTHEAST TX BUT A LACK OF GREATER INSTABILITY SHOULD BE A
SIGNIFICANT LIMITING FACTOR WITH REGARDS TO RAIN RATES.
EVENTUALLY, LOW LEVEL CONVERGENCE AND FRONTOGENESIS WEAKEN AS
MID-LEVEL HEIGHTS RISE ACROSS THE REGION WITH THE DEPARTING
NORTHERN STREAM JET.
THERE MAY STILL BE SOME EXCESSIVE RAINFALL CONCERNS ACROSS
PORTIONS OF CENTRAL TO NORTHERN TX GIVEN ANTECEDENT HEAVY RAINFALL
WITH AS MUCH AS 5-10 INCHES OVER THE PAST 7 DAYS, BUT THE THREAT
IS EXPECTED TO SLOWLY DIMINISH THROUGH THE PERIOD AS FORCING
WEAKENS. THE LATEST 12Z HI-RES MODELS SHOW AN ELONGATED WSW-ENE 24
HR QPF MAX THROUGH 12Z/17 OF 2-4 INCHES OVER PORTIONS OF CENTRAL
TO NORTHERN TX WITH ONLY MINOR LATITUDE DIFFERENCES. 3-HOURLY RAIN
RATES ARE EXPECTED TO PEAK IN THE 1 TO 1.5 INCH RANGE, MAINLY
PRIOR TO 00Z/17, WHICH WOULD OVERLAP WITH THE WET ANTECEDENT
CONDITIONS IN PLACE. ONLY MINOR ADJUSTMENTS WERE MADE TO THE
PREVIOUS DAY 2 OUTLOOK TO EXPAND THE MARGINAL AND SLIGHT AREAS A
BIT WEST, EAST AND SOUTH BASED ON THE LATEST QPF GUIDANCE.
..ARIZONA
A CLOSED LOW IS FORECAST TO REMAIN QUASI-STATIONARY OVER AZ FROM
TUESDAY MORNING INTO WEDNESDAY MORNING WITH WEAK CAPE GIVEN THE
500 MB TEMPERATURES OF -20C. PRECIPITABLE WATER VALUES ARE
EXPECTED TO DECREASE DURING THE PERIOD, BUT MAY START OFF NEAR 1
INCH AT 12Z/16. GIVEN THE LOCATION BENEATH THE CLOSED LOW, ANY
CONVECTION THAT DEVELOPS MAY BE SLOW MOVING. BASED ON THE PIVOTING
AXIS OF THE CLOSED LOW/VORTICITY ALOFT AND DIMINISHING MOISTURE
FEED, FEEL THAT THE POTENTIAL FOR EXCESSIVE RAINS WILL RAPIDLY
DIMINISH AFTER 00Z/17. WHILE A LACK OF HIGHER INSTABILITY/CAPE
PRECLUDES THE ADDITION OF A MARGINAL RISK AT THIS TIME, IT IS AN
AREA WE ARE WATCHING FOR A POSSIBLE UPGRADE ON THE NEXT CYCLE.
OTTO/PAGANO
DAY 3
VALID 12Z WED OCT 17 2018 - 12Z THU OCT 18 2018
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER SOUTH
TEXAS...
..SOUTH TEXAS
AS A CLOSED LOW JUST WEST OF THE CENTRAL ROCKIES AT 12Z/18 BEGINS
TO OPEN AND LIFT TOWARD THE EAST-NORTHEAST, A 850-700 MB RIDGE IS
EXPECTED TO EXPAND NORTHWESTWARD FROM THE EASTERN GULF COAST INTO
OK AND KS. THIS ORIENTATION WILL ALLOW A STRENGTHENING OF
EASTERLY/SOUTHEASTERLY 850 MB FLOW ACROSS THE GULF INTO THE SOUTH
TEXAS COAST WITH WIND SPEEDS PEAKING NEAR 35 KT VIA A CONSENSUS OF
THE 12Z MODELS, MANLY BEYOND 00Z/18.
WHILE A SURFACE FRONT IS EXPECTED TO BE LOCATED FAR ENOUGH
OFFSHORE WEDNESDAY MORNING TO LIMIT ANY APPRECIABLE CAPE OVER
LAND, THE BOUNDARY IS FORECAST TO EDGE CLOSER TO THE COAST BY
THURSDAY MORNING. THE INCREASE IN LOW LEVEL MOISTURE IS EXPECTED
TO INCREASE PRECIPITABLE WATER VALUES TO PEAK OVER 2 INCHES BY
THURSDAY MORNING FROM NEAR MATAGORDA BAY TO THE RIO GRANDE AND THE
SHALLOW NATURE OF THE FRONT SHOULD ALLOW FOR AT LEAST WEAK
ELEVATED INSTABILITY TO DEVELOP FOR COASTAL LOCATIONS.
GIVEN THE HIGH MOISTURE AND WEAK INSTABILITY IN PLACE, ALONG WITH
THE INCREASE IN LOW LEVEL FLOW, THERE MAY BE SOME SLOW MOVING OR
TRAINING OF CONVECTIVE CLUSTERS LIMITED TO LOCATIONS WITHIN 25-75
MILES OF THE COAST OVER SOUTH TEXAS WITH COULD PRODUCE LOCALIZED
MAXIMA OF 2-4 INCHES.
OTTO
DAY 1 THREAT AREA: HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/94EPOINTS.TXT
DAY 2 THREAT AREA: HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/98EPOINTS.TXT
DAY 3 THREAT AREA: HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/99EPOINTS.TXT
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