Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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

000
FOUS30 KWBC 210049
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
848 PM EDT TUE SEP 20 2016

...VALID 01Z WED SEP 21 2016 - 12Z WED SEP 21 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 ENE HSE 30 SE MQI 35 SW MQI OAJ 20 W CPC 10 E HFF 15 ESE TDF
10 NNE JGG 65 ESE WAL.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 SE SGU 15 SW PGA 60 N INW 25 S INW 60 NW SAD 30 SW SAD
25 N DUG 20 SW DUG 35 SE OLS 35 W OLS 20 E GBN 10 NW LUF
55 W LUF 20 SSW NYL 40 SSW NJK NRS CRQ 20 NNW NFG EMT 15 NNE BUR
15 ESE PMD 30 SSW DAG 20 E NXP 30 NW IFP 45 SE SGU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
ALO 15 S MCW EST 10 E OTG 20 NW MWM RWF 10 SSW HCD 10 WSW FCM
25 N ONA 10 NW VOK 10 NNE DLL EFT 15 ESE MXO ALO.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
55 ENE HSE 15 ESE MQI 25 SSE EDE 15 NW EWN 10 NNE GWW
10 SSE EMV 45 SE MFV.




01Z UPDATE...
NO CHANGES TO PREVIOUS DISCUSSION OR REASONING.  ACRS THE
SOUTHWEST...HAVE NOTED A FEW LIGHTNING STRIKES ACRS SRN CA IN
ADVANCE OF WEAK S/WV NEAR THE SRN CA COAST...WELL IN ADVANCE OF
WEAKENING TD PAINE..BUT OVERALL INSTABILITY IS LACKING TO SUPPORT
MUCH MORE THAN A MARGINAL RISK ACRS THAT REGION AS WELL AS MUCH OF
THE REMAINDER OF THE 4 CORNERS REGION.  RECENT HRRR IMAGERY
SUPPORTS CURRENT PLACEMENT OF MARGINAL RISK AREA ACRS THE UPR
MIDWEST WITH EXPECTED NOCTURNAL DVLPMENT POTNLY LEADING TO SOME
CELL REGENERATION/TRAINING TOWARD THE LATE NIGHT OR EARLY MORNING
HOURS ACRS THE REGION..BUT NOT SUFFICIENT MODEL SUPPORT TO LEAD
TOWARD ANYTHING MORE THAN A MARGINAL RISK AT THIS TIME.  SULLIVAN
  PREVIOUS DISCUSSION FOLLOWS...

...NORTHEAST NORTH CAROLINA INTO FAR SOUTHEAST VIRGINIA...

AN UPPER TROUGH AND CLOSED LOW LEVEL CENTER WERE POSITIONED OVER
THE CAROLINAS AND SOUTHEAST VIRGINIA. WHILE THE LARGE SCALE TROUGH
REMAINS NEARLY STATIONARY...THE LOW LEVEL CENTER IS FORECAST TO
DRIFT INLAND OVER VA/NC AND THEN GRADUALLY SOUTHWESTWARD. MOIST
CYCLONIC FLOW...WITH PW VALUES 2.00-2.25 INCHES ...ALONG WITH SLOW
MEAN CLOUD LAYER WIND SPEEDS...SETS UP THE POSSIBILITY OF LOCALLY
HEAVY PRECIPITATION TOTALS. THE MOST LIKELY AREA TO EXPERIENCE
HEAVY RAIN WILL BE NEAR AND NORTH OF THE LOW LEVEL CENTER WHERE
CONVERGENCE IS MAXIMIZED WITH EASTERLY FLOW OFF THE ATLANTIC
MOVING INTO THE LOW AND ASSOCIATED INVERTED TROUGH AXIS. LIMITING
FACTORS INCLUDE A LACK OF INSTABILITY AND A GRADUAL WEAKENING OF
THE SYNOPTIC FORCING AS THE UPPER TROUGH FORMS A
BROAD...STACKED...CLOSED LOW. THE HI-RES MODELS PRODUCE VERY
LITTLE CAPE INLAND OF THE OUTER BANKS AND TIDEWATER AREAS THIS
AFTERNOON...AND THE HRRR SUGGESTS FURTHER CONTRACTING THE SLIGHT
RISK AREA FOR EXCESSIVE RAINFALL HERE. GIVEN THE AVAILABLE
MOISTURE...ISOLATED RAINFALL OF 2 TO 4 INCHES IS CERTAINLY
POSSIBLE OVER SHORT DURATIONS...IN EXCESS OF FLASH FLOOD GUIDANCE.


...SOUTHERN CALIFORNIA INTO ARIZONA...

WHILE TROPICAL STORM PAINE IS EXPECTED TO WEAKEN...AS PER THE
LATEST NHC DISCUSSION...MUCH ABOVE AVERAGE PW VALUES WILL CONTINUE
TO BE DRAWN NORTHWARD IN THE MID LEVEL SOUTHERLY FLOW BETWEEN THE
SOUTHERN PLAINS UPPER HIGH AND THE CLOSED LOW OFF THE SOUTHERN
CALIFORNIA/NORTHERN BAJA COAST. WIDESPREAD RAIN IS EXPECTED FROM
SOUTHERN CALIFORNIA INTO ARIZONA...ESPECIALLY WESTERN AND NORTH
ARIZONA. WIDESPREAD CLOUD COVER WILL LIMIT INSTABILITY IN MANY
CASES TO NEAR ZERO...WHICH WILL GREATLY INHIBIT THE TYPE OF RAIN
RATES CAPABLE OF PRODUCING FLASH FLOODING. PARTICULARLY SENSITIVE
AREAS...INCLUDING BURN SCARS IN SOUTHERN CALIFORNIA...MAY
HOWEVER...EXPERIENCE RAPID RUNOFF. IN THESE VERY CLOUDY
SCENARIOS...WE OFTEN LOOK TO HEATING ALONG THE EDGES...AND
DIFFERENTIAL HEATING BOUNDARIES...IN ADDITION TO TERRAIN...TO ACT
AS A FOCUS FOR DEEPER CONVECTION AND HEAVY RAIN RATES. THERE IS
SOME HI-RES MODEL SIGNAL FOR THIS TO OCCUR IN THE MOUNTAIN AREAS
OF SOUTHEAST ARIZONA...ALTHOUGH THE SIGNAL IS INCONSISTENT AND
DOES NOT SHOW UP IN THE HRRR. THE 12Z TUCSON SOUNDING WAS
COMPROMISED...BUT BLENDED TPW SATELLITE IMAGERY DID SHOW A
GRADIENT TOWARD DEEPER MOISTURE MAKING SOME LIMITED EASTWARD
PROGRESS THROUGH ARIZONA...CLOSE ENOUGH TO MAINTAIN A MARGINAL
RISK IN THE 15Z UPDATE. WE DID REMOVE THE RISK FROM SOME OF THE
LOW DESERT AREAS WHERE BOTH THE LACK OF INSTABILITY AND LACK OF
LOW LEVEL FORCING MECHANISMS SHOULD YIELD A MINIMUM POTENTIAL FOR
HEAVY RAINFALL...WHICH IS CONSISTENT WITH THE MODEL QPFS.


...UPPER MS VALLEY...

LOW LEVEL SOUTHWESTERLY TO WESTERLY FLOW EXPECTED TO STRENGTHEN
TUESDAY EVENING INTO THE EARLY HOURS OF WEDNESDAY ALONG AND INTO
THE STRENGTHENING WARM FRONTAL BOUNDARY FORECAST TO STRETCH FROM
THE NORTHERN PLAINS INTO THE UPPER MS VALLEY THIS PERIOD. THIS
WILL SUPPORT INCREASING CONVECTION ALONG AND NORTH OF THIS
FRONT--WITH ACTIVITY STRETCHING FROM SOUTHERN MN---INTO NORTHEAST
IA AND SOUTHWEST WI. THIS WILL BE THE FIRST DAY OF A POTENTIAL
MULTI DAY ACTIVE CONVECTION PATTERN ALONG AND NORTH OF THIS
BOUNDARY. FOR THIS FIRST DAY---MODEL CONSENSUS IS FOR MODERATE TO
LOCALLY HEAVY PRECIP TOTALS---WITH INCREASING PRECIP POTENTIAL
DURING THE DAY 2 TIME PERIOD.  STILL---CAN`T RULE OUT A PERIOD OF
ORGANIZED CONVECTION AND ISOLATED RUNOFF ISSUES IN AREAS WHERE
TRAINING OCCURS---WITH A MARGINAL RISK AREA DEPICTED FOR THIS OVER
SOUTHERN MN---NORTHEAST IA INTO SOUTHWEST WI.

BURKE/ORAVEC
$$





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