Graphic for MPD #0880

MESOSCALE PRECIPITATION DISCUSSION 0880
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
424 AM EDT MON OCT 09 2017

AREAS AFFECTED...SRN ALABAMA...FL PANHANDLE...WC GEORGIA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 090821Z - 091400Z

SUMMARY...A BAND OF SLOW MOVING CONVECTION SHOULD CONTINUE TO
DEVELOP OVER THE NEXT FEW HOURS...WITH LOCALIZED FLASH FLOODING
POSSIBLE THROUGH AT LEAST 15Z...PARTICULARLY WHERE THE GROUND IS
STILL SATURATED FROM HEAVY RAINFALL FROM NATE.

DISCUSSION...OVER THE PAST FEW HOURS (05-08Z) CONVECTION HAS
GRADUALLY DEVELOPED ALONG A LOW-LEVEL CONVERGENCE AXIS THAT
STRETCHES FROM JUST NORTHEAST OF COLUMBUS GA...TO NEAR ENTERPRISE
AL...TO NEAR FORT WALTON BEACH FL AND SOUTHWESTWARD INTO THE GULF
OF MEXICO. THE LATEST RAP ANALYSIS SUGGESTS THESE CELLS ARE LIKELY
TAPPING INTO THE NEAR-SURFACE LAYER WITH MLCAPE VALUES AROUND 1000
J/KG. ALTHOUGH THIS MAY DIMINISH SLIGHTLY OVER THE NEXT FEW HOURS
WITH THE DIURNAL CYCLE...SIMILAR VALUES ARE PROJECTED TO PERSIST
THROUGH MUCH OF THE MORNING. THE COMBINATION OF THIS INSTABILITY
AND AROUND 20-25 KNOTS OF EFFECTIVE DEEP LAYER SHEAR SUGGESTS THAT
CONVECTION SHOULD BE ABLE TO AT LEAST MAINTAIN ITSELF OVER THE
NEXT SEVERAL HOURS...WITH SOME MODEST ORGANIZATION ALONG THE
CONVERGENCE AXIS POSSIBLE. PRECIPITABLE WATER VALUES IN THE AREA
ARE LIKELY ON THE ORDER OF 2.1 TO 2.2 INCHES (SUGGESTED BY CIRA
BLENDED TPW AND RAP ANALYSIS) WHICH WOULD SUPPORT VERY HEAVY RAIN
RATES IN THE MORE ORGANIZED BANDS.

HI-RES MODEL GUIDANCE SHOWS A GRADUAL ESCALATION IN RAIN
RATES...PEAKING AROUND 11-13Z AS CONVECTIVE BANDS WILL HAVE HAD
SEVERAL ADDITIONAL HOURS TO EXPAND AND ORGANIZE...AND SOME
LOCALIZED TRAINING OF CELLS/BANDS CAN TAKE PLACE. MOST MODELS SHOW
LOCALIZED RAINFALL RATES PEAKING AROUND 3 INCHES IN 3
HOURS...WHICH IS CLOSE TO FLASH FLOOD GUIDANCE VALUES IN
ALABAMA...PARTICULARLY AREAS THAT RECEIVED HEAVY RAINFALL LAST
NIGHT FROM NATE. QPE ANALYSIS FROM THE ENTIRE EVENT SHOWS THE
HEAVIEST RAIN LIKELY FELL FROM SANTA ROSA AND OKALOOSA COUNTIES IN
THE FLORIDA PANHANDLE...NNE TO NEAR TROY AL. THE NATIONAL WATER
MODEL SHOWS 80 PERCENT SATURATION IN THE TOP 40CM SOIL MOISTURE
ANALYSIS OVER THESE SAME AREAS...SO IT MAY NOT TAKE MUCH
ADDITIONAL RAINFALL TO GENERATE SOME FLOODING ISSUES. GIVEN THAT
THE CURRENT ORIENTATION OF THE PRIMARY CONVECTIVE BAND IS VERY
CLOSE TO THE FORT WALTON BEACH FL TO TROY AL AXIS PREVIOUSLY
MENTIONED...FLASH FLOODING APPEARS POSSIBLE WITHIN THE NEXT
SEVERAL HOURS. RAIN RATES OF UP TO 2 IN/HR APPEAR POSSIBLE...AND
MRMS AND KEVX DUAL POL ESTIMATES HAVE ALREADY REACHED 1.5 IN/HR IN
SOME OF THE HEAVIER BANDS.

LAMERS

ATTN...WFO...BMX...FFC...MOB...TAE...

ATTN...RFC...SERFC...

LAT...LON   33708388 33538364 33448355 33198354 32828382
            32348427 31678478 31148529 30648571 30308601
            30258641 30288693 30208752 30298788 30708799
            31178766 31858705 32798584 33498456


Last Updated: 424 AM EDT MON OCT 09 2017