MESOSCALE PRECIPITATION DISCUSSION 0905
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
431 PM EDT SUN OCT 22 2017

AREAS AFFECTED...SOUTHERN AL...WESTERN FL PANHANDLE...

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 222030Z - 230200Z

SUMMARY...SLOW MOVING HIGHLY EFFICIENT AND MERGING THUNDERSTORMS
LIKELY TO CONTINUE TO POSE A FLASH FLOOD THREAT ALONG COASTAL
COUNTIES. 

DISCUSSION...20Z MESOSCALE ANALYSIS SUPPLEMENTED WITH GOES-16
VISIBLE PSEUDO RGB LOOP SUGGESTS A WEAK SURFACE INFLECTION NEAR
THE CHANDELEUR ISLANDS ALONG THE STALLING OUTFLOW BOUNDARY
CURRENTLY ORIENTED N-S NEAR THE MS/AL BORDER ANGLING SW INTO THE
NORTHWEST GULF.  A SE TO NW ORIENTED TROPICAL CONFLUENCE TROF IS
DEPICTED OFF THE SW FL COAST/NW OF THE KEYS INTERSECTING THE
OUTFLOW BOUNDARY NEAR THE MOUTH OF THE MS RIVER.  NORTH OF THIS
BOUNDARY STRONG SFC/900MB FLOW IS ADVECTING VERY RICH MOISTURE
REPRESENTED BY SFC TDS OVER 75F AND TPW RANGING FROM 2.1 NEAR
MOBILE BAY TO 2.5 IN THE SOUTHEAST GULF.  A WEAK SECONDARY
BOUNDARY IN THE SOUTHEASTERLY FLOW HAS BEEN PROLIFIC IN
DEVELOPMENT OF SHALLOW SUPERCELLS THAT HAVE BEEN TRAINING ACROSS
BALDWIN COUNTY AL...THIS FEATURE IS LIKELY TO PLAY A PART IN
FUTURE TRAINING/MERGING ACROSS W FL AS WELL.

WV LOOP ALSO DEPICTS A STRONG BAROCLINIC LEAF OVER THE MID-MS
VALLEY WITH A WESTERLY PUSH OF THE BASE OF THE TROF INTO LA ATTM. 
THIS WILL CONTINUE TO SUPPORT STRONG UL RIGHT ENTRANCE ASCENT
DYNAMICS AND OUTFLOW ALOFT FOR MAINTAINING HEALTHY CONVECTION. 
ADDITIONALLY WITH THE WEAK SURFACE INFLECTION...THE OVERALL
STRONGER SURFACE RIDGE IN THE SOUTHEAST IN COMBINATION WITH THE
APPROACHING TROF/COLD FRONT IS AMPLIFYING THE TROF NORTHWARD
ACROSS S AL/WESTERN FL PANHANDLE AS WELL AS SLOWING EASTWARD
PROGRESS OF THE ACTIVE CONVECTION REGION.  THIS WILL ADD TO
INCREASING LOW LEVEL CONVERGENCE/FLUX FOR CELLS TO SUPPORT 3"/HR
OR EVEN POSSIBLY HIGHER GIVEN POTENTIAL FOR MERGERS. ADDITIONALLY
STRONG INFLOW OFF THE GULF WILL SUPPORT BACKBUILDING/
REDEVELOPMENT NEAR THE COAST AS PROPAGATION VECTORS FIELD SHOWS
MODEST DIFLUENCE IN THE THICKNESS FIELD.  AS SUCH FLASH FLOODING
REMAINS HIGHLY LIKELY THROUGH THE EVENING HOURS WITH THE POTENTIAL
OF ADDITIONAL LOCALIZED MAXIMA OF 6" THROUGH 03Z PERHAPS HIGHER. 

BELIEVE GREATEST THREAT WILL BE ACROSS BALDWIN COUNTY AL INTO
SANTA ROSA COUNTY, FL ...WITH MORE MODEST (3-4" TOTALS) DOWNSTREAM
INTO MONROE/ESCAMBIA,AL/CONECUH COUNTY THROUGH STILL POSING A FF
RISK THERE AS WELL. 

GALLINA

ATTN...WFO...MOB...TAE...

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

LAT...LON   31758741 31698645 31328596 30488559 29938541
            29968589 30148659 30148698 30098742 30108797
            30208827 30418834 31268809