916  
FXUS64 KMOB 271755 AAC  
AFDMOB  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE MOBILE AL  
1255 PM CDT THU APR 27 2017  
   
DISCUSSION
 
SEE UPDATED INFORMATION FOR MARINE AREAS AND AVIATION  
DISCUSSION BELOW.  
 

 
   
MARINE
 
MARINE PACKAGE WILL BE UPDATED TO DROP EXPIRING SCY FOR  
OFFSHORE WATERS.  
 
/16  
 

 
   
AVIATION
 
 
18Z ISSUANCE...STALLED SURFACE FRONT ALONG I65 WILL WASH OUT THIS  
AFTERNOON THROUGH TONIGHT, WITH ISENTROPIC UPGLIDE SHOWERS  
DEVELOPING OVERNIGHT AND LASTING INTO FRIDAY MORNING. CIGS ARE  
EXPECTED TO DROP NEAR THE MVFR/IFR BORDER OVERNIGHT, BUT REMAIN  
AT LOW END MVFR LEVELS. LOCAL IFR CIGS POSSIBLE, THOUGH. INTO  
FRIDAY MORNING, CIGS ARE EXPECTED TO BE SLOW TO RISE DUE TO THE  
UPGLIDE SHRA, REMAINING IN MVFR LEVELS.  
 
/16  
 

 
   
PREV DISCUSSION
 
/ISSUED 1147 AM CDT THU APR 27 2017/  
 
DISCUSSION...SEE UPDATED INFORMATION FOR LAND AREAS BELOW.  
 
UPDATE...A WEAKENING BOUNDARY HAS STALLED ALONG THE I65 CORRIDOR  
AS EXPECTED. PRECIP COVERAGE IS CONFINED TO THE NORTHEASTERN  
QUARTER OF THE FORECAST AREA, AND CONTINUES TO STEADILY DECREASE  
AS THE UPPER TROUGH STRETCHING SOUTHEAST FROM A CLOSED LOW OVER  
THE NORTHERN MISSISSIPPI RIVER VALLEY. CLOUD COVER HAS ERODED  
NICELY NORTHWEST OF I65, AND WITH A BIT DRIER AIR MOVING OVER FROM  
THE WEST, DO NOT SEE ANY PRECIP THESE AREAS. NO UPDATES PLANNED  
FOR THE CURRENT PACKAGE.  
 
/16  
 
PREV DISCUSSION... /ISSUED 648 AM CDT THU APR 27 2017/  
 
DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.  
 
AVIATION...  
12Z ISSUANCE...MVFR TO IFR CONDITIONS THIS MORNING IN SCATTERED  
RAIN SHOWERS. THE RAIN WILL END FROM WEST TO EAST THIS MORNING  
WITH VFR CONDITIONS DEVELOPING THROUGH THE AFTERNOON. LOW CLOUDS  
AND PATCHY FOG DEVELOP LATE TONIGHT INTO FRIDAY MORNING WITH MVFR  
CONDITIONS POSSIBLE. /13  
 
PREV DISCUSSION... /ISSUED 448 AM CDT THU APR 27 2017/  
 
NEAR TERM /NOW THROUGH THURSDAY NIGHT/...A COLD FRONT CONTINUES  
TO MAKE SLOW PROGRESS ACROSS SOUTHEAST MISSISSIPPI THIS MORNING  
AND SLOWLY SHIFT EASTWARD THROUGH THE DAY. A BROKEN LINE OF  
SHOWERS AND THUNDERSTORMS ALONG THE FRONT CONTINUES TO MOVE EAST  
AND WEAKEN AS THE UPPER DYNAMICS MOVE WELL NORTH OF THE REGION.  
THEREFORE, THE SEVERE THREAT FOR THE REST OF THE DAY IS VERY LOW.  
THE COLD FRONT IS EXPECTED TO STALL ACROSS EASTERN ZONES THIS  
AFTERNOON AND HAVE MAINTAINED CHANCE POPS ACROSS THE EASTERN THIRD  
OF THE AREA THROUGH THE AFTERNOON HOURS. A DRIER AND COOLER  
AIRMASS WILL WORK INTO WESTERN AREAS IN THE WAKE OF THE FRONT  
BRIEFLY THIS AFTERNOON AS THE FRONT STALLS OUT. THE FRONT WILL  
RAPIDLY RETURN NORTHWARD AS A WARM FRONT TONIGHT AS THE NEXT STORM  
SYSTEM DEVELOPS ACROSS THE WESTERN STATES. AN ISOLATED SHOWER IS  
POSSIBLE ALONG THE RETREATING FRONT, HOWEVER THE PROBABILITY IS  
TOO LOW TO INCLUDE AT THIS TIME. HIGHS TODAY WILL CLIMB INTO THE  
LOW 80S INLAND TO UPPER 70S ALONG THE COAST. LOWS TONIGHT RANGE  
FROM THE LOW 60S ACROSS NORTHWEST AREAS TO LOW 70S ALONG THE  
COAST. /13  
 
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...AN UPPER LEVEL RIDGE  
OF HIGH PRESSURE WILL CONTINUE TO BUILD FROM THE FL PENINSULA TO  
THE WESTERN ATLANTIC THROUGH SATURDAY NIGHT, WHILE THE NEXT UPPER  
LEVEL LOW PRESSURE SYSTEM DEEPENS OVER THE FOUR CORNERS REGION  
FRIDAY, THEN ADVANCES EASTWARD TOWARD THE TX/OK PANHANDLES  
VICINITY SATURDAY INTO SATURDAY NIGHT. OUR FORECAST AREA WILL  
REMAIN WITHIN A MEAN SOUTHWEST FLOW PATTERN ALOFT BETWEEN THESE  
FEATURES THROUGH SATURDAY NIGHT. A SOUTHERLY LOW LEVEL FLOW,  
BREEZY AT TIMES, WILL PERSIST ACROSS OUR REGION THROUGH THE SHORT  
TERM PERIOD BETWEEN A SURFACE RIDGE OF HIGH PRESSURE OVER THE  
WESTERN ATLANTIC AND THE DEEPENING LOW PRESSURE SYSTEM OVER THE  
PLAINS. PLENTIFUL LOW LEVEL MOISTURE WILL CONTINUE TO STREAM INTO  
THE AREA ON THE SOUTHERLY WINDS THROUGH SATURDAY NIGHT, WITH  
SURFACE DEWPOINTS LOOKING TO RANGE FROM THE MID 60S TO LOWER 70S.  
SHORT TERM MODELS CONTINUE TO TREND WITH POTENTIAL DEVELOPMENT OF  
ISOLATED SHOWERS AND POSSIBLY A THUNDERSTORM WITHIN THE LOW LEVEL  
WARM ADVECTION REGIME FRIDAY, PARTICULARLY DURING THE MORNING  
HOURS, AND HAVE MAINTAINED A SLIGHT CHANCE OF CONVECTION ACROSS  
THE REGION. RAINFALL AMOUNTS SHOULD BE LIGHT. A DEEP LAYER DRY  
AIRMASS WITHIN THE SOUTHWEST FLOW SHOULD ALLOW FOR DRY WEATHER  
FRIDAY NIGHT. HIGHS FRIDAY LOOK TO RANGE FROM THE MID TO UPPER 80S  
INLAND, WITH UPPER 70S TO LOWER 80S ALONG THE BEACHES. LOWS FRIDAY  
NIGHT WILL BE WARM, WITH READINGS RANGING FROM AROUND 70 TO THE  
LOWER 70S.  
 
A SIMILAR PATTERN WILL CONTINUE SATURDAY, WITH SOUTHWEST FLOW  
ALOFT CONTINUING IN ADVANCE OF THE DEEP UPPER LEVEL LOW/TROUGH  
OVER THE SOUTHERN ROCKIES AND ADJACENT PLAINS STATES. WEAK ASCENT,  
AVAILABLE INSTABILITY AND A SLIGHT INCREASE IN DEEP LAYER MOISTURE  
WILL FAVOR DEVELOPMENT OF ISOLATED TO SCATTERED SHOWERS AND  
THUNDERSTORMS AROUND THE REGION SATURDAY, AND WILL KEEP 20-30%  
POPS IN PLACE. COVERAGE SHOULD TEND TO DECREASE BY SATURDAY  
EVENING. HIGHS SATURDAY ARE ONCE AGAIN FORECAST TO RANGE IN THE  
MID TO UPPER 80S INLAND, WITH UPPER 70S TO LOWER 80S ANTICIPATED  
AGAIN ALONG THE IMMEDIATE COAST AND BEACHES. /21  
 
LONG TERM /SUNDAY THROUGH WEDNESDAY/...WE ARE STILL EXPECTING A  
POTENTIAL SEVERE WEATHER AND HEAVY RAINFALL EVENT TO IMPACT MUCH  
OF OUR FORECAST AREA SUNDAY INTO SUNDAY NIGHT. THE AFOREMENTIONED  
DEEP UPPER LEVEL LOW WILL LIFT NORTHEASTWARD ACROSS OK/KS DURING  
THE DAY SUNDAY, WHILE AN ASSOCIATED COLD FRONT ADVANCES EASTWARD  
ACROSS THE MISSISSIPPI VALLEY REGION. DEEP LAYER FORCING/SYNOPTIC  
SCALE LIFT WILL SPREAD ACROSS THE MISSISSIPPI VALLEY DURING THE  
DAY SUNDAY, ALLOWING FOR THE ORGANIZATION OF AN INTENSE  
COMPLEX/LINE OF THUNDERSTORMS TO SPREAD EASTWARD FROM AR/LA INTO  
MS DURING THE DAY SUNDAY. A RATHER STRONG LOW LEVEL JET STILL  
LOOKS TO DEVELOP ACROSS OUR FORECAST AREA AHEAD OF THE UPPER LEVEL  
STORM SYSTEM SUNDAY, ESPECIALLY ALONG AND WEST OF I-65 WHERE 40-55  
KNOTS OF 850 MB SOUTHERLY FLOW IS EXPECTED. SCATTERED TO NUMEROUS  
SHOWERS AND STORMS SHOULD DEVELOP OVER MUCH OF THE AREA AHEAD OF  
THE MAIN LINE TO OUR WEST DURING THE DAY SUNDAY, WITH THE BEST  
COVERAGE ALONG AND WEST OF THE I-65 CORRIDOR. THERE ARE STILL SOME  
TIMING DIFFERENCES NOTED IN THE OPERATIONAL MEDIUM RANGE GUIDANCE,  
BUT IT GENERALLY APPEARS THAT THE MAIN COMPLEX OF SHOWERS AND  
THUNDERSTORMS SHOULD CONTINUE TO ADVANCE EASTWARD ACROSS OUR  
FORECAST AREA SUNDAY EVENING INTO LATE SUNDAY NIGHT, BEFORE  
PROGRESSING EAST OF OUR AREA FOR THE MOST PART BY LATE MONDAY  
MORNING. THE COMBINATION OF THE STRONG LOW LEVEL JET, FAVORABLE  
0-6 KM SHEAR, UP TO AROUND 1000-1500 J/KG OF MLCAPE, AND 0-1KM SRH  
VALUES UP TO 200-300 M2/S2 WILL BE SUPPORTIVE OF SEVERE STORMS,  
WITH ALL MODES POSSIBLE. RIGHT NOW SEVERE POTENTIAL LOOKS MOST  
FAVORED ALONG AND WEST OF I-65 WHERE SHEAR/INSTABILITY PARAMETERS  
ARE MOST COINCIDENT, AND THIS IS WHERE THE LATEST DAY 4 OUTLOOK  
FROM SPC HIGHLIGHTS A 15% SEVERE RISK. WOULD NOT BE SURPRISED TO  
SEE THIS RISK LEVEL INCREASE WITH TIME AND WILL CONTINUE TO  
MONITOR CLOSELY. HEAVY RAINFALL AND LOCALIZED FLASH FLOODING MAY  
BECOME A CONCERN AS PRECIPITABLE WATER VALUES RISE BETWEEN 1.75"  
AND 2.25", WHICH IS VERY IMPRESSIVE. RAINFALL AMOUNTS BETWEEN 2-4"  
WITH LOCALLY HIGHER TOTALS WILL CERTAINLY BE POSSIBLE WITH THIS  
EVENT, AND WILL ALSO MENTION POTENTIAL HEAVY RAIN/FLOODING  
CONCERNS IN THE HWO SUNDAY INTO SUNDAY NIGHT. DRIER ZONAL FLOW IS  
ANTICIPATED MONDAY INTO TUESDAY. HOWEVER, YET ANOTHER ROUND OF  
SHOWERS AND STORMS RETURNS WEDNESDAY INTO WEDNESDAY NIGHT AS THE  
NEXT SYSTEM MOVES ACROSS THE REGION. /21  
 
MARINE...SOUTHERLY WINDS WILL DECREASE TODAY AS A COLD FRONT STALLS  
OVER NORTHERN PORTIONS OF MARINE AREA. WINDS WILL INCREASE AGAIN  
ALONG WITH BUILDING SEAS THIS WEEKEND AHEAD OF ANOTHER APPROACHING  
COLD FRONT. THIS FRONT IS EXPECTED TO MOVE ACROSS THE MARINE AREA  
SUNDAY NIGHT INTO EARLY MONDAY. /13  
 

 
   
MOB WATCHES/WARNINGS/ADVISORIES
 
 
AL...HIGH RIP CURRENT RISK THROUGH FRIDAY MORNING FOR ALZ265-266.  
 
FL...HIGH RIP CURRENT RISK THROUGH FRIDAY MORNING FOR FLZ202-204-206.  
 
MS...NONE.  
GM...SMALL CRAFT ADVISORY UNTIL 1 PM CDT THIS AFTERNOON FOR GMZ650-  
655-670-675.  
 

 
 

 
 
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