Area Forecast Discussion
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000
FXUS64 KMOB 020433 AAB
AFDMOB

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MOBILE AL
1130 PM CDT WED OCT 1 2014

.AVIATION...
02.06Z TAF CYCLE
HIGH BASED CLOUDS CONTINUE TO STREAM EASTWARD OVER THE CENTRAL GULF
COAST. STARTING TO SEE SOME PATCHES OF LOWER CIGS BEGINNING TO
DEVELOP OVER LOUISIANA AND SOUTHWEST MISSISSIPPI WITH BASES AT MVFR
CATEGORIES.WILL MAINTAIN VFR CONDITIONS IN THE NEAR TERM BUT WILL BE
MONITORING FOR AMENDMENTS IF LOWER CIGS EXPAND. SOME PATCHY LATE
NIGHT MIST (BR) LATE WITH VSBY AT MVFR AFTER 02.10Z. LIGHT SOUTHEAST
WIND FORECAST TONIGHT. BRINGING IN SOME SHRA/FEW TSRA AFTER
DAYBREAK. /10

.PREV DISCUSSION... /ISSUED 343 PM CDT WED OCT 1 2014/

SHORT TERM (TONIGHT THROUGH SATURDAY NIGHT)...FOR TONIGHT...SURFACE
HIGH ALONG THE ATLANTIC COAST WILL CONTINUE TO PUSH INTO OUR AREA
FROM THE NORTHEAST THROUGH TONIGHT. MODEL CALCULATIONS INDICATE UPPER
RIDGING WILL INCREASE SLIGHTLY THROUGH TONIGHT MEANING LITTLE TO NO
CHANCE OF RAIN HERE THROUGH SUNRISE THURSDAY MORNING. AS WE MOVE INTO
THE DAY THURSDAY...THE WESTERN EDGE OF THE SURFACE RIDGE WILL HAVE
ALREADY BROUGHT A DEEP RETURN FLOW WITH ISOLATED SHOWERS THROUGH MOST
OF THE FIRST 24 HOURS OF THE SHORT TERM. SKIES PARTLY TO MOSTLY
CLOUDY THROUGH TONIGHT...WITH PATCHY FOG POSSIBLE OVERNIGHT.

ON THURSDAY AFTERNOON...GFS PHYSICAL OUTPUT INDICATES A SMALL
ANOMALOUS FEATURE SOUTH OF ORANGE BEACH BRINGING A RISE IN
PRECIPITABLE WATER 2.1 TO 2.2 INCHES AND INCREASINGLY NEGATIVE
LIFTED INDEX OF -5 ALBEIT WITH A MODEST CAPE AROUND 1000 TO 1500.
WITH THE MODEST CAPE THERE...OTHER SIGNALS...SUCH AS POSITIVE
Q-VECTOR DIVERGENCE AND DOWNWARD OMEGA...ARE CONVINCING ENOUGH TO
COUNTER THESE TWO ITEMS...ESPECIALLY CONSIDERING THE SIZE AND SHORT
LIVED NATURE OF THE FEATURE. THE MOS GUIDANCE IS NOT PICKING IT UP
FOR POPS...NOR ARE WE CONVINCED IT WARRANTS INCREASED POPS.

GENERALLY LIGHT EAST TO SOUTHEAST WIND TODAY AND TONIGHT. FOR THE
REST OF THE PERIOD WE LOOKED AT THE MOS WINDS CALCULATED FOR THE
10.12Z RUN AND FOUND THEM TO BE NOT SIGNIFICANTLY DIFFERENT FROM
WHAT THE PREVIOUS SHIFT HAD...SO WE LEFT THE WIND AS THEY HAD IT
AFTER FRIDAY NIGHT.

LOWS AND HIGHS RESPECTIVELY TONIGHT AND TOMORROW WILL BE JUST ABOUT
SEASONABLE FOR OCTOBER...WHICH ON AVERAGE ARE AROUND THE MID TO
UPPER 70S FOR HIGHS AND MID 50S FOR LOWS. 77/BD

FOR THURSDAY NIGHT THROUGH SATURDAY NIGHT...A LONGWAVE TROF OVER THE
CENTRAL STATES CONTINUES TO STRENGTHEN WHILE ADVANCING INTO THE
EASTERN STATES AS AN UPPER LOW DEVELOPS OVER THE NORTHERN PLAINS
THURSDAY NIGHT THEN DEEPENS SIGNIFICANTLY WHILE MOVING TO NORTH OF
THE OHIO RIVER VALLEY FRIDAY NIGHT INTO SATURDAY MORNING.  OF
INTEREST IS THAT THE UPPER LOW BECOMES PARTICULARLY INTENSE BY
FRIDAY NIGHT...DEEPENING TO 4 STANDARD DEVIATIONS BELOW
CLIMATOLOGICAL NORMALS FRIDAY NIGHT INTO SATURDAY.  THE UPPER LOW
EJECTS OFF TO THE NORTHEAST SATURDAY NIGHT WHILE THE LONGWAVE TROF
AMPLIFIES SOMEWHAT MORE OVER THE EASTERN STATES.  A SURFACE LOW WILL
HAVE DEVELOPED OVER THE CENTRAL PLAINS IN RESPONSE TO THIS SYSTEM
AND DEEPENS WHILE MOVING TO THE GREAT LAKES REGION THURSDAY NIGHT
AND WELL TO THE NORTH ON FRIDAY...MEANWHILE BRINGING A STRONG COLD
FRONT THAT MOVES THROUGH THE FORECAST AREA FRIDAY AFTERNOON INTO
FRIDAY EVENING.  A DOME OF COLD HIGH PRESSURE BUILDS INTO THE REGION
IN THE WAKE OF THE FRONT...SETTLING OVER THE FORECAST AREA SATURDAY
NIGHT AND BRINGS THE COLDEST TEMPERATURES SO FAR THIS SEASON.

DESPITE THE INTENSE UPPER LOW AND OVERALL STRENGTH OF THE UPPER
TROF...WITH THE SURFACE LOW EJECTING SO FAR TO THE NORTH...THE
SOUTHWESTERLY 850 MB FLOW OVER THE FORECAST AREA MAXIMIZES AROUND 25
KNOTS LATE THURSDAY NIGHT INTO EARLY FRIDAY MORNING THEN DECREASES TO
AROUND 20 KNOTS AS THE THE FRONT APPROACHES AND THEN MOVES THROUGH.
THIS RESULTS IN 0-1 KM HELICITY VALUES REACHING AT BEST 70-100 M2/S2
LATE THURSDAY NIGHT INTO FRIDAY MORNING THEN DECREASING QUICKLY TO
50 M2/S2 OR LESS UNTIL THE FRONT MOVES THROUGH.  THE BEST
INSTABILITY PRESENT WILL BE NEAR 2000 J/KG NEAR THE IMMEDIATE COAST
TAPERING TO VALUES NEAR 1100 J/KG WELL INLAND...AND WITH A VERY
MOIST ENVIRONMENT IN PLACE AHEAD OF THE FRONT WITH PRECIPITABLE
WATER VALUES AROUND 1.8-2.1 INCHES...AM EXPECTING GENERAL
THUNDERSTORMS WITH SOME STRONG STORMS CAPABLE OF STRONG GUSTY WINDS
AND HEAVY RAINFALL.  THE CURRENT HAZARDOUS WEATHER OUTLOOK MENTIONS
A POSSIBLE ISOLATED STRONG TO SEVERE STORM ON FRIDAY WHICH LOOKS OK
AT THIS POINT.

WILL HAVE CHANCE POPS FOR MOST OF THE AREA THURSDAY NIGHT THEN LIKELY
POPS CONTINUE FOR FRIDAY AS THE FRONT MOVES THROUGH. SMALL POPS
FOLLOW GENERALLY EAST OF I-65 FRIDAY EVENING WITH OTHERWISE DRY
CONDITIONS THROUGH SATURDAY NIGHT.

LOWS THURSDAY NIGHT WILL BE RATHER MILD FOR THIS TIME OF YEAR AND IN
THE LOWER TO MID SEVENTIES...WHICH IS AT LEAST TEN DEGREES ABOVE
NORMAL.  HIGHS ON FRIDAY WILL BE NEAR NORMAL AND IN THE LOWER TO MID
EIGHTIES THEN LOWS FRIDAY NIGHT IN THE WAKE OF THE COLD FRONT WILL
BE NEAR NORMAL VALUES RANGING FROM THE LOWER TO MID SIXTIES NEAR THE
IMMEDIATE COAST TO LOWER TO MID FIFTIES WELL INLAND. SATURDAY WILL
BE A FEW TO SEVERAL DEGREES BELOW NORMAL WITH HIGHS IN THE MID TO
UPPER SEVENTIES. THE COLDEST TEMPERATURES SO FAR THIS SEASON ARE IN
STORE FOR THE AREA SATURDAY NIGHT AS THE SURFACE HIGH SETTLES OVER
THE AREA WITH LIGHT WINDS MAXIMIZING RADIATIVE COOLING AND RESULTING
IN LOWS RANGING FROM THE LOWER TO MID FORTIES OVER INLAND AREAS
RANGING TO AROUND FIFTY NEAR THE IMMEDIATE COAST...WHICH WILL BE
ABOUT 13-15 DEGREES BELOW NORMAL. THESE UNSEASONABLY COLD
TEMPERATURES WILL BE NEAR THE RECORD VALUES FOR MOBILE AND PENSACOLA
BUT EXPECTED TO BE ABOUT TWO DEGREES ABOVE. HERE IS A COMPARISON OF
THE FORECAST AND CURRENT RECORDS FOR MOBILE AND PENSACOLA SUNDAY
MORNING (SATURDAY NIGHT):

        FORECAST  RECORD
MOBILE     46       44 (2010)
PENSACOLA  51       49 (1987)

/29

LONG TERM (SUNDAY THROUGH WEDNESDAY)...THE LONGWAVE TROF PERSISTS
OVER THE EASTERN STATES AT LEAST THROUGH MONDAY NIGHT THEN EJECTS
OFF TO THE EAST WITH BROAD UPPER RIDGING BUILDING INTO THE REGION
THROUGH WEDNESDAY.  A SURFACE HIGH OVER THE AREA SUNDAY MORNING
MOVES OFF INTO THE ATLANTIC ALLOWING FOR A RETURN OF SOUTHERLY WINDS
AND A RETURN TO SEASONABLE TEMPERATURES BY MONDAY AND SLIGHTLY
WARMER TEMPERATURES BY WEDNESDAY.  DRY CONDITIONS ARE EXPECTED
THROUGH THE PERIOD EXCEPT HAVE KEPT SMALL POPS MAINLY FOR MONDAY
NIGHT AND TUESDAY AS A SERIES OF SHORTWAVES MOVE ACROSS THE AREA. /29

MARINE...A SURFACE HIGH NORTHEAST OF THE COASTAL WATERS WILL DRIFT
EAST OFF THE US ATLANTIC COAST TODAY THROUGH EARLY FRIDAY. THIS
FEATURE WILL BRING LIGHT TO MODERATE WINDS OVER THE REGION THROUGH
EARLY FRIDAY. MEANWHILE A COLD FRONT WILL APPROACH FROM THE WEST AND
MOVE ACROSS THE COASTAL WATERS LATE FRIDAY AFTERNOON AND EVENING. A
STRONG HIGH WILL BUILD BEHIND THE FRONT BRINGING MODERATE TO STRONG
OFFSHORE WINDS AND BUILDING SEAS AS THE FRONT MOVES OFFSHORE.
NUMEROUS SHOWERS AND THUNDERSTORMS EXPECTED THURSDAY AND FRIDAY AS
THE FRONT APPROACHES AND PASSES ACROSS THE MARINE AREA. THE WNA DID
NOT QUITE CATCH THE EFFECTS OF ENHANCED POST FRONTAL WAVE HEIGHTS IN
WHICH THE NORTHEAST PROPAGATING GROUP AND THE SOUTHWARD PROPAGATING
GROUP INTERSECT. NOR WERE THE EFFECTS OF DOWNWARD MOMENTUM TRANSPORT
UNDER COLD ADVECTION VERY PROMINENT. HOWEVER...THE SWAN MODEL HANDLED
THE PROCESS BEAUTIFULLY WITH A SMALL MAXIMUM WAVE HEIGHT AREA
CALCULATED JUST BEHIND IT. WE SMOOTHED THE BOUNDARIES AND RESTORED
WHAT WE SAW THE SWAN TRYING TO DO THERE. 77/BD

&&

.PRELIMINARY POINT TEMPS/POPS...
MOBILE      71  87  73  85  58 /  20  40  50  60  20
PENSACOLA   72  85  74  84  62 /  10  30  40  60  30
DESTIN      77  83  74  84  64 /  10  20  30  60  30
EVERGREEN   67  90  71  83  53 /  10  30  40  70  20
WAYNESBORO  65  89  71  83  51 /  20  50  60  60  10
CAMDEN      66  90  72  83  51 /  10  30  50  70  10
CRESTVIEW   68  88  73  85  57 /  10  20  30  70  30

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
FL...NONE.
MS...NONE.
GM...NONE.
&&

$$










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