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Area Forecast Discussion

282
FXUS62 KCAE 211812
AFDCAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
112 PM EST SUN DEC 21 2014

.SYNOPSIS...
A FRONTAL ZONE WILL REMAIN NEAR THE SOUTHEAST COAST THROUGH
TUESDAY. A SERIES OF LOW PRESSURE SYSTEMS WILL MOVE NORTHEASTWARD
ALONG THE FRONT...KEEPING WEATHER UNSETTLED. A STRONG COLD FRONT
APPROACHING FROM THE WEST WILL MOVE THROUGH THE FORECAST AREA LATE
WEDNESDAY OR WEDNESDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
SUB-TROPICAL PLUME OF MOISTURE EXTENDING FROM CENTRAL MEXICO TO
THE SOUTHEASTERN STATES CONTINUES TO BE EVIDENT ON THE WATER VAPOR
IMAGERY THIS AFTERNOON. VISIBLE IMAGERY SHOWS THAT SKIES CLEARED A
BIT ACROSS THE CENTRAL AND NORTHERN MIDLANDS ALLOWING TEMPERATURES
TO RISE INTO THE MID 50S. ISENTROPIC LIFTING WILL INCREASE LATE
AFTERNOON INTO EARLY EVENING IN RESPONSE TO THE APPROACHING
SHORTWAVE FROM THE GULF COAST.

LIGHT RAIN EXPECTED TO DEVELOP AND MOVE NORTHWARD INTO THE
FORECAST AREA FROM THE SOUTH AROUND SUNSET. ISENTROPIC LIFT
MAXIMIZES OVER THE FORECAST AREA DURING THE 03Z-09Z TIME FRAME AND
THE AREA FALLS WITHIN THE RIGHT ENTRANCE REGION OF A STRONG 120+
KNOT UPPER JET THROUGHOUT MUCH OF THE NIGHT...AIDING IN FORCING
FOR PRECIPITATION. LEANED TOWARDS THE HIGHER MET POP GUIDANCE AND
WILL CARRY CATEGORICAL POPS FOR THE ENTIRE FORECAST AREA...WITH
THE HIGHEST POPS CENTERED AROUND THE 06Z-09Z TIME FRAME.
TEMPERATURES WILL FALL INTO THE LOWER TO MID 40S LIMITED BY
WETBULB TEMPERATURES. DESPITE THE HIGH POPS OVERNIGHT...TOTAL
RAINFALL AMOUNTS ARE EXPECTED TO BE LIGHT AT GENERALLY A TENTH OF
AN INCH OR LESS...WITH SOME ISOLATED AMOUNTS CLOSER TO A FEW
TENTHS OF AN INCH.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
THE MODELS SHOW THE WEDGE RIDGE PATTERN CONTINUING. MOISTURE
APPEARS TO BECOME MORE SHALLOW BEHIND A MID-LEVEL SHORTWAVE TROUGH
MONDAY BUT CONTINUED ISENTROPIC LIFT SUPPORTS RAIN OR DRIZZLE. THE
MODELS ARE CONSISTENT WITH LIGHT RAINFALL AMOUNTS AND THE TYPE MAY
BE MAINLY DRIZZLE. FORECASTED THE MEASURABLE RAIN CHANCE AROUND 50
PERCENT WHICH IS CLOSE TO AN ECMWF AND GFS MOS AVERAGE. THE HIGH
TEMPERATURE GUIDANCE IS LIKELY TOO WARM BECAUSE OF THE WEDGE
PATTERN MONDAY. USED THE GUIDANCE CONSENSUS FOR THE TEMPERATURE
MONDAY NIGHT.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
THE MODELS HAVE BEEN CONSISTENT SHOWING DEEP UPPER TROUGHING
DEVELOPING WITH HIGH MOISTURE IN THE FLOW OVER THE FORECAST AREA
AHEAD OF THE TROUGH TUESDAY AND WEDNESDAY. THE NAM SURFACE-BASED
LI PATTERN INDICATES THE WEDGE RIDGE PATTERN WILL HOLD TROUGH
TUESDAY NIGHT. ISENTROPIC LIFT AND THE HIGH MOISTURE PLUS A SERIES
OF MID-LEVEL SHORTWAVE TROUGHS SUPPORTS HIGH POPS. THE WARM FRONT
MAY LIFT THROUGH THE FORECAST AREA WEDNESDAY AHEAD OF THE STRONG
COLD FRONT WEDNESDAY. THE GFS AND ECMWF HAVE TRENDED SLOWER WITH
THE COLD FRONT TIMING AND NOW INDICATE FRONTAL PASSAGE WEDNESDAY
EVENING.

IF THE FORECAST AREA GETS INTO THE WARM SECTOR THERE MAY BE
ENOUGH INSTABILITY FOR THUNDERSTORMS AHEAD OF THE COLD FRONT
WEDNESDAY. THE GFS AND ECMWF DISPLAY H85 WINDS OF 40 TO 60 KNOTS.
THE SHEAR AND POTENTIAL FOR SUFFICIENT INSTABILITY INDICATES A
POSSIBILITY OF SEVERE THUNDERSTORMS.

EXPECT A DIMINISHED SHOWER CHANCE LATE WEDNESDAY NIGHT BEHIND THE
FRONT WITH BREEZY CONDITIONS. THE MODELS HAVE BEEN CONSISTENT
SHOWING A DRY WEST FLOW FOR CHRISTMAS DAY. BREEZY CONDITIONS MAY
CONTINUE DURING THE DAY...BUT THE MODEL TREND HAS BEEN TO SHOW THE
RIDGE FARTHER NORTHWARD WITH LESS OF A PRESSURE GRADIENT IN THE
FORECAST AREA.

MOISTURE MAY INCREASE ASSOCIATED WITH ANOTHER COLD FRONT MOVING
INTO THE AREA FRIDAY NIGHT INTO SATURDAY. THE ECMWF HAS SHOWN
HIGHER MOISTURE WITH THIS SYSTEM COMPARED TO THE GFS.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
VFR CONDITIONS BECOMING MVFR AFTER SUNSET...AND IFR/LIFR LATE
TONIGHT THROUGH MONDAY MORNING.

SKIES HAVE CLEARED A BIT THIS AFTERNOON BUT INCREASING CLOUDS
EXPECTED LATE THIS AFTERNOON WITH LOWERING CIGS TO MVFR AROUND 00Z
AGS/DNL/OGB AND BY 03Z AT CAE/CUB AS ISENTROPIC LIFT INCREASES
AHEAD OF APPROACHING SHORTWAVE ENERGY. LIGHT RAIN SHOULD
OVERSPREAD THE TERMINALS FROM SOUTH TO NORTH OVERNIGHT. CIGS
EXPECTED TO DROP TO IFR AFTER 06Z WITH THE RAINFALL AND INCREASING
WEDGE CONDITIONS. PERSISTENT SOUTHWESTERLY FLOW ALOFT ATOP THE
NORTHEASTERLY LOW LEVEL FLOW WILL KEEP WEDGE CONDITIONS IN PLACE
AFTER 12Z WHICH WILL RESULT IN LOWERING VSBYS IN DRIZZLE AND LIGHT
RAIN WITH IFR/LIFR CIGS.

EXTENDED AVIATION OUTLOOK...WIDESPREAD MVFR TO IFR CONDITIONS
EXPECTED MONDAY THROUGH WEDNESDAY EVENING AS A SERIES OF SYSTEMS
CROSS THE REGION. BREEZY CONDITIONS POSSIBLE WEDNESDAY AFTERNOON
INTO THURSDAY MORNING.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
GA...NONE.
&&

$$






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