#2627 Postby Stormcenter » Fri Jan 07, 2011 5:30 pm
A little bit of everything (rain,wind,sleet,freezing rain) possible this weekend per the NWS out of N.O.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
422 PM CST FRI JAN 7 2011
...A RETURN TO WINTER WEATHER IS EXPECTED SUNDAY AND SUNDAY NIGHT
ALONG WITH STRONG ONSHORE WINDS AND THE POTENTIAL FOR COASTAL
FLOODING...
.SYNOPSIS...
SURFACE MAP SHOWS LOW PRESSURE OVER THE SOUTHERN APPALACHIANS AND
HIGH PRESSURE OVER THE WESTERN PLAINS AND SOUTHERN GULF OF MEXICO.
WATER VAPOR IMAGERY SHOWS UPPER LOW PERSISTS OVER THE GREAT LAKES
REGION...BUT THE SHARP UPPER TROUGH OVER THE SOUTHEAST STATES AND
EASTERN GULF OF MEXICO HAS WEAKENED AND MOVED EAST INTO THE ATLANTIC
WHILE A PROGRESSIVE RIDGE ADVANCES EAST ACROSS THE SOUTHERN PLAINS.
OUR NEXT FEATURE OF INTEREST IS AN UPPER LOW THAT IS SPINNING AND
NUDGING EAST OFF THE SOUTHERN CALIFORNIA/NORTHERN BAJA COAST.
&&
.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
HAVE ADDED MENTION OF SLEET TO THE FORECAST STARTING LATE SATURDAY
NIGHT THROUGH SUNDAY NIGHT ACROSS MUCH OF THE NORTHERN ZONES AT
VARIOUS TIMES. THIS FORECAST PACKAGE ALSO INCLUDES THE ISSUANCE OF
A COASTAL FLOOD WATCH AND GALE WATCH FOR MOST OF THE COASTAL
AREAS. REFER TO THE MARINE SECTION FOR DETAILS ON THE COASTAL
FLOOD AND GALE WATCHES.
UPPER LOW OVER THE GREAT LAKES WILL MOVE EAST LEAVING BEHIND
CONVERGENT UPPER FLOW OVER THE EASTERN CONUS BY SUNDAY. THE UPPER
LOW OFF THE WEST COAST WILL MAINTAIN A FAIRLY DEEP TROUGH AXIS AS IT
MOVES EAST NEAR THE U.S./MEXICAN BORDER AND ACROSS NORTHERN MEXICO
THROUGH SATURDAY...THEN THE UPPER SYSTEM WILL SHIFT SOME ITS ENERGY
FARTHER NORTH AS IT MOVES EAST THROUGH THE SOUTHERN PLAINS TOWARDS
THE LOWER MISSISSIPPI VALLEY SUNDAY. THE SURFACE LOW TRACK AND
TIMING OF PRECIPITATION IS CRITICAL TO DETERMINE PRECIPITATION TYPE.
LOOKING AT THE 12Z MODEL RUNS TODAY...THERE IS PRETTY GOOD AGREEMENT
WITH THE SURFACE LOW TRACKING FROM THE LOWER/MID TEXAS COAST ON
SUNDAY MORNING TO THE SOUTH CENTRAL LOUISIANA COASTAL WATERS SUNDAY
AFTERNOON...AND THEN EAST TO EAST-NORTHEAST POSSIBLY BRUSHING THE
EXTREME SOUTHEAST MISSISSIPPI RIVER DELTA SUNDAY NIGHT BEFORE MOVING
EAST ACROSS THE NORTHEAST GULF MONDAY.
LIQUID PRECIPITATION AMOUNTS ARE STILL EXPECTED TO BE MOSTLY IN THE
1 TO 2 INCH RANGE...POSSIBLY A BIT HIGHER WITH SOME 3 TO 4 INCH
AMOUNTS POSSIBLE NEAR THE SOUTHEAST LOUISIANA COAST. REGARDING
PRECIPITATION TYPE...WET-BULB TEMPERATURES WILL BE BELOW FREEZING
ACROSS AREAS NORTH OF I-10/12 CORRIDOR AT THE ONSET OF PRECIP LATE
SATURDAY NIGHT AND SUNDAY MORNING. THIS COULD LEAD TO A MIX OF RAIN
AND SLEET OVER SOUTHWEST MISSISSIPPI AND SOME ADJACENT AREAS OF EAST
CENTRAL/SOUTHEAST LOUISIANA BEFORE LATENT HEAT WARMS MOST OF THE AIR
COLUMN ABOVE FREEZING SUNDAY AFTERNOON.
THE MODEL SOUNDINGS INDICATE A ELEVATED WARM LAYER OF +2 TO +5C AT
850 MB DURING THE PERIODS OF MEASURABLE PRECIP. THIS SHOULD CAUSE
MOST OF THE SNOW TO COMPLETELY MELT LEAVING THE LOWEST LEVEL
TEMPERATURES TO DETERMINE WHETHER THE PRECIP FALLS AS
RAIN...FREEZING RAIN...OR SLEET. GIVEN THE FORECAST SURFACE
TEMPERATURES MOSTLY ABOVE FREEZING...THIS LEAVES MAINLY RAIN AND
SLEET. THE AMOUNT OF LIQUID EQUIVALENT PRECIPITATION FALLING IS
CAUSE FOR CONCERN IF SOME OF THE NORTHERN AREAS BECOMES MOSTLY
SLEET. EVEN WITH A RELATIVELY WARM GROUND...A PERIOD OF SUSTAINED
MODERATE TO HEAVY SLEET COULD TRY TO ACCUMULATE ON SOME ELEVATED
ROADS AND BRIDGES. CONFIDENCE IN THIS SCENARIO IS STILL SLIGHTLY
TOO LOW TO ISSUE A WINTER STORM WATCH FOR SUNDAY/SUNDAY NIGHT...BUT
THAT COULD BECOME NECESSARY LATER TONIGHT/SATURDAY MORNING IF THE
MODELS CONTINUE TRENDING THE WAY THEY DID TODAY.
NEAR AND SOUTH OF THE SURFACE LOW TRACK...THERE WILL BE SOME
INSTABILITY...POSSIBLY SURFACE BASED...OVER THE COASTAL WATERS.
THERE IS A CHANCE OF STRONG TO SEVERE THUNDERSTORMS OVER THE
COASTAL WATERS MAINLY WEST AND SOUTH/SOUTHEAST OF SOUTHWEST PASS
SUNDAY AFTERNOON AND EVENING...BUT SOME ELEVATED...EMBEDDED
THUNDERSTORMS ARE POSSIBLE FARTHER NORTH IN THE COLD AIR. TRIMMED
BACK MENTION OF THUNDER TO NEAR NEW ORLEANS.
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