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Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
02-11-2009, 10:58 PM (This post was last modified: 02-11-2009 11:05 PM by ROLLTIDE.)
Post: #1
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
SPC has 5% out for much of AL/southern MS/LA. Looks like significant low level moistening and destabilitation along and S of a retreating warm front with decent lapse rates. Primarily a modest elevated large hail wind north of boundary with wind/hail south of boundary - although at least a small TOR risk along boundary. SPC discusses sufficient shear for supercell development. Stilll differences to be ironed out in models but could be a SLGT risk day

Quote: DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0222 AM CST WED FEB 11 2009

VALID 131200Z - 141200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
MODELS GENERALLY INDICATE LITTLE CHANGE TO THE POSITION OF THE MORE
PROMINENT SOUTHERN BRANCH OF POLAR WESTERLIES ACROSS THE
SOUTHERN/CENTRAL TIER OF THE U.S. THROUGH THIS FORECAST PERIOD.
SOME WEAKENING MAY OCCUR...AT LEAST OVER THE OHIO/TENNESSEE VALLEY
REGION...AS A STRONGER JET CORE NOSES EAST OF THE MID ATLANTIC
COAST. BUT...ALL GUIDANCE CONTINUES TO FORECAST THE INTENSIFICATION
OF A SUBTROPICAL JET...JUST TO THE SOUTH OF THE POLAR JET...ACROSS
BAJA AND THE NORTHERN MEXICAN PLATEAU...THROUGH THE LOWER
MISSISSIPPI VALLEY AND...PERHAPS...THE EASTERN GULF STATES BY 12Z
SATURDAY. SOME VARIABILITY EXISTS AMONG THE MODELS CONCERNING THIS
FEATURE. BUT...GUIDANCE SUGGESTS THAT EMBEDDED SHORT WAVE IMPULSES
WITHIN THE TWO STREAMS WILL REMAIN OUT OF PHASE.

ONE MODESTLY STRONG SHORT WAVE IMPULSE...EMANATING FROM THE BROADER
SCALE POLAR TROUGH ACROSS THE SOUTHWEST...IS PROGGED TO CONTINUE
LIFTING OUT ACROSS THE SOUTH CENTRAL PLAINS THROUGH THE LOWER OHIO
VALLEY BY THE END OF THE PERIOD. THIS IS EXPECTED TO OCCUR AS
ANOTHER IMPULSE OF SIMILAR STRENGTH TURNS EASTWARD ACROSS CALIFORNIA
INTO THE FOUR CORNERS...AHEAD OF ANOTHER MUCH STRONGER SHORT WAVE
TROUGH/JET STREAK DIGGING SOUTH OF THE ALEUTIANS THROUGH THE
NORTHEAST PACIFIC.

...CENTRAL/EASTERN GULF STATES...
APPRECIABLE MID-LEVEL FORCING ASSOCIATED WITH THE LEAD POLAR IMPULSE
LIFTING OUT OF THE SOUTHWEST IS EXPECTED TO REMAIN WELL NORTH OF THE
CENTRAL GULF COAST REGION. HOWEVER...AN ASSOCIATED RETURN FLOW OFF
THE WESTERN GULF OF MEXICO IS EXPECTED TO CONTRIBUTE TO SUBSTANTIAL
LOW-LEVEL MOISTENING ACROSS PARTS OF SOUTHERN LOUISIANA AND
CENTRAL/SOUTHERN MISSISSIPPI AND ALABAMA DURING THE DAY FRIDAY.
THIS...COUPLED WITH ASCENT ASSOCIATED WITH LOW-LEVEL WARM
ADVECTION...IS PROGGED TO SUPPORT INCREASING CONVECTIVE
PRECIPITATION. WHILE THIS INITIAL ACTIVITY SPREADS EAST
NORTHEASTWARD...TOWARD THE SOUTH ATLANTIC COAST STATES... CONVECTIVE
REDEVELOPMENT IN AN EAST-WEST BAND ACROSS THE CENTRAL GULF
COAST/LOWER MISSISSIPPI VALLEY APPEARS LIKELY TO PERSIST THOUGH THE
PERIOD...PERHAPS ENHANCED BY SUBTROPICAL IMPULSES.

WHILE IT APPEARS MOST CERTAIN THAT STRONGEST INFLOW OFF THE GULF OF
MEXICO WILL REMAIN FOCUSED ACROSS THE CENTRAL GULF COAST REGION...IN
THE PRESENCE OF A STRONGLY SHEARED FLOW SUPPORTIVE OF SEVERE
STORMS...UNCERTAINTIES EXIST THAT WILL AFFECT POTENTIAL
DESTABILIZATION AND THE RISK OF SEVERE STORMS. IN ADDITION TO
UNCLEAR FORCING ASSOCIATED WITH THE SUBTROPICAL STREAM...
VARIABILITY EXISTS AMONG THE MODELS CONCERNING THE STRENGTH OF
MID-LEVEL INHIBITION ASSOCIATED WITH ELEVATED MIXED LAYERS ADVECTING
ACROSS THE REGION. AND...A RESIDUAL RAIN COOLED BOUNDARY LAYER
COULD BE SLOW TO ERODE. HOWEVER...SREF AND MREF GUIDANCE INDICATE A
GOOD LIKELIHOOD THAT CAPE ON THE ORDER OF AT LEAST 500 J/KG WILL
MATERIALIZE...WHICH MAY BE SUFFICIENT FOR A FEW SUPERCELLS
ACCOMPANIED BY AT LEAST THE RISK OF LARGE HAIL... REGARDLESS OF
WHETHER OR NOT IT IS ROOTED ABOVE A NEAR SURFACE STABLE LAYER.

[Image: day3prob_0830.gif]

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02-12-2009, 02:32 AM
Post: #2
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
Mobile,NWS

Quote:TONIGHT...BUT MAX TEMPS
WILL REBOUND TO AROUND 70 DEGREES ON THURSDAY. WILL HAVE A QUICK
RETURN FLOW DEVELOP ON FRIDAY AS THE FRONT THAT JUST MOVED THROUGH
THE AREA MOVES BACK NORTH AS A WARM FRONT. EXPECT WIDESPREAD COVERAGE
OF RAIN AND RAIN SHOWERS...WITH ISOLATED THUNDERSTORMS FRIDAY AND
FRIDAY NIGHT. THIS SYSTEM WILL LIKELY PRODUCE A SOAKING RAIN WITH
RAINFALL TOTALS OF 1 TO 2 INCHES ACROSS MOST OF THE REGION. MAX TEMPS
ON FRIDAY WILL BE COOLER THAN THURSDAY AS RAIN AND CLOUD COVER IS
EXPECTED...GENERALLY IN THE LOW TO MID 60S AND OVERNIGHT LOWS FRIDAY WILL
BE IN THE UPPER 50S AND LOWER 60S. 12/DS

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02-12-2009, 07:39 AM (This post was last modified: 02-12-2009 07:42 AM by ROLLTIDE.)
Post: #3
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
Spc day 1 outlook

Quote:LATE PERIOD -- CENTRAL GULF COAST/MS DELTA...
WIDELY SCATTERED TSTMS IN CLUSTERS ARE POSSIBLE LATE IN
PERIOD...AFTER 13/06Z...BOTH INVOF RETURNING SFC FRONTAL ZONE AND
ELEVATED WAA/MOISTURE RETURN REGIME N OF SFC FRONT. AIR MASS WILL
BE MOST FAVORABLE NEAR COAST...WHERE PERSISTENT ISENTROPIC LIFT AND
MOISTENING SHOULD RESULT IN ELEVATED MUCAPE APPROXIMATELY 500
J/KG...DECREASING NWD WITH INLAND EXTENT. ALTHOUGH IT NOW APPEARS
BULK OF INLAND CONVECTION SHOULD DEVELOP AFTER 12Z PER DAY-2
OUTLOOK...THIS PROCESS MAY BEGIN VERY LATE IN DAY-1
PERIOD...ESPECIALLY SERN LA/SRN MS REGION.

Day 2 outlook
Quote:SERN PLAINS/LWR MS VALLEY THRU ERN GULF/S ATLANTIC COAST...
APPRECIABLE MID-LEVEL FORCING ASSOCIATED WITH THE LEAD POLAR IMPULSE
LIFTING OUT OF THE SOUTHWEST IS EXPECTED TO REMAIN WELL NORTH OF THE
GULF COAST. BUT...THIS FEATURE SHOULD CONTRIBUTE TO A RETURN FLOW
OFF THE WESTERN GULF OF MEXICO. THE MOST SUBSTANTIAL MOISTENING IS
EXPECTED TO BECOME FOCUSED NEAR A DEVELOPING EAST-WEST ORIENTED
FRONTAL ZONE ACROSS THE GULF STATES...WHERE CONVECTION...INCLUDING
THUNDERSTORM ACTIVITY...COULD BECOME FAIRLY WIDESPREAD. THIS WILL
PROBABLY IMPEDE MOISTURE RETURN FARTHER NORTH...AND LIMIT CONVECTIVE
POTENTIAL WITH A WEAK SURFACE CYCLONE PROGGED TO MIGRATE FROM THE
SOUTH CENTRAL HIGH PLAINS THROUGH THE MIDDLE MISSISSIPPI VALLEY.

UNCERTAINTIES REMAIN...CONCERNING THE STRENGTH OF CAPPING ASSOCIATED
WITH LOWER/MID TROPOSPHERIC WARMING TO THE SOUTH OF THE POLAR
IMPULSE...THE TIMING AND STRENGTH OF FORCING ASSOCIATED WITH THE
SUBTROPICAL STREAM...AND THE POSSIBILITY THAT RAIN WILL SLOW THE
EROSION OF A LINGERING COOL/STABLE BOUNDARY LAYER OVER MUCH OF THE
CENTRAL/EASTERN GULF COAST. DEEP LAYER SHEAR WILL CERTAINLY BE
STRONG ENOUGH FOR ORGANIZED SEVERE STORMS...INCLUDING SUPERCELLS.
AND...LOW-LEVEL HODOGRAPHS MAY BE SIZABLE BENEATH SOUTHWESTERLY 850
MB FLOW ON THE ORDER OF 30 KT. BUT...BASED ON MREF AND SREF
INDICATING MOST UNSTABLE CAPE PEAKING IN THE 500-1000 J/KG RANGE
ACROSS PARTS OF SOUTHEAST TEXAS/LOUISIANA AND SOUTHERN
MISSISSIPPI...IN AN ENVIRONMENT WHERE LARGE-SCALE MID-LEVEL FORCING
IS MOST LIKELY TO REMAIN WEAK TO MODERATE AT BEST...POTENTIAL FOR
ANYTHING BEYOND AN ISOLATED STRONG/SEVERE STORM OR TWO STILL APPEARS
LOW.

..KERR.. 02/12/2009

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02-12-2009, 07:45 AM
Post: #4
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
Alabamawx update




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02-12-2009, 10:59 AM (This post was last modified: 02-12-2009 11:09 AM by ROLLTIDE.)
Post: #5
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
I am still thinking that isolated severe weather breaks out tomorrow evening in line from roughly 20 miles north of the coast from SE LA to the FL panhandle. This is your classic pattern where you have lots of shear and very low instability. There is a chance of a few supercells with strong winds and hail and this area should be outlooked by a slight risk later today by the SPC

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02-12-2009, 01:27 PM
Post: #6
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
Quote:DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CST THU FEB 12 2009

VALID 131200Z - 141200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
PROGRESSIVE LARGE SCALE FLOW REGIME WILL PERSIST OVER THE CONUS
THROUGH FRIDAY. A LOW AMPLITUDE SHORTWAVE TROUGH IS FORECAST TO
SPREAD EAST-NORTHEASTWARD FROM THE FOUR CORNERS VICINITY TO THE
UPPER MIDWEST FRIDAY NIGHT. FARTHER WEST...WESTERN STATES UPPER LOW
WILL PIVOT SOUTHEASTWARD TOWARD THE ORE/NORTHERN CA COAST...WITH
ASSOCIATED POLAR JET SPREADING INLAND ACROSS SOUTHERN CA AND THE
DESERT SOUTHWEST. FARTHER SOUTH...SUBTROPICAL JET STREAM IS FORECAST
TO CONSIDERABLY STRENGTHEN/SPREAD EASTWARD ACROSS NORTHERN
MEXICO...AND TOWARD THE LOWER MISSISSIPPI VALLEY BY EARLY SATURDAY.

...LOWER MISSISSIPPI VALLEY/GULF COAST STATES...
LOW LEVEL MOISTURE RETURN WILL CONTINUE ACROSS THE GULF COAST REGION
ON FRIDAY BENEATH WEAK BUT STEADY LARGE SCALE HEIGHT FALLS AND A
30-40 KT SOUTHWESTERLY LOW LEVEL JET AIDED LOW LEVEL WARM
ADVECTION/MOISTURE TRANSPORT REGIME. SCATTERED TSTMS WILL MAINLY BE
CONCENTRATED ALONG THE NORTHEAST-ADVANCING MARINE-TYPE WARM FRONT
ACROSS THE CENTRAL GULF COAST REGION. WITH THE PRIMARY SHORTWAVE
TROUGH WELL NORTH OF THE REGION...QUESTIONS EXIST REGARDING TSTM
COVERAGE/VIGOR IN THE AMBIENT WARM SECTOR AHEAD OF A WEAK SURFACE
LOW/COLD FRONT CROSSING EASTERN OK AND ARKLATEX. STRONG DEEP LAYER
SHEAR OF 50-60 KT AND VEERING WIND PROFILES WILL BE MORE THAN
ADEQUATE FOR ORGANIZED/ROTATING TSTMS. HOWEVER...THE PRIMARY
QUESTION FOR AN APPRECIABLE/WELL-ORGANIZED SEVERE RISK REVOLVES
AROUND MODEST TOTAL BUOYANCY /SBCAPE UP TO 500-1000 J PER KG/...AS
WELL AS THE POTENTIAL FOR CAPPING AND ONLY MODEST/AMBIGUOUS FORCING
ACROSS THE WARM/MOIST SECTOR. WHILE A CATEGORICAL SLIGHT RISK DOES
NOT APPEAR TO BE WARRANTED AT THIS TIME...THE STRONGER TSTMS MAY BE
CAPABLE OF DAMAGING WINDS AND PERHAPS A TORNADO ON FRIDAY.
[Image: day2probotlk_1730_any.gif]

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02-12-2009, 04:08 PM
Post: #7
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
Should the weather be cleared up by Saturday afternoon and night? (Parade, you know.)
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02-12-2009, 04:13 PM (This post was last modified: 02-12-2009 04:17 PM by ROLLTIDE.)
Post: #8
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
Windwatcher Wrote:Should the weather be cleared up by Saturday afternoon and night? (Parade, you know.)

Depends on where the parade is . If it is in the home of Mardi Gras Mobile,AL then there should still be some light rain in the area even Sat night . If it's in N.O then you are looking less likely to see rain as rain should be moving out of the area in the afternoon and evening. This is subject to change but based on the latest model data

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02-12-2009, 04:19 PM
Post: #9
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
[b][COLOR=DarkRed]Alabama wx update


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02-12-2009, 05:19 PM (This post was last modified: 02-12-2009 05:32 PM by ROLLTIDE.)
Post: #10
Severe Weather Potential 2/13/09-2/14/09 LA,MS,AL
nws n.o

Quote:afdlix

area forecast discussion
national weather service new orleans la
347 pm cst thu feb 12 2009

.short term...
Window of good weather slowly closing as frontal zone south of the
coast starts moving north later tonight and early friday.
isentropic lift light rain is expected to steadily onset by
daybreak friday and spread northward with some elevated convection
interspersed as warm frontogenesis strengthens in time. It would
appear a transition to surface based convection is possible though
some mid level inhibition may cut into full potential. Low level
shear could be sufficient for weak rotational cells that may or
may not be able to reach the surface. This will be the radar
challenge during the day tomorrow. Chap output using the nam did
show a 1 or 2 hour threat for ef-0 tornado/waterspouts and gusts
55 mph at peak shear time associated with warm frontal passage.
Given the large fetched southwest flow aloft and increasing
synoptic scale lift...can not totally rule out severe potential.
These threats were alluded to in latest hazardous weather outlook
though overall threat coverage does appear to be very low...
Greater than zero percent but not by much.
Much of the area will then be in an marginally unstable warm
sector into friday night before cold front sweeps through the area
saturday morning. Models seem to be hanging on to preciptiation a
bit too long so holding to optimism for parade times saturday and
saturday evening before flow becomes more favorable for yet
another warm frontogenesis saturday night and sunday. 24/rjr

Jackson,MS
Quote:MODELS AGREE THAT
WAA WILL INCREASE OVER OUR REGION AHEAD OF THIS APPROACHING SYSTEM
FRIDAY INCLUDING A WARM FRONT MOVING BACK INTO OUR SOUTHWEST DURING
THE AFTERNOON. ALTHOUGH THE NAM IS SLOWER THAN THE GFS...850MB FLOW
OF 35-40KTS IS EXPECTED TO BRING IN 326-328THETAE AIR WITH SURFACE
DEW POINTS RISING INTO THE LOWER 60S AND PWS NEAR AN INCH AT LEAST
NORTH TO THE HIGHWAY 84 CORRIDOR BY LATE AFTERNOON. THE NAM BUFR
SOUNDINGS ALSO SUGGEST CAPPING OVER OUR SOUTHERN ZONES FRIDAY
AFTERNOON. INSTABILITY LOOKS TO A LIMITING FACTOR FOR SEVERE
CONVECTION INCLUDING MLCAPES ONLY AROUND 200J/KG BUT WITH ADEQUATE
MOISTURE AND FAVORABLE DEEP LAYER SHEAR WL MENTION STRONG
THUNDERSTORM POTENTIAL SOUTH OF INTERSTATE 20 FRIDAY AFTERNOON AND
EVENING. WITH PWS NEAR AN INCH AND A HALF AND POSSIBLE TRAINING OF
STORMS...ONE TO TWO INCHES OF RAIN MAY BE REALIZED IN THE SOUTH
FRIDAY THROUGH SATURDAY.

Mobile, NWS

Quote:NATIONAL WEATHER SERVICE MOBILE AL
420 PM CST THU FEB 12 2009

.SHORT TERM (TONIGHT THROUGH SATURDAY NIGHT)...THE FRONTAL BOUNDARY
THAT DROP SOUTH OF THE REGION YESTERDAY HAS BECOME NEARLY STATIONARY
AND WILL BEGIN MOVING BACK NORTH AS A WARM FRONT LATE TONIGHT AS AN
UPPER LEVEL DISTURBANCE MOVES EAST OUT OF THE 4-CORNERS AREA. THIS
WARM FRONT WILL LIFT BACK NORTH ACROSS THE FCST AREA ON FRIDAY...WITH
WIDESPREAD RAINS DEVELOPING BY AROUND MIDDAY. THE PCPN WILL BECOME
MORE CONVECTIVE AS THE DAY WEARS ON AND THE AREA BECOMES WARM
SECTORED...AND ISOLATED THUNDERSTORMS WILL BE POSSIBLE BY AFTERNOON.
A COLD FRONT WILL MOVE EAST TOWARD AND ACROSS THE AREA ON
SATURDAY...MAINTAINING THE HIGH RAIN CHANCES WITH WIDESPREAD SHOWERS
AND ISOLATED THUNDERSTORMS CONTINUING THROUGH EARLY SATURDAY. AT THIS
TIME...NO SEVERE WEATHER IS ANTICIPATED BUT HEAVY RAINFALL TOTALS OF
1 TO 2 INCHES ACROSS MOST OF THE REGION ARE EXPECTED AND THIS WILL BE
THE PRIMARY WEATHER ELEMENT TO BE MONITORED. WENT CLOSE TO MAV MOS
TEMPERATURE GUIDANCE.

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