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November Discussion


DaculaWeather

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More detail for the watch area:

ww0891_radar.gif

URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 891

NWS STORM PREDICTION CENTER NORMAN OK

430 PM EST WED NOV 16 2011

THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF

FAR EASTERN GEORGIA

WESTERN AND CENTRAL NORTH CAROLINA

CENTRAL AND EASTERN SOUTH CAROLINA

EFFECTIVE THIS WEDNESDAY AFTERNOON FROM 430 PM UNTIL MIDNIGHT EST.

TORNADOES...HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS

TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

DISCUSSION...CLUSTERS OF SUPERCELLS FROM UPSTATE SC INTO ERN GA ARE

EXPECTED TO MOVE/DEVELOP NEWD ACROSS THE WATCH AREA LATE THIS

AFTERNOON INTO TONIGHT...IN ADVANCE OF MIDLEVEL VORTICITY MAXIMUM

EMERGING FROM THE CNTRL/SRN APPALACHIANS. THE LOW-LEVEL MASS

RESPONSE TO THIS MIDLEVEL IMPULSE WILL RESULT IN A 50+ KT SWLY LLJ

BEING FOCUSED ACROSS THE REGION...ENHANCING ALREADY STRONG VERTICAL

SHEAR. GIVEN THE MOIST...UNSTABLE AND LCL WARM SECTOR AIR

MASS...THE POTENTIAL WILL EXIST FOR TORNADOES AND WIND DAMAGE WITH

ANY SUSTAINED SUPERCELL AND/OR BOWING STRUCTURES.

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Wow, sry haven't posted in awhile...

Impressive Disco out of ILM, this evening...

Area forecast discussion

National Weather Service Wilmington NC

318 PM EST Wednesday Nov 16 2011

Synopsis...

a cold front over the Tennessee Valley will slide eastward bringing

showers and a chance of thunderstorms...including severe

weather...tonight through Thursday morning. Much cooler and drier

air will follow late Thursday and Friday. High pressure will move

overhead with temperatures moderating during the weekend. A second

front will drop south through the area Tuesday.

&&

Near term /until 6 am Thursday morning/...

as of 300 PM Wednesday...tropical warmth and humidity will come to a

crashing halt late tonight as a strong cold front arrives from the

west. The transition from a tropical to an Arctic airmass will not

be an easy one...and severe thunderstorms appear possible across the

eastern Carolinas tonight.

Instability parameters are impressive for a cool-season event.

Although surface cape falls away to a few hundred j/kg after dark

with 75-100 j/kg of inhibition to overcome...starting to lift a

parcel from around 925 mb yields 600-1500 j/kg of uninhibited cape

aided by reasonably steep middle and upper level lapse rates. Unlike

our typical wintertime "severe shower" scenarios there could

actually be deep (40+ kft) convection tonight. Wind shear parameters

are also impressive: 50-60 knots of 0-6 km bulk shear...200-300 m^2/s^2

0-3 km helicity...and 50 knots wind speeds within 2500 feet of the

ground all point toward organized storms...perhaps even

supercells...with the potential for wind damage and tornadoes.

Synoptically a 300 mb jet streak will move east through the

Middle-Atlantic States tonight. This will place the eastern Carolinas

within the right-entrance region of the jet streak aiding in

deep-layer lift. Timing-wise...the last three runs (15-16-17z) of

the hrrr rapid update model all place the leading edge of the squall

line in western Darlington County at 7 PM...moving into Florence...

Dillon and Lumberton by 8 PM...and to the coast between 10 PM and

midnight. Our highest probability of precipitation (80-90%) extend from Florence...Marion

and Myrtle Beach northward through southeastern North Carolina.

Lower probability of precipitation (50-60%) are forecast south into the Georgetown area

where this first batch of convection may be too far north for

impacts. Additional showers and possibly thunderstorms may develop

behind this first batch...associated with subtle upper disturbances

working on residual elevated instability. This second batch of

convective activity could continue up until the time of the frontal

passage around daybreak Thursday.

Low temperatures tonight will be tricky with the surface cold front

likely arriving around 12z. We are forecasting middle 60s on the coast

and 59-63 inland...however there is significant bust potential in

either direction if the front is only a couple hours faster or slower

than is currently forecast.

&&

Short term /6 am Thursday morning through Friday night/...

as of 300 PM Wednesday...concern during the period revolves around

cold frontal passage and associated convection early

Thursday...followed by a drastic drop in temperatures which will

make it feel once again like early winter.

Strong cold front will be just inside western edge of the County Warning Area

Thursday morning and rapidly moving east. The uncertainty with

strength of convection revolves around the fact that frontal passage is

occurring at a non-ideal time with respect to instability.

However...parameters do suggest that convection will be ongoing at

the beginning of the period...especially across the eastern zones.

Ridge of low level Theta-E air remains in place through Thursday

morning along with steep middle level lapse rates and precipitable waters near 1.5

inches. Additionally...some positive vorticity advection near a vorticity lobe trailing through

the eastern Carolinas...locally enhanced diffluence in the right

entrance region of an exiting upper jet...and the cold front itself

will help force some lift and keep convection going through late

morning. 12 hour sref precipitation probs do not drop below 50 percent

until after 03z Friday...so although the severe threat after sunrise

Thursday appears limited will keep thunderstorm mention through late morning

along the coast...with some light rain possible until early afternoon.

Frontal passage occurs across the entire County Warning Area by the afternoon bringing an end to

precipitation through the remainder of the short term. Drying will occur

behind front as high pressure builds into the region...but Post

frontal cloud cover/stratus will exist through much of Thursday

before clearing on Friday.

The highest temperatures of the period will occur Thursday morning along

and ahead of the front...dropping rapidly in the afternoon as strong cold air advection

develops. Large bust potential on maximum temperatures Thursday depending on

exact timing of frontal passage...but expect temperatures around 60 inland...middle 60s

at the coast at daybreak Thursday...then falling through the day.

Mex/mav in agreement with maximum temperatures Friday in the middle 50s...but

guidance has a tendency to over forecast highs the day after a strong

frontal passage. Will trend maxes down to the low/middle 50s...but note this may

still be too warm. Mins each night will be in the middle 30s at the

coast...around 30 in the colder spots.

:lightning:

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well I've got a lot of catching up to do. I had to take care of parents this morning then the afternoon in Cherryville, so I've been out of the loop all day. The scud type clouds are really racing just above the ground here now, and I've had .93" of rain, and a decent thunderstorm a few minutes ago. Hope everyone stays safe tonight, its looking rough. By the way this is the event the models missed if you looked for explicitly on GFS and ECMWF about a week or 8 days ago I think. It had us in zonal type flow but the southern stream 5H closed low in Baja got ejected nicely. The GFS was first to catch on to it later on and I was skeptical of a non-event since the Bermuda ridge was nicely placed with supressed westerlies out west and strong s/w embedded.

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