STORM2K

Severe weather is looking possible Friday into Saturday

WEST CENTRAL AND SOUTHWEST FLORIDA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY AREA - RUSKIN FL
252 AM EST WED FEB 4 2004

.CURRENTLY...DISSIPATING COOL FRONT ACROSS THE SOUTHERN FA.
TEMPERATURES ARE IN THE MID TO UPPER 50S...WITH SOME MID TO UPPER 40S
IN LEVY COUNTY. SUBTROPICAL PLUME OF MOISTURE HAS BROUGHT MID AND
HIGH CLOUDS OVER THE NORTHERN ZONES...WITH PATCHY FOG BEGINNING TO
DEVELOP ACROSS THE CENTRAL AND SOUTHERN ZONES.

.SHORT TERM (TODAY - FRI)...COOL FRONT WILL CONTINUE LIMPING SE TODAY
AS HIGH PRESSURE BUILDS INTO THE REGION. COULD AGAIN SEE PATCHY FOG
AFTER MIDNIGHT TONIGHT WITH LIGHT FLOW AND MOIST LOW LEVELS. THE
RIDGE WILL THEN PUSH EAST AS UPPER TROUGH MOVES ACROSS THE PLAINS
STATES. ASSOCIATED SFC LOW TRACKS NORTHWEST OF THE AREA WITH THE COLD
FRONT PUSHING THROUGH THE CWA FRIDAY NIGHT THROUGH SAT MORNING. PRE-
FRONTAL CONVECTION IS POSSIBLE FRIDAY AFTERNOON AND HAVE KEPT
SCATTERED POPS IN WITH THE GREATEST CHANCE IN THE NORTH. TEMPERATURES
WILL CONTINUE TO BE ABOVE NORMAL UNDER E/SE FLOW.

.LONG TERM (FRI NIGHT - TUE)...ALL DATA NOW LOCKING IN ON A STORMY
NIGHT FRI AS STRONG FRONT (RELATIVE TO AIR MASSES ON EITHER SIDE)
ACCELERATES THROUGH THE AREA. TIMING OF HEAVIEST PCPN IS SQUARELY
IN THE 00Z-12Z TIME FRAME...AND HAVE ADJUSTED QPF VALUES UPWARD TO
MATCH. AS FOR PCPN TYPE...DESPITE SOMEWHAT COOLISH SHELF WATERS
(MID 60S)...DYNAMICS HAVE STRENGTHENED A BIT SINCE THIS TIME
YESTERDAY IN ALL MODELS...ESPECIALLY THE GFS AND CANADIAN GEM.
THEREFORE...EXPECT A SQUALL LINE OF TSTMS FOLLOWED BY SEVERAL HOURS
OF STRATIFORM RAIN...ENDING WITH RESIDUAL LIGHT SHOWERS SAT MORNING.

THREAT OF STRONG TO SEVERE STORMS STILL IN QUESTION...BUT WE SHOULD
HAVE A BETTER IDEA THIS TIME TOMORROW. CERTAINLY...WIND FIELDS AND
LOCATION OF RR QUAD OF 130 KT JET SUPPORT THE THREAT...WHICH LOOKS
TO BE BEST FROM TAMPA BAY N. STAY TUNED.

THEREAFTER...THE QUESTION BECOMES HOW COOL WILL IT GET SAT NIGHT/SUN?
GFS/CANADIAN MODELS BOTH SHOW EXCELLENT LOW LEVEL THICKNESS COOLING
WHILE THE NOGAPS HOLDS 850 TEMPS ERRONEOUSLY HIGH (PERHAPS
GULF/ATLC FEEDBACK OVER THE PENINSULA). AMOUNT OF COOLING APPEARS...................................................

FORECAST FOR FRIDAY NIGHT NEAR MIDNIGHT FOR TAMPA BAY AREA.
For whoever lives near the Tampa Area, This forecast is for you.

Dewpoint Forecast shows a dewpoint at 64= 50%
Surface Temperature will be at 65 degrees= 20%
Low Level Jet inflow at 850mb will be at 30-35 knots= 50%
Surface Moisture Carrying Wind= 100%
700MB Dry Air Carrying wind= 100%
Upper Level Jet Stream will be blowing at 95 knots= 25%
500MB vort values= 20%

Probability of Severe Thunderstorms is 56%
So with that 56% it corresponds with my charts on........

Moderate/High Severe Thunderstorm Risk
GREEN ALERT
YELLOW ALERT
ORANGE ALERT
RED ALERT
PINK ALERT

On a weather map, it would be SEVERE red shading.
WEAK THUNDERSTORMS
STRONG THUNDERSTORMS
SEVERE THUNDERSTORMS

Thunderstorm probability is 70%
no Thunderstorms expected.
Slight Chance
Chance
Possible
Likely
Run For the Hills

CAPE=25%

HELICITY=300-350 STRONG TORNADOES POSSBILE!
HIGHEST VALUES F2-F3

Hail values.

75%
100%
25%
50%
50%

added together is 300 or...

3/4 inch hail size expected or SEVERE THRESHOLD

Forecast Discussion.
Well They beat me to the squall line as it looks like one will go through. This squall line should be a fast and sharp one at that. looking to your west from Tampa, you could be treated to an intense lightning show on friday night. 6pmEST models show the activity and dynamics well off to the west. 6am Saturday shows them to the East of the area. In between that time, i'd say 12am Saturday morning, the squall should arrive, bringing a Severe Threat overnight. Dewpoints will be high, as the temperature sits near 70. A unstable setup is already there with those two values. Severe Activity should start to rapidly slow down as the squall line passes.

Within the Squall Line.
The squall line enviroment has a 56% potential for becoming Severe. Dewpoint will be high, and temps are okay, but enough. The Jet stream will be nearing 100kts, so enough divergence for severe weather. vort max will be lower than 12 value, so not much vort vertical divergence to work with, however all the values cancel having to need a positive vort value. Helicity Values from 300 to 350, so Strong Tornadoes are possible, with the highest possible being between F2-F3. CAPE in this squall will be around 500, so slightly unstable CAPE there. All together, this Squall Line should pack a powerful punch on Tampa within this 6hr period.

Severe Watches I would issue.

Severe Thunderstorm Watch for Friday Night from 9pmCST to 3amCST.
a 6 hr Watch.

Tornado Watch from from 10pmCST to 3amCST.

Kevin Martin

Thanks Kevin..sounds like things could get a tad turbulent around here Friday Night

Thanks Kevin and Jonathan.. Sounds a little eerie..

look at the low pressure system rolling through the southern midwest/south tonight. by tomorrow evening that thing will have a tail. looks like my area could be in for some rough weather friday night.

just can't get over the size of the low pressure complex. it's downright huge.

Florida Panhandle looks to have the best chance of storms as it looks like the majority of the severe weather threat will go around the Penisula as usual....

Nws Jacksonville....
BULK OF PRECIP STILL SLATED TO MOVE ACROSS THE
AREA FRIDAY AFTN AND EVENING. STRONG TSTMS STILL APPEAR POSSIBLE.
HOWEVER...AS USUAL...BEST DYNAMICS LIFT JUST N OF AREA AND BEST
INSTABILITY REMAINS ALONG GULF COAST. LOW-LEVEL JET WILL ALLOW ANY
SHOWERS OR STORMS TO PRODUCE WIND GUSTS IN EXCESS OF 40 MPH.


NWS Tallahassee...
THE POTENTIAL FOR SEVERE WEATHER ALSO EXISTS ON
FRIDAY...WITH THE LATEST ETA SOUNDINGS SHOWING PLENTY OF AVAILABLE
MOISTURE ALONG WITH VERTICAL WIND PROFILES WHICH ARE QUITE
FAVORABLE. WITH A PROJECTED >50 KT JET AT 850 MB AND BELOW ALONG
WITH STORM RELATIVE HELICITIES APPROACHING 400 M2/S...THE MAIN
LIMITING FACTOR FOR SEVERE WEATHER ONCE AGAIN IS LIKELY TO BE
INSTABILITY. AT THIS TIME IT LOOKS MARGINALLY FAVORABLE...BUT A
SMALL CHANGE EITHER WAY COULD MAKE A BIG DIFFERENCE TO OUR
POTENTIAL. AS FOR OUR RAINFALL POTENTIAL...WOULD NOT BE SURPRISED TO
SEE GENERAL 1-2 INCH AMOUNTS ALONG THE COLD FRONT WITH ISOLATED 3
INCH TOTALS...BUT WITH THE SYSTEM BECOMING INCREASINGLY
PROGRESSIVE...AND SINCE OUR AREA WILL MISS OUT ON ANY OF THE INITIAL
ISENTROPIC PRECIP...DO NOT SEE THE NEED FOR A FLOOD WATCH AT THIS
TIME.

NWS Melbourne....
FRIDAY NIGHT...LINE OF WEAKENING STORMS WILL CROSS FCST AREA DURING
THE OVERNIGHT HOURS. BOTH ETA AND GFS AGREE IN LIFTING BEST SUPPORT
N OF FCST AREA. WHILE STRONG UL JET WILL BE TO OUR N...BEST
DIVERGENCE WILL BE DISPLACED BEHIND THE CURVED JET. PROGRESSIVE
TROUGH SHOWS NO SIGNS OF ADDITIONAL DEEPENING AND AS A RESULT NO
REAL THERMAL MODIFICATION OCCURS ALOFT RESTRICTING OVER INSTABILITY.
H85 WNDS DO INCREASE UPWARDS OF 35-40KT OVER THE NRN AREAS BUT LOW
LEVEL FLOW VEERS WELL IN ADVANCE OF BNDRY. MAIN THREAT WILL BE FROM
STRONG STRAIGHT LINE WNDS AND MAINLY OVER THE NORTH.

Sounds like Central Florida has again dodged a bullet lol.. I'm getting tired of being told "severe weather" and nothing comes. This could turn into another 1998 scenario..

People could ignore the warnings for so long not realizing it's actually the real thing..

It continues to look like the storms will begin to loose their punch as they enter the Peninsula as the slight risk area is to the left of the Yankeetown - St Augustine line.

NWS Tallahassee

THE ISSUE TODAY IS NOT WHETHER WE WILL HAVE RAIN...BUT
WHAT OUR SEVERE WEATHER PROSPECTS ARE. DIFFLUENT UPPER JET STRUCTURE
EVIDENT THURSDAY AFTERNOON AND EVENING OVER MS AND NRN AL IS PROGGED
BY MODELS TO DETERIORATE...IMPLYING LESS IMPRESSIVE UPPER DIVERGENCE
TODAY OVER OUR CWFA RELATIVE TO WHAT HAS OCCURRED UPSTREAM.
HOWEVER...LOW LEVEL FLOW REMAINS STRONG...WITH 0-1KM SHEAR STILL AT
OR ABOVE 30 KT OVER OUR CWFA THIS AFTERNOON. INSTABILITY WILL BE
MARGINAL. SPC ALSO FORESEES A SLIGHT RISK FOR SEVERE WEATHER OVER
OUR ENTIRE CWFA. PLEASE SEE THE SWODY1 FOR MORE INFORMATION. WE
EXPECT THE LINE OF THUNDERSTORMS TO BE PROGRESSIVE ENOUGH TO
PRECLUDE A SIGNIFICANT FLOODING THREAT.

NWS Jax...

SQUALL LINE WILL BEGIN TRANSLATING MORE QUICKLY TO THE
E TODAY...ENTERING OUR W ZONES DURING THE AFTN. SPC STILL HAS AREA
IN A SLIGHT RISK TODAY. A 50 KT 850MB JET WILL TRAVERSE THE AREA
COINCIDING WITH SQUALL LINE. LOW-LEVEL INSTABILITY MAY BE A BIT
UNDERESTIMATED CONSIDERING THE NEARLY 2 DAYS OF SOLID S INFLUX OF
WARMTH AND MOISTURE. HOWEVER...MID-LEVELS FAIRLY WARM AS WELL.
UPPER JET APPEARS TO LAG BEHIND THE LINE AS IT MOVES THROUGH. UPPER
DIVERGENCE LOOKS TO BE FAIRLY STRONG THRU THE DAY. ONLY LOOKS LIKE
A NARROW ZONE OF PVA...AND NOT PARTICULARLY STRONG. PRESENT THINKING
IS NARROW LINE OF STRONG TSTMS WILL HOLD TOGETHER AS THEY MOVE
ACROSS THE AREA...WITH ISOLATED SVR STORMS POSSIBLE...MAINLY OVER
EXTREME W ZONES. AS LINE MOVES INTO E SECTIONS...DIURNAL COOLING
CYCLE WILL HAVE BEGUN...SOMEWHAT LIMITING INSTABILITY. OF COURSE...
ANY WELL-DEVELOPED SHOWER MAY BE CAPABLE OF TRANSPORTING 40+ KTS OF
WIND TO THE SFC.

NWS Melbourne...

FRONT SHOULD MOVE ACROSS THE FORECAST AREA AND BE OVER THE
SOUTHERN COUNTIES AROUND DAY BREAK. LATEST SATELLITE LOOPS ARE NOT
THAT IMPRESSIVE OVER THE NORTHEASTERN GULF OF MEXICO AND ARE SHOWING
THE ENTIRE TRAILING END OF THE COLD FRONT LIFTING NORTH. THERE IS
DIFFERENCES BETWEEN THE GFS/MAV AND THE ETA/FWC POPS. THE MAV
NUMBERS STILL HOLD LIKELY/70 POPS FOR THE NORTHERN CWA TONIGHT WHILE
THE ETA AND FWC ARE MORE CONSERVATIVE WITH 6 HOUR POPS AROUND 30
PERCENT. WILL LEAVE THE CURRENT 60 POP FOR THE NORTHERN CWA BUT
TRANSITION TO 30 POPS VERO BEACH SOUTH. OVERNIGHT TIME HEIGHT CROSS
SECTIONS SHOW PRECIPITATION STARTING OVER THE NORTHERN CWA LATE
AFTERNOON AND WORKING ITS WAY DOWN THE PENINSULA OVERNIGHT. THE
CROSS SECTIONS ALSO SHOW THE DECREASING SUPPORT THE FURTHER SOUTH
ONE GOES.

NWS Tampa...

WHILE THE BULK OF THE UPPER LEVEL
ENERGY SHOULD STAY NORTH OF THE AREA THERE WILL BE ENOUGH FOR A
SLIGHT RISK OF SEVERE TSTMS ACROSS THE NORTH END OF THE CWFA AND
LIKELY POPS AS THE FRONT ROLLS DOWN THE AREA TONIGHT.

That is definitely 1 mean looking line of storms. Guess we shall see what happens

The activity in the northeastern Gulf of Mexico has developed some since the disorganization in the last several hours.

Rockstock wrote:FORECAST FOR FRIDAY NIGHT NEAR MIDNIGHT FOR TAMPA BAY AREA.
For whoever lives near the Tampa Area, This forecast is for you.

Dewpoint Forecast shows a dewpoint at 64= 50%
Surface Temperature will be at 65 degrees= 20%
Low Level Jet inflow at 850mb will be at 30-35 knots= 50%
Surface Moisture Carrying Wind= 100%
700MB Dry Air Carrying wind= 100%
Upper Level Jet Stream will be blowing at 95 knots= 25%
500MB vort values= 20%

Probability of Severe Thunderstorms is 56%
So with that 56% it corresponds with my charts on........

Moderate/High Severe Thunderstorm Risk
GREEN ALERT
YELLOW ALERT
ORANGE ALERT
RED ALERT
PINK ALERT

On a weather map, it would be SEVERE red shading.
WEAK THUNDERSTORMS
STRONG THUNDERSTORMS
SEVERE THUNDERSTORMS

Thunderstorm probability is 70%
no Thunderstorms expected.
Slight Chance
Chance
Possible
Likely
Run For the Hills

CAPE=25%

HELICITY=300-350 STRONG TORNADOES POSSBILE!
HIGHEST VALUES F2-F3

Hail values.

75%
100%
25%
50%
50%

added together is 300 or...

3/4 inch hail size expected or SEVERE THRESHOLD

Forecast Discussion.
Well They beat me to the squall line as it looks like one will go through. This squall line should be a fast and sharp one at that. looking to your west from Tampa, you could be treated to an intense lightning show on friday night. 6pmEST models show the activity and dynamics well off to the west. 6am Saturday shows them to the East of the area. In between that time, i'd say 12am Saturday morning, the squall should arrive, bringing a Severe Threat overnight. Dewpoints will be high, as the temperature sits near 70. A unstable setup is already there with those two values. Severe Activity should start to rapidly slow down as the squall line passes.

Within the Squall Line.
The squall line enviroment has a 56% potential for becoming Severe. Dewpoint will be high, and temps are okay, but enough. The Jet stream will be nearing 100kts, so enough divergence for severe weather. vort max will be lower than 12 value, so not much vort vertical divergence to work with, however all the values cancel having to need a positive vort value. Helicity Values from 300 to 350, so Strong Tornadoes are possible, with the highest possible being between F2-F3. CAPE in this squall will be around 500, so slightly unstable CAPE there. All together, this Squall Line should pack a powerful punch on Tampa within this 6hr period.

Severe Watches I would issue.

Severe Thunderstorm Watch for Friday Night from 9pmCST to 3amCST.
a 6 hr Watch.

Tornado Watch from from 10pmCST to 3amCST.

Kevin Martin

thats an interesting system you have going there. but i dont think its very effective when instability is lacking. you may want to modify it slightly to compensate for that weakness.

but when one has weak ML (mixed layer) CAPE values, generally less than 1000 J/kg (joules per kilogram) but strong helicity values (above 200 m^2/s^2) its usually a signal that instabilty is weak, and shear is very strong, so its likely that the Bulk richardson number is lower than the thershold needed for tornadic development.

thus, as a result you would need tremendous vertical motions in order to lift parcels to the where they need to be for convective initiation to occur. otherwise your left with little more than weak/low topped convetion, incapible of tapping the shear.