I dont get this....Severe wx overnight JAX CWA???

[Anonymous]

The radar is void of precip except for one lonely storm over Camden Co, Ga...And we have lost daytime heating...Yet NWS is forecasting Severe wx for parts of the area overnight...

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HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE JACKSONVILLE FL
930 PM EDT TUE JUL 13 2004

FLZ020>025-030>033-035>038-040-GAZ132>136-149>154-162>166-141000-
ALACHUA-APPLING-ATKINSON-BACON-BAKER-BRADFORD-BRANTLEY-
CAMDEN (COASTAL)-CAMDEN (INLAND)-CHARLTON-CLAY-CLINCH-COFFEE-
COLUMBIA-DUVAL-ECHOLS-FLAGLER-GILCHRIST-GLYNN (COASTAL)-
GLYNN (INLAND)-HAMILTON-JEFF DAVIS-MARION-NASSAU-PIERCE-PUTNAM-
ST JOHNS-SUWANNEE-UNION-WARE-WAYNE-
930 PM EDT TUE JUL 13 2004

THIS OUTLOOK IS FOR NORTHEAST FLORIDA AND SOUTHEAST GEORGIA.

.DAY ONE...TONIGHT...
ISOLATED THUNDERSTORMS ACROSS THE AREA WILL WEAKEN BY MIDNIGHT. AN
UPPER LEVEL SYSTEM WILL MOVE INTO SOUTHEAST GEORGIA LATE TONIGHT
BRINGING A NEW LINE OF SHOWERS AND THUNDERSTORMS INTO THE AREA.
SOME OF THESE STORMS MAY BECOME SEVERE.


[Dan]

It might be hard to believe but the derecho that is currently slamming through Tennesse may be going fast enough to make it into Northern Florida by daylight, if it was to hold together. That's a big IF right now.

[USAwx1]

It will weaken considerably before it gets anywhere near FL.

the conditionally unstable 7.0-7.5 DEG c/km mid level lapse rates over TN drop off to less than 5.5 DEG C/km over SRN GA and FL.

Not to mention CAPE is decreasing and CIN is increasing due to loss of diurnal heating as evidenced by the increasing spread between the LCL and LFC.

any wetbulb temperature inversion would also put a cap on the damaging wind potetnial.

[ColdFront77]

I have been listening to my three NWS office NOAA Weather Radio broadcasts, like I often do, so I've obviously heard
about the first upper level system that moved at least into the Florida during today and the approaching one.

It will weaken considerably before it gets anywhere near FL.

the conditionally unstable 7.0-7.5 DEG c/km mid level lapse rates over TN drop off to less than 5.5 DEG C/km over SRN GA and FL.

Not to mention CAPE is decreasing and CIN is increasing due to loss of diurnal heating as evidenced by the increasing spread between the LCL and LFC.

any wetbulb temperature inversion would also put a cap on the damaging wind potetnial.

What is the reasoning behind forecasting thunderstorms overnight with the parameters indicating otherwise?

Upper level disturbances can and do bring activity at any time or day. I know the chances are more likely during the day (especially across Florida), however
the seabreeze and outflow boundaries can produce severe storms, too for days in a row without an upper level low pressure system near the state.

[USAwx1]

I have been listening to my three NWS office NOAA Weather Radio broadcasts, like I often do, so I've obviously heard
about the first upper level system that moved at least into the Florida during today and the approaching one.

It will weaken considerably before it gets anywhere near FL.

the conditionally unstable 7.0-7.5 DEG c/km mid level lapse rates over TN drop off to less than 5.5 DEG C/km over SRN GA and FL.

Not to mention CAPE is decreasing and CIN is increasing due to loss of diurnal heating as evidenced by the increasing spread between the LCL and LFC.

any wetbulb temperature inversion would also put a cap on the damaging wind potetnial.

What is the reasoning behind forecasting thunderstorms overnight with the parameters indicating otherwise?

Upper level disturbances can and do bring activity at any time or day. I know the chances are more likely during the day (especially across Florida), however
the seabreeze and outflow boundaries can produce severe storms, too for days in a row without an upper level low pressure system near the state.

Tom, It's harder at night to get severe weather for many reasons. Most specifically due to loss of instability.

Across the plains Warm air advection (WAA)as a reasult of the LLJ (low-level jet) can keep MCS's going through the night even as the boundary layer stabilizes.

Normally it takes stronger upward vertical motion to get a parcel to the required level when large amounts of CIN are present. CIN reflects a parcel which has a temperatue that is cooler than the surrounding environment and thus is not positively bouyant (In other words it sinks). it shows up as the negative area between the Surface and LFC on a skew-t plot. CAPE (positive energy in which a parcel is warmer than the surrounding environment and is encouraged to rise) is the area between the LFC and EL (Equilibrium Level)

if strong enough lift is present to push air parcels upward to the LFC -- thunderstorms can develop and become severe even in spite of less instability.

The relationship between CIN and the amount of lift required to overcome it can be defined by the following equation:

Wlift = sqrt2 * CIN

[ColdFront77]

I've known for years that it is more difficult for severe weather to occur at night/overnight.

The National Weather Service in Jacksonville, FL should obviously understands this, so they must being seeing data indicating possible thunderstorm development, severe or not.

Doesn't make any sense why the information have looked and/or are looking at is that much different than they have in their office in northeast Florida.