"But seeing they could not See; hearing they could not Hear"
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"From its chamber comes the whirlwind, and cold from the scattering winds." - Job 37:9.

"The wind blows to the south and turns to the north; round and round it goes, ever returning on its course".

Sunday, January 16, 2011

Rotating Storms/Severe Weather Possible Early Monday Afternoon/Evening!

Four (4) images included in this post. Descriptions of each follows below:
(1) The Global Forecast System (GFS) forecast for tonight at 7pm. We see a suspect area in the southern gulf, somewhat of an inverted trough near the Loop Current awaiting mid-upper level energy now crossing Mexico to be enhanced. Another low pressure system near the Texas Gulf Coast which created rains over East Texas yesterday which have spread into Louisiana this morning. Also note the trough mentioned in yesterday's post near the Cape. Still there today/tonight. (2) Forecast for 7am Monday morning. The suspect Gulf area is now being over-ridden by energy out of Mexico and surface or low level shortwave is enhanced and is moving ENE along a developing warm front across Central Florida (3) Current local temperature depiction shows the trough off shore which is being enhanced offshore by mid-level energy dropping through the upper level trough also offshore which runs down the U.S. Eastern Seaboard. Temperatures up and down the Florida east coast are nearly uniform, in fact the temperature at Cape Canaveral is one degree warmer than Ft. Lauderdale this morning, but mid/upper 50s are widespread. Some cities in the panhandle are below freezing still though.
(4) The Storm Prediction Center's (SPC) forecast for Monday shows a chance of severe weather over the south half of the state (south of the green line) is of no surprise as this was noted as a possibility in yesterday's post. The fact that this area is now in a "Slight Risk" (for severe weather) indicates an increased potential and/or confidence level that severe level category weather affects could be experienced within this area. The treat at time is in the form of wind gusts and/or tornadoes, but not severe category hail size.

TODAY: Very little change from yesterday with all the same features in place. We have the trough still in place off shore, which has organized a bit better as was suspected would occur due to it being continuously fed by mid-upper level energy from short wave troughs that have been crossing the Great Lakes region and the NE U.S., then dropping into the overall trough aloft located offshore. Over our heads, we still have a very stout inversion now located around 760mb or about 6500ft aloft. The atmosphere below that level continues to be fed/enhanced with increasing moisture and warmer dew point air which prevented overnight low temperatures from dropping much after 10pm last night over Central and South Florida. This inversion will remain through the day, and as such a cloud deck will persist off and on throughout the day in lower portions of the 'mid-levels' where moisture accumulates as clouds at the inversion level. Little temperature change from yesterday, with the extent of cloud cover dictating temperatures namely over Central Florida where clouds are currently most prevalent as well as proximity to bodies of cool water. Winds very light with a light sea breeze developing close to the coast this afternoon less than 10mph.

TONIGHT/MONDAY MORNING: The low near the Texas coast, albeit very weak, will continue east toward North Florida while the 'suspect area' in the South Central Gulf will be enhanced by mid/upper level energy generalized in description as a 'short wave' passing over it. As that surface region with supporting features passing over it becomes better organized so too will frontal boundaries. The main player being a warm front forming and lifting north from the Florida Straits to Central Florida by daybreak. This boundary finally merges with the trough that has been just offshore the Cape since Friday which will be the 'final starting point' to get the show rolling in terms of some active weather Monday afternoon and evening across the South Half of the Florida Peninsula. Remember my stating yesterday that boundary off the coast would eventually prove to be important which was why it was brought to attention (?).

Very mild temperatures again overnight with partly cloudy to cloudy skies with a SE wind developing ahead of the formulating northward moving warm front overnight. Clouds will be enhanced by isentropic lift (escalating upglide) along/ahead of the northward moving warm front within the increasingly juiced up air mass over the South Half of the state. Stratiform light rain (non-convective/non-thunderstorm type) could form along this boundary, especially on the west side of the state which will be stretched eastward toward Orlando overnight, but for the most part I mostly expect denser/greater extent of cloud coverage at day break, at which time the temperature should be close to 56-60F degrees. Warmer over South Florida.

MONDAY AFTERNOON EVENING: Weak low passes across North Florida with their own mixed bag of tricks (mainly in the form of rainfall and some elevated thunderstorms well north of the warm front), whereas south of the warm front storms will have a much better chance of becoming surface based and stronger, moving from the W-WSW while surface winds will be from the SSE-S.

As the Gulf System/shortwave trough approaches and crosses the state, strong winds aloft near 50 knots at 20,000 from the WSW will overspread the area while surface winds will remain from the south. This will result in 40+ knots of shear in effect, which will be locally enhanced where the low level jet of 30-35kts intersects the warm front. Net effect, as the warm, moist air rises through the veering atmospheric wind profile with height, storms that do develop within these rising currents can rotate as they build in height and rise through these low level columns of varying wind direction. Rotating, long lasting storms (supercells) and bowing line segments (which can be seen on radar imagery as a 'bowed' line) will be possible. Both entities are capable of producing wind gusts over 55mph and/or a tornado in the case of tomorrow's set up. This is why the Storm Prediction Center (SPC), seeing this potential tomorrow, has placed the south half of the state within a "Slight Risk", at least as of last night around 2A.M.

Again, the greatest risk for surface based storms will be south of the warm front, which appears will get about as far north as perhaps a line running through Brevard/Volusia County line westward toward Tampa Bay or a bit north of there before it runs into the more predominant area of high pressure that has resided across the Deep South and most northern portions of the Gulf of Mexico since Friday (which, by the way, has been responsible for the persistent cold mornings over north Florida and those locations in south central Georgia and Alabama.

Outside of the potential for some severe category weather/twisting winds, I'd say the chance of receiving measurable rain (0.01" or above) between sunrise and sunset Monday statewide is dang close to a 90% coverage of this area within that time frame. Some areas could get over 1.5" inches where more than one heavy storm crosses and/or where moderate rainfall persists. We could use the rainfall over much of Florida where severe and exceptional drought conditions currently exist and have been spreading in coverage since late spring.

SPECIAL NOTE: Any severe weather that may happen to develop, especially closer to Central Florida Monday afternoon/early evening, will likely be embedded within light rain and thus not be easily visible by looking outside. Thus, if interested, it is best to monitor local TV networks for what may be on the approach. If you hear thunder with each subsequent roll louder than the previous, chances are you are within, or close to, the path of an approaching storm which 'could' contain a tornado. The first visible sign of a storm's approach, should this end up being the case, will be a rapidly darkening sky toward a westerly direction, and with a fast storm motion anticipated, by the time one sees the dark sky it's almost already there!

BEYOND MONDAY (TUESDAY): Leaving this very brief due to much greater elements to tackle in the shorter term, but all other elements remain ALMOST status quo from yesterday's post. As noted, we again will not see just one front go though with a cool down, but instead see perhaps 3 fronts before colder air arrives which at this time might be just short of a week from now (quite a way down the road).

Tuesday, after this system moves on east and somewhat phases with the more northern low pressure that will cross North Florida off the Carolina Coast, winds will be westerly with a clearing sky; clearing enough, that is, to allow enough sunshine in to permit temperatures to be warmer behind the system than they will be on Monday ahead of it when clouds/rain/storms will be present. Additionally, along the east coast, the onshore wind component will be absent, thus colder Atlantic shelf waters air will not be advected to the A1A corridor. With a lot of ground moisture in place and a clearing sky overnight, and a brief pocket of high pressure passing overhead in the wake of Monday's system, morning fog could be widespread across the peninsula through mid-morning Tuesday. Otherwise, Tuesday looks rain free.

WEDNESDAY: Timing still looks in place for the second front to cross the state on Wednesday, which again could be accompanied by a period of just light rain, but more clouds seems more likely, but still no temperature falls with this front either except over North Florida, just some drier air throughout the atmosphere. It appears the first system on Monday will not scour/dry out the atmosphere entirely or enough to disregard the possibility of shower development, but chances are slim.

FRIDAY NIGHT/SATURDAY: Final front finally makes it through with a brief period of cold air, but nothing as bad as what we've felt with the past two cold blasts. Things are looking up. Each model run has been delaying the cold air, and then when they do bring it in it's not as cold as the previous model run nor lasts as long. Most notably over the the South half of the state.

(*I'd like to thank the reader who sent a link to the interactive Google maps based GFS weather model. I received your message in a responding comment to yesterday's post, but I'm not able to identify the sender. If you are reading this blog post today, thank you!)

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