"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".

Thursday, May 5, 2011

Chance of Showers/ Isolated Strong/Marginal Severe Storm East Coast Friday??

GFS Just Stream Forecast For Early Friday Afternoon. Area in Green Shows where the best chance of there being  a few isolated strong/marginally severe storm during the morning or  mid-afternoon hours

TODAY: No question at this time as to where the richest atmospheric resides this afternoon; that being over South Florida. It is rounding the ridge over NE Florida and trying to work up the west coast, as well as lifting slowly north everywhere as the high starts to move out late this afternoon.  In viewing the latest visible satellite image, we can see the more extensive cloudiness over South Florida with the expanding cloud field to the north as moisture tries to work north but can't with the ridge continue to be in place, but pulling off to the east this afternoon. As such, circulation around the high is creating some easterly winds this afternoon.   

Lower Clouds are interesting this afternoon if you happened to catch them just right. The low clouds are trying to form at the that level but are capping off with their tops making little curly tufts breaking off to the if catching stronger mid level west winds at that level, yet models are showing little in the way of winds up there. Could be they are simply hitting dryer air.  In the satellite image we see what looks a bit like a 'mackerel sky' pattern from the top down, with little north/south stretched bands of clouds such as in the red circle and over West Central Florida. This would indicate wind shear.

In close inspection the red circled area (for instance) is showing scalloped cloud patterns. Also, but hard to tell unless in animation, thin cirrus clouds are pushing quickly across from west to east in the increasing winds from 20,000 to 35,000 '
TODAY: Winds will continue from the ENE-NE this afternoon becoming more easterly and decreasing some tonight as the veer toward the SE overnight into the early morning hours. Shower activity should start to let up and shift more toward the West Coast up toward Tampa toward sunset and there after until around 8-9pm. Skies will remain partly cloudy over Central and South Florida, with a occasional mostly cloudy periods under either the cirrus clouds or increasing low - mid level clouds, especially heading toward sunset.  There is a slight chance of a few isolated coastal rain showers well after dark through early morning, but only worth a hint of mention.

EARLY FRIDAY: Virtually every model is painting a different picture just to set the record straight right from the get go. Therefore, confidence level is low.  With that said, I'll paint the two extremes of possibilities first.

1) Chance of showers and coastal thunderstorms as moisture returns north up the east coast, namely after 5-6am Friday. Best chance of showers is from Brevard County and south. One model is indicating a prelude to a prefrontal boundary to approach in the early afternoon to generate this activity, which would include thunder near South Brevard to Vero Beach - my take? I think the model is over done, and would leave it as a chance of showers along and east of I-95 during this transitional period, mainly from Volusia County and South.  Otherwise, day should break under partly cloudy to most cloudy skies, perhaps clearing a bit after mid-morning with heating of the day.

2) Noon time. Meanwhile, a weak low pressure circulation is expected to form roughly 150 miles west of West Central Florida in the Gulf underneath the lift provided by approaching very strong jet stream level winds of nearly 110 kts.  This circulation could be briefly closed, but not expecting the strength of the circulation as it stands now to make too great an impact in the overall scheme of things.  This circulation will cross Central Florida during the early - mid afternoon and likely lose its characteristics as it interacts with daytime heating over the land mass, of which I don't expect to be much (in the heating category).

By noon this area is expected to approach West Florida with showers and some isolated thunder perhaps and then enter and cross the spine of the state around noon-1pm, accompanied by showers and thunderstorms. Some of which could be strong. Over the past 36 hours the favored areas for a strong storm have been near Daytona,  Cocoa Beach/Cape Canaveral, and Vero/Ft. Pierce areas.

**However: If one looks at the Topsy-turvy NAM model, which for two days has showed variables such as favorable wind fields for tornadogenesis near St. Augustine (last night), to a strong storm at Cape Canaveral (in two previous runs) has now gone to the opposite extreme and shows barely any rain at all over the state tomorrow other than a few showers THE ENTIRE DAY.  This might be because of two reasons : 1) too much cloud cover in the upper levels associated with the jet streak cutting off instability potential below combined with a near uniform vertical  moisture profile throughout the boundary layer with no dry slots in an otherwise favorable one with  the cold temperatures aloft department for strong storms. In short, not enough heating to get anything going in the absence of a trigger (earlier, it showed numerous triggers) such as liitle vorticity maxima and vertical velocity pockets at various levels.

On the other hand, the GFS is the same with the timing of rain from west to east after noon time..but more generous with more showery type rains.  Even with cold air aloft which would favor strong/severe storms, accompanied by the strong upper level winds..the mid-level winds (in both cases) do not change much in strength with height and are fairly uniform in direction as well.  This leaves us with just cloudy skies and some rain showers with lack of instability at the low levels.

And on the third hand (should you have one), we have the local WRF model which, like the SPC one, is showing early morning (even before sunrise) thunderstorms/showers near the East coast between Daytona to Vero Beach. This is what I'm thinking might just be some showers if anything.

Both models then bring in the second wave in the afternoon associated with the weak surface low and the main 850-700mb short wave trough axis which actually is mainly to the north of the state  when again, there could be some thunderstorms.

To add to the post, numerical guidance is showing anything from  a 20% chance of rain to as much as 50% percent (The Weather Channel for my location reads 40%). Most of what we are hearing, I think, is just a best guest' ruf-estimate mish-mash' of all the available information, none of which will be close to reality in all likelihood.

  I do have a problem with believing there will be ample moisture for storms in the low-mid level state wid..and like an older version of the GFS which had the best moisture return limited to Central and South Florida, namely from Brevard County -Tampa and South, then favoring up the east side of the state toward at least Ormond Beach if not St. Augustine for an isolated storm, which could be strong if it holds of until mid-afternoon. Guidance hints at moisture north of Brevard but varies on when it will be there, and as such, whether it will just be showers or a strong/severe storm.  On model shows something very strong up there in fact...that is in the afternoon associated with the mid-level trough axis.

SPC is NOT making any mention of strong or severe storms. In fact, they don't even MENTION the state at all in their discussion (but do mention the mid-Atlantic region and somewhere else that i don't even recall where now though..but it wasn't Florida) despite the near favorable credentials for as said storms.

  In the world of weather though, the sum total of 'near favorable conditions and parameters' mater how many variables are 'close', does not add up to a sum total of 'severe' or 'strong". Often, everything  being "almost good enought' ends up with nothing other than clouds...that is, the NAM solution.  BTW: The RUC model today has been out to lunch. It did not even initialize the rains over Southeast this morning, and is not initializing them yet in successive runs since early in the morning. This means neither here nor there though in regard to tomorrow, since it does not run out that far in time.

I'll add just as an observation which is likely only 'in my mind' since I'm looking for answers;  that all of the NWS offices and SPC seem to be strangely 'mute' about tomorrow..sounding a bit in-definitive. But the point is, despite the strong winds aloft tomorrow (limited to the upper most levels and not the mid levels) and cold air aloft, weak instability seems to be the factor that would limit to some extent if not entirely an active weather day. Perhaps the NAM has it correct with almost nothing at all?  Only later model runs and closer scrutiny of satellite imagery will reveal what is to come.

In closure, as written in the prelude of today's post, should thunderstorms develop tomorrow, they could be strong to severe..most likely on the East Side of the state. Best chance of said will be from 1:30pm - 5pm from near Ormond Beach to Ft. Pierce. Other thunder storms could form just about anywhere, but would most favor the east coast. It will be interesting though to see what moves in on the West Coast earlier in the day. That, and how it trends as it pushes east (assuming something does move in)..will dictate how the end result of the day on the east side of the state.

Expect most if not all activity everywhere to end by sunset or shortly thereafter with a few stragglers, if there is anything to 'straggle'.

BEYOND: Quiet through the weekend as NW flow moves in. This might actually be a warm, dry NW flow..but it is way to sketchy to say for sure until after tomorrow is through. It does look to be dry though. Only exception would be continued shower chances far South Florida, possibly another shot at thunder close to Miami Metro area on Saturday, perhaps on Sunday if they play their cards right.

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