"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, April 21, 2013

Thunder with Heavy Downpours (and Small Hail/Coastal waterspouts Central?) Into Mid-Evening

Explanation Required for image (see below)
As usual, forecast is privy to signficant faults, but will base this one on the previous post of a few days ago despite big model differences between that time and the current time. Over the past 36 hours guidaance indicated that in the previous post where it was alluded to that we could see more rains (Central) by sunrise Sunday, that this would no longer happen. However, guidance is now realigning with that previous thinking, thus, this post will remain with persistence of the previous suppostiion:

TODAY: The surface warm front of the other day is washing out over South Florida and is forecast to invert as shown above in Light Blue (as noted in previous post). This could become a focus with showers or even thunder, especially near the Coast Central and more inland South Florida.  The highest helicity and energy index late today into tonight at this point is forecast to exist across Central Florida at and just offshore the coast along the 2000 ft., slightly 'elevated warm front' which is really only a wind shift line. Further north at a higher atmospheric level is another wind shift line of pseudo-warm front nature at 5000 ft along which mostly rain fall will occur or simply considerable cloudiness.

Impulses aloft will begin to move in from the west and cause the pattern to 'buckle north' in response to their approach. Some will be quite weak, others stronger. Vertical velocities as high  up as 20,000 feet above a only slightly unstable air mass might occur as a result of the energy riding over aloft in a very cold aloft (unusually so), could (emphasis) result in heavy down pours, with a few model runs indicating between 1- 2.5" inches of rain fall coastal Brevard in particular to Southern Volusia County.  Most of these bigger totals, if it occurs, would be due to very slow storm motion if at all long the 2000 ft boundary shown above where there will be little steering. 

The highest instability is expected to remain offshore though (and South Florida), and there will be some steering from west to east. Thus, expect the heaviest activity, should it materialize to remain mainly just off shore. There could be a surprise strong wind gust or surge here or there after 11AM and/or into tonight should large activity send outflow back to the coast from off shore. Also, if conditions materialize such that mid level to low level lift is enhanced, a waterspout might not be out of the question along SE Florida and off Central coasts.

Will note that as of this time before sunrise, the Storm Prediction Center is watching South Florida (only) for strong storms today which very well could end up being the case; however, given the current conditions closely matching up with the NAM (reluctantly), the RAP. and  the HRRR model guidance, will trend in that direction. If the GFS verifies, all calls are OFF.

The implication being, that it is the 2000 ft  'wind shift front" that will be the active parameter going into late day and early evening which is forecast to lie directly across Central by late afternoon if not a bit sooner as the impulses ride in from the west., missing South Florida entirely by that time.  In short, strong storms are possible over much of South Florida although I am only showing a smaller area, and then along the east coast up toward Southern or Central Volusia within 5-10 miles of the immediate coast. Suspect most activity will remain off shore. Those parameters which could result in small hail and strong wind gusts Central might get made up for with heavy localized rainfall instead, should said 'worst case scenario' end up evolving. Off shore waterspouts might become a forecast issue as well for those in the 'know' at the offices.

IN SUM TOTAL: Chances of heavier rain and or storms possible mainly near the coast and off shore today from current time, and again mid morning, and then again late afternoon into mid-late evening.

MONDAY: Rain chances or cloud cover continues into Monday , but rain ends for the remainder of the week. Cloud cover might persist a bit longer.

The more notable warming trend to occur Tuesday or Wednesday with coastal tempered temperatures due to onshore wind off the slowing warming ocean waters, but quite pleasant through the remainder of the week after Monday. The next rain chance comes next weekend as it appears now, but it is way too soon to say with any degree of certainty.

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