"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".

Saturday, October 15, 2011

Potentially Volatile Period Monday-Wednesday Awaits a Verdict

Full Moon and Jupiter Prior To Sunrise Friday

OVERALLTODAY: Short lived cold frontal impacts quickly modifying today, with the boundary along the northern Florida Straits. Breezy NE-NNEwinds will gradually veer to ENE-E on Monday through mid-day.

Rain and some isolated thunder has been on going across the Keys today, with totals already over 1" in some locations. This activity is expected to continue through tomorrow and gradually lift northward into Dade, Broward , and Southern Palm Beach Counties later today through Sunday afternoon bringing some larger rainfall totals to mainly Collier, Dade, Broward and at least the southern 1/2 of Palm Beach County.

Meanwhile, low pressure in the northern Great Lakes is expected to lift north toward James Bay and merge with another low pressure area trekking across Southern Canada through Tuesday. This second low pressure area will gradually aid to develop a stern cold front appendage across the North and Central Plains States after interacting with the Lee of the Rocky Mountain chain on Monday which will head toward the Deep South on Tuesday.

Further south, our old cold front, after having made a visit to the tropics, will be lifting north in response to the approaching trough out West,   as what I'll refer to as a modified sub-tropical warm front (for purposes here only). Sub-tropical in the sense that it will be transporting tropical moisture with it from the Caribbean. Low pressure in the far SW Caribbean appears will drift WNW-NW in the next 48 hours, but never congeal into a certified tropical system, at least not at this point.  

As this modified cold front turned sub-tropical warm front lifts north, so too does the rain chance into South Central Florida on Monday afternoon through evening. After 24 hours worth of various depictions (which have varied vastly), the GFS is back to where it started, only about 6-12 hours faster with the moisture and rain return northward.

SUNDAY: For the region north of Palm Beach county Sunday will be much like today, with continued high clouds and perhaps more mid-level clouds and a few lower clouds. Further south, rain showers and thunderstorms will continue, with several inches total anticipated as the boundary lifts north. Winds to remain from the NE-ENE but gradually veer toward the East on Monday and E-ESE with the approaching boundary.

TODAY: Green shows best chance of showers and thunder today. Yellow is the cold front of yesterday morning. Arrows point to anticipated lift of the boundary through Monday, with more northward motion from the east than from the west side. Low pressure in the SW Caribbean, low pressure near Lake Superior, and High Pressure which is generating the winds of today and Sunday over the Deep South combined with low pressure to the south. 

MONDAY: The GFS of 8AM has sped up both the approach of the warm front as well as that of the developing cold front in the Plains. Thus, since this is the first run of this nature, timing remains uncertain in regard to when the rain will reach Dead Central (mainly only at the coast initially until the cold front moves closer).  But all in all, the GFS and morning North American Model (NAM) match close enough that rain will work up to Southern Brevard by Monday afternoon with some reaching North Brevard by shortly after sunset. Meanwhile, rain will continue over South Florida but begin to decrease as the boundary lifts north. Just how far north this rain will proceed is another big question. Previous runs had the boundary clearing completely all of Florida, but with the now faster  approach of the cold front of the morning GFS, it never gets much further north than Southern Volusia County (??!) 

MONDAY NIGHT/TUESDAY: Potential  for volatile weather across any portion of Central Florida. To Be Re-Evaluated Through Sunday Morning.

The latest NAM and GFS agree in general on some of the wind fields that eventually are to unfold, but the timing differs by as much as 12 hours with the GFS being the faster for a change and more turbo-charged.

This is quite a surprise, so not sure exactly what to make of it yet. The ECMWF, per discussions, is not as dynamic with the depth of the approaching trough. This , in turn, would have a considerably assuaging effect on the outlook for this time frame (less potent).  Winds to become more ESE-SE-SSE on Monday night as the warm front lifts north and meets the gradually lifting out divergent southern branch jet stream winds. Showers increase, with the potential for thunder along the east coast from Ft. Pierce to Port Canaveral by sunrise.

Meanwhile, the GFS is forming a disturbance along the boundary in the SE Gulf which greatly impacts the southern Tampa Bay region toward Sarasota. Thus, the focus shifts from South Florida to Central Florida on Monday no matter which model of preference or timing is chosen.

With the faster approach of the morning GFS run, the bigger impact is now toward Tampa rather than the Big Bend area. 

The greater concern other than the astounding 9+ inches of rain the GFS forecasts on the West Coast is the  increasingly veering of winds with height. The latest GFS has a disturbance accompanying (or rather, responsible) for these winds to develop a  swath from near South Tampa Bay, across the state toward North Brevard during daylight Tuesday. On the other hand, the NAM is faster at this point, developing it overnight into Tuesday morning. In either case, wind profiles are supportive for what could be a tornado watch, lasting or varying in location for up to 18 hours anytime from post Midnight Tuesday morning through Tuesday afternoon.  The one ingredient missing during the time of favorable wind profiles is instability and only mediocre lapse rates. But given the wind fields shown, and the large loop in the hodograph (left ,below),  and using Orlando as a central point of reference..... :

...the chance of a tornado threat seems to be a viable option to investigate in greater detail with subsequent releases/versions of the NAM and GFS models. Accompanying which would be very heavy rain in thunderstorms and rainstorms working across the state. Thus, this is nothing like the event of last weekend.

WEDNESDAY: The actual cold front will essentially absorb the warm front, stretching out a mid level trough across North Central Florida. It looks like there could be yet another form of rain resultant from isentropic lift along and behind a rapidly moving but very shallow and potent  warm front turned cold front heading into the late Tuesday through Wednesday time frame.

 Again, timing remains a big issue at this point, but this was shown to occur in yesterday morning's run (but not shown in subsequent runs). So who knows. One run showed literally no rain event anywhere. But already, South Florida's (so far, just the Keys) event seems to be in the works.

THURSDAY: The cold front could sweep through, as is shown in several runs, but it will shallow, brief, and a bit  more 'potent' in the temperature department compared to what we are used to. On the other hand, like this last front it looks relatively brief, with a wind shift to the NNE to NE by Saturday morning. Even this temperature potency of lows in the 40Fs and 50Fs to South Florida is debatable, the GFS has tended to over extend itself with the previous two fronts in the long range.  In the mean time, the mid-level trough never really clears the state as high pressure builds rapidly behind this potentially dynamic system quite quickly well to the north of Florida.

FRIDAY: By this time, we might be talking about a wind surge moving in on northeast Florida and working down the coast, eventually engulfing the entire east coast by late Saturday. ..with rapidly modifying temperatures in tow. If the GFS is correct (which it seldom is this far out in time so far this season), mid-level temperatures are very cool aloft, but upper level temperatures are relatively warm. The net affect is considerable cloudiness and brief, low topped rain showers working down the coast with time during the course of next weekend.

By the next Saturday time frame I quit looking since  reliability in the model decreases logarithmically in the "Great Beyond", and next Saturday is getting beyond even that.    

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