Fall Phase II Begins Today - Winter Like Weather By Thanksgiving?

One Year Ago This Morning -  2016

TODAY: Weak frontal boundary characterized mainly by low and mid-level cloud cover and wind shift to northeast wind progressing southward will lay across South Central Florida near day break along a line near Central Brevard Country to south of Tampa Bay on the west coast. Just ahead to behind the boundary satellite imagery indicates what appears to be rather extensive cloud cover in the lower to mid-levels. There is no rain showing up along this boundary and none is anticipated but for perhaps later today for near St. Lucie - Palm Beach counties.

Wind behind the boundary is from the northeast gusting toward 20 mph and with cloud cover in the offing today, mainly for parts  of South Central Florida and northward, afternoon high temperatures will be inevitably cooler than the past few days other than for areas across South Florida where cloud cover will not be extensive and any affect from the dwindled boundary will be but hardly realized at all.

TONIGHT-SATURDAY: Some guidance indicates the chance of onshore moving rain-shower activity mainly for Indian River County northward toward Flagler County sometime after 2AM Saturday morning with the 4KM NAM model favoring Central - North Brevard to Volusia county initially.

What is to remain of the boundary either way will have lifted just a bit northward  but mainly above ground level. The surface boundary itself will have been fully absorbed into the synoptic scale high pressure area north of the state with little trace of its remains other than a moisture boundary.  No changes will be realized temperature/wind wise at the surface other than a bit of a veering more toward an ENE component. 

 Most guidance does indicate rain however, but exactly where is a tough call. Any rain that does fall would be 1/4" or less. All in all Saturday does not look like a wash-out anywhere, but cloud cover might continue to be a real bug-a-boo.

SUNDAY:  Sunday morning temperatures right near the coast will be closer to 70F (south of Daytona Beach) and cooler just a bit inland, but the bigger change and hence 'Fall Phase II" will be afternoon highs not reaching 80F (though some might see 80F from Vero and South) but more toward the middle-upper 70Fs depending on cloud cover. Chances for now favor upper 70Fs. 

Any rain-shower activity that might occur earlier on Saturday  will have worn thin and made history.

Otherwise, this day looks to be characterized by typically mid 'fall' like conditions of easterly to ENE wind and  little to no chance of rain -  cloud cover varying from scattered to perhaps a bit cloudy at times. 

MONDAY-TUESDAY: Decreasing cloud cover but not much warmer with highs remaining in the 70Fs . Coolest locations in the morning inland from the immediate east coast (where closer to 70F will be realized). 

WEDNESDAY: Another back door front presses down the state either later Tuesday into Wednesday. This front will only serve to re-enforce the air mass already in place. 

Rain chance  with this boundary appears to be even lower than with the one currently at hand. The difference with this boundary is that   cooler morning lows might be realized  along the immediate coast (lower-mid 60Fs and 50Fs inland).  

Those temperatures look very close to being 'here to stay' for the most part, though the GFS might be over-dramatizing the situation a bit (which would be typical for that model). 

Overall it looks like 80Fs will be increasingly few and far between and hence the 'Fall Phase II" period.

BEYOND:  The current trend is for continued cooler with this second boundary's passage, but with a lighter (less breezy conditions) wind from more of a northerly component come mid-late week. 

 The GFS is flopping around quite a bit lately heading toward the week of Thanksgiving and in parallel is the Climate CFSV2 model showing a similar picture.

 That being, not one , but several cold air intrusions beginning any time from around Tuesday of the week  of Thanksgiving to the day after Thanksgiving, and in both cases , it just goes downhill from there. 

By cold is meant  widespread morning lows in the 40Fs if not some 30Fs accompanied by the expected gusty winds (and wind chill factor) that herald in  'goodbye to fall'.   

 How reliable is that portion of the outlook? Not necessarily very, but then again: 

The CFSV2 was showing what the blogger would consider the 'typical first cold blast of the winter season' to occur during the first week of December (two days ago). History has shown that in many years the period between the 4th - 8th of December might be seen as a 'classic time frame' for that first true 'wintry feeling' cold air mass to intrude into and across the state. Such abrupt changes take a bit of getting accustomed to as coats suddenly get hauled out of hibernation.

However, the last run as of last night suddenly shifted that to Tuesday of the week of Thanksgiving, though the GFS which was showing something similar suddenly backed off. These discrepancies indicate the increasing disparities and uncertainty in long  range forecast model skill. 

Both of them  attribute any said wintry blast'  to a very large area of low pressure, and re-enforcements to it,  forming over the Eastern Great lakes and into Northeast states  with nowhere for the low to go but sit in place and deepen as it extends well into the Deep South -- with Florida being on the receiving end of air flowing southward along the back side of 'said prognosed region of blocked low pressure'.

For now, such speculation could well change.  On the other hand, one way or another, days ahead for those who favor truly cooler to colder dry weather is showing up on the horizon, if not for now, only hypothetically.

November 23, 2016