"But seeing they could not See; hearing they could not Hear"
“The views expressed herein are those of the author and do not necessarily represent those of the National Weather Service or affiliate/related organizations. Please consult .gov sites for official information”

"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, March 6, 2011

Tricky 8-Hour Forecast Today, Next Rain Chance Thursday

Image: Contrail from yesterday's Atlas V Launch. Skies cleared as expected in yesterday's post and winds were within the threshold to meet launch criteria as we know now. Surprised the contrail for this launch was so 'wimpy' considering that a 5000ft cloud deck had just cleared the pads area less than an hour before, so moisture was there. Contrail seemed to form, based on the sounding, where the atmosphere was the most dry.

TODAY: Scrambling this morning to make heads/tails of recent evolution of events since 7AM. As noted yesterday, the cold front shown in the image below still well out in the Gulf of Mexico this hour would be preceded by a pre-frontal trough to cross the East side of the state around the 1-3pm time frame. Surface winds after day break were to  veer to SW by late morning, and skies would be mostly cloudy. In fact, they did shift somewhat earlier prior to the area of rain showers that passed earlier this morning, but have backed to south or even SSE in some locations once again.

Some form of a pre-frontal trough evolved early and raced across the state at 70mph as the main storm system well to the north of Florida continues to lift away. Believe this event was associated with the main storm features / upper support pulling away.  This boundary was accompanied by some rain showers, one of which I watched race from Polk County to the coast near Cape Canaveral in about one hour's time. Was this the pre-frontal trough (if there is every going to be one at all?).  Winds behind this boundary continue to remain from the South (even SSE some locations) all the way over to the west side of the state after becoming SSW earlier this morning, meaning that either (A): More significant activity could be in the works for the hatched area shown in the image below later today as another pre-frontal trough forms along the region of lower pressures shown over West Central Florida in the image below, or; (B) All activity will await the actual front and be weak; OR (C) neither of these cases with near no activity anywhere across the state with a dry frontal passage. These seems unlikely.

MODEL DISCUSSION: In watching local WRF model runs and comparing to the NAM, GFS, and RUC it is plain that none of the models agree when it comes to the precipitation fields which is what today's post is pretty much all about, especially in light of the fires over all parts of Florida during the past week (there are many more fires than have made the 'headlines").  In other words, all areas could use some rain.  The RUC has been consistent with showing the bulk of the rains to occur over the East Side of the state south of Brevard county, in other words, SE Florida. On the other hand, local WRF runs are showing the bulk over East Central Florida where I've drawn the lavender hatching, with nearly nothing over South Florida other than some scattered showers near the coast. Very little north of  Daytona / Ormond Beach and western portions of North Central Florida.  However, latest RUC as I just peaked, is starting to share the wealthy just about everywhere. The NAM falls somewhere in between the two, but the GFS seemed to have a handle on the situation as of last night (and continues to remain the most consistent) that would match the local WRF run. So I am running with that, which happens to be the best case scenario for rains over Iron Horse (which by the way, last I saw is now 95% contained).

FORECAST: Clouds this morning, per visible satellite loops, should clear some over East Central from west to east between 11AM -2PM. Winds to remain primarily from the South to SSW (SSE southeast Florida).  Could see another pre-frontal trough develop near that area of low pressure shown on this map over West Central. However, this anomalous area of low pressure has been showing up every afternoon the past few days (oddly). Only difference today is that it popped quite early, normally reserved for the afternoon hours/thermally induced. Highs today under clouds in the low-mid 70s, upper 70s where clouds break more, and some low 80s South Florida, away from the coasts.

Best chance of rains will be from 12pm through 5pm spreading from West to east. If the WRF model is to verify, we'll have to see a broken line of showers developing in about 2 hours from now (or after noon time) on the west side of the state which will move east and strengthen once it reaches that area shown in purple above. This broken line of showers with embedded lightning (possibly) will progress east and south through the afternoon, never making it much further south than Ft. Pierce. SE Florida could see showers just about anytime toward noon and beyond, but is never impacted by the more organized activity further north.  Best chance of a thunder storm or heavier rain showers, again, in the purple area. All models agree that Central Brevard will have decent values of CAPE today no matter which model one looks at.  But the models do disagree overall of where the majority of this will exist which is important for storm sustenance.  

The other thing to consider is that the best wind fields will be from the Beach Line - Orlando - I/4 line and north, whereas the best instability will be further south.  Additionally, these 'best winds' are in the process of pulling off and away as I write, well before peak afternoon heating/instability time. 

This is the case time and time again, not only this year but others as well.  Storm systems this time of year are making weaker passes at the state in general, and lifting the strongest winds fields to the north of South Central and South Florida, leaving this area without the benefit of at least a high shear/low CAPE environment conducive for heavier rainfall, with just enough instability to generate rain showers. No matter how one slices the pie, once one gets north of Daytona/Ormond Beach the rain chances wane greatly.

So in a nut shell, expecting rain showers just about anytime from noon and beyond SE Florida. Maybe some heavier activity/thunder just off the coast later this afternoon. Best chance of rain/thunder East Central beginning 12-1pm in the area shown above, spreading west to east. Rain chances end all areas between 7-8pm, assuming they manifest at all. Keep the umbrella handy if heading out today, just in case. 

Any heavy rain shower or thunder could contain a very brief period of gusty winds of 40-45mph immediately preceding and during initial onset of rainfall. Again, assuming they occur.  WRF at this point is hopeful thinking in regards to rainfall right over what is left of the fire most inappropriately dubbed "Iron Horse". Be real, an official names a fire after where he CAN'T go to party during Bike Week. "Duh-Winning!". What a troll.

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