Area Forecast Discussion
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FXUS62 KKEY 181834

Area Forecast Discussion
National Weather Service Key West FL
234 PM EDT Wed Jul 18 2018

The Saharan Layer is well entrenched over the Keys and coastal
waters. No showers can be found over the area, somewhat rare for
a late July afternoon. Any efforts towards cu- line development
have been quickly squashed, and even small streamers off the
islands rapidly dissipated. Winds through 3 kft over the region
have organized out of the southeast to south near 5 knots through
the morning and early afternoon.

Overnight through Thursday night...Persistence will rule over the
next 24 hours at least. Conditions are just too dry and stable
for any significant convection to develop. Effectively removed
pops from the forecast by dropping them to a nickel. For the most
part, winds will be variable near 5 knots as the axis of weak
ridging meanders over the area. Will go with dime pops for
Thursday night just out of respect for the wet season and
nocturnal marine boundary layer instability. However, the dime
pops are probably an overestimation.

Friday through Saturday...Forecast guidance points towards a
temporary slight increase in moisture through the mid troposphere
moving around the western periphery of the Bermuda high. This
relative moisture is associated with a mid and upper level shear
zone induced by a high amplitude trough digging into northeastern
gulf and north Florida. This may be enough to bring about isolated
showers and a possible thunderstorm or two.


Saturday night through Wednesday...By Saturday night the SAL
slowly begins to get scavenged by the approaching shear zone and
associated vorticity lobe. By Sunday evening the trough will be
digging into south Florida. At the very least, this will eliminate
the last vestiges of the SAL and increase rain chances above
climatology. How far above at this point is somewhat uncertain,
and depends on the proximity of vorticity and upper level
diffluence. The low chance pops inherited will remain. If the
model forecast comes to fruition, it will probably be necessary
to increase rain chances in subsequent forecasts for Monday
through Wednesday (possibly substantially).


Light breezes will persist this evening though tomorrow
(Thursday), becoming variable at times. Skies should be mostly
clear with only a shower or two around, mainly in the Gulf waters
north of the lower Keys.


VFR conditions will prevail at both EYW and MTH terminals. Light
southeast winds at less than 8 knots will become variable at less
than 5 knots after 18/20Z at MTH and 18/22Z at EYW. Dry airmass in
place will minimize rain chances through the weekend.


Key West  82  93  82  92 / -  -  10 20
Marathon  81  95  81  93 / -  -  10 20




Data Collection......BT

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