Area Forecast Discussion
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FXUS62 KKEY 161754

Area Forecast Discussion
National Weather Service Key West FL
154 PM EDT Mon Jul 16 2018

The cu-line has been struggling to organize so far this afternoon.
Vertical development seems limited, which would point towards dry
air entrainment. However, it is early days yet, and it is still
possible the cu-line can coalesce and produce a few showers and
maybe a thunderstorm. The line is setting up north of the lower
Keys, as flow in the lowest kilometer has organized out of the
southeast, albeit relatively light. From a larger perspective, a
few showers and occasionally a thunderstorm have persisted in the
Gulf waters west of the mainland, spawned from the old mainland
land breeze and have managed to develop new convection from
outflow. The Straits are mostly clear outside of a few small

Model analysis, as well as examination of layer precipitable
water and the GOES RGB dust product find a diffuse SAL layer just
to our southeast moving into the region. This will be occurring
during the overnight hours, so how much the leading edge of this
drier mid-level air will trigger convection is questionable. From
Tuesday through Saturday morning, SAL air will dominate the mid
levels of the troposphere holding precipitation chances to only
slight chance. There is one interesting feature in the GFS model,
which is not as robust in the other available GSM, is a slot of
moist air moving up from the Caribbean around Wednesday morning.
The GFS shows this linking with a shear zone on the tail end of
the high amplitude trough setting up along the eastern seaborad,
and scavenging the SAL overhead. The other model shows only a
shallow feature, and no larger scale shear zone dipping into south
Florida and the straits. If the GFS were to come to fruition, the
chance of rain on Wednesday to Wednesday night would be much
higher. Will hold off on forecast changes until there is more of
consensus among models. Winds through the entirety of the
forecast, through the weekend and into Monday, will remain light
and variable at times. The large trough along the east coast will
keep the Bermuda high at bay, and leave the Keys and coastal
waters in a dynamically forced col once again with troughing over
the peninsula, and a weak ridge axis sitting over the Keys. By
Saturday evening and into next week the SAL will begin to wash out
with moisture returning in the mid levels. Out of respect for
climatology, will hold my horizon pops from Saturday evening
through Monday at low chance.


Light easterly breezes, becoming variable at times, will persist
over all Florida Keys coastal waters through this evening and
overnight. There will be isolated showers and thunderstorms which
will drift slowly towards the west northwest.


VFR conditions will prevail at both EYW and MTH terminals. Low
confidence for thunderstorms at either terminal. Cloud line
showers drifting northward could briefly produce MVFR conditions.
South winds less than 8 knots will become southeast at less than 5
knots after 17/00Z .


Key West  83  92  83  92 / 20 20 20 20
Marathon  82  92  83  93 / 20 20 20 20




Data Collection......BT

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