861 FXUS62 KKEY 041608 AFDKEY Area Forecast Discussion National Weather Service Key West FL 1108 AM EST Sat Jan 4 2020 .DISCUSSION... The weather will change abruptly over the Keys early this evening with the arrival of one of the season's stronger cold fronts. Until then, a warm and unseasonably muggy afternoon will prevail with a dearth of shower activity. The 12z KEY sounding showed a low- hanging subsidence inversion based near only 1,500 feet. Such a low inversion has squashed any shower activity. MIMIC Precipitable Water (PW) imagery also shows a wedge of drier air lifting north across the Keys right now, with PW values under 1" in the axis of driest air. Then queue cold front. The front currently extends southwest from near Jacksonville past Cedar Key into the Gulf. The latest round of 12z mesoscale models has delayed passage of the front across the Florida Keys until early this evening. At this point, we are just looking for a narrow, broken line of showers along the front. The thunderstorms that we see off the coast of Tampa Bay are not likely to get this far south, owing to warm mid-level temperatures under the northwest edge of the strong and vast upper high over the Caribbean. The low-level air mass behind the front should be the coolest so far this cold season for the Keys. Strong northerly breezes tonight funneling down the FL Peninsula will usher in a Sunday in which temperatures hold steady in the 60s and dewpoints fall into the 40s. A fully sunny sky should take the edge off the chill. By Sunday night, low-level winds will already be clocking around enough out of the northeast to modify the incoming air mass over the warm Gulf Stream waters off the Southeast Florida coast. So following a chilly Sunday afternoon, low temperatures on Sunday night will only fall off a little more into the upper 50s and lower 60s. Northeast breezes will continue to warm and modify the air mass from early Monday through Tuesday morning. The depth of low-level moisture return will remain fairly shallow during this time. So scattered coverage of strato-cumulus clouds will return, but showers are currently forecast to remain confined over warmer Gulf Stream waters and stay away from the island chain through Tue morning. && .MARINE... A strong cold front will reach the deep Gulf waters late this afternoon, then cross Florida Bay and the Straits early-mid evening. The front will come with a sudden wind shift out of the northwest and a sharp increase in wind speed. The wind increase over the Gulf waters will happen soon enough to issue a Small Craft Advisory. Expecting to issue a SCA for the remaining waters with the late afternoon marine forecast. In the wake of the cold front, a strong high pressure center will move from near the mouth of the Mississippi River on Sunday to north Florida on Monday. At first, this will maintain strong northerly breezes until Sunday evening, then winds will turn northeasterly and ease later Sunday night. A reinforcing cold front on Tuesday will freshen northerly breezes again. This time, the high pressure following the front will be even stronger will passing further north over the Southeast States on Wed, then merging with even stronger high pressure over the U.S. Mid-Atlantic region on Thu. Here on the southern periphery of the strong and sprawling high pressure area, our easterly winds will really crank up on Wed night and Thu, with strong breezes likely. && .AVIATION... VFR conditions will prevail at both island terminals for the rest of this morning and afternoon, with FEW to SCT cloud coverage expected through 22z and south to southwest winds near 10 knots. Confidence is not high that showers associated with an approaching cold front will survive and make it to the island chain, although this warrants at least mention of VCSH 00-03z at this time. Behind the cold front, windy and gusty conditions are expected, with at least MVFR conditions expected for a period late this evening due to low ceilings. && .CLIMATE... If this morning's low temperature of 76F holds at Key West, it would be a new record high minimum temperature for today. However, this record is not likely to stand, as this evening's cold front will cause temperatures to cool off quickly by late evening. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...Small Craft Advisory for GMZ033-034. && $$ Public/Marine/Fire...Haner Aviation/Nowcasts....BT Data Collection......BT Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest