FXUS63 KJKL 060323 AAA

National Weather Service Jackson KY
1123 PM EDT Fri Jun 5 2020

Issued at 1123 PM EDT FRI JUN 5 2020

Some scattered low level clouds are noted across portions of the
area. Otherwise, besides some thin cirrus clouds, more
concentrated to our west, skies are mostly clear. The latest
Nighttime Microphysics channel is highlighting the fog well,
having already set in across our east and southeast. Models seem
to have trended a bit drier aloft tonight, and with general 500 mb
height rises and at least modest subsidence expected, nearly calm
winds, and saturated low levels, expect the fog to continue to
expand and become locally dense in the typical places. As such,
have issued a Dense Fog Advisory overnight into early Saturday
morning. Forecast lows continue to look on target and have only
made some minor adjustments based on the trends in observations.
Updates have been sent.

UPDATE Issued at 822 PM EDT FRI JUN 5 2020

Clouds have cleared across most of the area early this evening. A
few showers are dotting portions of the I-75 corridor, but these
should dissipate in the next hour as we lose heating. Have mainly
freshened up the hourly temperatures and dew points, accounting
for the latest trends in observations. Otherwise, the forecast
remains on track. Will reassess the dense fog potential in a few
more hours. Certainly, the quicker clearing favors its
development; however, will continue to monitor model and satellite
trends for some additional cloud cover that may redevelop
overnight. Updates have been sent.


.SHORT TERM...(This evening through Saturday night)
Issued at 442 PM EDT FRI JUN 5 2020

A shortwave trough aloft which brought showers and isolated
thunderstorms to the area overnight and into today is departing to
the east. The only remaining showers are in far southeast KY, and
will exit with the wave early this evening. Dry air is moving into
the region in the mid/upper levels in its wake, but there is no
change in surface air mass. With relatively light winds clear to
partly cloudy skies, this will set us up for fog development. It
should become widespread and dense in many valleys. The main
question concerns how much it spreads. This will need to be
monitored for advisory potential tonight.

Under weak west to northwest flow aloft, a weak cold front will
move through the area on Saturday. A moist and unstable surface
air mass will be in place, and a few thunderstorms can't be ruled
out. However, as mentioned, the mid/upper levels will be dry, and
there will not be any significant support aloft, so the
probability for precip is barely mentionable. The front will
slip to our south on Saturday night and a drier and somewhat
cooler air mass will arrive.

.LONG TERM...(Sunday through Friday)
Issued at 500 PM EDT FRI JUN 5 2020

A welcome respite from the heat, humidity and rain chances is in
store for Sunday before another round of mid-summer heat arrives
for Monday and especially Tuesday. The interaction between the
remnants of tropical storm Cristobal and a couple of frontal
boundaries will bring the renewed threat for showers or storms
from late Tuesday through early Thursday.

Model agreement remains fairly good through the extended period.
The 12Z Sunday model analysis shows an upper level trough axis
along the Mid-Atlantic and Northeast US coastlines. Meanwhile, an
~ 590 dam high will drift across the Mid-Mississippi Valley on
Sunday as it squeezes north of tropical (or possibly subtropical)
storm Cristobal spinning over the northern Gulf of Mexico. By 00z
Monday, the upper level high will morph into a rex-type blocking
ridge, extending from the Southeast US northwestward across the
Ohio Valley and Lower Great Lakes. The ridge will slowly break
down through mid-week as Cristobal’s circulation rides along the
western periphery of the ridge. At the surface, Saturday’s cool
front will remain stalled well to our south Sunday into Monday
while high pressure drifts from the Great Lakes to the Mid-
Atlantic and Cristobal makes landfall along the Louisiana Coast.
Current model runs suggest that the low will track along or west
of the Mississippi Valley through Tuesday, keeping the greatest
impacts to our west. By later Tuesday, the stalled cool front will
gradually be pushed back northward as a warm front while
Cristobal transitions into an unseasonably deep mid-latitude
cyclone. A trailing cold front sweeps through late Wednesday or
early Thursday.

In terms of sensible weather, a gorgeously sunny day is in store
for Sunday as the nearby trough and associated cooler air aloft
will cap highs in the low to mid 80s while dew points fall off
into the 50s! Clear skies, light winds, and very dry air aloft
should allow temperatures to radiatively cool Sunday night into
low 50s through the most sheltered hollows to the lower 60s over
over the ridges and in broad southwest valleys. The low-level flow
turns more ESE on Monday as we become situated between the ridge
axis and Cristobal. The resultant downsloped flow should
facilitate the mixing down of some very dry and potentially
warmer air aloft. As a result, temperatures are expected to soar
towards 90 while dew points stay in the 50s for much of the day.
Another very warm day is in store for Tuesday with widespread
highs in the upper 80s to lower 90s, although temperatures over
southwest portions of the CWA might be capped by some increasing
cloudiness. Shower and storm chances will also start to ramp up
late Tuesday as the transitioning tropical system lifts along or
west of the Mississippi and pushes its developing warm front
toward the area. Additional shower and storm chances are expected
into Wednesday night as Cristobal’s remnants accelerate
northward across Lake Superior toward James Bay while sending a
trailing cold front across the area. At this point, the models
still place the heaviest rains along to the Gulf Coast and
along/west of the Mississippi River. Even so, a watchful eye on
this system is still warranted as a plume of deep tropical
moisture will be pushed eastward by the fronts and the 12Z NAEFS
and ENS indicate PWATs nearing/exceeding the 99th percentile with
respect to climatology. Given this very moist air mass, any
showers or storms that form would be capable of torrential


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)

VFR conditions and mostly clear skies can be expected through this
evening, before fog develops closer to midnight. This will form in
the deeper river valleys initially, and then expand with time.
Have included IFR at all TAF sites for a period during the overnight
and early morning hours of Saturday; however, there is potential
for LIFR or lower. The only fly in the ointment is the possibility
of some clouds redeveloping overnight, which some of the guidance
indicates. The fog will burn off by around 13z, with mainly some
scattered cumulus expected during the day. Any convective
potential looks too isolated to include a mention at this time.
Winds will average less than 5 kts through the period.


Dense Fog Advisory until 9 AM EDT Saturday for KYZ044-050>052-



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