Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 220813
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
413 AM EDT Wed Mar 22 2017

.SHORT TERM...(Today through Thursday)
Issued at 400 AM EDT WED MAR 22 2017

Early this morning, the axis of shortwave trough is moving across
Ontario to the eastern Great Lakes to Appalachians. Meanwhile,
the axis of an upper level ridge extended from northern Mexico
north across the high plains. At the surface, a cold front
continues to push further south across the Gulf states in
response to the upper level trough. Meanwhile, surface high
pressure centered over MN and far west Ontario is building across
the Great Lakes and OH Valley region.

As the axis of the mid and upper level ridge moves east near the
start of the period, mid and upper level heights will begin to
rise and center of surface high pressure will reach the central
Great Lakes by evening. As this trough departs clouds should thin
with any cu and ac becoming more thin through the day and
dissipating. At the same time, a very dry airmass, especially
aloft will move into the area with 1000 to 500 mb mean layer rh
progged to be 20 percent or less this afternoon. PW is also
expected to plummet to well below average for this time in March,
below 0.20 inches this afternoon. All of these and some mixing
into this very dry subsidence layer point toward dewpoints
reaching the lower MET MOS numbers as compared to model blends for
mid to late afternoon and yielding rh briefly reaching the 18 to
26 percent range area wide. The dry airmass should also warm
despite cold air advection and reach the mid 40s far north to low
to mid 50s south.

The dry airmass will remain in place tonight as the axis of the
upper level ridge approaches and the center of the surface high
reaches upstate NY by dawn. There will be some increase in clouds
initially high and then low mainly after midnight. However, with
the dry airmass and a slackening pressure gradient, deeper valley
locations should decouple around or shortly after sunset and
broader valleys a few hours later. The airmass will be driest and
clouds will arrive later generally east of I 75 and the latest in
the far northeast. COOP MOS guidance and dewpoints support
typically colder spots such as Sandy Hook and the Paintsville KY
Mesonet site reaching the lower 20s with temperatures for most of
the area east of I 75 bottoming out in the 20. Since the
dewpoints will be low and dewpoint depressions expected to not
close in on the 0-2F range, frost formation will be minimal. Most
ridgetop and southwest locations should experience temperatures
reaching around 30 degrees. With the increase in high clouds and
eventually mid clouds between 2 AM and 8 AM from southwest to
northeast confidence in hourly temperatures later at night is on
the low side. Some valley locations may actually warm during that
period as net radiational cooling decreases. However, a freeze
warning will almost certainly be needed for some portion of the
area for tonight given the advanced nature of some vegetation due
to the warm February.

Warm air advection which will already have begun tonight will
increase substantially on Friday with 850 mb temps expected to
rise to around 5C by late afternoon. There will be some mid and
high clouds from time to time and probably some cu around 850 mb
or just below as upper levels and then mid and lower levels begin
to moisten with the flow from the surface 850 mb becoming more
southerly. A downslope component will linger, however, in the far
east and dewpoints will be slower to increase nearer to the VA and
WV borders. Temperatures will warm to above normal levels on
Wednesday and should reach the upper 50s in the far north to the
mid 60s in the south. This will begin a period of above normal
temperatures that should linger well into the long term period and
beyond.

.LONG TERM...(Thursday night through Tuesday)
Issued at 352 AM EDT WED MAR 22 2017

Above normal temperatures and multiple rain chances will be the
story for the long term period.

An area of surface high pressure will be parked of the Mid
Atlantic Coast to begin the period and heights will be on the rise
as upper level ridge builds east. This will combine with lifting
warm front to bring above average temperatures to the region.
Right now looks like this warm front will be dry here in the
eastern side of the state Thursday night. All eyes then turn to
the Rockies for already developed upper level closed low and
nearly vertically stacked system. This will system will eject east
and then northeast into the Mississippi River Valley by Saturday.
Given the models are backing off on speed with this did opt to
back off on POPs for Saturday. Overall think the best chances will
occur Saturday night into Sunday based on the latest guidance.
Keep some slight thunder in the grids with some instability
Saturday afternoon through Sunday. Overall this system becomes
less significant, as the surface low weakens as it moves NE into
the Great Lakes. The ridging behind this will be brief, as another
wave ejects east out of the Rockies into the Mississippi River
Valley Monday. Given timing uncertainty with this will keep some
POPs in the grids on Monday, but could see a small window of
drying before precipitation chances rise again Late Monday into
Tuesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 220 AM EDT WED MAR 22 2017

Expect VFR conditions across eastern Kentucky through the TAF
period. A few low and some mid level as a shortwave trough passes
through the area. Winds will average out of the north to northeast
at 5 to 10 KT as high pressure builds into the area. Winds will
slacken to closer to 5KT or less during the 22Z to 6Z period with
gradual loss of solar insolation and deeper mixing combined with
a decrease in the pressure gradient.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Freeze Warning until 10 AM EDT this morning for KYZ044-050>052.

&&

$$

SHORT TERM...JP
LONG TERM...DJ
AVIATION...JP



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