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Area forecast discussion...updated
National Weather Service Jackson Kentucky
138 PM EDT Wed Sep 18 2019

issued at 138 PM EDT Wednesday Sep 18 2019

The forecast generally remains on track this afternoon. Scattered
cumulus has developed across the area. Current temperatures range
from the low to mid 80s at most locations. Will mainly freshen up
the hourly temperatures through the rest of the day, in order to
account for the latest trends in observations.

Update issued at 1112 am EDT Wednesday Sep 18 2019

Temperatures are running a bit cooler compared to yesterday at
this time. The 12z 850 mb raobs also confirm a cooler air mass in
place compared to yesterday. Cumulus is already starting to nose
in from Virginia, and the latest forecast soundings suggest at
least few to scattered cumulus developing across most locations
into the afternoon. As such, think the forecast highs will mostly
be in the mid to upper 80s today, around a degree or two cooler
compared to yesterday. Updates will be out shortly.

Update issued at 703 am EDT Wednesday Sep 18 2019

Updated the forecast to input the latest observations into the
grids and trend them into the mid morning hours. The rest of the
forecast is on track.


Short term...(today through thursday)
issued at 417 am EDT Wednesday Sep 18 2019

Current surface analysis across the region features mainly clear
skies with the exception of some cirrus passing through eastern
Kentucky. Surface high pressure is in place and centered over the
PA and New York region bringing easterly flow aloft into eastern
Kentucky. Clear skies in place over the area and light winds has
lead to some fog development but due to the dry airmass in place
and strong subsidence, the fog is suppressed and only to the river
valleys. The continued dry conditions and clear skies has lead to
some valley temps dropping to around 60 this hour and a min temp
of 57 is likely. Heading into the day today, fog should dissipate
by 13 or 14z with high based cumulus development likely. High
pressure shifted to northeast of the area has allowed for an
easterly down slope through the day resulting in some slightly
higher temperatures and a dry surface layer. The lack of gradient
in place will also result in some light east winds today around 4
to 6 mph through the day.

By tonight, the clear skies in place will begin to see some cloud
cover developing towards dawn as the high pressure shifts further
east allowing some return flow to bring some moisture into the
I-75 corridor and west. This cloud cover developing will keep much
of the fog development from reoccurring. The rest of eastern
Kentucky will take some time for this moisture to infiltrate the
region as the current dry conditions in place will keep fog
development even less with a few wisps in the river valleys.
Heading into the day on Thursday, the moisture moving into the
area will be enough for some more cumulus development than the
previous day. This will also result in temps being a degree or two
less for highs across eastern Kentucky. The one concern will be
the continued dry boundary layer as dew points both afternoons
will drop into the 50s.

Long term...(thursday night through tuesday)
issued at 430 am EDT Wednesday Sep 18 2019

An upper level ridge is expected to be centered over the Tennessee
Valley to southeastern states to begin the period, with sfc high
pressure centered over the mid Atlantic states and extending into
the southeast conus. The model consensus is for the ridge to build
north across the area Thursday night into Saturday with 500 mb
heights generally increasing during that time as well. Meanwhile,
sfc high pressure will be centered to the east and southeast of
the area during this time and this will lead to light southerly to
southwest low level winds. Overall, the highest 500 mb heights on
average across the region still to on Saturday. The ridge will
flatten to end the weekend and become centered near the Gulf
Coast. This will lead to the upper level winds becoming more
southwest and then west to end the weekend and into the start of
the new week. As the ridge flattens, a shortwave trough that will
have moved from The Rockies east and northeast across the plains
and into southern Canada is expected to moves across the Great
Lakes and eventually Ohio Valley during the late Saturday night to
Monday period, reaching the Canadian Maritimes on Tuesday. An
associated sfc cold front should approach the Ohio Valley Sunday to
Sunday night and then move across the commonwealth Monday to
Monday evening. This boundary will likely settle south of the area
and then begin to stall toward the end of the period. Models
still are showing some run to run and model to model differences
in the strength of the end the week and in particular with the
timing and strength of shortwave trough and cold front to end the
weekend and early next week.

Dry weather is still expected be the main story through the
weekend, with capping from the ridge likely preventing convection
each day. Moisture should be sufficient for some diurnally driven
cumulus Friday and Saturday. Moisture will increase through the
entire column ahead of the shortwave and cold front from late
Saturday night and into Sunday with more in the way of cloud cover
expected on that day across the board. Clouds and isolated to
possibly scattered showers are anticipated initially in the north
late Sunday night and across the entire area Monday to Monday
evening. Instability should be sufficient on Monday combined with
some forcing from the synoptic features that a thunderstorm or two
cannot be ruled out. At this time, it appears that some locations
could receive some rainfall. However, it seems doubtful that this
will have any meaningful affect on our drought status in any
widespread fashion.

We continued to go close to the blended/nbm guidance for the
highs/lows which was reasonably close to the European model (ecmwf) MOS guidance
and considerably warmer than the GFS/mex MOS guidance. The recent
dryness and a preference toward the stronger ridge in the recent
ecwmf runs led to this Route. The only changes were normal terrain
adjustments, mainly to allow for slightly cooler valley
temperatures in the eastern valleys and Widen the valley to ridge
differences in temperatures for Thu night through Sat night.

Given the run to run variability and model to model differences
in timing of features and associated precipitation chances Sunday
night to Monday night, went close to the blended guidance. This
led to continued slight chance pops further south and southeast
and scattered pops in the north.


Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 138 PM EDT Wednesday Sep 18 2019

VFR conditions are expected to prevail through the period.
Scattered cumulus ranging from 3-5k feet agl will dissipate early
this evening. Scattered high clouds will move in later tonight,
before at least scattered cumulus either develop or move in once
again after 08z. East winds of around 5 kts will gradually veer
around to the south southeast by early Thursday afternoon.


Jkl watches/warnings/advisories...


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