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Area forecast discussion
National Weather Service Jackson Kentucky
633 am EST Tue Dec 10 2019

Update...
issued at 633 am EST Tuesday Dec 10 2019

Another surge of rainfall is spread across the Coal fields
presently and will yield a very wet morning. The cold front has
now pushed through the entire area with cold advection ongoing.
Temperatures in the Bluegrass region have fallen to around 40 with
precipitation pulling out of that region. The cold air thus far
has lagged far enough behind the precipitation to limit any
snowfall potential. Even the surge coming out of Tennessee looks
to be tracking across areas that are still too warm for any snow.
Thus, the all rain forecast this morning still looks reasonable.
At some point, the cold air may catch up with the precipitation
shield, but cams continue to show there will be a limited time
window when this occurs and thus, should not really see much in
the way of accumulation. Thus, going to hold with the forecast as
it is right now with any accumulations remaining above 2500 feet
in southeast Kentucky.

&&

Short term...(today through wednesday)
issued at 321 am EST Tuesday Dec 10 2019

A shield of rain continues to impact east Kentucky this morning as
a surface cold front continues to advance east across eastern
Kentucky. The front is actually showing up fairly well as a line
of enhanced radar reflectivity from near Huntington, WV,
southeast through Campton, to Mount Vernon. While models are in
fairly good agreement on the synoptics, a few of the models
(gfs/nam) are continuing to struggle with the mid level dry air
intrusion this afternoon. Cams, including the rap and hrrr seem to
be showing a better handling of the dry air with less overall quantitative precipitation forecast
for this afternoon. This seems reasonable based on model
soundings. Without a saturated column it will be hard to maintain
precipitation rates enough to lead to much in the way of
measureable precipitation.

Precipitation rates this morning will be helped out as eastern
Kentucky will reside in the right entrance region to a 250mb jet
streak. This will allow for more robust rainfall across southeast
Kentucky through midday. Rainfall amounts up to three quarters of
a inch will be possible in some areas. The colder air will filter
into the area through the morning, with rain eventually mixing
with a period of snow and/or sleet. Given the sounding profile
will be very isothermal near the 0 degree isotherm this afternoon,
its possible we could see enough positive energy aloft to yield
some partial melting of snowflakes and leading to more sleet than
snow for a time this afternoon. Either way, given the dry air
intrusion and lessoning rates as we head into the afternoon,
snowfall/sleet accumulations will be minimal to say the least with
most areas likely not to measure any snowfall.

The exception will be across the higher terrain of southeast
Kentucky, primarily above 2500 feet. These areas should see
temperatures cool off a bit faster allowing for a quicker
changeover to snow before the better rates depart. Thus, amounts
in excess of an inch may be possible in these areas. However, the
window for modest snowfall accumulations will be small, so there
is much that could impact final amounts. The other consideration
is the ground remains very warm and thus, impacts are not expected
with any snowfall. For this reason, there are no plans to issue
any headlines at this time. We will maintain an Special Weather Statement for the
counties bordering Virginia as we could see some slick spots developing
above 2500 late this afternoon or evening as temperatures drop
below freezing. Should be more of a lag with the sub-freezing
temperatures for the rest of the area to limit potential slick
spots developing.

Precipitation will quickly exit this evening with high pressure
building into the area by dawn on Wednesday. This will allow winds
to weaken and temperatures to drop well into the 20s for most
areas by dawn on Wednesday. The cooler weather will stick around
on Wednesday with temperatures struggling to get back to 40
despite plenty of sunshine.

Long term...(wednesday night through monday)
issued at 508 am EST Tuesday Dec 10 2019

The period will start off quiet, with surface high pressure
passing through under benign zonal flow aloft. With a glancing
blow from a dry Arctic air mass, temperatures should drop to the
coldest we've seen since mid November. Warm air advection then
returns with sunshine on Thursday, giving many valleys a 30+
degree diurnal rise.

Although not a perfect match, models are coming into better
agreement concerning our next round of inclement weather late in
the week. Moisture from the Gulf and Atlantic will round the
southwest side of departing surface high pressure as a shortwave
trough aloft approaches in the southern part of the flow over the
Continental U.S.. rain could develop as early as Thursday night, but the
greater probability will be on Friday and Friday night as a
shortwave from the northern part of the flow moves east southeast
over the Midwest and acts to further deepen a larger scale upper
trough developing over the eastern Continental U.S.. each of these
shortwaves will have surface lows associated with them, which
eventually consolidate into a large coastal system traveling from
the mid Atlantic coast to New England during the weekend. This
will again pull colder air south into our area. Models differ a
little bit on how this plays out, and the European model (ecmwf) is more aggressive
at bringing in colder air as compared to the GFS. This has
ramifications down the line with development of the next system.

Both the European model (ecmwf) and GFS indicate a larger scale upper trough
developing and moving east across the Continental U.S. Early next week. Where
and when a warm front sets up in advance of the system is in
question. The GFS, with its lesser intrusion of cold air, has
this happening sooner and further north as compared to the ECMWF,
and the GFS allows for an increase in the pop to occur sooner for
our area. A generalized blended solution has the next significant
increase in pop for our area on Monday (but still only high chance
category). Precip type is also in question due to the uncertainty
of just how cold our preceding air mass will be.

&&

Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 633 am EST Tuesday Dec 10 2019

A mix of IFR/MVFR ceilings will be seen this morning as widespread
light to moderate rain pushes across east Kentucky. As
precipitation ends this afternoon and evening, ceilings will
slowly lift. Clouds should exit the area tonight from north to
south as high pressure builds into the region. This will bring VFR
conditions back to the area tonight. Northwest winds at 5 to 10
knots will continue today, before going light and variable
tonight.

&&

Jkl watches/warnings/advisories...
none.
&&

$$

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