Scientific Forecaster Discussion
fxus63 kjkl 250850
Area forecast discussion
National Weather Service Jackson Kentucky
350 am EST Sat Nov 25 2017
Short term...(today through sunday)
issued at 350 am EST Sat Nov 25 2017
A cold front currently stretches from about Detroit to just south of
St. Louis, with semi-breezy winds and slightly cooler temperatures
in its wake. Upper support consists of an upper trough from Hudson
Bay to the upper Ohio Valley, becoming absorbed in a much broader
trough spanning eastern North America. While mid-high clouds will
certainly increase and continue to lower this morning, low level
moisture recovery remains quite meager. Will likely see some low
clouds develop in a Post-frontal airmass into this afternoon as
veering northwesterly winds converge with the higher terrain of
eastern Kentucky, but substantial drying above roughly 3k feet will
keep precipitation chances silent as this occurs this afternoon.
However, a brief sprinkle may be possible this morning and early
afternoon underneath virga prior to stronger subsidence descending
aloft. Cooler temperatures will be in store this afternoon in a cool
air advection regime, but the lack of substantial low level cloud
cover and the lagging nature of the cooler air filtering in until
mid afternoon should still promote highs in the mid-upper 50s.
Deep layer northwest flow will take shape this evening and tonight
as a 1025 mb surface ridge builds into the Ohio River valley.
Sounding profiles indicate some lingering and shallow boundary layer
moisture tonight as a subsidence inversion builds and lowers. This
in combination with light northwest winds should preclude complete
decoupling, so have therefore kept fog out of the forecast at this
time as fairly uniform temperatures in the low 30s occur by
Sunday morning. High pressure and clearing skies will round out
the weekend with the refreshed airmass keeping high temperatures
in check, topping out in the upper 40s to lower 50s.
Long term...(sunday night through friday)
issued at 300 am EST Sat Nov 25 2017
The extended portion of the forecast begins on Sunday night with an
amplified but still rather progressive upper level pattern in
place. Current trends place the upper level in a split flow with
a northern stream flowing over The Rockies and a southern jet
stream coming out of The Four Corners region. With the northern
stream starved for moisture and lacking any significant flux, the
eastern Kentucky area has and will remain dry for the first half
of the extended forecast. This is in good agreement between the
GFS and Euro with the area remaining dry at least through
Wednesday. As such, with this scenario, no real change in air mass
is expected through the first half of the extended as well. In
fact, temperatures will remain near normal, if not a bit above.
By Wednesday night, a shortwave tracking over the plains along
with a separate piece of energy along the southern stream by
Thursday morning will form a front tracking into the Ohio Valley.
This will provide the first strong surge of a change in air mass
as warmer air is drawn north into the area with high temps
reaching near 60. This will also provide a good chance of showers
lasting into Friday. With a lack of good instability as well, will
keep thunder out of the forecast. Models seem to be coming in
better agreement but still lack strong consistency. Thus, will
continue to stick with the super blend solution.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1255 am EST Sat Nov 25 2017
VFR conditions currently expected to prevail through the period.
Cloud decks will lower overnight into this morning as ceilings
develop. Still anticipating these to remain in the 5-10k foot
range or above, but could see some brief periods of ceilings
nearing MVFR criteria at around 3k feet from mid morning into the
afternoon as a cold front moves through eastern Kentucky.
Regarding precipitation, a few sprinkles will be possible into
mid-late afternoon. Increasing southwest winds of 5-10 knots
tonight will further increase and veer northwesterly through the
day Saturday while remaining near 10 knots with periodic gusts.
May have to monitor lingering low clouds for ceiling potential
this evening into tonight depending on how quickly high pressure
builds in and low level moisture scours out.