Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Jackson Kentucky
327 PM EST Tuesday Nov 24 2015
Short term...(this evening through Wednesday night)
issued at 252 PM EST Tuesday Nov 24 2015
Surface analysis across the region as of 19z features high
pressure still well in control of our weather. Though a weak
boundary will pass by to the north associated with a weak upper
level disturbance. This will provide nothing more than some cirrus
passing by the area. Eastern Kentucky still in the center of the
high will see another night of cold temperatures with lows in the middle to
lower 20s in the deeper valleys and around 30 elsewhere.
Tomorrow...the high will shift a bit further east as southerly
flow increases. With this...our cold air mass will modify a bit
more with temperatures getting to around 60 for highs. Drier air still in
place will leave relative humidity values below 30 percent again but with a Stout
subsidence inversion in place...deeper mixing tomorrow afternoon
is unlikely. Hence winds should be relatively light once again.
Tomorrow night...with high pressure still holding strong to the
east...the next system to the west will slowly push against this
feature as some cloud cover begins to move into the region. Due to
this...have brought in a bit of cloud cover tomorrow night. This
will also impact overnight temperatures with more insulation as
slightly warmer lows are expected.
Long term...(thursday through tuesday)
issued at 326 PM EST Tuesday Nov 24 2015
Period will start with high pressure hung up over the Appalachians
to our east...bringing light but warmer southerly flow to much of
the Ohio Valley region. Meanwhile...a strong upper level low will
encompass much of the western Continental U.S....creating deep troughing across
this portion of the US...and tightly packed rising heights as you
head eastward towards the Ohio River valley. Several waves of energy
are expected to ride along this Lee side of the trough...which will
impact eastern Kentucky heading into the weekend. At the surface...a cold
front will set up along the greatest pressure gradients from SW to
NE across the Central Plains by 12z Thursday connected to a low
pressure system and upper level low over eastern Canada. As this
eastern Canadian low shifts eastward...so too will the cold
front...encroaching on western Kentucky during the day Friday. Strong
southerly flow ahead of this front will result in a large area of
warm air advection and moisture advection into Kentucky...with precipitation expected to
reach eastern Kentucky as early as Friday afternoon. Temperatures will
increase to the low 60s both Thursday and Friday afternoons ahead of
this system...so any precipitation should be in the form of rain.
Models at this point in the forecast are in very good agreement...
with the NAM...GFS...and European model (ecmwf) all showing precipitation moving into
Kentucky within a few hours of each other and covering much of the
same area. As we head into the weekend...the upper low over eastern
Canada will continue to shift eastward...while the upper low over
the western Continental U.S. Will remain nearly stationary. This will create a
more zonal flow across the Ohio River valley and will work to slow
the driving motion of the cold front. As such...expect it to weaken
substantially while becoming hung up along the appalachian region.
Temperatures are expected to decrease between Friday and
Saturday...due to the brief wind shift that will happen behind the
initial cold frontal passage...allowing colder air to filter into
the region. High temperatures will generally be in the 50s for both
Saturday and Sunday afternoons...though clouds in place will keep
conditions insulated overnight and prevent subfreezing temperatures.
Another surface low will make its way into the southern Mississippi
Valley during the day Saturday...driven by a weaker shortwave
aloft...and shifting northeast towards western Tennessee and Kentucky by Sunday.
The combination of the stalled and weakening frontal boundary to our
east...and the presence of another low pulling moisture up along the
southern Mississippi River valley...will result in continued precipitation
chances throughout the weekend. It seems as though the latest run of
the European model (ecmwf) and the GFS are starting to come into much better
agreement with the precipitation across the region during the second half
of the weekend...with the best moisture located along the western
half of the state...weakening across our far east and along the
eastern Appalachians as the initial cold front continues to lose
strength and moisture influx.
The new surface low is expected to gain strength as it moves
northeast during the day Sunday. This will lead to another surface
cold front development...which should push through western Kentucky Monday
and eastern Kentucky by Tuesday. As a result...expect continued rain
chances into the day Monday and Tuesday as well. Given the scattered
nature of the latest model outputs...and the uncertainty in timing
and placement this far out in the forecast...chose to limit values
to only chance probability of precipitation at this time.
Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1237 PM EST Tuesday Nov 24 2015
VFR conditions and light winds are expected through Tuesday
afternoon. A few wisps of cirrus will pass through.