Scientific Forecaster Discussion
fxus63 kjkl 170828
Area forecast discussion
National Weather Service Jackson Kentucky
428 am EDT Tue Sep 17 2019
Short term...(today through wednesday)
issued at 418 am EDT Tuesday Sep 17 2019
The current surface analysis as of 08z across the Ohio and Tennessee
valleys show a weak boundary slowly sagging south through the area
into the predawn hours. This boundary has been responsible for a
few showers over the south and southeast the past evening but
those have since dissipated. Some lingering cloud cover will
remain with and ahead of the front. This cloud cover heading into
the dawn hours will keep some fog from developing but the usual
river valleys are still seeing some fog development this morning
but not as widespread due to the cloud cover. Through the day
today, as surface high pressure shifts to the eastern Great Lakes
region, northeast winds will settle into the area. Despite a
cooler flow, the light winds and drought conditions will allow Max
temperatures today to warm into the upper 80s. The nearly
dissipated boundary will be along the mountains to the southeast
in Tennessee and Virginia. This region will be a point for cloud cover to
develop during the day.
Heading into tonight, with the ever present ridge in place aloft
and surface high pressure shifting southeast into the Middle
Atlantic States, this will allow clear skies to be in place
tonight. Dry conditions, light winds, and clear skies will create
some ridge to valley temperature differences of around 5 to 7
degrees. Some of the deeper valleys will drop into the upper 50s.
The dropping temps, light winds, and any lingering moisture will
allow fog to develop a bit more than the previous night. Thus will
go with some areas of fog developing in the deeper and river
valleys tonight. By Wednesday, some additional cumulus development
will occur as some 850mb moisture will stream into the area but
with the lower level flow being easterly due to the surface high
shifting further east, the weak downslope may significantly dry
out the surface. This will result in warmer temps than the
previous day and will go several degrees above MOS to account for
this. Some low 90s will be possible. While some elevated Cape May
have yielded some shower development for Wednesday, the strong
cap and dry surface will make this development nearly impossible.
So will keep the dry and warm temps through the short term.
Long term...(wednesday night through monday)
issued at 420 am EDT Tuesday Sep 17 2019
An upper level ridge is expected to be centered over the MS
valley to southeastern conus from Wed into Fri with the axis of
the ridge shifting east across the area to begin the weekend. The
highest 500 mb heights on average across the region will be on
Saturday. At the same time, sfc high pressure will remain centered
east to northeast of the area through Saturday. The ridge will
flatten to end the weekend and begin next week as a shortwave
trough moves across the Great Lakes and Ohio Valley to the
northeast. A sfc cold front should approach the commonwealth to
end the period. Models still vary from run to run and model to
model with the timing and strength of these features.
Dry weather is still expected be the main story through the weekend,
as capping should be enough to prevent convection each day with only
some shallow to perhaps moderate diurnally driven cu development
possible. Opted to go fairly close to the blended/nbm guidance for
the highs/lows through given the recent dryness and trends opted to
go an average of two above this guidance for highs Thu to Sat. The
only other changes were normal terrain adjustments, mainly to allow
for slightly cooler valley temperatures in the eastern valleys.
Highs will average in the mid to upper 80s from Thursday into
Sunday, still around 10 degrees above normal for this time of year.
Some of the normally warmer valley locations could reach 90 on
Saturday. With more in the way of cloud cover and precipitation in
the area highs should be in the low to mid 80s for Monday.
Given the run to run variability and model to model differences in
timing of features and associated precipitation chances Sunday night
to Monday, went close to the blended guidance. This led to slight
chance pops south and southeast and scattered pops in the north.
Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 153 am EDT Tuesday Sep 17 2019
Convection has waned as the last of the showers have dissipated.
Predawn the fog potential in the valleys will increase. Given the
dry conditions, and the rain that did fall, will at least go MVFR
at loz and IFR at sme. The Post frontal stratus potential looks
low based on the lack of upstream stratus and the fact that this
is a weak boundary. This fog will burn off around 13 to 14z on
Tuesday leaving US with VFR cigs and visible through the remainder of
the taf period. However, some diurnal cumulus remains possible for
Tuesday afternoon at around 5 kft. The winds will remain light
out of the north and northeast as weak front passes.