Scientific Forecaster Discussion
fxus64 kmeg 231125
Area forecast discussion
National Weather Service Memphis Tennessee
625 am CDT Sat Sep 23 2017
Updated for the 12z aviation discussion
Previous discussion... /issued 338 am CDT Sat Sep 23 2017/
the calender says it's now fall, but you wouldn't know it by
looking at the temperatures. Friday's high of 93 degrees in
Memphis was the warmest temperature recorded in The Bluff city
this month. The good news is that we'll see temperatures moderate
a bit closer to climatology over the next week. The bad news is
that this decline will be very slow with above normal temperatures
expected through Wednesday.
So, what's driving the late September heat? The remnants of Jose
continue to spin off the New England coast with a deep longwave
trough digging over the western Continental U.S.. an upper-level ridge has
developed between these two features, extending from the Southern
Plains into the southern Great Lakes states. This ridge is
forecast to build northward over the northeast Continental U.S. During the
weekend as a cut-off upper-level low drifts west on the southern
periphery of the anticyclone. The weakening ridge (decreasing
subsidence) and approaching low will result in a slight decrease
in mid-level temperatures and should allow a bit more cloud cover
to develop across the County Warning Area today through Monday.
Expect high temperatures over the next few days generally in the
upper 80s and lower 90s with overnight temperatures falling into
the mid 60s to lower 70s. A slight increase in afternoon showers
and thunderstorms is expected this afternoon, mainly south of
I-40. Coverage of diurnal convection is forecast to increase
further on Sunday but will likely taper down a bit on Monday.
Nonetheless, coverage will likely remain rather isolated, with
pops in the neighborhood of 20 percent.
Dry conditions are anticipated on Tuesday the upper low moves
east, influenced by the circulation surrounding Hurricane Maria as
it moves north off the Carolina coast. The western Continental U.S. Trough
is progged to lift northeast over the Great Lakes by midweek,
leaving a cut-off upper-level cyclone over the Desert Southwest.
As the main trough lifts northeast, the ridge is progged to
flatten and retreat over the lower Mississippi Valley, leaving the
mid-south on the northern extent of its influence. This trough
will drive a cooler airmass south into the area sometime Wednesday
or Thursday. Expect a gradual cool down with high temperatures
around 80 degrees on Thursday and in the mid 70s by Friday. That
certainly sounds better than 90 degrees!
Regarding rain chances with this system...it's not looking very
good right now. Confidence was low yesterday given the lack of
consistency between the models and it's only become lower after
looking at the 00z global runs. Slight chance pops were
maintained across most of the area both Wednesday and Thursday,
but may need to be trimmed as the finer details emerge. The
strongest dynamics remain north of the County Warning Area and there really isn't
much in the way of frontal convergence to help initiate
12z taf cycle
VFR conditions should persist for much of the forecast period.
Some dense fog has formed in the kmkl area which should burn off
later this morning. More fog could form the in the kmkl area
overnight tonight. Isolated thunderstorms could form this
afternoon over southern sections of the forecast area but coverage
is too small to be mentioned in tafs. Winds will be mainly from
the southeast at around 5 knots for most of the forecast period.