Scientific Forecaster Discussion
fxus64 kmeg 201101
Area forecast discussion
National Weather Service Memphis Tennessee
601 am CDT Fri Oct 20 2017
Discussion... /issued 411 am CDT Fri Oct 20 2017/
Mild mid-autumn temps to prevail today and Saturday, with
increased winds and humidity levels on Saturday. Rain chances
arrive late Saturday night west of the MS river, and spread east
through the midsouth on Sunday and Monday.
The medium range models remain consistent in depicting upper
level height falls through the plains on Saturday, and eventual
cut-off low formation over the lower MS River Valley by late
Sunday. Showers and thunderstorms will increase in coverage ahead
of this system, embedded in modestly unstable airmass over la and
Arkansas. An initial neutral to slight positive orientation to the
upper low will limit low level shear as the rain enters the
midsouth. Along with midlevel lapse rates at or below 6 c/km,
severe storm threat will be limited on Sunday. Most of Monday will
see the midsouth to the north of closed low. By Monday afternoon,
the elevated moist conveyor belt shifts into Alabama and middle TN,
with wrap-around showers possible over west Tennessee and north MS.
These light showers should exit the midsouth Monday night.
Looking upstream, significant height falls will occur from the
upper MS River Valley to Ohio River valley on Tuesday, eventually
forming a deep longwave trof over the eastern third of the U.S. By
Wednesday. A cold front will sweep through the midsouth on
Tuesday, bringing colder and much drier air. Temps will likely
drop into the upper 30s over the Tennessee River valley Wednesday and
Thursday mornings, but midlevel clouds Wednesday morning and
gradually returning low level warm advection Thursday limit
confidence of frost occurrence.
Rain chance return Friday, associated with upper level trof
passage. GFS and European model (ecmwf) quantitative precipitation forecast late next week may be a bit overdone,
given limited time for low level moisture return.
12z taf set
Some patchy fog is developing across the area which may impact
kjbr, kmkl, and ktup through 14z. Otherwise, VFR conditions are
expected through the period. Although, a 4000-6000 feet deck may
spread into kmem and kjbr after 8z due to warm air advection.
Kjbr may also see some light rain showers. Thus also mentioned vicinity
wording to kjbr. Southeast winds of 5-8 kts will occur today.
Speeds will diminish after 00z.