Scientific Forecaster Discussion
fxus64 kmeg 200911
Area forecast discussion
National Weather Service Memphis Tennessee
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.
06z taf cycle
VFR conditions are expected to continue for the entire forecast
period. Winds should be mainly from the south at around 5 knots
for much of the forecast period.