Scientific Forecaster Discussion
fxus64 kmeg 242025
Area forecast discussion
National Weather Service Memphis Tennessee
325 PM CDT Wed may 24 2017
temps across the midsouth were running 15 to 20 degrees below
normal this afternoon, courtesy of an upper level low centered
over MO. Despite the cool boundary layer, temps aloft were
sufficiently cool to steepen low level lapse rates to 8 c/km,
helping to sustain numerous showers. Given sufficiently strong
updrafts, small hail will be possible given freezing levels near
7 kft above ground level. The steep lapse rates may also lead to isolated
occurrences cold air funnels over the Delta until late afternoon.
The upper low will track southeast through the midsouth during
the evening, with gradually shrinking shower coverage mainly south
of/ahead of the upper low center. By sunrise Thursday, the upper
low will have departed with clouds likely cleared except near the
Thursday will begin the warming trend, as upper level ridging
builds in. Low level pressure gradient will tighten through Friday
afternoon, under moderately fast zonal flow aloft. Modified
marine air will spread into the midsouth Friday, driving surface
dewpoints into the upper 60s and lower 70s. The boundary of this
marine airmass will set up to the north, near the periphery of
mid level ridge. A few storms may affect northeast Arkansas through
northwest Tennessee Saturday. Despite warm and humid conditions, the
atmosphere will likely be capped to deep convection along and
south of I-40 Saturday afternoon.
Saturday night and Sunday morning should see rain chances
considerably increase over the midsouth, as steep midlevel height
falls occur over the middle and lower MS River Valley help drive
the surface front south. Weak directional shear and timing of the
morning frontal passage will likely limit organized severe thunderstorm
potential. Best chance for severe will likely occur north of I-14
Saturday evening, where daytime instability is greatest.
A longwave trof will prevail over the eastern U.S. Early next
week, returning below normal temps to the midsouth. GFS and European model (ecmwf)
depict a secondary cold frontal passage, but differ on the timing.
Confidence on rain chances early next week is thus a little less
than normal at this point.
18z taf cycle
VFR conditions should persist for much of the forecast period.
Scattered showers and thunderstorms will move across the forecast
area mainly during the afternoon hours. Some fog may develop
overnight over eastern portions of the forecast area. Winds will
be mainly from the west at 5 to 10 knots for much of the forecast