Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Memphis Tennessee
642 PM CDT Tuesday Sep 2 2014
Updated to increase probability of precipitation across portions of the middle south.
A slow moving boundary was noted this evening across west
Tennessee into eastern Arkansas to the north of Interstate 40. An
upper level shortwave moving through the region has initiated the
redevelopment of showers and thunderstorms along this boundary.
Storms continue to slowly move east and train over the same areas
which may increase the short term risk for flash flooding as the
airmass remains very moist...characterized by middle 70s dewpoints
and precipitable water values around 2 inches. This boundary should be forced
slowly southward by ongoing convection towards Interstate 40
through the evening with the best chances for storms in these
areas in the vicinity of the boundary. These storms should slowly
diminish late this evening with slight chances for showers and
thunderstorms lingering after midnight.
The forecast has been updated to reflect the latest trends and
analysis. New grids and zones have been sent.
Previous discussion... /issued 315 PM CDT Tuesday Sep 2 2014/
thunderstorms have developed this afternoon along an outflow
boundary from a decaying nocturnal mesoscale convective system over the Ozark Plateau. This
outflow boundary delineated the warm sector...which was southeast
of a Forest City Arkansas... to Memphis to Dyersburg Tennessee line at 3 PM.
Best low level instability was noted over north MS... this will be
the area most favored for thunderstorms into early evening.
While thunderstorms gradually dissipate over north MS this evening...
models depict additional thunderstorm formation over the Central
Plains. Models may be overdoing the immediate upstream convective
potential... given the cool bubble high from this morning/S mesoscale convective system
over the Ozark Plateau. In any case...building midlevel heights
and weaker zonal steering winds should keep the bulk of overnight
thunderstorms to the north.
Thunderstorms chances for Wednesday and Thursday will likely be
driven by differential surface heating and subtle low level boundary
interactions under the upper ridge. Temperatures will average well above
normal...with heat indices Thursday likely in excess of 100 degrees.
Upper level heights falls over the much of the central and
northern Continental U.S. Will drive a surface cold front into the Ohio
Valley and Southern Plains by Friday evening. Low level moisture
pooling and stronger midlevel winds will bring an increase in
daytime rain chances for the midsouth. GFS mex guidance temperatures
appear too warm for the pattern...particularly if prefrontal
thunderstorms develop as depicted by the GFS and European model (ecmwf).
European model (ecmwf) and GFS models have remained consistent in bringing a cold
front through the midsouth on Saturday. Scattered to numerous
showers and thunderstorms and low level cold advection should
provide a noticeable cooldown following the midweek heat.
Sunday will see best rain chances follow the front on it/S way to
central/south MS. Drier air will edge in from the north to close
out the weekend and persist into Monday. Low level will return to
the southerly direction on Tuesday...as upper heights build in
advance of a midweek longwave upper trough dropping into the Central
Plains and northern plains.
00z taf cycle
Weak frontal boundary over east central Arkansas and west
Tennessee will keep evening convection around the taf
sites...with mkl having a period of on station activity. Later
in the night confident that IFR stratus and fog will develop and
persist through middle morning...otherwise conditions will be VFR.
Light south/variable winds will increase to 5-9 kts after 03/18z.