Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Memphis Tennessee
1242 PM CDT Friday Aug 29 2014
updated for 18z aviation discussion below.
Previous discussion... /issued 1057 am CDT Friday Aug 29 2014/
Discussion...15z surface analysis places a ridge of high pressure
over the southeast United States while a weak cold front stretches
from the upper Midwest back through the Central Plains.
Meanwhile...water vapor satellite/WSR-88D VAD wind profiles
indicate a 700 mb shortwave trough moving through portions of the
Southern Plains and western sections of the lower Mississippi
Valley. As of 10 am CDT...temperatures across the middle south are in
the middle 80s at most locations.
Latest short term analysis still indicates a potential for isolated
showers and thunderstorms this afternoon...predominantly triggered
by convective temperatures being reached. Will make some
adjustments to temperatures to account for current trends.
Otherwise...forecast overall in good shape.
Updated grids will be available shortly.
Previous discussion... /issued 407 am CDT Friday Aug 29 2014/
the radar across the midsouth is quiet at 3 am. Temperatures are
in the low to middle 70s with the exception of the Memphis metropolitan
area where temperatures remain in the upper 70s. We will likely
see two to three more degrees of cooling before sunrise resulting
in morning lows ranging from the upper 60s to middle 70.
It looks like we are transitioning into a much wetter patter for
the last couple of days of August into early September. The ridge
and surface high pressure that has kept US hot and dry for the
past couple of weeks will shift along the East Coast and a highly
amplified longwave trough will shift across the Mississippi River
valley...though it will Delaware-amplify significantly as it does so.
This afternoon...southerly flow will strengthen ushering in deep
moisture across the midsouth. Precipitable water values will
increase from less than 1.5 inches today to in excess of 2.25
inches by tomorrow afternoon. Showers and thunderstorms will be
scattered late this afternoon...most numerous in east
Arkansas...becoming widespread across all of the midsouth by
middle morning Saturday. The heaviest rain is expected Saturday
afternoon...lasting into Sunday. There is not expected to be much
in the way of dynamic support for severe thunderstorms...but
lightning will likely be abundant and rainfall will be heavy at
times. Did not add any mention of heavy rainfall to the severe weather potential statement...but
if precipitable waters get as high as the NAM indicates...near 2.5 inches...we
may begin to see some localized flooding issues by Sunday morning.
Temperatures over the weekend will be much cooler...several degrees
below normal...with highs in the middle 80s.
Monday into the middle of next week...a broad trough will
transition into zonal flow from the plains across the southeastern
US. Temperatures will trend warmer. Guidance brings highs back
into the middle 90s by Tuesday. That seems a bit warm given the
overall pattern. Scattered showers/thunderstorms should also help
to keep temperatures down a bit so will undercut guidance highs by
2-4 degrees for most of next week. Do not see any overly organized
weather systems in the making through the end of the week...expect
gradually warmer temperatures...near to slightly above normal
after midweek with at least a slight chance of thunderstorms each
period...most likely during the afternoons.
VFR to prevail areawide through early evening. Rain showers/thunderstorms and rain chances
will increase after 03z...slowly edging east with the approach
of the upper trough from the Southern Plains. 18z tafs were based
primarily on the 12z NAM model...with best thunderstorms and rain chances associated
with an approaching warm front after 06z.