Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Memphis Tennessee
640 PM CDT sun Mar 29 2015
Updated for the 00z aviation discussion.
Previous discussion... /issued 602 PM CDT sun Mar 29 2015/
updated to lower early evening probability of precipitation.
new hrrr guidance showing convection ahead of front developing
quickly between 03-05z tonight with north Mississippi still having
the best chance for widespread rainfall amounts...and the
potential for isolated have updated the forecast accordingly.
Previous discussion... /issued 308 PM CDT sun Mar 29 2015/
Main concern in the near-term concerns thunderstorm chances this
evening/overnight...with the potential for an isolated wind/hail
event across east Arkansas/southern Tennessee/northern Alabama.
Currently...moisture has been continuing to slowly return this
afternoon with dewpoints in the middle to upper 40s common across the
region. A surface frontal boundary was analyzed from southern OK
through MO extending into the Great Lakes region. This front will
continue to progress southeast through the afternoon.
By this evening...the frontal boundary will begin to impinge upon
a modest tongue of boundary layer moisture. Elevated instability
on the order of 750-1000 j/kg will develop collocated with a zone
of better moisture at 850 mb. Showers and isolated thunderstorms
will develop along and just ahead of the the surface front after 7
PM this evening. While most severe parameters remain
marginal...cloud-bearing shear values at or above 35 knots will
support some organized thunderstorms. Hrrr guidance supports this
as 2-5 km updraft helicity values do show some sustained
rotation...albeit marginal. That being said...overall severe
threat looks low with a few isolated incidents of severe hail
and/or wind gusts during the overnight. Storm-total quantitative precipitation forecast was
increased with this forecast package given the thunderstorm
potential and better coverage of rainfall expected.
After the front moves through tonight...the moderation trend will
continue through early this week with temperatures rising into the
low to middle...and potentially upper 70s by Thursday. A progressive
but largely zonal flow pattern develops aloft through the week
with general southerly flow maintaining itself through the period.
This should provide a window for sustained moisture return from
the Gulf of Mexico...but nothing anomalous for this time of year.
Several chances for thunderstorms exist during this period as well
as a warm advection regime/isentropic lift impinge upon a weakly
convergent zone left over from a stalled frontal boundary. With
time...this boundary completely washes out as southerly flow
increases. By Thursday and Friday...a stronger shortwave will
force another frontal boundary southeast. Disagreement currently
exists in model guidance but a decent signal exists for more
organized thunderstorm development given the very moist boundary
layer forecast to be in place ahead of the approaching front. It
is too early to assess the severe threat but this period will be
For the long-term...another strong high pressure system builds
into the central and southern US cooling the middle-south down
significantly. Seasonal temperatures are expected with dry weather
during this period.
00z taf cycle
A cold front will move across the middle south this evening. As the
front progresses south...showers and thunderstorms should develop
across east Arkansas into southwest Tennessee after 03z. Have
timed convective potential as such from north to south. There will
likely be a period of MVFR ceilings and visibilities with any convection.
Skies should clear behind the front late tonight into Monday.
Southwest winds will switch around to northerly and northeasterly
at speeds of 7 kts or less through Monday.