Scientific Forecaster Discussion
fxus64 kmeg 152356 aaa
Area forecast discussion...updated
National Weather Service Memphis Tennessee
556 PM CST sun Dec 15 2019
updated for 00z aviation forecast discussion below.
Previous discussion... /issued 314 PM CST sun Dec 15 2019/
a potent trough continues to take shape over the southern rockies
this afternoon. Mid-level height falls are spreading eastward into
the plains aiding in the development of a surface cyclone along a
stationary front in central Texas. The cold front that moved through
the mid-south yesterday is now lifting poleward across north MS
as a warm front. Analysis as of 3 PM places this front from near
the Interstate 40 corridor. Warm sector dewpoints are creeping
back into the 50s with temperatures approaching 60f in a few
areas. North of the front, temperatures are mainly in the 40s.
Strong, quasi-zonal flow aloft will gradually become more
southwesterly through tomorrow as the trough approaches. The
attendant upper-tropospheric jet will begin to shift to the east
tonight, placing the mid-south in the right entrance region, a
favorable location for forced ascent. We've already seen scattered
light radar returns in the warm sector but rain and drizzle will
continue to develop north of the warm front as moist, isentropic
ascent continues over the frontal zone. Light rain may be
widespread north of I-40 by sunset and will continue through the
overnight hours as the warm front stalls. Some elevated
instability will be present late tonight and may support a few
rumbles of thunder.
As the trough approaches the region tomorrow, the Texas surface low
will zip northeastward along the stationary front. This will
maintain the warm sector over northeast MS (and possibly into
extreme southwest tn) as southerly winds continue east of the
surface cyclone. Instability is forecast to increase in the warm
sector with MLCAPE peaking between 500-1000 j/kg tomorrow
afternoon. Shear will be quite strong across the region with long,
cyclonically curved hodographs. There remains a potential for
some strong to severe storms, mainly during the afternoon hours
across north MS, while the threat will be minimal north of I-40.
The primary hazard will be damaging wind, but there is also a
threat for large hail and a tornado or two. Cam ensemble guidance
continues to show the most significant updraft helicity swaths
south of the cwa, perhaps as far north as Tupelo.
Post-frontal rain will end from west to east Monday night as the
upper-level trough axis crosses the region. There is a brief
window where some lingering light rain could mix with light snow,
but it shouldn't amount to anything as it quickly ends before
sunrise. A cool and dry air mass will settle over the region
Tuesday with temperatures in the mid 40s. Shortwave ridging aloft
will promote light winds and clearing skies, setting the stage
for a chilly Wednesday morning. Expect lows in the low/mid 20s in
most areas. We'll otherwise see a nice weather period midweek as
the dry spell continues through Thursday night. Temperatures will
moderate back into the lower 50s for highs and 30s for lows, which
is pretty close to climatology for mid- December.
A progressive trough will move across the region Friday into
Saturday, providing another chance of rain for the mid-south. Quantitative precipitation forecast
doesn't look impressive with this system and dry weather should
return by Saturday evening. Medium range models indicate some
upper-level ridging Sunday into early next week. This should
provide for a quiet start to the work week with temperatures on a
slow warming trend.
Weak surface front along a mem-mkl line will sharpen up this
evening, with influx of additional maritime moisture. Kgwx VAD
wind profiler showed fl030 winds from 210 degrees at 65 to 70
knots just prior to 00z. Despite clearing noted on GOES infrared
imagery lifting into north MS, expect the maritime air to cloud up
at least a bit through the evening.
Regarding ts chances, hrrr and NAM 3km convection-allowing models
(cams) did not depict much in the way of ts overnight, while GFS
lamp guidance painted a broad swath of 40 to 50 percent chance ts
through mem and mkl. For the 00z tafs, have left thunderstorms in the vicinity in overnight
- but with lower than normal confidence. Main impact will be llws,
associated with the aforementioned fl020 winds.