Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Memphis Tennessee
1133 PM CST Wednesday Dec 18 2013
Updated for the 06z aviation discussion
Previous discussion... /issued 959 PM CST Wednesday Dec 18 2013/
Surface high pressure prevails across the southeast U.S. This
evening resulting in milder southerly flow across the midsouth.
Temperatures are in the 40s to around 50. Meanwhile a few high clouds
are streaming across the region. Added a few clouds to the
forecast otherwise things are right on track.
Previous discussion... /issued 323 PM CST Wednesday Dec 18 2013/
Middle afternoon temperatures are mostly in the middle 60s across
the midsouth with expected afternoon highs in the upper
50s...generally 5 to 8 degrees above normal. Warmer than normal
temperatures are expected to continue through Sunday with the
warmest temperatures expected Saturday afternoon. Highs could be
as much as 20 degrees above normal Saturday...with much of the
area in the 70s. Such a warm airmass in late December can be a
The main focus of this discussion will be the potential for strong
to severe thunderstorms Saturday into Saturday night. Dry
conditions will continue tomorrow with highs in the low to middle
60s. Tomorrow afternoon we should begin to see signs of a powerful
cutoff...but progressive...low digging along the West Coast moving deep
into the Baja California peninsula by Friday morning. This pattern will
result in southwest flow across the midsouth. At the
surface...high pressure will shift to the east of the midsouth
resulting in southerly flow across most of the southeast. This
flow will usher in deep Gulf moisture into east Arkansas...the
Missouri bootheel and north Mississippi. Some showers are expected
Friday into Friday night...as a broad 100-125kt upper level jet
develops and streams from southwest Texas across the central
Mississippi River valley.
Saturday...the upper low will shift into the Southern Plains and
a surface low will deepen in south Texas. As this low
deepens...the pressure gradient will tighten further strengthening
the south winds at the surface. Sustained wind speeds may reach 20
miles per hour. A slow moving cold front will sag into the midsouth by
midday Saturday helping to focus surface lift. The upper level jet
will continue to strengthen Saturday...to around 125-135kt. The
surface low will track across central Arkansas into west Kentucky
Saturday into Saturday night keeping most of the midsouth in the
warm sector. A 50 to 60 knots low level jet will develop late Friday into
early Saturday...strengthening to near 70 kts Saturday night over
north Mississippi as it shifts out of the area. Shear profiles
will be impressive. However...the main limiting factor looks to be
instability. Rain will likely be ongoing Saturday morning with
extensive cloud cover. I generally do not put a lot of Faith in
instability parameters more than a couple of days in the
future...but as of now guidance only brings convective available potential energy to around 450
maximum Saturday afternoon...likely too little to balance the extreme
shear. Without breaks in cloud cover I have my doubts that will
even be realized. That should limit severe potential for organized
individual thunderstorms...but a line of strong to severe
thunderstorms is possible...and with 60-70 knots winds only
4-5000 feet off the ground...it would not take much to Transfer
damaging wind to the ground. Will maintain a threat for severe
thunderstorms area wide...but feel like the main threat will be
late Saturday over north Mississippi as the stronger low level jet develops
and is shifting out of the midsouth. Luckily we have a couple more
days to nail down the specifics of this powerful storm.
Additionally...rainfall totals are expected to be on the order of
2-4 inches. Some localized flooding is possible.
Conditions will improve Sunday and any severe threat will wane.
Temperatures will turn cooler...back near normal Monday with dry
conditions through midweek.
VFR conditions will persist for most of the forecast period.
Ceilings will gradually lower by late Thursday afternoon and into
Thursday evening with MVFR conditions expected at kjbr by Thursday
night. Winds will be from the south at 5 to 1o knots overnight and
then increase to 10 to 15 knots by late Thursday morning. Some
higher gusts will be possible Thursday afernoon.
Preliminary point temps/pops...
mem 44 65 57 72 / 0 10 40 50
mkl 38 63 52 68 / 0 10 40 50
jbr 41 62 54 69 / 0 10 50 50
tup 39 64 53 69 / 0 10 20 50