Scientific Forecaster Discussion
fxus64 kmeg 151000
Area forecast discussion
National Weather Service Memphis Tennessee
400 am CST sun Dec 15 2019
Currently...surface high pressure extends from the upper MS valley
into the mid-south with light north-northeast winds. Mostly cloudy skies
prevail across the region with temps in the upper 30s to mid 40s.
Today...an upper level trough will eject out of the SW U.S. Today
as surface high pressure over the mid-south moves east. In
response, winds turn southerly across the lower Mississippi
Valley as a developing warm front lifts north into the mid-
south. Expect mainly dry weather this morning but rain chances
will begin to increase this afternoon especially along and north
of I-40. Temps will range from the lower 60s across north MS to
the lower to mid 40s over NE Arkansas and the MO bootheel.
Tonight...the upper trough will push into the Southern Plains
tonight with deep, moist SW flow aloft across the mid-south. 00z
guidance has shown a trend toward a more southerly track of the
upper trough. As a result the associated surface low will track a
little further south across southern Arkansas/northern la and the warm
front across the mid-south will sag a little south overnight to
more a Clarksdale-Holly Springs-Parsons Tennessee line by 12z Monday.
Expect precipitation to continue to develop overnight, especially
after midnight as lift increases across the region with the
approach of the upper trough. Will start to see some embedded
thunderstorms mainly along and north of the warm front as some
elevated instability moves into the area.
Monday...as the upper trough pushes into the mid-MS valley the
surface low will track along the warm front and through the mid-
south. Expect the track to be south of I-40 now and as a result
the severe potential will shift slightly to the the southeast. There will
be a wide range of temps across the mid-south with highs in the
lower 70s over parts of NE MS to only the lower 40s across NE Arkansas
and the MO bootheel. Expect surface dewpoints to climb into the
lower 60s in the warm sector with sbcapes of 250-750 j/kg. Strong
vertical wind shear is expected as a 80-90 kt mid level jet pushes
into the area. The surface low should serve to back low level
winds a bit and model soundings are indicating this and producing
0-1km helicity values over 200 m2/s2, suggesting rotating storms
are possible. As the surface low tracks through the region Monday
afternoon and the trailing cold front pushes across north MS
expect storms to intensify. The positively titled upper trough
and flow parallel to the front will produce a messy storm Mode
with lines and clusters likely. Expect a few of these storms will
become severe across the warm sector with damaging winds the main
threat. A tornado is also possible. Hail could occur with any
cells that remain semi-discrete. Best chances for severe storms
will be across north-central and NE MS during the afternoon and
Monday night...severe threat will continue until about 02z before
the surface low and front track east. Rain will taper off overnight.
Any changeover to snow threat remains minimal. By morning temps
will drop into the upper 20s north to upper 30s over parts of NE
MS on gusty northwest winds.
Tuesday and Wednesday...back to winter. A stiff northwest breeze and
strong low level cold air advection will bring back the chills. Highs will only
be in the lower 40s Tuesday. Tuesday night will see temps back in
the 20s followed by another day in the 40s on Wednesday.
Thursday through Saturday...high pressure moves east and southerly
flow and slightly milder temps will prevail for Thursday. A weak
moisture starved system moving through Friday and Friday night
could bring some light precip but does not look significant attm.
Weekend looks decent at first blush with perhaps a significant
warming trend into early next week as upper level high pressure
builds into the region.
A few changes for the 06z tafs, as models have come into better
agreement with the position of the stationary front on Sunday,
keeping mem and mkl in the warm sector late afternoon through
evening. Some brief dip down to IFR not out of the question at
mem and mkl around 21z before the warm front lifts through. Winds
off the surface (around fl020) will preceded a surface wind shift
to the south, and have retained the low level wind shear mention at mem and mkl.
In the interim, steady as she GOES on a light traffic night at
mem. Late evening GOES infrared imagery showed low level marine stratus
lifting north through south MS. The deck was on track to arrive in
tup prior to sunrise, and mem shortly thereafter. Not confident
we'll see IFR, given the extensive midlevel deck above, but MVFR
at least appears likely toward sunrise.