Area Forecast Discussion
Issued by NWS Memphis, TN
FXUS64 KMEG 210951
Area Forecast Discussion
National Weather Service Memphis TN
351 AM CST Sat Jan 21 2017
Strong to severe thunderstorms continue early this morning across
central and southern MS in advance of a fast moving, shortwave
trough. Radar returns have intensified across central MS over the
past few hours, with a few cells developing just to the south and
southwest of Memphis. A few strong to marginally severe storms
are possible this morning, generally south of I-40, but this first
batch of convection will be east of the CWA by 10 AM.
Subsidence in the wake of this initial wave should provide for a
rather benign afternoon with temperatures approaching 70 degrees
across the Mid-South. We`ll see an uptick in instability as
surface temperatures. There remains some model disagreement
regarding how much instability is realized, but MLCAPE values may
push 1000-1500 J/kg across the Mississippi Delta by 00z. The cap
is expected to hold throughout the afternoon hours, but it should
erode quickly by early evening as strong forcing for ascent
overspreads the area.
A good number of the short-range models develop a mesoscale
surface cyclone over AR this afternoon, resulting in backing low-
level flow across the Mid-South. This will enhance deep-layer
shear this evening, concurrent with convection lifting across the
region. This convection may be discrete initially as it develops
over the ArkLaTex, but is expected to congeal into more of a
linear mode as it approaches the County Warning Area (CWA). Given
the steep lapse rates aloft, large hail will be a primary threat,
in additional to damaging winds. However, if the backed low-level
winds do set up as progged, there is a potential for a few
tornadoes embedded within the line segments. That said, the
tornado potential appears greatest south of the CWA.
We could see a lull in convection in the wake of this band of
storms during the overnight hours, but rain chances will ramp back
up during the day Sunday as the main upper-low moves across the
area. With the cold core of the cyclone overhead, lapse rates will
remain steep, maintaining at least a marginal hail threat on
Sunday. However, the severe threat appears much lower than what
we`re looking at this evening. Cooler temperatures are expected
Sunday afternoon, with highs in the ballpark of 60 degrees. Rain
chances continue Sunday night on the backside of the departing
upper-low. At this time, we`re only carrying mention of showers
and QPF amounts are rather light.
A few showers could linger into Monday morning along the
Tennessee River Valley, but we`ll see an otherwise cool and dry
day across the Mid-South. Expect temperatures primarily in the 50s
Monday afternoon. Mostly clear skies and light winds Monday night
will allow temperatures to fall into the 30s across much of the
area. Some areas across the Mid-South may even fall into the upper
20s. Ridging aloft will result in another nice day Tuesday.
Temperatures are forecast to warm a bit under partly cloudy skies,
topping out in the mid 50s to lower 60s.
The next chance of rain is focused on the midweek period as
southwesterly flow aloft intensifies over the central CONUS. As a
trough moves to our north on Wednesday, the trailing trough axis
will hang up over the Mid-South, providing some large scale
forcing for ascent. At the surface, a cold front will move east
across the area. Most of the precipitation is expected to occur
east of the CWA, but slight chance PoPs were warranted for much of
the area Wednesday. These low PoPs were confined to the southeast
portion of the CWA Wednesday night and Thursday.
It looks like we`ll finally see some cooler air arrive by
Thursday as the polar jet dips south of Interstate 40.
Temperatures are forecast to remain in the 40s Thursday and
Friday, but dry air and subsidence aloft should maintain a dry
forecast during this cool period.
VFR conditions will continue tonight and through much of
Saturday...except at KTUP where a shortwave moving to the south
may spread showers and thunderstorms and potentially MVFR cigs
into the area late tonight/early Saturday. Also...some MVFR vsbys
in fog may develop ahead of the rainfall. Elsewhere...conditions
should remain dry until Saturday evening. Winds will remain
southerly around 5 kts tonight...increasing to around 10 kts on
Reductions in cigs and vsbys can be expected at all terminals
Saturday evening as showers and thunderstorms impact the region.
Winds should back at the surface and increase in speeds Saturday
evening as low pressure passes to the west.