Forecast Discussion

FXUS64 KMEG 230831

Area Forecast Discussion
National Weather Service Memphis TN
331 AM CDT Mon Apr 23 2018

Rain chances will continue across the Mid-South today as an upper-
level cyclone remains nearly stationary over the region. The water
vapor continues to indicate a broad circulation with two centers of
circulation - one being over north AR and the other over west TN. To
the south of the cyclone, a well defined dry slot continues to move
north and east around the low. This trough will be in no hurry to
move east and will continue to provide large scale ascent over the
Mid-South. Rain chances will be greatest today to the north and east
of the mid-level circulation. There will likely be periods of
drizzle across portions of the Mid-South as well, at least through
the morning hours. As the dry slot continues to wrap around the
cyclone, instability will increase across the Tennessee Valley.
Thus, a few thunderstorms are possible across portions of west TN
and extreme northeast MS. However, vertical shear will be weak in
the proximity of the upper low and the severe potential will be
quite low.

The trough begins to move east late tonight and Tuesday, so rain
chances will persist through at least midday tomorrow. Despite the
low PoPs, much the CWA is expected to remain dry on Tuesday,
especially in the afternoon. We may actually see a bit of sun in
the west, allowing temperatures to rebound into the mid 60s to
lower 70s. Two fast-moving shortwave troughs will affect the area
during the latter half of the week. The first will arrive on
Wednesday, sending a weak, reinforcing cold front across the Mid-
South. There does appear to be sufficient moisture to squeeze out
some rain showers as this wave passes, but instability looks
pretty lame, so no thunder was included. Rain chances will
increase during the day Wednesday and continue during the
overnight hours, but QPF should remain relatively light. Average
rainfall amounts look to be around 1/4 inch at this time.

The ECMWF moves this system south and east of the area faster than
the GFS, while the Canadian sort of splits the difference. Given
this uncertainty, PoPs were included for Thursday, mainly south
of I-40. Rain chances will likely end by midday but there remains
enough uncertainty in this timing to retain the PoPs through the
afternoon. Look for refinements in the timing as the models
converge on a solution.

A brief dry period is expected Thursday afternoon and evening, but
the next wave will arrive by Friday morning. This system looks to
drive a more substantial front through the area on Friday. Dewpoints
of 45-50 degrees will limit instability with this system so the
potential for significant convection doesn`t look very good. That
said, showers, and possibly a few thunderstorms, are possible as the
front moves across the Mid-South.

Dry and mild weather is anticipated over the weekend. The dry-post
frontal air mass is expected to persist through early next week as a
blocking upper-level ridge develops over the Plains. Temperatures
will moderate back into the 70s to round out the weekend with
overnight lows in the 40s and 50s.



/06z TAFs/

Surface low pressure over west Tennessee should pivot back to the
northwest through Monday morning. Low stratus and fog should
continue to redevelop with IFR expected at all terminals, and
potentially LIFR cigs at all sites except KTUP later tonight.
Winds should remain below 8 kts at all locations and will have
minimal impact as compared to cigs.

Additional showers and thunderstorms are expected Monday with
continued low IFR cigs at KJBR, and low end MVFR at KMEM. Further
east, at KMKL and KTUP, the surface and upper low should remain to
the west, allowing increased instability. Cigs should improve to
at least MVFR and potentially VFR by afternoon. The increased
instability and lift from the low pressure will support showers
and thunderstorms.

IFR cigs should again develop by Monday evening in the lingering
moist environment. Later Monday night, some LIFR is possible.