Forecast Discussion

FXUS64 KMEG 212343

Area Forecast Discussion
National Weather Service Memphis TN
643 PM CDT Sat Oct 21 2017

Updated to include the 00z aviation discussion.


.PREV DISCUSSION... /issued 238 PM CDT Sat Oct 21 2017/


Breezy and mild conditions this afternoon as pressures fall ahead
of the approaching front/upper trough in the Central Plains.
Temperatures this hour were in the upper 70s to low 80s...with a
few stations seeing dewpoints cresting 60F. Skies were a mix of
clouds and sun.

For tonight through Monday...models are in good agreement with a
faster solution for the shortwave trough in the Plains to briefly
become a closed low at 500mb in the Ozarks late tonight...then
sliding east into the Ohio Valley and quickly dampening by Monday
afternoon. Thus most Midsouth locations will see a window of
20-24 hours of precipitation...with points east of the
Mississippi River receiving upwards of 3 inches. A welcoming need.
The best instability with the associated cold front will be
confined to areas west of I-55 from roughly 10-18z tomorrow
morning...with the focus quickly shifting to points south of I-20
beyond this time. Moderate to heavier showers though will remain
well into the night across portions of west Tennessee and north
Mississippi. By Monday westerly surface winds will begin drying
the region...with brief break before the next wave and front
arrive on Tuesday. Only the far east may see lingering clouds and
a few isolated showers. The downsloping winds off the Ozarks
should raise temperatures to the low 70s in the west....while the
east stays in the 60s.

Tuesday through next weekend...models this period slowly begin to
diverge. Initially a second reinforcing cold front will slide
through the area with very little moisture left to work with.
Timing of this boundary on Tuesday may pose a tricky temperature
forecast. Behind the front northwesterly winds will make it
blustery across the north where 60F for a high may be a struggle.
Diminishing winds overnight will lead to the best chance during
the week for patchy frost to form in the east. Surface high
pressure will remain in control Wednesday and Thursday with winds
slowly becoming southerly. Highs will warm from the low to mid the upper 60s to the mid 70s. Clouds will be on the
increase as the next shortwave and Canadian airmass drops into the
Upper Midwest by Friday. The axis position of this wave differs
considerably between the GFS and ECMWF...with the GFS farther
east...cooler and less precipitation. The mean ensemble members
show this trend as well. The Euro places a longer period of
southwesterly flow over the region and warmer temperatures. Have
leaned with the cooler and drier GFS.



/00z TAFs/

A few thunderstorms continue to the SW of KCKM but should have no
impact on forecast terminals this evening. Generally benign
conditions are expected over the next 8-10 hrs although S to SE
winds will increase as the low-level jet intensifies. A line of
showers and thunderstorms will move from west to east across the
Mid-South early Sunday and VCTS was included at all TAF sites. In
addition to convection, MVFR (and potentially brief IFR)
conditions are expected across most of the area through at least
midday, if not well into the afternoon hours.