Area Forecast Discussion
Issued by NWS Memphis, TN
FXUS64 KMEG 201745 AAA
Area Forecast Discussion...UPDATED
National Weather Service Memphis TN
1145 AM CST Fri Jan 20 2017
Updated for 18Z Aviation Forecast Discussion below.
.PREV DISCUSSION... /issued 1039 AM CST Fri Jan 20 2017/
At 1030 AM CST around the Mid-South... Temperatures are currently
in the mid 50s to lower 60s around the region with clouds still
present. Winds are generally less than 5 kts from the south.
Latest visible satellite imagery depicts some clearing well off
to the southwest over the Arklatex region. Some clearing of
clouds will be possible over southern portions of the Mid-South
later this afternoon, and as such have updated sky grids a bit.
Otherwise, no other updates are necessary at this time.
PREV DISCUSSION... /issued 401 AM CST Fri Jan 20 2017/
A deep mid-latitude cyclone is lifting north across the Upper
Midwest early this morning. One shortwave trough associated with
this cyclone moved across the Mid-South Thursday, with a strong,
westerly upper-level jet nosing into the area aloft. Subsidence is
noted on the water vapor loop, but we`ll be seeing the effects of
the next wave entering the Southern Plains in the short-term.
Relatively quiet weather conditions are observed across the region
this morning. Very few radar returns were noted, but low clouds
will persist through much of the morning. There could be some
patchy drizzle over the next few hours and some A.M. sprinkles,
but this shouldn`t amount to anything. Thus, no PoPs were included
in today`s forecast. Temperatures will be a bit warmer, with
highs in the mid 60s to lower 70s.
Dry weather will continue this evening, but showers and
thunderstorms are expected to develop after midnight as the next
shortwave trough approaches. This convection is likely to develop
in an area of warm advection and will mainly affect north MS.
However, rain chances were included as far north as the I-40
corridor given the spatial uncertainty. We anticipate sufficient
instability to support a few strong storms during the early
morning hours, but the current thinking is that the stronger
storms will generally remain south of the CWA.
Instability will remain in place throughout the day Saturday with
temperatures approaching 70 degrees. MLCAPE progs of 1500-2000
J/kg are indicated by both the GFS and NAM. Although there will
be a bit of a cap to deal with, scattered diurnal showers and
thunderstorms are expected across much of the area. Some storms
may become severe given the thermal and kinematic environment in
place, mainly south of I-40.
A better chance for thunderstorms will be Saturday night into
Sunday as a deep upper-level cyclone traverses the region.
Guidance is fairly consistent in moving this low across the
southern portion of the CWA during the day Sunday. Cooler temps
aloft will enhance instability, but the weaker winds in the center
of the cyclone should reduce vertical speed shear, especially
least across the northern half of the CWA. This will diminish the
severe weather threat late Saturday evening. An attendant surface
low will move east across the CWA Saturday afternoon, dragging a
cold front across the area. This will advect cooler and drier air
into the area for the early part of next week.
Highs on Monday will largely be in the 50s, warming into the 60s
in some areas on Tuesday. Morning lows will also be closer to
seasonal norms, falling into the 30s for most of the Mid-South by
Tuesday morning. Dry weather is anticipated Monday and Tuesday as
a transient mid/upper-level ridge migrates east across the region.
Southwesterly flow aloft will resume by midweek as a deep trough
digs over the western CONUS. The lingering surface boundary in the
vicinity will provide a focus for light precipitation Wednesday
and Thursday. PoPs remain at slight chance during this time frame
given the uncertainty on where this boundary will be. Temperatures
will be near to slightly above normal on Wednesday, but a stronger
cold front is progged to arrive on Thursday, possibly knocking
temperatures back to slightly below normal.
Mild and humid maritime airmass will prevail through midday
Saturday. A midlevel clear slot, combined with daytime mixing
should bring VFR to most sites by midafternoon. High clouds will
arrive this evening, but may not be sufficient to prevent low
stratus formation, particularly at TUP, where low level pressure
gradient is the weakest, and where greater rainfall occurred
Expect some dissipation of low stratus with the arrival of a
solid midlevel deck toward sunrise. Better TSRA chances for
MEM after 18Z Saturday.