Area Forecast Discussion
Issued by NWS Memphis, TN
FXUS64 KMEG 272321
Area Forecast Discussion
National Weather Service Memphis TN
521 PM CST Mon Feb 27 2017
Updated for 00Z Aviation Discussion.
.PREV DISCUSSION... /issued 329 PM CST Mon Feb 27 2017/
A complex convective scenario in store for Tuesday and Wednesday.
A maritime warm front will lift into the Midsouth late tonight
enhancing moist isentropic lift mainly along and north of the
I-40 corridor. 18Z NAM Bufr soundings depicted a weakly-capped
unstable layer around 925mb. This isentropic lift in this layer may
be sufficient to overcome weak convective inhibition, allowing
deep updrafts to form and persist into the morning daylight hours
along and north of I-40.
For Tuesday, NAM Bufr soundings depict an elevated mixed layer
above 850mb late morning into the afternoon. The EML is shown to
weaken during the mid to late afternoon, but likely sufficient to
cap deep convection. Should storms manage to break this weaker cap,
quick intensification to severe levels would be possible given
CAPE in excess of 1500 J/KG and near 7C/KM midlevel lapse rates.
Given the expected limited coverage of storms, have reduced Tuesday
afternoon rain chances by 10 percent over most areas.
Short range models begin to diverge by the Tuesday evening period,
with the NAM showing a significant EML redevelopment above 900mb,
capping deep convection. GFS soundings showed no such capping
mechanism and as as such, more thunderstorm coverage late evening
and overnight. Tend to favor the GFS in this scenario, given the
midlevel height falls. Instability won`t be as impressive east of
the MS River overnight, but still adequate, given midlevel lapse
rates near 7.25 C/KM. A marginal overnight tornado threat would
be associated with any storms that form out a head of a developing
line and with any of the stronger QLCS line segments.
Storms should exit to middle TN by midmorning Wednesday. A secondary
enhanced risk of severe storms will develop over northeast MS,
where a secondary Enhanced Risk exists early in the SPC Day 3
Following Wednesday morning`s cold frontal passage, a dry and
cool midcontinental airmass will spread into the Midsouth.
Thursday will see afternoon relative humidity levels fall below 30
percent east of the MS River. A reinforcing dry cold front will
bring enough cold advection to moderate afternoon humidity levels
slightly, but may be offset by stronger north winds.
Return flow will develop behind a departing surface high pressure
late Saturday. A few showers will be possible late in the weekend,
associated with a maritime warm front lifting through the lower
MS River valley. This warm and humid airmass will prevail until a
cold frontal passage on Tuesday.
.AVIATION...00Z TAF Set
VFR to start...but short term models key in convection developing
by midnight...then lasting through the mid morning hours Tuesday.
Scattered showers and thunderstorms at all the TAF sites will
decrease cigs/vsby. Sites will likely drop and then bounce between
IFR and MVFR through most of the period...with VFR weather possible
at MEM...JBR...and MKL late as warm front lifts north. Southeast
through south winds will start off around 7-12kts...with frequent
gusts of 19-24kts developing during the latter half of the
period. In addition low level wind shear is likely late tonight.