Severe Thunderstorm Warning 17, NWS Memphis, TN

Area Forecast Discussion
National Weather Service Memphis TN
521 PM CST Mon Feb 27 2017

.DISCUSSION...
Updated for 00Z Aviation Discussion.

&&

.PREV DISCUSSION... /issued 329 PM CST Mon Feb 27 2017/

DISCUSSION...
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
Outlook.

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.

PWB

&&

.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.

JAB

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&

Hazardous Weather Outlook...UPDATED
National Weather Service Memphis TN
238 PM CST Mon Feb 27 2017

ARZ008-009-017-018-026>028-035-036-048-049-058-MOZ113-115-
MSZ001>017-020>024-TNZ001>004-019>022-048>055-088>092-282245-
Alcorn-Benton MS-Benton TN-Calhoun-Carroll-Chester-Chickasaw-Clay-
Coahoma-Craighead-Crittenden-Crockett-Cross-DeSoto-Decatur-
Dunklin-Dyer-Fayette-Gibson-Greene-Hardeman-Hardin-Haywood-
Henderson-Henry-Itawamba-Lafayette-Lake-Lauderdale-Lawrence-
Lee AR-Lee MS-Madison-Marshall-McNairy-Mississippi-Monroe-Obion-
Panola-Pemiscot-Phillips-Poinsett-Pontotoc-Prentiss-Quitman-
Randolph-Shelby-St. Francis-Tallahatchie-Tate-Tippah-Tipton-
Tishomingo-Tunica-Union-Weakley-Yalobusha-
238 PM CST Mon Feb 27 2017

This hazardous weather outlook is for portions of East Arkansas...
the Missouri Bootheel...North Mississippi...and West Tennessee.

.DAY ONE...This Afternoon and Tonight

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

There is limited potential for thunderstorms across the Midsouth
Tuesday afternoon, but storms do develop, they may quickly intensify
to severe levels. Large large hail, damaging winds and a brief
tornado will be possible.

The potential for severe weather will increase by midevening
Tuesday over eastern Arkansas, the Missouri bootheel and far
northwest Tennessee, ahead of an approaching cold front. The
severe weather threat will lift east through the remainder of the
Midsouth late Tuesday night and Wednesday morning. Large hail and
damaging winds will be the primary threats. A brief tornado or
two cannot be ruled out. The storms should exit the Midsouth
Wednesday afternoon.

Wildfire danger will likely reach elevated levels Thursday
afternoon, due to low relative humidity. North Mississippi and
west Tennessee will likely see humidity levels drop to readings of
20 to 30 percent.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be requested Tuesday and Wednesday.

PWB

Special Weather Statement
National Weather Service Memphis TN
814 PM CST MON FEB 27 2017

ARZ017-280245-
Lawrence AR-
814 PM CST MON FEB 27 2017

...A SIGNIFICANT WEATHER ADVISORY HAS BEEN ISSUED UNTIL 845 PM CST
FOR...

Lawrence County in eastern Arkansas...

At 813 PM CST...a strong thunderstorm producing pea size hail or
larger and winds at least 40 mph was located over Lynn, or near Lake
Charles State Park, moving northeast at 40 mph.

Very heavy rain along with continuous cloud to ground lightning are
also possible with this thunderstorm.

People in Lawrence County should monitor this storm closely.

LAT...LON 3616 9122 3615 9108 3612 9107 3612 9106
      3615 9106 3615 9076 3589 9106 3589 9136
TIME...MOT...LOC 0213Z 238DEG 33KT 3600 9121