Severe Thunderstorm Warning 184, NWS Memphis, TN

Area Forecast Discussion
National Weather Service Memphis TN
435 AM CDT Sat May 27 2017

.DISCUSSION...

An active weather period is anticipated for the next 48 hours as a
series of shortwaves initiate thunderstorm activity within a
strongly unstable and sheared environment. Severe thunderstorm
potential will be a concern throughout this period.

An initial shortwave early this morning has initiated a cluster
of severe thunderstorms over northern Arkansas into southern
Missouri. This complex of storms will continue to advance east
southeast with the latest CAM model solutions suggesting an
expansion further south with activity to at least the Interstate
40 corridor and potentially into northeast Mississippi by late
morning. The environment in advance of these storms remains quite
favorable with MLCAPES between 2000-3000 j/kg and steep mid level
lapse rates around 8.0 c/km. In addition, deep layer shear around
40 kts will be sufficient to maintain storm organization. A severe
potential should be maintained across the northern portions of the
Mid South this morning in association with this cluster of storms
as it progresses southeast and maintains an increasingly QLCS mode
with embedded supercell structures. The primary threats this
morning will be large hail and damaging winds as the flow remains
primarily unidirectional in nature. This activity should shift
east of the forecast area by this afternoon. There still may be a
few scattered new storms across portions of northwest Tennessee
near the Tennessee River, but further west expect mainly a return
to dry conditions. Temperatures should warm this afternoon into
the middle and upper 80s behind the morning convection with very
humid conditions expected as dewpoints remain in the lower to
middle 70s. This should result in afternoon heat index values into
the upper 90s across the Delta counties.

Attention will turn upstream across southern Missouri this evening
as a more significant shortwave rotates around the base of a large
scale upper trough over the Northern Plains and Upper Mississippi
Valley. This should initiate storms to our northwest over Missouri
this afternoon which should organize into a forward propagating
Mesoscale Convective System (MCS) which should advance into
portions of northeast Arkansas, the Missouri Bootheel, and far
northwest Tennessee towards or just after sunset. The airmass will
become strongly unstable and remain so through tonight. Even
overnight, MLCAPE between 1500-3000 j/kg can be expected along
with steep mid level lapse rates around 8.5 c/km and LI/s around
-8c. These impressive instability parameters will be combined with
 ample deep layer (0-6km) shear to support severe weather. A
 moderate risk for severe weather is in place for tonight across
 our northern tier with an enhanced risk further south to the
 Interstate 40 corridor. The primary severe weather threat will be
 damaging winds, some potentially widespread and significant
 across these areas. In addition, large hail and isolated
 tornadoes may occur, especially with any QLCS circulations that
 develop within the MCS. Storms may gradually weaken in intensity
 as they drop south of the Interstate 40 corridor, but some severe
 weather is likely to continue just not as widespread in nature.

Any overnight activity should diminish by Sunday morning as the
lead shortwave rotates northeast of the area. Latest model
guidance suggests that the atmosphere should destabilize again by
afternoon with steepening mid level lapse rates around 8.0 c/km
and MLCAPE values between 1500-3000 j/kg ahead of the main upper
level trough as it pushes into the Mid South. There is some
uncertainty with regard to how the Saturday night convection
impacts the instability on Sunday. It appears that the best
potential for reinitiation of storms on Sunday afternoon and
evening will be along and south of the I-40 corridor. Again, if
the expected instability can be realized, then deep shear should
be sufficient to support a few severe storms with damaging winds
and large hail. This should occur ahead of a surface cold front
that will push slowly south through Sunday night and be positioned
across north Mississippi into Monday.

Warm and moist conditions will persist into next week with a
continued threat for wet and stormy weather. A stalling front
combined with ample gulf moisture and a slow moving upper low
approaching from the west should keep scattered to numerous storms
in the forecast through much of next week. Temperatures should
remain near seasonable levels through the extended forecast
period.

JLH

&&

.AVIATION...

VFR conditions will prevail through much of the overnight before
low clouds develop toward sunrise and continue into Saturday
morning. Latest guidance points toward the possibility of sct
shras/tsras during the 10z-18z time frame so included a VCTS for
that time period at KJBR, KMEM and KMKL. Cigs will gradually
improve to VFR by Saturday afternoon. Next concern is a line of
thunderstorms that will likely be entering the forecast area
toward the end of the period. SSW winds at 7-9 kts will increase
to 10-15 kts Saturday morning with higher gusts.

SJM

&&

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

Hazardous Weather Outlook
National Weather Service Memphis TN
451 AM CDT Sat May 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>092-281200-
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-
451 AM CDT Sat May 27 2017

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

.DAY ONE...Today and Tonight

An initial round of severe thunderstorms is expected this morning
across northeast Arkansas, the Missouri Bootheel, west Tennessee,
and portions of far northern Mississippi. Damaging winds and large
hail are expected with a line of storms moving across the region.
These storms should exit our eastern areas by early afternoon.

For later this evening and tonight, there is a Moderate Risk for
severe thunderstorms north of a line from Jonesboro, Arkansas, to
Dyersburg, Tennessee, to Martin, Tennessee. There is an Enhanced
Risk for severe thunderstorms south of the Moderate risk and north
of a line from Marvell, Arkansas, to Hernando, Mississippi, to
Savannah, Tennessee. The Enhanced Risk area includes the Memphis
Metropolitan Area. The primary severe weather threat will be
damaging winds, which may be widespread and significant. In
addition, large hail and isolated tornadoes are also possible. The
primary timing for severe weather will be later this evening and
overnight.

A Slight Risk for severe weather remains across the remainder of
the area. Although not as widespread, the potential will exist for
severe storms in these locations tonight.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

There is a Slight Risk for Severe Thunderstorms across the entire
Mid South on Sunday and Sunday night. The primary severe weather
risks during this period will be damaging winds and large hail.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed today through Sunday
night.

JLH