River Flood Warning 75, NWS Memphis, TN

Area Forecast Discussion
National Weather Service Memphis TN
1127 PM CST Thu Feb 21 2019

.UPDATE...

Updated for the 06Z Aviation Discussion

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.PREV DISCUSSION... /issued 928 PM CST Thu Feb 21 2019/

DISCUSSION...

Surface warm front located well to the south of the area tonight.
Moist SW flow aloft lifting over the boundary is resulting in
widespread showers with a few embedded thunderstorms across North
Mississippi. Moderate amounts of elevated instability combined
with strong low level moisture transport into the area should lead
to more showers and embedded thunderstorms overnight. The latest
hi-res model data focuses continued development over North
Mississippi for the remainder of the night. Added mention of heavy
rain to the forecast for NE Mississippi. Latest regional radar
indicates that development occurring over west central Mississippi
will translate into the area over the next several hours. Much of
this area has received 3 to 5 inches of rain and the ground is
saturated with a lot of ponding water already across NE
Mississippi. The flash flood threat will increase as the night
goes on especially if any heavier thunderstorms train over the
same area. Areal and river flood warnings are in effect across the
Mid-South. Do not drive across flooded roads at night! Make sure
your weather radios are plugged in or that you have a way to get
notified of a warning.

SJM

PREV DISCUSSION... /issued 303 PM CST Thu Feb 21 2019/

Currently next surge of rain has reached the I-40 corridor...with
intensity light to moderate attributing to hourly rates up to a
quarter of an inch. Rainfall totals are approaching one inch
across southern Calhoun County where 3-hour flash flood guidance
of 2 inches may be to high. Temperatures this hour across the
Midsouth are fairly uniform in the mid to upper 40s. Winds were
northeast at 5-15 mph.

For tonight through tomorrow...A deep fetch of subtropical
moisture will continue to spread from Texas to the Southern Great
Lakes this period providing for several rounds of rain to fall
over the Midsouth. Temperatures will remain cool and generally
steady this period as the surface warm front remains near the I-20
corridor...at least through Friday afternoon. As the next potent
midlevel shortwave ejects east from the southern Rockies Friday
night the warm front will quickly surge north into the Lower Ohio
Valley and Midwest. At the same time a 999mb surface low will
begin deepening in the Oklahoma Panhandle. Until then the heaviest
of precipitation for the region will remain along and south of
the I-40...points between the 925mb and 850mb upper front. Points
closer to the MO border will receive lighter amounts until Friday
night when the surface front makes its move. Overall an
additional 2-4 inches...and perhaps localized higher amounts are
expected to fall causing a prolonged period of both flash
flooding and areal flooding. Parts of the Midsouth have been
upgraded to a High Risk for flooding from WPC for tomorrow. A few
counties along the Mississippi River were added to the flash-
flood watch to capture the lifting warm front Friday night. Most
rainfall rates will be under a quarter of an inch per hour...with
embedded thunderstorms tomorrow producing half inch or better amounts.

Saturday...the aforementioned warm front will shift north of the
area...allowing for a jump in temperatures and dewpoints. Have
lowered rain chances in the morning hours across the southern
counties as they will be much deeper in the warm sector by then.
As the surface low shifts into the Midwest during the day it is
progged to deepen to 993mb by 23/18z and 988mb by 24/00z...so
nearly a millibar per hour. This will only increase the gradient
wind field over the area...with a wind advisory likely. Now for the
severe potential. Models are in good agreement that CAPE amounts
will range between 300-800 j/kg during the afternoon...with
greater disparity in helicity amounts....200 to as much as 600
m^2/s^2. Thus the overall tornado threat for the Midsouth is just
not in focus yet. The straight line winds though are...as a
midlevel jet of 100+kts and a low level jet of 65+kts overspread
the area. Storms will likely fire up on the Pacific cold
front/Pseudo dry- line over central Arkansas midday
Saturday...with models surging these storms to the Tennessee River
by 6pm. That's a storm motion of nearly 65mph. Bowing segments
are expected with perhaps a fair amount of the Midsouth receiving
wind damage. Confidence of any discrete storms out ahead will
only occur if a few hours of sunshine can be realized...otherwise
the tornado threat will be undercut from the increasing stronger
linear shear along the front. This would provide for weaker
intensity...fast moving and briefer life-spans for any spin-ups.

Have continued a cooler forecast trend from thicker cloud cover
and the southward progression of the pacific front occluding...with
highs in the upper 60s and low 70s. The front should exit the
area early Saturday evening with southwest to west winds still
peaking near advisory levels through midnight across the north.
Drier air will provide for lows in the 40s for most.

Sunday through Thursday...overall a drier period and great drying
conditions. The only possibility of light rainfall will arrive
late Tuesday into Wednesday as a weaker disturbance transverses
the midlevels. Temperatures will be seasonal through Wednesday.
By Thursday a cold front will usher in the southern fringes of
polar airmass dropping south from the Upper Midwest. Temperature
highs will fall back into the 40s with lows near freezing.

JAB

&&

.AVIATION...
06Z TAF cycle

Low clouds will continue to spread across the entire forecast area
overnight. Rain showers will move across the forecast area for
much of the forecast period with some isolated thunderstorms
expected over portions of northeast Mississippi. Winds will be
mainly from the northeast at around 10 knots for much of the
forecast period.

ARS

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...Flash Flood Watch through Saturday evening for Crittenden-Cross-
     Lee AR-Mississippi-Phillips-St. Francis.

MO...Flash Flood Watch through Saturday evening for Pemiscot.

MS...Flash Flood Watch through Saturday evening for Alcorn-Benton MS-
     Calhoun-Chickasaw-Coahoma-DeSoto-Itawamba-Lafayette-Lee MS-
     Marshall-Monroe-Panola-Pontotoc-Prentiss-Quitman-
     Tallahatchie-Tate-Tippah-Tishomingo-Tunica-Union-Yalobusha.

TN...Flash Flood Watch through Saturday evening for Benton TN-Carroll-
     Chester-Crockett-Decatur-Dyer-Fayette-Gibson-Hardeman-
     Hardin-Haywood-Henderson-Henry-Lake-Lauderdale-Madison-
     McNairy-Obion-Shelby-Tipton-Weakley.

&&