Tornado and Flash Flooding in Arkansas, March 17, 2021

Area Forecast Discussion
National Weather Service Little Rock AR
104 AM CDT Wed Mar 17 2021

.AVIATION...17/06Z TAF CYCLE

FLight conds wl be deteriorating thru the overnight and mrng hrs
as several rounds of convection wl affect the FA. VFR conds early,
wl transition to mainly MVFR arnd daybreak as lower CIGS
overspread the region. There wl be an initial round of convection
moving NWD thru the early mrng hrs. Then another round wl affect
the area fm arnd midday thru the aftn hrs, assocd with a dryline/
CDFNT movg thru fm the west. Conds wl briefly improve post-fntl
but lower clouds wl quickly move in to close out the PD. /44/
&&

.PREV DISCUSSION...(ISSUED 235 PM CDT Tue Mar 16 2021)
SHORT TERM...Tonight Through Thursday

.Main focus remains on a widespread threat for severe wx across
the Natural State...

.Synopsis...

Latest WV sat imgry depicted a robust vorticity max traversing over
the Srn periphery of the Four Corners region, and mesoanalysis data
is further indicative of this upper lvl low. At the sfc, broad
cyclonic flow was noted over Ern NM and the OK/TX panhandle region.
The aforementioned upper trof is progged to quickly translate
Ewrd across the Srn plains Tues, further enhancing the low-lvl
mass response as the two features become juxtapositioned. A
strengthening sfc pres grad will spread Srly to S/Erly sfc winds
over the fcst area, allowing for rampant WAA and poleward moisture
transport. By Wed morning, an environment characterized by robust
synoptic ascent overtop plentiful low-lvl moisture and deep layer
wind shear veering w/ height will be prevalent across the Srn
Cntrl US, and will be extremely conducive for widespread severe
thunderstorm activity, some of which may be significant in nature.

.Today and Tonight...

You could certainly call today the calm before the storm...Settled
wx condns will prevail as strengthening sfc low pressure over
NM/OK/TX spreads S/Erly winds across the state. A warm frnt, which
was located over Srn AR near the LA border earlier this morning will
lift N/wrd over the next 24 hrs, w/ a plume of Td's in the mid-50s
extending into Nrn AR, and 60s over portions of Srn AR. As WAA ramps
up, seasonably warm temps will be noted over the fcst area this
afternoon w/ readings in the upper 70s across much of the state
accompanied by increasing cloud cover later this afternoon. Lows
around the region tonight lkly won't fall too far as WAA continues
overnight w/ lows in the mid-60s across the Srn portion of the
state, and mid-50s to the N.

.Wednesday...

.A few rounds of thunderstorms are anticipated to move across the
state through the day, w/ increasing intensity and svr potential
through each round...

Early Wed morning (06-12Z)...Strong sfc low pressure is progged to
be centered over Cntrl OK w/ a warm frnt lifting N/wrd over the
state, lkly invof the I-40 corridor. Low-lvl moisture will have lkly
increased further from Tues evening due in part to a H850-H700 30-40
kt LLJ, w/ a nose of 65F Td's extending as far N as the I-40
corridor, and 60F Td's possibly extending into the Nrn row of
counties in AR. The upper trof is progged to be moving across OK,
and increasing synoptic forcing for ascent atop low-lvl isentropic
ascent coupled w/ WAA/moisture advection will supply the fuel for
early morning convection. Based on the last few synoptic suites of
CAM guidance, early Wed morning storm activity will be limited to
invof the warm frnt as it advances N/wrd, lkly impacting portions
of Srn AR. Pt fcst soundings are indicative of this activity
staying somewhat elevated in nature, however given the antecedent
environment and bndry movement, storms could transition to become
more sfc based as time progresses. Primary svr hazards will lkly
be limited to large hail during this time frame.

Wed morning (12Z-18Z)...As the bndry continues to move N/wrd,
increasing forcing for ascent will drive another round of scattered
storms over the Cntrl third of the state around 12Z Wed morning. Sfc
based buoyancy is expected to become more prevalent as diurnal
heating takes effect, however mixing will also need to be considered
w/ Srly winds of 10-15 kts lkly invof the approaching sfc low. A
plume of ML buoyancy of 1500-2000 J/kg w/ locally greater pockets is
progged over the majority of the state. The extent of this round of
convection will play a role into the evolution of the afternoon rd
of storms though...primarily, how quickly and how thoroughly will
destabilization occur...e.g., how much will lingering cloud
cover/cirrus shields limit radiational heating, however
persistent WAA still looks to keep afternoon temps near the low to
mid 70s. W/in this second rd of storms, all three svr hazards
will become more lkly as low-lvl wind profiles become more
favorable for sustaining rotating updrafts.

Wed afternoon and evening (18Z and beyond)...The upper trof and H500
70+ kt jet max will be moving across the state at this point,
supplying a plentiful amount of vertical shear...e.g. bulk shear
values of 70+ kts. At the sfc, the warm frnt is expected to have
advanced N/wrd into MO, w/ a dryline mixing E/wrd into Cntrl AR. CAM
guidance continues to depict initialization of a third rd of storms
during the 18-20Z timeframe along this bndry, and slight separation
of bndry movement and bulk shear vectors may support a brief window
of discrete cell development, where cells would advance into a
slightly worked over environment from morning precip. However, pt
fcst soundings still indicate a very unstable environment w/
favorable low-lvl veering wind profiles, particularly should sfc
winds become more backed ahead of the dryline. 00Z and 12Z HREF
guidance have depicted modest signals over Cntrl and Ern AR for
persistent and sustained updrafts, of which a few may become
significant. W/ the potential for discrete rotating updraft
development, all svr hazards will become much more prevalent during
the afternoon and evening hours as storms initialize...including
large hail, damaging winds, and a few tornadoes.

As the evening progresses, upscale development will lkly occur w/
some embedded supercells remaining in a broken line of storms
advancing E/wrd, and a QLCS threat will increase into the later
evening for Ern AR, including brief QLCS tornadic activity, and
damaging winds. Once consolidation begins, the line is expected to
move E/wrd quickly, and will lkly clear the state after 00Z Wed
night. As storm activity is quickly ushered out of the region, the
sfc low will continue to advance to the E, and a tailing cold frnt
will sweep through the state overnight.

.Thurs...

A stout airmass change will be noticed by Arkansans Thurs morning w/
Td's back down into the upper 30s to low 40s for most. Strong and
gusty Wrly winds will prevail through the day following the cold
frnt with sustained values of 15-20 kts, and gusts of 25 kts. Under
forcing for descent as the upper trof slides to the E, drier condns
will be seen across the state w/ clearing skies and cooler temps in
place.

LONG TERM...Thursday Night Through Monday

Much quieter long term forecast when compared to the short term with
12z models looking fairly similar to earlier runs and therefore only
minor tweaks were made to the previous forecast. Long term begins
with upper level low hanging around to the NE of the state...NAM is
suggesting some wrap around precip will be possible across NE
Arkansas. Add this point did not add PoPs to the forecast, but will
monitor this for future forecast updates. Pressure gradient will
remain fairly tight Thursday night before it finally relaxes close
to midday on Friday. As a result will keep winds fairly elevated
during the overnight hours and a good chunk of the day on Friday. As
the system departs to the east an upper level ridge of high pressure
will try to build into the region. This combined with a surface low
to our northeast will result in northerly winds to the region on
Saturday both at the surface and aloft. Combine this with clear
skies and low temperatures Saturday morning will be at or just below
freezing across northern portions of the state with temperatures in
the mid 30's as far south as Hot Springs and Pine Bluff. Depending
on how much vegetation has greened up over the past warm spell may
determine the need for frost/freeze headlines. Beyond Saturday the
aforementioned ridge will build into the region and temperatures
will gradually warm each day with moisture on the increase across
the region. This will set the stage for our next system that moves
into the state on Monday. Rain chances will increase through the day
with the best chances for precipitation just beyond the long term.
&&

.LZK Watches/Warnings/Advisories...NONE.
&&

Hazardous Weather Outlook...UPDATED
National Weather Service Little Rock AR
249 PM CDT Tue Mar 16 2021

ARZ003>008-012>017-021>025-030>034-037>047-052>057-062>069-172000-
Boone-Marion-Baxter-Fulton-Sharp-Randolph-Newton-Searcy-Stone-
Izard-Independence-Lawrence-Johnson-Pope-Van Buren-Cleburne-
Jackson-Logan-Conway-Faulkner-White-Woodruff-Scott-Yell-Perry-
Polk-Montgomery-Garland-Saline-Pulaski-Lonoke-Prairie-Monroe-Pike-
Clark-Hot Spring-Grant-Jefferson-Arkansas-Dallas-Cleveland-
Lincoln-Desha-Ouachita-Calhoun-Bradley-Drew-
249 PM CDT Tue Mar 16 2021

This Hazardous Weather Outlook is for a Large Part of Arkansas.

.DAY ONE...Tonight

Isolated thunderstorms...a few of which could be strong to severe...
will be possible late Tuesday night over far southern Arkansas as a
warm front lifts slowly northward into the state. Large hail and
damaging winds will be the main threats.

.DAYS TWO THROUGH SEVEN...Wednesday Through Monday

The potential for severe thunderstorms will continue early
Wednesday morning ahead of a cold front. Hail and damaging winds
will be the main threats, but by Wednesday afternoon all modes of
severe weather will be possible. The main concern will be across
central and eastern Arkansas midday on Wednesday and continue
through Wednesday afternoon and early evening. One last round of
severe weather will be possible across northern Arkansas late
Wednesday night with a few hail storms possible.

Besides the severe weather potential, strong winds in the 15 to 25
mph range with higher gusts will be possible Wednesday and Thursday.

A few locations across northern Arkansas may dip down into the
lower to mid 30s during the morning hours Saturday and Sunday.

.Spotter Information Statement...

Spotter activation may be needed later tonight and Wednesday.

Visit NWS Little Rock on the web. Go to http://weather.gov/lzk.