Tornado Warning 26, NWS Little Rock, AR

Area Forecast Discussion...UPDATED
National Weather Service Little Rock AR
550 PM CDT Tue Apr 28 2020

.DISCUSSION...

Updated to include the 00Z aviation discussion below...

&&

.AVIATION...

A line of SHRA/TSRA will drop SE through the state this evening
into the early morning hrs on Wed. Some strong to SVR storms could
be seen...with MVFR or lower conditions possible with this
activity. Some improvements will be seen by daybreak into the
late morning hrs on Wed...though breezy NW winds will be seen.
Some additional SHRA may also be seen for the NRN terminals on Wed
afternoon.

&&

.PREV DISCUSSION...(ISSUED 359 PM CDT Tue Apr 28 2020)

..Severe weather possible tonight over much of the area...

SHORT TERM...Today Through Thursday

Overall, no significant changes were introduced this cycle. Did
make minor adjustments to the slow the timing of convection based
on this morning's trends. Otherwise, another severe weather event
appears likely late this evening through early Wednesday morning.

Water vapor imagery depicts the leading edge of a potent upper
shortwave trough digging into western NE as of 20Z. At the
surface, the primary surface cyclone is analyzed across IA/WI with a
cold front draped south and southwestward across the central
Plains and then westward to the Four Corners region. A secondary surface
cyclone is analyzed over western OK into the Caprock region of
TX with a warm front stretching across eastern OK then arcing
southeastward into deep East TX and western LA.

Anticipating robust convection will initiate near the cold front
over KS around 21Z, then push southward into northwestern AR late
this evening, then through central AR near midnight, and finally
through southern AR during the pre-dawn hours Wednesday. The
airmass ahead of this convection, especially for western AR and
areas west, will be characterized by large CAPE and gradually
increasing flow in the low and mid levels. 18Z sounding data from
OUN shows impressive instability characterized by SBCAPE values
>4000 J/kg and MLCAPE values >2000 J/kg. Farther east, the LZK 18Z
sounding shows far less instability, likely due to the influence
of morning convection from the ArkLaTex eastward. Model progs do
continue showing the reservoir of higher instability shifting east
with time, effectively boosting instability over roughly the
western half of the state. Surface obs over the last few hours do
show increasing low-level moisture and strong heating where cloud
cover has been less persistent, so no reason to discount further
destabilization through the afternoon.

Deep layer shear is expected to increase as well with the
approach of the upper shortwave trough and this will support
organized convective modes. It still appears most likely
convection will consolidate into a large squall line owing to
broad frontal forcing and front- parallel deep layer flow.
Despite only modest flow anticipated in the lower troposphere,
still quite concerned with damaging wind potential, especially
over western portions of the area where better instability will
be realized. Steep mid- level lapse rates will support large
hail as well, although the thermodynamic environment is less
impressive across AR versus farther west over OK. Forecast
soundings do show increasing low-level SRH so tornadoes, while not
the primary or secondary hazard, will be possible as well.

Farther east where surface-based instability values are forecast
to be less... convection will be likely given at least 2000 J/kg
of MLCAPE to ingest. That said, higher near-surface stability and
farther proximity from the primary instability axis should
mitigate the severe threat some, but not entirely.

Finally, PWAT values >1 inch will support heavy rain with
convection this evening through tonight. 1 to 2 inches is entirely
plausible with the highest values across western Arkansas. Given
wet antecedent conditions, flash flooding is also a possibility
and rises on local rivers/streams is likely.

Through the remainder of the period, the lead shortwave trough
will eject northeast Wednesday with steep northerly flow
persisting in the mid/upper levels through Thursday. A bit of
lingering moisture may be enough to generate some rain over
northern and northeastern areas Wednesday before precip ends
completely. Anticipating a dry weather late Wednesday and beyond.

LONG TERM...Thursday Night Through Monday

Dry conditions will be in place at the start of the long term
portion of the forecast as both mid level and surface ridging build
over the area in the wake of an H500 low moving toward the eastern
US. Through the weekend, as H500 ridging increases and the surface
ridge shifts east a bit, temperatures will begin to warm. Some
portions of southern Arkansas could be looking at temps approaching
90F Sunday afternoon.

From Sunday into the early part of next week as a series of troughs
in the H500 flow cross the northern US, this will dampen the effects
of the ridge southwest of the state. Some influence from these
troughs will extend southward toward the state and as a cold front
approaches from the NW, chances begin to increase for rain and
thunderstorms across the state.

&&

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

Aviation...62

Hazardous Weather Outlook...UPDATED
National Weather Service Little Rock AR
354 PM CDT Tue Apr 28 2020

ARZ003>008-012>017-021>025-030>034-037>047-052>057-062>069-291000-
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-
354 PM CDT Tue Apr 28 2020

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

.DAY ONE...This Afternoon and Tonight

Severe thunderstorms are possible across all of Arkansas through
tonight.

The threat of severe storms will be highest over the western half
of the state during the evening hours as a line of strong
thunderstorms develops along a cold front moving through.

All modes of severe weather are possible.

The most serious threat with any stronger storms will be damaging
wind gusts of 60 MPH or higher, especially with the storms along
the front. Large hail will also be a concern with stronger
storms.

There will be a threat of tornadoes, but this will be highest if
any isolated supercells develop out ahead of the main line of
storms.

Though the threat of flash flooding will not be widespread, some
of the stronger storms will be capable of producing one to two
inches of rainfall in a very short period of time, which will
cause localized flash flooding issues.

The severe threat will decrease after midnight, as the storms
weaken and move into eastern and southeast Arkansas.

.DAYS TWO THROUGH SEVEN...Wednesday Through Monday

No hazardous weather is expected at this time.

.Spotter Information Statement...

Spotter activation may be needed this evening. Please relay any
information about observed severe weather to the National Weather
Service while following all local, state, and CDC Guidelines.

&&

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