Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 081734
AFDLZK

Area Forecast Discussion
National Weather Service Little Rock AR
1234 PM CDT Sat May 8 2021

.AVIATION...Updated w/ a discussion for the 08/18Z TAFs

Band of SHRA w/ ocsnl TS was noted on mosaic radar imgry over far
Nrn AR, however precip wl lkly not impact terminals through the
remainder of the afternoon/evening. Most notably over the next
24-36 hrs, a strong pres grad wl setup over the FA as a sfc low to
the west deepens and strengthens. Srly to S/Wrly sfc winds wl
intensify w/ sustained readings of 15-20 kts and gusts up to 25-35
kts. A strong S/Wrly LLJ wl overspread the region as well Sat
night, contributing to an extremely unsettled overnight PD...Have
included LLWS at all terminals accordingly. Sun morning, some VCSH
may be seen across Nrn terminals, however confidence remains lower
on PoP coverage during this timeframe. Lastly, rapidly
deteriorating CIGs wl move in from the W later Sun morning, w/
condns falling to MVFR/IFR levels across the FA from W to E.

/232/

&&



PREV DISCUSSION...(ISSUED 442 AM CDT Sat May 8 2021)

SHORT TERM...Today Through Sunday Night

Mosaic radar imagery as of 09Z shows a band of storms stretching
from northeastern KS through southeastern MO with more isolated
showers and occasional thunder over the remainder of the area.
Banded convection to our north appears to be tied to
frontogenetical forcing within the 850 mb layer and this corridor
of enhanced lift is progged to slide southeast through the
morning.

As such, kept the highest PoP over roughly the northeastern third
of the area, although subtle larger-scale ascent over the region
could support isolated activity elsewhere, but confidence is very
low for areas outside north/northeast AR. Steep mid-level lapse
rates on the order of 7 to 8 C/km will support small hail in
storms.

Activity should begin to wind down and exit this afternoon,
although additional isolated showers/storms may persist as warm
air advection increases over the area. Despite cloud cover and
some rain, do anticipate temperatures will climb up to several
degrees above average with highs in the 70s north to 80s
elsewhere. Overnight, lows will fall into the 60s area wide.

Meanwhile, in the mid/upper levels, broad troughing continues
over the eastern CONUS as well as the Intermountain West with
ridging between these features. Embedded within the western
trough is a well-defined negatively-tilted shortwave trough
positioned over the northern Rockies. This feature is progged to
dig into the western high Plains by Sunday morning and will have
significant bearing on local weather through the day Sunday.

Height falls have already begun to overspread the Rockies and
corresponding pressure falls are occurring at the surface, most
notably over eastern WY/CO. This will continue today into tonight
with a closed surface cyclone emerging over the central Plains by
this evening. A warm front currently just to our west will lift
northeast through the state today, placing us well within a
developing warm sector ahead of the approaching system.

Winds will increase markedly today into tonight as the surface
pressure gradient tightens and strong southerly flow develops
south of the lifting warm front. Sustained speeds of 20 to 25 mph
with gusts of 30 to 35 mph will be fairly common, although these
fall below advisory criteria. The development of a strong low
level jet overnight will further increase speeds in higher terrain
where locations above 1000 ft could see gusts of 40+ mph.

Vorticity maxima ejecting from the northern Rockies trough will
push the surface cyclone into southern MO tonight with an
attendant cold front moving east towards AR. Rain/thunder will
increase around or after midnight tonight -- first over the
northwest and north, then spreading towards central and southern
AR by around dawn on Sunday.

Despite abundant cloud cover, ongoing precipitation, and near
average temperatures on Sunday, steep lapse rates aloft will
overspread the warm sector and should yield SB/MLCAPE values on
the order of 2000 J/kg. Deep layer shear values in the 40 to 50 kt
range will offer enough dynamic support for strong to severe
storms with the highest probabilities along/south of the front as
it works into the state. Most of the area save for northwestern
sections will see some risk for severe weather through the
afternoon Sunday with damaging winds, hail, and isolated tornadoes
possible.

One potential fly in the ointment will be early day convection to
our south. If widespread storms develop over northern LA, we
could see rapidly increasing uncertainty on how storms will
evolve Sunday afternoon over our area. No reason to deviate from
ongoing forecast thinking for now, but will watch this closely in
subsequent forecast cycles.

In addition to the potential for severe weather, precipitable
water will surge ahead of the advancing front with values well
above climatological norms (on the order of 1.5 to 1.75 inches or
greater, perhaps approaching or exceeding the daily max) across
the southeastern half of AR. Deep layer flow aloft will not be
entirely parallel to the front as it moves through, but the
anomalously moist atmosphere will support torrential rain in
stronger cells and, at the very least, isolated flash flooding
will be possible.

Another large vorticity maximum will eject from the northern
Rockies trough Sunday night and kick the surface cyclone over
southern MO to the east. The cold front will gradually sink south
through AR Sunday night with ongoing showers and storms near the
boundary. Temperatures will fall below average in the wake of the
front with lows Sunday night falling into the 40s north to 50s
elsewhere.

LONG TERM...Monday Through Friday Night

The unsettled weather pattern of late should continue through early
Thursday morning. The upper pattern will be quasi-zonal with small
ripples translating through the flow as large scale features pass
well N of the region. With the subtropical jet located across the
Srn/Cntrl CONUS, upper level impulses will move through the flow
promoting showers and thunderstorms through early Thursday.

At the surface, a frontal boundary should be located just S of the
AR border. This boundary will slowly push Swrd a bit more before
stalling over TX/LA/MS. The combination of weak upper level systems
and abundant moisture pooling along the front should trigger shower
and thunderstorm development which will then move E/NE across the
Srn MS Valley. A few strong storms can not be ruled out, especially
over Srn portions of AR where greatest instability is anticipated to
reside. Large hail and damaging winds would be main threats.

Rainfall rates may become heavy at times, which could lead to areas
of flash flooding. The greatest concern will be over the Srn third
of AR where a couple to several inches of rainfall will be possible.
Lower totals are expected towards the Missouri border. Across the
Nrn third of the state, less than an inch of rainfall is expected
due to the increased distance from available moisture source and the
surface boundary.

Temperatures through Wednesday will be below average with highs
mainly in the 60s to near 70 degrees and lows in the 40s and 50s.
Beyond Thursday, drier weather will return as upper level ridging
moves into the plains. Surface high pressure will build into the
region continuing below average temperatures through the end of the
long term.

&&

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

$$


Aviation...GREEN


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