Area Forecast Discussion
Issued by NWS Little Rock, AR
FXUS64 KLZK 262346
Area Forecast Discussion
National Weather Service Little Rock AR
646 PM CDT THU MAY 26 2016
Scattered convection continues to wane across the area at this
time but will not end completely this taf period. More widespread
convection will develop across the area after 18z on Friday. MVFR
to VFR conditions are expected except under the strongest storms
where IFR conditions will be possible. Winds will generally be
light with higher gusts near the stronger convection.
.PREV DISCUSSION...(ISSUED 255 PM CDT THU MAY 26 2016
SHORT TERM...Tonight Through Friday Night
Summerlike conds noted acrs the FA this aftn...with temps running in
the 80s and sfc dewpoints AOA 70 degrees. Starting to see a few
SHRA/TSRA form this aftn acrs the FA, and expect coverage to incrs
later this aftn and tngt. Another area of convection was working
into SWRN AR as well...assocd with an apchg upr impulse.
Airmass is quite unstable ovr the area...with 18Z LZK sounding data
showing SBCAPE values arnd 5000 J/KG. Capping inversion has also
weakened compared to earlier today. Overall concern for any svr
storms rmns the same...with large hail and damaging downburst winds
the being the primary threat.
Cont with current fcst trends by incrsg POPs ovr the FA this
evening. Timing/location of small scale features wl cont to have an
impact on convective trends as the fcst pd progresses. This
factor...combined with a contd series of upr lvl impulses lifting
NEWD acrs the mid-south...wl result in several additional rounds of
convection acrs AR Fri and Fri ngt. Heaviest rainfall still looks to
be ovr WRN AR where 1 to 3 inches are possible. Not planning for any
FF watches attm, but wl cont to monitor trends into Fri.
Saturday through Monday...
A strong shortwave trough will rotate northeast from the base of a
large trough over the western CONUS towards the Central Plains. This
will place Arkansas under west-southwest flow aloft within a broad
upper level ridge axis. The lower troposphere is expected to remain
cool behind the Saturday night/Sunday morning cold front. The weak
upper level ridge axis moving over Arkansas will spread some weak
forcing for subsidence over the region...but is also associated with
increasing tropospheric thickness values. Increasing thickness
values with cool air in place implies that warm air advection or
latent heat release must be occurring to compensate for the
unusually cool air near the surface. With ongoing rain shower or
thunderstorm activity unlikely due to weak subsidence aloft... warm
air advection aloft is the most likely explanation for the
increasing thickness values over the state.
The GFS and ECMWF both advertise a persistent warm air advection
pattern from the 850 - 700 mb layer through Monday. This will send
warm moist air over the state resulting in cloudy skies and
increasing rain chances after sunset Sunday through Monday morning.
Temperatures will stay cool on Monday due to the cloud cover in
place...but elevated rain showers and thunderstorms will become more
likely and increase in coverage Monday morning as the persistent
warm air advection pattern and associated isentropic lift continues.
The threat of severe storms appears to be very low at this
time...but some locally heavy rainfall and localized flooding is
Monday evening through Thursday...
The persistent warm air advection during the day on Monday will
eventually result in a warm front moving north across Arkansas
Monday afternoon. This will likely result in a decrease in the
coverage of rain showers and thunderstorms as the primary lifting
mechanism driving that activity will move north with the low-level
cool air mass north of the warm front. Isolated to scattered storms
are still possible south of the front Monday late afternoon and
evening. If any storms develop during this time...they are more
likely to be strong as they will not be elevated above a cool low-
The Central Plains shortwave trough will continue to move slowly
east towards Missouri on Tuesday while a strong shortwave trough
will dive south out of Canada over the western Great Lakes region.
The combination of these two features will result in some large
scale forcing for ascent over Arkansas Tuesday and Tuesday night.
Scattered to numerous storms are likely across the state during this
time with ample moisture...and little cap in place for free
convection. The lack of significant capping does at least make
severe thunderstorms less of a threat as storms are likely to
develop before CAPE values can increase too high resulting in many
strong storms instead of scattered severe storms. Localized heavy
rainfall and flooding may become more of a threat on Tuesday as
precipitation efficiency will be fairly high.
The shortwave troughs will move east of Arkansas Tuesday night into
Wednesday sending a cold front south across the state. As the front
moves across the area...another round of showers and thunderstorms
will likely accompany its passage. Behind the front on Wednesday...
we will likely catch at least a short break from rainfall as low-
level cold air advection and subsidence aloft help to dry out the
atmosphere a bit. With another upper trough over the southwestern
CONUS though...a return to southerly flow over the cool low-level
air mass will bring moisture back into the region quickly Wednesday
night through Thursday. This return to southerly flow aloft will
result in a veering wind profile with height indicative of large
scale warm air advection and the potential for hit and miss rain
shower and thunderstorm activity across the state.
Friday through next weekend...
Another strong shortwave trough is expected to move over Arkansas on
Friday...possibly allowing for widespread showers and thunderstorms
for Friday and Friday night. That said...the coverage and intensity
of precipitation on Friday will depend on exactly where the
shortwave trough moves...therefore this forecast may change in the
coming days. Behind this trough however...nearly all guidance agrees
that an amplified upper level ridge will build over the Mississippi
valley resulting in a return to dry conditions for next weekend and
possibly into early next week.