Scientific Forecaster Discussion
fxus64 klzk 182332 aaa
Area forecast discussion...updated
National Weather Service Little Rock Arkansas
632 PM CDT Fri Oct 18 2019
For the 00z tafs, VFR conditions are expected through the forecast
period, with winds remaining near or below 10 kts. Cloud cover
will increase across the state during the overnight and early
morning hours, with isolated to scattered showers possible across
northwestern Arkansas during the late morning and afternoon.
Previous discussion...(issued 257 PM CDT Fri Oct 18 2019)
short term...tonight through Sunday
basically, anything I can write about the short term periods
pales in comparison to today's long term forecaster's discussion.
But, regardless, here GOES...
At the surface, high pressure was northeast of Arkansas, with a
frontal boundary out in the plains, and tropical storm Nestor in
the central Gulf of Mexico. The high will shift eastward through
the weekend, with the frontal boundary approaching and moving
through Arkansas Saturday. Nestor will rob what low level moisture
we would have gotten otherwise with the system. So, rain chances
will largely be confined to northwest Arkansas as the front moves
through and an upper level trough interacts with it.
The boundary will stall out and shift back to the north on Sunday,
as a stronger upper trough digs down into the Southern Plains and
pushes a stronger cold front toward Arkansas. More on this in the
Long term...Sunday night through Friday
an active and amplified upper level flow regime is expected to
continue through the long term period. Aloft, deep troughing is
expected to reside over the northern plains/just east of The
Rockies. Along the eastern conus, ridging will be in place up and
down the East Coast. Between these systems, flow will be out of
the southwest across the Southern Plains, mid MS valley, and Ohio
Valley regions. By Sunday evening, the upper trough should eject
into the northern plains while taking on a negative tilt. This
activity will be centered invof NE/South Dakota well to the north of the
At the surface, a warm front is expected to lift north out of la
ahead of an approaching cold front on Sunday. Moisture will begin to
advect into the state with dew points returning to the 50s and 60s.
Late Sunday into Monday, a surface cold front will move towards the
state from the northwest associated with a strong surface low
pressure system over South Dakota. Along and ahead of the boundary, showers
and thunderstorms are expected to develop. The Main Point of
uncertainty arises to the speed and extent of the warm/moist air
mass associated within the warm sector. A slower warm front would
really limit surface based cape potential to southern Arkansas whereas a
faster front would allow decent amount of surface based cape and
instability to lift into central and northern Arkansas. South of the warm
front, dew points should quickly rebound into mid 60s to the lower
70s. A blend of solutions puts best moisture and instability across
the southern half of the state and generally western areas of the
state where diurnal heating can best be utilized by convection.
Abundant wind energy will also be associated with the approaching
trough, for the most part, it appears most of the shear will be in
the form of speed shear as opposed to directional shear. However,
some directional shear will be possible in the lower levels,
especially near the warm front boundary intersection. Best shear
will be found across northwestern Arkansas closer to the aforementioned
upper level system. For AR, more specifically the cwa, showers and
thunderstorms will be moving into the area after sunset. Instability
will begin to decrease with the onset of nocturnal cooling, however
cooling will be limited by warm air advection and brisk south winds.
Still, as the night progresses a cap is expected to develop limiting
the possibility of storms maintaining their surface based
characteristics. Thus best potential for severe thunderstorms should
remain across the western half of the state and south/along of the
final location of the warm front within warm sector. The greatest
threat of severe weather appears to be be high winds with isolated
large hail and tornado risk with the strongest of storms that can
remain surface based. The overall severe potential will continue to
be monitored closely as newer model data becomes available.
By mid day Monday, precipitation should rapidly come to an end as
high pressure builds into the region from the plains. Precipitation
should exit southeastern Arkansas by Monday afternoon. Tuesday and
Wednesday are shaping up to be nice and dry across the natural state
thanks to northwesterly flow aloft across the central Continental U.S. And high
pressure settling in. The upper pattern should become zonal
Wednesday afternoon ahead of the next weather maker.
Thursday, upper level pattern becomes southwesterly again ahead of a
new trough digging across The Rockies. This trough is expected to
quickly eject into the plains and towards Arkansas during the day. By
early afternoon, pops return to the northwestern portion of the
state. Precipitation will overspread the entire state from northwest
to southeast overnight Thursday into Friday. Temperatures will
remain in the 60s and 70s for highs and mainly 40s for lows.
winds will be elevated on Monday as a frontal boundary passes
through the state. However, winds should remain below critical
thresholds. Otherwise, no significant fire weather issues are
expected through the next seven days.