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Area forecast discussion...updated 
National Weather Service Little Rock Arkansas
550 am CDT Sat Jul 23 2016

Discussion...

Updated to include the 12z aviation discussion below...

&&

Aviation...

VFR conditions should again be dominant through this taf period.
Some isolated to scattered rain showers/thunderstorms and rain will be possible late this
morning through early this evening. Some gusty winds could be
seen near this activity as outflow boundaries form from
dissipating storms. Tonight...some patchy fog may be
seen...especially in/near areas that seen rainfall.

&&

Previous discussion...(issued 356 am CDT Sat Jul 23 2016)

Short term...today through Sunday night

After another hot and humid day on Fri...conditions overnight have
actually Bee a bit cooler/drier than observed this time on Fri
morning as a result of the afternoon/evening convection and outflows.
Regional radar imagery does show a cluster of convection over the
western Tennessee area early this morning...which was gradually drifting south
over time.

With the center of the upper ridge shifting a bit further west
today...will likely see additional convective activity this
afternoon. With less influence from this upper ridge...the coverage
of convection may a bit greater than seen on Fri. As a result...have
mentioned low end chance pops for isolated to scattered diurnally
driven convection. Will also have to see what influence the ongoing
convective activity over western Texas will have for this afternoon as any
outflow boundaries generated this morning may provide more focus for
initiation...if they move far enough west.

As for temps...will likely see similar conditions to Fri...though
maybe a deg or 2 cooler as a result of less influence of the upper
ridge. Even so...highs will be in the 90s to just over 100. Heat
index values will also peak over 100...with may locations seeing
heat index values over 105 this afternoon. The heat adv continues
through sun as a result...with temps on sun in the 90s for highs.
Even though temps may be cooler on sun...dewpts may be
higher...resulting in similar heat index values.

On sun...have higher pops forecast as The Heights aloft decrease a
bit more. Some near term model guidance is also showing a weak upper
disturbance slowly drifting west-southwest this evening through sun
evening...which could also aide in seeing additional precip
activity. Given this feature/weak perturbation in the upper flow
develops as a result of some meso-scale convection...not completely
on board with some of the quantitative precipitation forecast and coverage of rain showers/thunderstorms and rain activity the
model guidance is suggesting...yet. If the influence from this
feature pans out...will likely need to increase pops as there will
be more coverage of rain showers/thunderstorms and rain across the County Warning Area...especially across the
southern half of the County Warning Area.

Long term...Monday through Friday

Beginning on Monday...the large upper level ridge that has been in
control of the weather over the central Continental U.S. Will stretch out and
become anchored over the Carolinas and over the southwest Continental U.S..
this is in response to an active jet stream over the Great Lakes
region to the north...and a series of westward moving shortwave
troughs over the Gulf Coast to the south of Arkansas. The northerly
pattern is fairly typical of this time of year but the southerly
train of westward moving shortwave troughs is at least slightly
abnormal. These westward moving cold core shortwave troughs may be
associated with a larger tropical upper tropospheric trough that has
simply migrated farther north than normal. Most model guidance is in
favor of both of these areas remaining active for shortwave troughs
in the week ahead...so confidence is fairly high that the upper
level ridge in place will continue to weaken throughout the week.

For the week ahead...model guidance indicates that both north and
southern stream shortwave troughs remain too far away from Arkansas
to spread any significant lift over the state. However the combined
effect of shortwaves to the north and south is to significantly
weaken the upper level ridge in place which should lead to slightly
cooler temperatures and remove the large scale forcing for
subsidence that has been around for the past several days. Despite
being under the influence of subsidence all week... isolated to
scattered convection developed during the peak heating hours of the
day each day across Arkansas. With forcing for subsidence removed
and little change in the thermodynamic characteristics of the
atmosphere...think that the coverage of storms will only increase a
bit Monday and Tuesday afternoons as the upper level ridge loses
influence.

This pattern of holding in between upper troughs moving by to the
north and south is expected to hold in place through Friday. With a
prolonged period of more or less sitting in a col in the flow field
aloft between two ridges to the west and east...would expect that
eventually flooding may become an issue across the state. Nothing
particularly organized is expected at this time...but if convection
becomes more widespread at any point during this period...it could
result in enough latent heat release to cause a mesoscale convective
vortex to develop across the state. If this happens in the
thermodynamic environment characterized by 2 inch precipitable water
values each day...a mesoscale driven flash flooding event would
likely evolve. The chances of flooding like this taking place over
the 5 day period of next week are somewhat high...but confidence in
when this might happen remains too low to pin down on a particular
day for now. Will simply have to keep a close eye on the duration
and intensity of convection each day next week and carefully assess
the flooding potential on 12 to 24 hour timescales.

The uptick in convection each day associated with the weakening
ridge should be enough to keep the heat in check next week. At this
time do not expect that heat advisories will be needed for most of
the week ahead...but we will continue to assess the threat of
excessive heat/heat index values each forecast moving forward.

&&

Lzk watches/warnings/advisories...
heat advisory until 9 PM CDT Sunday for Arkansas-Baxter-Boone-
Bradley-Calhoun-Clark-Cleburne-Cleveland-Conway-Dallas-Desha-
Drew-Faulkner-Fulton-Garland-Grant-Hot Spring-Independence-Izard-
Jackson-Jefferson-Johnson-Lincoln-Logan-Lonoke-Marion-Monroe-
Montgomery-Newton-Ouachita-Perry-Pike-Polk-Pope-prairie-Pulaski-
Saline-Scott-Searcy-sharp-stone-Van Buren-white-Woodruff-Yell.

&&

$$



Aviation...62

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