Area Forecast Discussion
Issued by NWS Little Rock, AR
FXUS64 KLZK 280507
Area Forecast Discussion
National Weather Service Little Rock AR
1207 AM CDT TUE JUN 28 2016
Generally speaking, expect VFR conditions to prevail through a
majority of this TAF period. Clouds will clear in the north shortly
and expect there to be some patchy fog develop as temperatures falla
little quicker beneath clear skies. Elsewhere clouds should linger
enough to make the formation of fog difficult and left it out of the
TAFs accordingly. Surface high pressure will begin to build into the
region on Tuesday. Resulting surface winds will be out of the
northeast tomorrow...with FEW-SCT afternoon CU between 5000-6000 ft.
.PREV DISCUSSION...(ISSUED 1007 PM CDT MON JUN 27 2016)
Issued a quick forecast update for the rest of tonight and into
Tuesday morning. Convective activity has waned in the last couple
of hours but some isolated showers and thunderstorms will be
possible through the rest of tonight from the I-40 corridor
southward. Most areas will remain dry for the overnight hours
however. Patchy fog may be of concern tonight. However the influx
of drier air and leftover convective debris clouds makes this a
difficult forecast and whatever develops may be very hit and miss.
Decided to leave this out of the forecast for the time being.
PREV DISCUSSION...(ISSUED 644 PM CDT MON JUN 27 2016)
Updated for the 00z aviation discussion below.
Outflow boundaries abound this evening, with the most dominant
boundary moving from NE to SW across central Arkansas as of 23z.
This will turn winds to roughly 05006kt for most central and
southern terminals through the evening and overnight hours. Still
have some scattered convection in northern and also central
Arkansas as well. Expect a general decline in convective coverage
over the next few hours and have all sites clear of SHRA/TSRA by
06z or thereabouts. Flight categories should generally be VFR but
patchy fog may become an issue during the overnight hours where
rain is observed. Confidence in visibility restrictions is not
high enough to include in the TAFs at this time however. More
isolated storms are possible tomorrow afternoon but again,
confidence in the placement of storms on Tuesday is not high
enough to mention at this time.
PREV DISCUSSION...(ISSUED 300 PM CDT MON JUN 27 2016
SHORT TERM...Today Through Wednesday Night
Early afternoon water vapor satellite imagery showed an elongated
zone of cyclonic shear over south central Missouri moving
southeast towards Arkansas. While this zone of cyclonic vorticity
aloft does not represent strong forcing for ascent...it should be
sufficient to support scattered showers and thunderstorms across
the state this afternoon through early this evening. Arkansas has
been under the influence of upper ridging and its associated
subsidence/sinking for several days now...so a simple transition
to a lack of subsidence should help rain chances through sunset.
At the time of this discussion...clusters of thunderstorms were
ongoing across far northeastern Arkansas and far southwestern
Arkansas with some isolated activity in between. The upper shear
axis will help drive a cold front south across Arkansas this
evening...this boundary was currently in place over the northern
portion of the state with its leading edge pushing south towards
the Interstate 40 corridor. The cooler and slightly drier air
behind the front was still located north close to the Missouri
border as of 230 pm CDT. The leading edge of the boundary was
responsible for the isolated to scattered shower and thunderstorm
activity across the central portion of the state.
The morning weather balloon showed a nearly saturated atmosphere
in the middle to upper troposphere with signs of subsidence and
drying in the lower part of the atmosphere. This is likely due to
early morning convection that spread quite a bit of cool air and
rainfall around Hot Springs before moving east and dissipating
before sunrise. Heating and weak lift ahead of the front will help
to deepen the moist layer and increase instability through late
this afternoon. Short range model guidance indicates that
precipitable water values will increase above 2 inches out ahead
of the front this afternoon. Assuming this occurs...expect that
shower and thunderstorm activity will increase along the front as
it sinks south.
The primary hazards associated with storms this afternoon should
be from locally heavy rainfall/flooding and microburst winds from
collapsing storms. Did not go with a flash flood watch for today
as the threat of flooding is expected to remain localized in
nature due to a lack of stronger upper level forcing for ascent.
With a scattered coverage expected for storms...but an incredible
amount of moisture available for storms to develop...locations
that see storms may pick up a quick 2 to 3 inches of rain while
others see little if any rainfall at all. Spread out this will
equate to around one half inch of rainfall across the state but
this is very misleading as almost no one will receive one half
inch of rain...folks under a storm will see heavy rain while those
not under a storm will remain mostly dry through tonight.
The front is expected to sink south towards the Louisiana border
overnight...and its final resting position will largely determine
the area of best rain chances for Tuesday. Kept some low rain
chances in across the southern third of the state on Tuesday with
some uncertainty as to how far south the front will make it. If
the front pushes farther south into Louisiana then rain chances
could be dropped from the front Tuesday. Temperatures should be
slightly cooler behind the front Tuesday...but it`s late June and
skies will be mostly clear...so highs are still expected to climb
into the low 90s.
On Wednesday a weak upper level shortwave trough is expected to
move southeast towards Arkansas as upper level ridging starts to
nudge west of the plains. This should result in an increase in
cloud cover from northwest to southeast as weak lift spreads over
the region. Rain chances will also increase over the northwestern
portion of the state Wednesday afternoon as this trough
approaches. Rain chances remain fairly low at this time... only 20
to 30 percent...but the additional cloud cover should help shave
another few degrees off of forecast highs with many locations
topping out in the upper 80s.
LONG TERM...Thursday Through Saturday Night
By Wednesday night the ridge will have moved west allowing for
northwest flow aloft through Friday. By Saturday, the ridge flattens
and remains elongated across the southern gulf states resulting in a
more zonal flow aloft. However, this change in upper flow will have
mininal impact on the overall weather pattern across the area. The
northwest flow pattern will allow a front to move into the state and
become stationary through much of the extended. Models seem to
indicate that the stationary boundary will reside across central
Arkansas. While scattered thunderstorms will be possible across the
entire state, the better chances for thunderstorms will occur along
and north of the boundary favoring the northern half of Arkansas. In
addition to the frontal boundary acting as a focus for storms, weak
disturbances in the upper flow will periodically move across the
area and each time will enhance the rain potential a bit.
Regardless, widespread thunderstorm activity is not expected but
there will be several opportunities for rainfall during the extended.
With the frontal boundary in the area and lower 5H heights,
temperatures will be "less hot" through the extended with temps at
or slightly below seasonal normals.