Area Forecast Discussion
Issued by NWS Little Rock, AR

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046
FXUS64 KLZK 241633
AFDLZK

Area Forecast Discussion
National Weather Service Little Rock AR
1133 AM CDT SUN JUL 24 2016

.UPDATE...

Extensive cloud cover remains across the CWA at this time as an
upper level impulse moves through south central Arkansas. Feature
is generating some light precipitation over eastern Arkansas at
time. Convection still expected to develop later today but will be
delayed and pops reworked as a result.

Have also lowered temperatures due to the cloud cover a few
degrees across the board. Dew points also reworked based on
current observations and trends. Resulting numbers barely get the
area to heat advisory but with numerous holes in the overcast
already showing up, some areas will get there and will let the
heat advisory continue.

&&

.PREV DISCUSSION...(ISSUED 620 AM CDT SUN JUL 24 2016
)

Aviation...

Overall VFR flight conditions are expected. Mid and high clouds will
be seen this morning, with patchy MVFR conditions possible but will
be too isolated to include with Tafs. Convection has held off and
will mainly be later this afternoon and evening. Used VCTS in Tafs
to show this. Winds will start light and variable to light from the
south to southeast, then become more southeast to south at 5 to
10 mph. (59)

Prev Discussion.../ Issued 354 AM CDT SUN JUL 24 2016/

DISCUSSION...

Main concerns in this forecast cycle remain the high heat today
and chances of convection. Heat index values are expected to lower
in the coming week due to clouds and convection chances. While any
threat of severe storms will be low and isolated.

Currently the upper high pressure ridge has weakened and is more
centered over west central U.S. This weakening has allow some
short wave energy to move along the southeast and southern areas
and bring a better chance of convection to AR. Saturday saw more
convection than previous days, and Sunday and into the coming week
will also see a bit more. Moisture levels remain high with surface
dew point temperatures in the 70s.

SHORT TERM...Today Through Monday Night

Today temperatures will again warm to the mid and upper 90s, with
a few locations to 100 degrees, and with the high humidity, heat
index values will be around 105 degrees. A heat advisory will be
in effect. Convection is mainly expected this afternoon to
evening, and mostly over central to southern AR. On Monday the
upper ridge weakens more and centers more west, while northwest
upper flow will bring some possible shortwave energy to the
region. Convection chances come up a bit, also as a frontal
boundary sags closer to AR later Monday. Highs on Monday will be a
few degrees lower due to additional clouds and rain chances.

LONG TERM...Tuesday Through Sunday

Arkansas is expected to remain in a col/saddle in the height
field between upper level ridges located over the Carolinas and
the southwestern CONUS...and between upper trough axes associated
with the jet stream to the north and a tropical upper tropospheric
trough (TUTT) to the south for much of the week ahead. This col is
expected to shift north and south throughout the week allowing
Arkansas to come more under the influence of northern or southern
stream shortwave troughs. The timing of these troughs will
determine the best rain chances and most likely impacts from
storms throughout the week...and this will likely change in the
coming days as these smaller scale features are not as well
resolved as large scale features in model guidance. Based on the
consensus of 00Z model guidance...this is what the forecast looks
like for now:

On Tuesday...Model guidance indicates that a southern stream
shortwave trough will have moved over Louisiana and will continue
west towards Texas leaving Arkansas under weak forcing for
subsidence. This subsidence will likely be maximized Tuesday
morning...allowing for a return to neutral forcing and the potential
for scattered thunderstorms across the state Tuesday afternoon
during the peak heating hours of the day. Despite this...actually
lowered POPs a bit on Tuesday because even though subsidence may
have ended...its impacts are expected to linger. 00z model guidance
indicates that precipitable water values will be at their lowest
point for the entire week on Tuesday across Arkansas. This is likely
due to mid-tropospheric drying behind the shortwave trough. This
will not completely inhibit thunderstorm development on Tuesday...
but it is expected to limit the coverage of convection. Expecting
more isolated convection versus scattered or widespread on Tuesday
as a result of this mid-level drying.

Wednesday through Friday...Precipitable water values are on the
increase Wednesday across Arkansas...although there is not obvious
mechanism to support lift moving across the state. Went ahead with
40 pops during the peak heating hours of the day expecting better
coverage simply due to increased moisture over the region. On
Thursday a southern stream and northern stream shortwave trough seem
to converge on the col over Arkansas. This has been advertised for
around 48 hours now...so assuming this timing holds Thursday should
represent the day with the most widespread thunderstorm activity
across Arkansas. Precipitable water values are also expected to
increase above 2 inches across much of the state by Thursday... so
we could see a flash flooding threat materialize Thursday afternoon
and evening. This far out...a lot can change in terms of the timing
of the upper troughs...but we will continue to watch this scenario
closely as we move through the week. Friday looks very similar to
Wednesday with good moisture in place but no strong lifting
mechanisms to focus convection.

Next weekend...Current model guidance indicates that a northern
stream shortwave trough could bring widespread showers and
thunderstorms across Arkansas. If this verifies...rain chances will
need to be increase on Saturday and lowered on Sunday behind the
trough. Confidence in the timing and strength of a shortwave trough
6 days out in the forecast is very low though...so kept POPs around
30 percent on Saturday and 20 percent on Sunday for now.

&&

.LZK Watches/Warnings/Advisories...
Heat Advisory until 9 PM CDT this evening 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.

&&

$$

56



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