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fxus64 klzk 281719 aab 

Area forecast discussion...update
National Weather Service Little Rock Arkansas
1220 PM CDT Wed Jun 28 2017


Overall VFR flight conditions are forecast for the next 24 hours.
Winds will start south to southwest at 5 to 15 mph with isolated
higher gusts. After sunset, winds will become south to southeast and
lower to 5 to 10 mph. Patchy MVFR clouds may form early Thursday
morning over southern AR, but coverage will be low and not included
in tafs at this time. VFR Thursday with south to southwest winds at
5 to 15 mph with some gusts to around 20 mph. (59)


Prev discussion.../ issued 1010 am CDT Wed Jun 28 2017/

Overall forecast on track. The surface high pressure was to the east
of Arkansas and a southeast wind flow will continue to bring moisture
levels up gradually over the state. 12z klzk sounding indicated this
flow, while the precip water value was still less than 1 inch, with
a dry area noted in the mid-levels of the atmosphere. While surface
dew point temperatures were in the 60s to a few around 70 degree
readings. Aloft, weakening upper high pressure over the region shows
currently most of the lift over the Central Plains and upper mid-
west, where convection was noted. Only scattered lower and high
clouds were seen over Arkansas. Almost all convection is expected to
remain out of Arkansas today, while during the heat of the afternoon to
early evening, an isolated shower or thunderstorm could be seen.
Coverage will be too low to include in the forecast. Highs will warm
to the mid and upper 80s, with a few around 90 degrees. Otherwise,
the better chances of rain will be later in the week with the next
frontal boundary. (59)


Previous discussion...(issued 420 am CDT Wed Jun 28 2017)
short through Thursday night

Rather benign wx pattern in place acrs Arkansas early this mrng, with a
weak ridge of sfc high pres noted over the forecast area. A light east/southeast wind
flow was observed, with temps ranging from the mid 60s to the lower

No sig changes were made to the going fcst this mrng. The sfc ridge
wl cont to weaken, allowing southerly winds to return, along with incrsg
low lvl moisture. Daytime highs wl also trend upward a degree or two
in the coming days, with most areas rmng just below seasonal norms.

Dry conds wl persist thru today, with small rain chcs returning to
the fcst for parts of Arkansas on Thu. Low pres is fcst to lift northeastward along
the Gulf Coast region on Thu, with a slight chance of convection already
mentioned acrs the southeastern part of the forecast area. On Thu ngt, convection is
fcst to form to the northwest of AR, ahead of slow moving cold front. This
activity is not expected to affect the area until Fri.

Long term...Friday through Wednesday

A strong upper level trough is expected to move southeast over
Nebraska and Iowa by Friday evening. The upper trough axis is
expected to extend to the southwest over Kansas and Oklahoma
spreading some weak large scale forcing for ascent over Missouri and
Arkansas. This lift is expected to be sufficient to cause
thunderstorms to develop along a cold front located northwest of
Arkansas early Friday afternoon. Assuming that thunderstorms develop
along the front as expected...thunderstorms will likely grow upscale
into a line effectively aiding the front southward into Arkansas
from late Friday afternoon through the overnight hours.

There will be some threat of severe weather Friday afternoon and
overnight...however the farther storms move into the state from the
northwest the weaker the shear that they will encounter. Models
indicate that cape will be on the order of 3000 - 4000
j/kg...maximized over northwestern Arkansas. Deep layer shear is
expected to be at 30 to 35 kts with the shear vector oriented nearly
parallel to the front. Strong forcing for ascent along the front
combined with the orientation of the deep layer shear vector should
promote cold pool mergers favoring a linear or qlcs storm Mode. The
primary threat from this storm Mode is damaging straight line winds
with hail and isolated tornadoes possible...but less likely to
occur. This threat should be maximized over the northwestern
portions of Arkansas Friday afternoon and evening. Assuming storms
organize into a line and accelerate southeast...the lack of stronger
low-level wind shear should allow the outflow boundary to outpace
updrafts causing them to become tilted and reducing the overall
strength and organization of the line of storms. This will reduce
the threat of severe weather for the remainder of the state Friday

Storms are expected to dissipate along the front Saturday morning.
This should leave a frontal boundary or strong outflow boundary
stalled out somewhere across the state. Wherever the front stalls
out should provide a focus for new thunderstorm development across
Arkansas on Saturday. This front may remain baroclinic enough to
provide lift for additional storms on Sunday as well. Confidence in
thunderstorm location is inherently low this weekend as it seems to
depend on how organized storms are on Friday and where the front or
effective frontal boundary stalls out on Saturday. With lower
confidence in these details...went ahead with a 60 pop along the
front on Friday...but went with more broad brushed 30-50 pops on
Saturday and Sunday afternoons. Thunderstorms are not expected to be
severe this weekend as deep layer shear is expected to be even
weaker than on Friday.

Monday through Wednesday...the large scale flow aloft is expected to
transition to northwest flow as upper level ridging amplifies over
the western Continental U.S.. the GFS and European model (ecmwf) both advertise the passage of
some shortwave troughs in this pattern providing forcing for ascent
over Arkansas. The timing and intensity of these troughs differ from
model to model and from model run to model run. As a result
confidence in thunderstorms during this period is high...but
confidence in their coverage and intensity is low. Went ahead with
20 to 30 pops during this period...with slightly higher rain chances
located over the northern portion of the state. Temperatures are
expected to remain near seasonal normals...but humidity will remain
high keeping heat index values up in the mid to upper 90s.

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