Special Weather Statement, NWS Amarillo, TX

Area Forecast Discussion
National Weather Service Amarillo TX
1223 PM CDT SUN JUN 26 2016

.Aviation...
18Z TAF Cycle

The remnants of a frontal boundary across the southern Texas
Panhandle today along with a closed upper low over southwest Texas
lifting north will help to trigger scattered convection mainly
across the Texas Panhandle this afternoon into this evening. The
Amarillo and possibly the Dalhart TAF sites will likely be affected
by the convection between 18Z today and 03Z Monday. Light mostly
southwest to southeast winds 10 knots or less are expected at all
three TAF sites this afternoon and then becoming light and variable
after 06Z to 08Z Monday. VFR conditions will prevail at all three TAF
sites except in and near the convection where MVFR conditions are
expected.

Schneider

&&

.Prev Discussion... /Issued 628 AM CDT SUN JUN 26 2016/

Aviation...
The fog at DHT with MVFR conditions should be short lived, so have
not inserted it into this forecast. Otherwise, VFR conditions should
prevail outside of thunderstorms at all sites through this forecast.
The best chance of thunderstorms will be this evening, so have
inserted a PROB30 at all sites during this timeframe. Winds will be
light and variable for the first part of the forecast, then they
should become southeast, but they should remain around 10 knots or
less.

Prev Discussion... /Issued 347 AM CDT SUN JUN 26 2016/

Discussion...
Thunderstorms formed last evening in a fairly narrow corridor near
a surface trough that extended from northeast New Mexico into
Kansas. This boundary probably had some tie to northern Plains
shortwave baroclinicity along the boundary was weak or non-existent
in analysis earlier in the day prior to convective development.
Thunderstorms became fairly numerous during the evening before
diminishing later in the night. Cold pool/mesohigh and outflow has
masked this boundary making it diffuse and recovery from this
tomorrow is in question. Models vary in surface pressure pattern
depiction tomorrow with most not showing a synoptic scale boundary
and several showing an increasingly diffluent surface wind field
during the afternoon. For this reason, have limited precipitation
probabilities to the high end of chance category during the afternoon
and evening. Despite lack of a notable low level convergent signal in
short term guidance, thermodynamics support convective development
with moist low-levels in an uncapped environment that will become
increasingly unstable as heating commences. Weak forcing for ascent
may be present on the northern edge of an upper low that will drift
slowly east-northeast into central Texas tomorrow afternoon. Highest
precipitation probabilities were aligned with model placement of
strongest pressure gradient on 1.5 PVU surface, but trends will be
monitored and adjustments to this will be made based on observational
data through the day.

Relatively weak mid level lapse rates should limit MLCAPE to
around 1,000-1,500 J/kg this afternoon. Winds aloft continue to be
weak with 0-6 km shear around or under 10 knots and cloud layer
shear around 15 knots at best. This is insufficient
for sustained/organized updrafts and will limit the severe potential
to isolated brief marginally severe gusts. Slow storm movement and
deep moisture (model projected PWAT around or slightly over 1.5")
will support locally heavy rainfall amounts. We saw this today with
1.68 inches measured at the Eva mesosnet.

Similar thermodynamics Monday along with subtle height falls by
evening from deepening Great Lakes trough should be enough to justify
high chance probabilities once again. There is some question on
placement and degree of amplification of western of southwestern
CONUS trough though and this could ultimately be further
east/stronger leading to reduced chances. The ridge should build in
substantially enough Tuesday to limit chances to slight/low across
most of the area.

Mid-upper level flow will increase and veer to northwesterly by
late Tuesday. This persists through at least the end of the week
with periodic shortwaves embedded within the flow affecting the
area. When and exactly where these enhance convective development
is uncertain, although models are in agreement on a fairly
pronounced shortwave passing by Wednesday, possibly resulting in an
MCS that may affect the northeastern portion of the forecast area
Wednesday evening. We have confined highest probabilities then to
those areas.

Late Thursday through Friday evening may be when the highest
chances for precipitation exist. Models shift or reorient the upper
ridge further south which results in west-northwesterly flow over
our area and a series of perturbations pass through. These along
with mountain diurnal convection and overall faster mid level
flow suggest an organized thunderstorm complex or two may pass
through during that period, especially across the northern half of
the area. A weak cold front may move southward into the area then
too bringing slightly cooler temperatures late in the week and into
the weekend.

BRB

&&

.AMA Watches/Warnings/Advisories...
TX...NONE.
OK...NONE.

&&

11/16

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