Area Forecast Discussion
Issued by NWS Amarillo, TX

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000
FXUS64 KAMA 212350 AAA
AFDAMA

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
650 PM CDT Mon Aug 21 2017

.AVIATION...
For the 00Z TAFs, there will be a renewed threat of showers and
tstms during this TAF cycle as a cold front moves south across the
OK and TX Panhandles Tuesday morning. Timing and location of tstm
development remains highly problematic at this time. Therefore,
due to low confidence, decided not to include tstms in any of the
TAFs for this fcst cycle. Will continue to closely monitor radar
trends this evening for possible amendments in the near term.

Andrade

&&

.PREV DISCUSSION... /Issued 456 PM CDT Mon Aug 21 2017/

DISCUSSION...
Southwest flow will begin to shift more westerly this evening, and
become northwest by Tuesday afternoon. With this northwest flow an
embedded shortwave is expected to move through. With deep layer
shear around 20-30 knots and CAPE values ranging from 1500-3000
J/kg, along with the forcing from the shortwave, storms will
likely be strong to marginally severe Tuesday afternoon.

We continue to track a frontal system and its impacts associated
with the aforementioned shortwave. Right now things have sped up
a bit with the arrival time, but position and orientation with
respect to the deep layer shear has changed. Low level positive
moisture advection will continue across all the Panhandles Tuesday
evening into early Wednesday morning, before drier cooler air
attempts to intrude from the northwest. Previous models had
suggested that the baroclinic zone would be oriented west to east
and given that the shear values were in the 15 to 20 knot range,
things looked favorable for training thunderstorms that could
produce flash flooding potential. But now shear values have
increased a bit and are still out of the west to east direction,
but the baroclinic zone combined with instability runs
perpendicular in the north to south direction. This will still
favor storm development mainly along the western and central
Panhandles, but training storms do not look to be as favorable.
Any storms that develop could still have heavy precipitation as
precipitable water values are looking to be +2 Standard Deviations
to being in the 99th percentile for this time of year.

Showers and storms under northwest flow will continue through
about Thursday afternoon where it begins to shift more westerly. A
cut off low near the southern CA coast will attempt to break away
bringing a shortwave across the OK and northern TX Panhandle on
Thursday night. Have bumped pops up to the 40 to 50 percent range
for this time period. Deep layer shear values look to be pretty
weak, but CAPE values around 3000 J/kg will probably support
strong to possibly severe thunderstorms Thursday night into
Friday assuming models hold together with the shortwave.

The exit of this shortwave on Friday will coincide with an exiting
upper level trof across the Pacific northwest. This will give way
to a strong four corners high that will attempt to set up.
Amplification of this high indicates that we may transition to a
dry northerly flow by Sunday.

One thing we will need to continue to monitor is a disturbance
that used to be a Tropical Storm currently between Cuba and
Central America, has a 70 percent chance of retuning to a Tropical
Storm in the next 48 hours. Regardless, this system is expected to
work up the Gulf coast and possibly along the Rio Grande River
towards western TX by the weekend. This system has the track that
appears to want to clip at least parts of the southern to maybe
southwestern Panhandles. But it depends on the strength and
position of the four corners high that`s expected. Current models
suggest that the ridge and that northerly flow over the Panhandles
will help suppress the tropical system to the south and it may
miss our area. But other areas, such as west and central TX may
not be so lucky as it may stall and retrograde over central and
southern TX, making for a significant hydro event for areas in the
central TX state area, especially southern TX along the Mexico
border. If conditions change this system could track partially or
completely over the Panhandles, which will make for a potential
long fused flood or even flash flood event. We will continue to
track this storm and see how things pan out toward the end of the
weekend.

Weber

AVIATION...18Z TAFS...
VFR conditions expected through the period. Winds will be
southwesterly around 12-18 knots before decreasing to around 10
knots this evening. A frontal boundary is expected to shift winds
to the north at 10-15 knots Tuesday morning. A few showers and
thunderstorms will be possible along and ahead of this boundary as
it sags south between 06z and 15z. Included prob30 at KGUY and
KDHT where confidence is slightly higher compared to KAMA.

Ward

&&

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

&&

$$


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