Area Forecast Discussion
Issued by NWS Amarillo, TX

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359
FXUS64 KAMA 202326
AFDAMA

Area Forecast Discussion
National Weather Service Amarillo TX
626 PM CDT Thu Apr 20 2017

.AVIATION...
00Z TAF Cycle

VFR conditions will prevail at all three TAF sites early but then
MVFR to IFR or even LIFR conditions can be expected after 06Z to
08Z Friday. VFR conditions may possible return to the Dalhart and
Amarillo TAF sites after 15Z to 17Z Friday while MVFR conditions
should prevail at the Guymon TAF site after 15Z to 17Z Friday.
Showers and possibly thunderstorms will impact primarily the
Guymon and Amarillo TAF sites mainly between about 08Z and 10Z
Friday until around 14Z to 16Z Friday. East and southeast winds 10
to 20 knots with occasional gusts near 25 knots early will
diminish to around 5 to 15 knots after 02Z to 04Z Friday. Winds
are expected to shift to the northwest and north 15 to 25 knots
with gusts near 30 knots after 15Z to 17Z Friday at the Guymon and
Dalhart TAF sites, and after 17Z to 19Z Friday at the Amarillo TAF
site. Winds will be stronger and erratic in and near any
thunderstorms at the three TAF sites.

Schneider

&&

.PREV DISCUSSION... /Issued 406 PM CDT Thu Apr 20 2017/

DISCUSSION...Winds have tapered off some behind a cold front that
passed through the region this morning. High temperatures observed
so far have been in the upper 60s to lower 70s, with mostly clear
skies. These conditions will be short lived another weather system
approaches the area tonight. Present satellite imagery shows this
system presently traversing through New Mexico and Colorado, with
increasing cloud cover along the Rocky Mountains. This area will
be the monitored for thunderstorm development this afternoon as a
source region for convection due to arrive and/or develop in the
Panhandles late tonight into early Friday morning. Latest hi-res
model guidance has suggested that these storms will move east into
the Panhandles between midnight and 3 AM, with storms growing
upscale and reaching the eastern Panhandles between 5 AM and 8 AM.

Threat assessment with these storms present a few factors that
work against overnight storms bringing severe hail and/or winds.
The first being the existence of a shallow cold layer below
850mb from our cold front this morning presently stalled over
northwestern Texas. This shallow cold layer is presenting a stable
layer close to the surface, which will result in all convective
potential being elevated. In addition, thunderstorm winds will
have some difficulty mixing to the surface in the presence of this
cold layer, which will likely prevent winds reaching the 60 MPH
threshold. The cold layer will also present problems for hail that
may fall out of thunderstorms, as this layer will (according to
forecast soundings) be nearly saturated. Another negative factor
is the time displacement of greatest instability and synoptic
scale forcing. Latest model guidance suggests that MUCAPE will be
maximized between 10 PM and 6 AM, while the best synoptic scale
lift will not be over the region until around sunrise. Finally,
isentropic lift necessary for forced ascent over the stable layer
is only marginally favorable to allow parcels to be forced in the
unstable layer.

With that said, factors favoring severe weather do include an axis
of MUCAPE around 1000 to 2000 J/kg favoring the Texas Panhandle,
coupled with 0-6 km bulk shear approaching 50 to 60 kts. Despite
the lack of coupling with synoptic scale lift over highest MUCAPE,
The left jet exit region will be over the combined Panhandles as
the upper level storm system begins to dig into the central United
States. All told, strong to marginally severe storms are possible
with hail up to the size of quarters being the main hazard. Wind
threat will be largely mitigated by the stable cold layer near the
surface, though should storms grow linear while going upscale, it
would not be surprising to see strong wind gusts with storms
capable of producing strong downdrafts.

Once the upper trough exits the area, another cold front will dive
south across the region Friday afternoon and evening. Model trends
have continued to trend down on the wind speeds along and behind
the front, with only a brief period of higher wind gusts due to
weakening pressure gradients during frontal passage. Behind the
front Friday night, temperatures will fall during the overnight
hours into the mid 30s northwest to mid 40s southeast. More
tranquil conditions will follow on Saturday (typical Panhandle
breezes notwithstanding) as high temperatures range from the upper
50s to lower 60s, or about 10 to 15 degrees below normal. Saturday
night may bring the potential for frost in spots, as winds calm
and temperatures fall into the mid 30s to near 40.

The extended forecast period will see drier conditions prevail Sunday
through Tuesday as the region falls under the influence of a
passing ridge. Temperatures will rebound from the lower 70s on
Sunday, to the mid to upper 80s on Monday behind a sharpening
dryline in the eastern Texas Panhandle. Elevated fire weather
potential exists on both Monday and Tuesday, with details below in
the fire discussion. The next storm system we will be monitoring
is due to influence the region by Wednesday and Thursday, with us
being too far out to tell whether severe weather potential is
possible with this storm system.

Bieda

AVIATION...Previous Discussion...18Z TAFs...VFR conditions will
prevail through the start of the TAF period. Tonight, clouds will
increase in coverage and ceilings should drop down to MVFR (to
perhaps IFR at times). Thunderstorms will potentially impact the
terminals tonight as well. KDHT might be far enough west to not be
impacted, but certainly KAMA and KGUY have a decent chance at
showers and perhaps thunderstorms. If these storms come to
fruition, there will be the chance for lightning, hail and perhaps
gusty wind speeds around 50-60 mph. Until we see the "whites of
the eyes" so to speak, I am going to mention only showers in a
tempo group for KAMA and KGUY. Models are suggesting perhaps a
line of convection tonight forming around 4 am over
western/central parts of the Panhandles, and pushing east across
the Panhandles through the morning hours. Certainly low ceilings
and reduced visibilities due to rainfall are both going to be a
possible factor. Confidence is moderate to slightly high for these
storms to form tonight and bring MVFR/IFR conditions. Its been
pretty consistent the last couple days. Certainly cannot rule out
IFR/LIFR conditions tonight.

Guerrero

FIRE WEATHER...A brief window of conditional elevated fire
weather conditions exist for the extreme southwestern Texas
Panhandle Friday afternoon. The condition that may check against
this occurring will be whether or not precipitation falls in the
area late tonight and Friday. The next possible period for
elevated fire weather conditions will be next Monday and Tuesday,
as a low-level thermal ridge passes over the area. The western
two-thirds of the Panhandles will be favored for elevated fire
weather conditions on Monday & Tuesday as RH values drop to
around 11 to 20%, with southwest winds around 15 to 20 MPH.

Bieda

&&

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

&&

$$

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