Area Forecast Discussion
Issued by NWS Amarillo, TX

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000
FXUS64 KAMA 211051
AFDAMA

Area Forecast Discussion
National Weather Service Amarillo TX
551 AM CDT WED SEP 21 2016

.AVIATION...
For 12z TAFs...VFR conditions expected through the period at all TAF
sites. South winds will gradually become more southwesterly through
15z. Winds will increase to around 15-20 knots with occasional gusts
up to 30 knots late morning through the afternoon. A few showers and
thunderstorms are expected to move across our northwestern zones
during the afternoon and evening. Kept VCTS at KDHT to account for
this potential even though latest guidance suggest activity may stay
northwest of terminal...can`t rule out storms near KGUY as well but
currently expecting storms stay north and west...KAMA and points
east expected to stay dry.

&&

.PREV DISCUSSION... /Issued 405 AM CDT WED SEP 21 2016/

DISCUSSION...
The influence of post-tropical cyclone Paine can already be seen on
regional water vapor imagery. The additional upper level moisture
will combine with vorticity lobes emanating from the Colorado
Rockies this afternoon to help bring rain chances to portions of the
Panhandles. We will see storms first develop across eastern New
Mexico and southeastern Colorado around midday. With northeastward
storm motions, these storms should move into the northwestern Texas
and Oklahoma Panhandles by the early afternoon. Overnight they will
spread to encompass most of the Oklahoma Panhandles as the vort lobes
track northeastward. We should see storms clear the Panhandles around
midnight. Instability and deep layer shear will be lacking so severe
weather is not anticipated at this time.

Thursday and most of Friday will be dry before all eyes turn to the
next system expected to bring widespread rain chances for the weeks
end. Before diving into specifics, it`s important to note that medium
range models continue to struggle with the exact evolution of the
weekend system and thus adjustments will likely be needed for this
portion of the forecast. Now, a closed upper low is forecast to move
into the Four Corners region by Friday afternoon. With this
proximity, we will likely see storms develop across eastern New
Mexico and we could see a few of these storms sneak across the state
lines during the afternoon hours. Rain chances will be on the rise
overnight Friday as the low moves closer to the Panhandles.

Models show an elongated trough extending from the low center
positioned over Montana early Saturday morning. This trough position
could be enough to bring a front/surface trough into the western
Panhandles Saturday which could limit rain chances across the west.
Better moisture, instability, and shear will be present across the
eastern Panhandles. A capping inversion should limit storm strength for
the better part of the day, but a window exists during the early
evening that a marginally severe storm can`t entirely be ruled out.

Saturday night into Sunday morning is where models start to diverge
from each other in the evolution of the upper system. The GFS shows
the trough deepening into northern Mexico while the ECMWF/CMC closes
off the low and keeps the location closer to the Panhandles. The
further north position of the low prolongs precip chances across the
Panhandle a good 12-18 hours longer than the southern GFS. The
quicker cut off of rain chances across the Panhandles is due to the
shifting of the Pacific moisture transport further south over central
Texas/Oklahoma while the further north positioning prolongs the
transport over the Panhandle. Have carried low end POPs during the
day Sunday for now, but may need to lower chances given recent
drying trends.

The positioning of the low also affects the timing of a cold front
expected to dive across the Panhandles. The GFS is the most
aggressive with this front, which is south of the area by Sunday
morning, while the ECMWF/CMC lag behind the GFS by about 6-12 hours.
With all that being said, the trend of the 00z model runs has been
towards the further southern evolution of the upper low. The
forecast reflects this trend and brings the front through Sunday
morning as well as ending rain chances quickly Monday morning. Did
go above guidance on winds behind the front on Sunday as model blends
have underdone the strength of the pressure gradient across the
Panhandles. It`s a little too early given the variation in model
runs/solutions, but we could be pushing wind advisory if recent
trends persist.

While there is disagreement on the exact upper pattern Tuesday into
next week, the general agreement is that it should be dry across the
Panhandles. Temperatures will also be a few degrees below climatology
for late September with highs in the lower to mid 70s.

&&

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

&&

$$

7/14



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