Area Forecast Discussion
Issued by NWS Amarillo, TX

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789
FXUS64 KAMA 260511 AAB
AFDAMA

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
1211 AM CDT Wed Apr 26 2017

.AVIATION...
Scattered showers will continue at the TAF sites through the pre-
dawn hours. MVFR cigs will also be likely through sunrise or a
couple of hours after. VFR conditions will then prevail from mid
morning through the rest of the forecast. North winds will be
gusty through the day and then they will decrease and become
easterly this evening.

&&

.PREV DISCUSSION... /Issued 718 PM CDT Tue Apr 25 2017/

AVIATION...
For the 00Z TAFs, gradually deteriorating weather conditions are
anticipated at all terminal sites for the first 12 hours of this
fcst cycle as an upper level low pressure system moves across the
region tonight and Wednesday morning, with improvement expected
for the last 12 hours. A cold front in the southern Texas
Panhandle will move through KAMA between 00Z and 01Z. Expect an
increasing threat of showers and isold tstms across the TAF sites
this evening and tonight, diminishing Wednesday morning with gusty
north winds and attendant MVFR cigs. Improving conditions are
slated for all TAF sites mid to late Wednesday morning.

Andrade

PREV DISCUSSION... /Issued 458 PM CDT Tue Apr 25 2017/

DISCUSSION...
Broad upper level trough over the west-central CONUS is evident
on water vapor imagery with moderately strong jet rounding base
into the Texas Panhandle. A cold front has pushed south and
stalled right along the I-40 corridor. South of the front,
temperatures are in the 70s and winds are westerly. There are
fairly strong winds in the far southwest Texas Panhandle where
clouds have dissipated and enhanced winds aloft are mixing down.
North of the front, temperatures are in the 50s and 60s with light
northerly winds and increased clouds cover. A few showers are
possible along and north of the front where some limited mid-level
moisture is available. An isolated thunderstorm is possible, but
unlikely given the fairly stable environment (~100-200 J/kg high
based CAPE along and just behind front).

Shower coverage will be increasing later tonight into early
tomorrow morning as the aforementioned upper trough axis
approaches along with a developing 700mb low. Height falls and
increased DCVA will provide some decent synoptic scale ascent
especially during the period between 06z and 15z Wednesday. In
addition, models are showing some weak 700mb deformation as the
low crosses the Panhandles. While there is some question as to how
strong the forcing will be, model sounding profiles do indicate
some decent negative omega values in conjunction with the area of
700mb deformation and mid/upper dynamics. Vertical moisture
profiles also look good for a few hours as mid level moisture
increases just ahead of the trough axis. Some models are
indicating enough CAA to result in near freezing temperatures
Wednesday morning (~34-36 deg F), however dew point values in the
40s and high 30s upstream should keep snow concerns minimized.
Given the progged cold profile above 800mb and a brief period of
saturation in the dendritic growth zone near sunrise, can`t rule
out a few snowflakes mixing in especially for the western
Panhandles. Should keep an eye on CAMs and latest Obs for possible
update to grids if needed. Thunderstorms will be isolated at best
with very minimal instability, elevated or otherwise. As the low
cross the area, a reinforcing cold front will push through the
Panhandles from about 09z to 15z. This front is expected to make
it all the way to the coast by Wednesday afternoon with highs only
making it into the low 60s for most areas in the Panhandles.
Shower activity will end during the late morning Wednesday as the
upper trough axis shifts east of the area.

Northwest flow on Wednesday will slowly become more zonal as the
broad cyclonic flow expands across the CONUS. A strong 70-80 knot
500mb jet is progged to develop and lift into the Panhandle region
Thursday ahead of a developing upper low over the Great Basin. A
surface low will develop below the jet left-exit region over the
Panhandles resulting in a tricky wind/temp/pop forecast. At this
time it looks like near advisory criteria winds could develop on
the southwest side of the sfc low over the far southwest Texas
Panhandle where mixing potential will be greatest. Showers and an
isolated thunderstorm are possible on the northeast side of the
sfc low where just enough moisture may be pulled up on the E/SE
winds. For now just went slight pops as moisture return will be
difficult given the Wednesday front.

The real interesting weather may be saved for the weekend as the
developing low over the Great Basin is expected strengthen
considerably as it moves over the Four-Corners region Friday. By
mid-day Saturday deterministic models show a closed ~555 DAM
500mb low over northern New Mexico and a strong sw/ne oriented jet
over the Panhandles. Meanwhile, a developing strong 700mb low is
expected to move across the the Panhandles. The GFS tracks and
strengthens this low in a very favorable manner so that the
Panhandles are in an area of deformation and maximum moisture
transport for an extended period of time. The ECMWF and Canadian
models are slightly faster and farther north with this low but
still favorable for precipitation. Furthermore, while there are
some small differences in the deterministic solutions, it does
appear a large portion of the Panhandles could see some rain from
late Friday through early Sunday. The ECMWF has started to come
more in line with the GFS with the last model runs, and if the GFS
is correct, strong CAA on the cold side of the low could result
in snow for a large portion of the area with accumulating snow in
the western and especially northwestern CWA mainly Saturday and
Saturday night. There are still a few days of data to collect on
this system, so stay tuned as we refine this forecast.

Ward

FIRE WEATHER...
Fire weather concerns will be minimal with the exception of
Thursday afternoon in the southwest Texas Panhandle where RH
values around 15 percent and windy conditions are possible. Twenty
foot winds as high as 20-30 knots will be possible in the far SW
Texas Panhandle. The green fuels and possible rain on Tuesday
night will continue to mitigate critical fire weather, but
elevated conditions will still be highlighted on Thursday if
needed.

Ward

&&

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

&&

$$

15/29



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