Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 172327 AAA
AFDAMA

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
627 PM CDT Sat Aug 17 2019

.AVIATION...
Thunderstorms are expected to remain to the east of the TAF sites
overnight. A wind shift will move across GUY and DHT overnight
causing the wind to go northwest, but speeds should continue to be
around 10 knots or less. Winds will then swing around to the
northeast at GUY and to the southeast at DHT by late Sunday
afternoon. The wind shift just barely makes it to AMA before it
dissipates, so winds are expected to go more westerly at AMA
toward sunrise. Skies are expected to remain VFR.

&&

.PREV DISCUSSION... /Issued 334 PM CDT Sat Aug 17 2019/

.SHORT TERM...Tonight and Sunday.
For the immediate short term, will continue the Heat Advisory until
expiration at 8 PM CDT this evening for parts of the central Texas
Panhandle based on current temperatures. Then for tonight, have
retained slgt chc pops for showers and thunderstorms across eastern
sections of the OK and TX Panhandles, mainly for the evening hours
based on decent instability and sufficient moisture. Given the
atmosphere will be well-mixed with associated inverted-V type
sounding profiles and corresponding DCAPE values between 1300 and
1800 J/kg, the strongest storms will be capable of producing
strong to severe wind gusts similar to the past few evenings and
nights.

For Sunday, the center of the upper level ridge of high pressure
will edge a bit closer to the forecast area, with a corresponding
warming of the mid levels such that the capping inversion will
likely become stronger, likely precluding tstm development.
Therefore, have retained a dry forecast for the area. A weak
boundary is forecast to slide through much of the region with winds
becoming northwest to north. Another Heat Advisory may become
necessary Sunday afternoon across parts of the central Texas
Panhandle.

02

Long term (Sunday Night through Saturday)...
H5 high will build across WRN TX through Monday, however models
generally agree the axis will remain just south of the area
through the evening. This more "dirty ridge" look is significant
as models show moisture transporting into the Panhandles from the
S and W just north of the ridge axis on Monday. By midday Monday,
there is a notable H7-H5 theta-e ridge positioned across the area
as well as an old retreating trough, and this may lead to
potential for ISO late aftn and evening TSTMS which could have
some influence on high temps for some areas. 3 km NAM is most
agressive with CAPE values which are 1000-2000 j/kg in some areas,
but this may be overdone some. Of course the downburst wind
threat will remain a concern if we indeed see ISO storms given
inverted V soundings.

Subtle differences in the position of the high center and s/wvs are
leading to much uncertainty for Tue and beyond. The GFS continues to
be quickest in breaking down the high center by basically spitting
it Tuesday which would help promote another chc for ISO storms and
perhaps slightly cooler cooler temps. The NAM12 and ECMWF keep a
stout ridge axis over or just north or the area with 595 to 596 DM
H5 heights in place Tuesday. Models agree that by Wed, S/WVs mvg out
of Canada will break down the ERN side of the ridge and cause the H5
high center to retreat into the desert SW. This will allow for NW
flow S/WVs to work into the area and will bring higher CHC POPs back
into the forecast by Wed/Thu given adequate moisture. The pattern
will also promote a cold front reaching into KS by Wed. While models
currently don`t show this front actually reaching far into the CWA
(if at all), we will have to see what influence convective outflow
will have once it reaches KS in bringing a boundary into the area.
Temps will decrease either way mid to late weak due to decreasing H5
heights and increasing precip chcs. ECMWF and GFS agree a developing
a significant h5 weakness/low on Fri, but do not agree on the
location. The GFS is further west (ERN CO and NE NM vs ERn KS/MO)
and slower in the east movement which would be more favorable for
precip chcs esp on Fri. This should help keep temps in check, but
bigger questions revolve around POPS which are limited to slt chc
attm Fri and Sat. Overall, really don`t see obvious opportunity to
disagree with model blends in the extended.

Gittinger

&&

.AMA Watches/Warnings/Advisories...
TX...Heat Advisory until 8 PM CDT this evening for the following
     zones: Armstrong.

OK...None.

&&

$$

15/24



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