825
FXUS64 KAMA 231732
AFDAMA

Area Forecast Discussion
National Weather Service Amarillo TX
1232 PM CDT Sat Sep 23 2017

.AVIATION...
MVFR conditions will persist through most of the 18Z TAF period as
showers are developing just west of the TX/NM state line. DHT
will be the first to see some showers and thunderstorms starting
as early as the beginning of the TAF period. Due to the slow
progression AMA and GUY may not see showers and thunderstorms till
around 06Z. Amendments may be needed if shower activity moves in
ahead of time. There may be a few pop up showers between 18Z and
03Z and will make amendments for these if needed, as confidence is
too low at this time to add into the AMA/GUY TAFs. CIGs will be
SCT to BKN around 5k ft and drop as low as 1k ft with
showers/thunderstorms. Overall CIGs expected to be MVFR through
the TAF period, with GUY being the exception as it will fluctuate
between VFR and MVFR CIGs. Winds will be out of the south to
southeast 15 to 20 kts sustained with gust up to 30 kts, maybe
higher with some thunderstorms.

Hoffeditz/Weber

&&

.PREV DISCUSSION... /Issued 1017 AM CDT Sat Sep 23 2017/

UPDATE...
Showers and storms that are along eastern NM will continue to
slowly propagate towards the TX Panhandle this afternoon.
Expected time of arrival to the Panhandles has backed off to early
afternoon. Therefore significantly pulled back POPs from east to
west, leaving a low end chance for the western TX Panhandle
Counties. This has had a trickle affect for the Panhandle
forecast and now the heavy rain potential for the western
Panhandles looks to be more late this afternoon through early
Sunday morning. With the central Panhandles best chances tonight
into mid to late Sunday morning. And the eastern Panhandles look
to receive most of the showers and storms during the day Sunday.

Weber

PREV DISCUSSION... /Issued 426 AM CDT Sat Sep 23 2017/

DISCUSSION...
Closed upper low over the Great Basin region to move east and then
northeast into the central and northern Rockies by Monday before
weakening into an open wave. Abundant mid and high level tropical
moisture to lift northward out of Mexico into the Panhandles by
tonight through early next week. Upslope surface flow will advect
low level Gulf moisture into the forecast area today through the
weekend before a cold front moves through the Panhandles Sunday
night and early Monday. Convection chances will be on the increase
today through much of next week, however the best chances will be
mainly after 21Z today and 00Z Sunday through Sunday and into
early next week. Initially, some of the convection this afternoon
and this evening may become strong to marginally severe with wind
being the main threat but hail up to quarter size could also
accompany the strongest convection. Heavy to very heavy rainfall
which could result in flooding or flash flooding remains the
greatest threat from convection later today and tonight through
Sunday and possibly Monday.

Another closed upper low is forecast to develop over the Great
Basin region by the middle of next week which should dig south
into the southwestern states and Four Corners region during the
latter half of next week. An upper ridge is forecast to build in
over the Panhandles ahead of this closed upper low late next week
which should allow for drier conditions. Cool surface high will
remain over the forecast area behind the cold front through most
of next week allowing for normal or slightly below normal
conditions across the Panhandles.

Schneider

HYDROLOGY...
Most of the short term hi-res models indicating convection with
very heavy rainfall primarily affect the western portions of the
Panhandles after 00Z Sunday. The RAP and the hi-res ARW are the
earliest with the heaviest rainfall between 21Z today and 00Z
Sunday. Otherwise, the HRRR, NAM and hi-res NMM holding off the
heaviest rainfall until after 00Z Sunday. All of the short term
models are in good agreement that heavy to very heavy rainfall
from slow moving convection could likely result in flooding or
flash flooding tonight into Sunday. Forecast model soundings
continue to indicate PWAT values of 1.25 to around 1.50 to 1.60
inches between 00Z Sunday and 00Z Tuesday which would put it in
excess of the 90th percentile for the forecast area for this time
of year. Confidence continues to increase for the threat of very
heavy rainfall resulting in flooding or flash flooding, therefore
decided to issue a Flash Flood Watch for the far western
Panhandles from 00Z Sunday until 18Z Sunday. Of course, this will
need to be adjusted in area and time depending on a faster or
slower onset of the heaviest rainfall from convection and also as
the convection progresses eastward tonight and Sunday. Rivers
will need to be closely monitored for rapid rises where gauges are
located.

Schneider

&&

.AMA Watches/Warnings/Advisories...
TX...Flash Flood Watch from 7 PM CDT this evening through Sunday
     afternoon for the following zones: Dallam...Deaf Smith...
     Hansford...Hartley...Moore...Oldham...Sherman.

OK...Flash Flood Watch from 7 PM CDT this evening through Sunday
     afternoon for the following zones: Cimarron...Texas.


&&

$$

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