Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 231123

Area Forecast Discussion
National Weather Service Amarillo TX
623 AM CDT Sat Sep 23 2017


For the 12Z TAFs:

VFR conditions will prevail through the beginning of the TAF
period until thunderstorms begin to impact the terminals late this
afternoon/early evening. Chances are pretty good for
thunderstorms to develop in eastern New Mexico and push east
across the Panhandles. Models have been pretty consistent with
developing a line of storms, and this would lead to decent chances
of impacting the terminals today/tonight due to a large coverage
area of storms. During this time frame impacts to both ceilings
and visibility will likely result within any thunderstorms that
develop. These are the main threats outside of the obvious strong
wind gusts and hail. Chances are high for MVFR within any
thunderstorms that develop, but one cannot rule out perhaps brief
periods of IFR as well. Storms will linger around into the evening
hours, but the extent of these storms is in question at this time.



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

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.


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



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

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


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