Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 252343 AAA
AFDAMA

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
643 PM CDT Tue Jul 25 2017

.AVIATION...
For the 00Z TAFs, have included VCTS at KDHT until around 03Z
based on current radar imagery. Expect isolated showers and tstms
over northern parts of the area to diminish after sunset with loss
of daytime heating. Isolated to scattered showers and tstms are
forecast to develop once again Wednesday afternoon across parts of
the area. However, due to uncertainty and associated low
confidence as to where any storms may form Wednesday afternoon,
have omitted mention of this weather element for this fcst
issuance at this time.

Andrade

&&

.PREV DISCUSSION... /Issued 400 PM CDT Tue Jul 25 2017/

DISCUSSION...

We finally get a break in the forecast for precipitation chances
today, but that will not last long as the forecast gets interesting
again Wednesday afternoon through Thursday. There is the potential
for appreciable rainfall amounts across western/central parts of the
Oklahoma Panhandle, as well as northern/northwestern parts of Texas
Panhandle. Biggest change to this forecast package was to increase
the probability of rainfall across these areas as it seems likely to
receive at least some measurable precipitation, with the potential
for moderate to heavy rainfall. Several more chances will exist for
rainfall later in the week, but this discussion will focus on the
potential beginning tomorrow through Thursday. Also of concern is
the fact our radar will be down all week. Could be back up as early
as Friday.

For today, we are lacking moisture in the atmosphere that we have
seen the last few days, especially the lower levels. In addition,
mid level lapse rates are very unimpressive. The chance for
showers/thunderstorms looks minimal at best this afternoon and
evening. Decided to decrease chances across the forecast area. The
one area that looks to have at least a chance would be
western/northwestern parts of the forecast area, albeit very small
chances today/tonight.

Moving into tomorrow, a zone of convergence will be noted at the
surface along a trough anticipated to move through tomorrow and then
intensify tomorrow as a weak cold front begins to come through
Wednesday night/Thursday morning. However, it should be noted that
overall there is little bulk shear to work with during the Wednesday
through Thursday timeframe. Severe weather doesn`t look likely. That
being said, there is some turning throughout the atmosphere noted in
the forecast soundings. I am not anticipating widespread severe
weather, but there could be some gusty winds, especially if the
storms become linear and create bowing segments, or any storms that
produce outflow from collapsing thunderstorms. I think the bigger
threat will be rainfall and potential localized flooding in the
heavier rainfall scenarios. Precipitable water values are progged to
be very high (2+ inches for some outputs), or basically well above
the 90th percentile. Moisture transport is also very good with
noticeable dewpoint depressions decreasing after 7pm tomorrow. Since
storms lack wind speeds aloft, I also anticipate storms to be slow
movers. Storm motions are around 20 mph or less. Additionally, the
mean flow aloft looks to be parallel to the zone of convergence. All
this being said, several factors are coming into place which hint
towards possible heavy rainfall, mainly northwestern parts of the
forecast area. Looking at analogs and the GEFS reforecast analysis,
several indicators are also evident where rainfall could be around
half an inch easily across northwestern parts of the forecast area.
One of the runs for the mean precipitation has over an inch in this
area during the 24 hour period starting around 7pm (00Z) tomorrow to
7pm (00Z) Thursday. Additionally, and probably one of the more
noteworthy outputs from the GEFS reforecast page is the probability
of "no precipitation" between 00Z Thursday and 00Z Friday...which is
zero percent for areas across our northwestern zones. Another
noteworthy output for probability of precipitation greater than a
tenth of an inch was 70%-80%. In other words, there is a good chance
for rainfall across western and central parts of the Oklahoma
Panhandle, as well as northern and northwestern parts of the Texas
Panhandle. There has been consistency with these outputs so that
increases confidence as well. Overall, predicting rainfall amounts
is probably one of the more difficult things as a forecaster, but
several signs are pointing to measurable rainfall across the
aforementioned areas. Unfortunately, we will be without our radar
tomorrow, which could lead to more difficulty in the forecast.

Guerrero

&&

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

&&

$$


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