Area Forecast Discussion
Issued by NWS Amarillo, TX

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954
FXUS64 KAMA 301750
AFDAMA

Area Forecast Discussion
National Weather Service Amarillo TX
1250 PM CDT MON MAY 30 2016

.Aviation...
Cumulus layer between 4000 and 6000 feet expected to develop this
afternoon.  Scattered thunderstorms expected to develop across
western sections late this afternoon and evening as disturbance seen
in water vapor imagery arrives from southwest.  Low-level
convergence expected to be higher near and along surface trof/dryline
feature as it moves into western sections.  Further support for
thunderstorm development occurs as 700 mb theta-e ridge develops and
intensifies while moving into western sections.  Will carry VCTS
remarks during hours of expected occurrence.

Thunderstorms should be ended at terminals after 06z Tuesday.  Cold
front expected to arrive late in the forecast at northern terminals,
shifting surface winds to north.  Some suggestion of stratus behind
cold front at KGUY, but will not forecast an MVFR or lower ceiling at
this time.  VFR forecast continues next 24 hours.

Cockrell

&&

.Prev Discussion... /Issued 609 AM CDT MON MAY 30 2016/

Aviation...
VFR conditions expected to continue for the first few hours of the
12z taf cycle. There is a chance the 3500-4000 ft stratus deck
across the far southwestern Texas Panhandle may be able to move into
kdht and kama this morning but we should be able to hold onto VFR
conditions. Surface winds should also pick up at 16z with gusts up to
25 kt. As we move into the afternoon hours we could see another round
of convection but confidence is far too low to mention in prevailing
conditions. Any convection that does impact the terminals should
clear out by 06z.

Prev Discussion... /Issued 354 AM CDT MON MAY 30 2016/

Discussion...
Early morning LAPS analysis shows surface flow is strongly
divergent centered near Childress in the wake of convective complex
last evening. Low level moisture has been depleted somewhat and it
may take some time to rectify this. The only observational data we
have now to gauge the degree of convective overturning is GNSS site
near Childress which has shown only modest reduction in precipitable
water from pre-convective peak of nearly 1.4 inches to the latest
observational value of around 1.1 inches.

In the short term guidance, 0-2 km mean theta-e and streamlines
suggest trajectories from generally along the edge or west of where
overturning was most pronounced. Nevertheless, significant cold pool
expansion from outflow propagation has occurred further south and
west than what is shown in short term guidance so it seems unlikely
that enough low level moisture will return for as much instability
as was seen yesterday, and this will tend to limit coverage and
intensity of convection. Have kept probabilities in the chance
category and used scattered wording as significant upscale growth
may be difficult to achieve at least on the level as was seen
yesterday. MLCAPE values should rise to around 1,500 J/kg in the
west but modest mid level flow will be present once again. 0-6 km
bulk shear values will only be 20-25 knots, although slightly higher
winds near the equilibrium level will yield higher storm depth shear
values. These values are insufficient for well-organized/persistent
storms. Models show noisy exaggerated shear values toward the end of
the day but this appears to be contaminated by convective
parametrization in the models and is not representative of or
derived from ambient flow.

Height and vorticity fields in the models early on are quite noisy
and it is difficult to pick out any substantial perturbations that
may aid in the development of convection once we destabilize
tomorrow afternoon. There is some indications of a weak wave in
Water Vapor across far west-central New Mexico and this may be well-
timed by mid afternoon. Furthermore, low level flow is at least
weakly confluent near sharpening/diffuse dryline close to the New
Mexico state line, and this should be where convection first
develops and initially becomes most concentrated. Current thinking
is by early afternoon convection will develop in a somewhat sparse
fashion across eastern New Mexico and continue eastward into the
Texas Panhandle during the afternoon. We retained at least small
probabilities further east during this time since even with the
conservative approach on low level moisture contribution to
instability, thermal profiles should be void of CIN by mid-
afternoon. Weak mid-upper ridging is likely to be present across the
central and eastern Panhandles though, and this should tend to limit
coverage, until perhaps later when 1.) this ridging deamplifies and
shifts east, and 2.) modest cold pool formation from convection back
to the west (if convection is extensive enough) moves east and aids
in thunderstorm persistence.

Hazards from afternoon convection include severe hail (although
updraft duration being limited by lack of storm organization from
weak deep layer shear will tend to limit hail size), damaging wind
gusts. Relatively slow storm motions could lead to locally heavy
rainfall and possibly flooding, although the moisture content and
spatial coverage of convection is expected to be less than
yesterday.

Deeper moisture is expected to return Tuesday. This in combination
with a southward moving cold front forced by northern stream wave
necessitates higher precipitation probabilities. A fairly high
confidence convective event is expected with enough instability
(1,500-2,000 MLCAPE) for severe thunderstorms. Mid level flow will
be weak again resulting in meager deep layer shear values generally
around 25 knots or less. Storms will tend to be weakly organized
multicellular with limited opportunity for transient supercell
characteristics. Thus, significant and/or widespread severe weather
is not expected. Storms may organize a cold pool similar to
yesterday and propagate eastward out of the area eventually
overnight. Heavy rain and flooding may again become a threat and
once spatial details on how convection will evolve become more clear
we will be able to better delineate threat areas for potentially
flooding or flash flooding. The greatest chance of heavy rainfall
amounts and flooding will be when storm motions are slow before cold
pool forms and storms accelerate eastward, like yesterday. Models
suggest PWAT values rising to 0.90-1.15 on the Caprock and around
1.25 or slightly higher off the Caprock across the eastern
Panhandles. We increased QPF for Tuesday slightly above model
consensus.

The front should continue southward bringing cool post frontal
potentially cloudy environment for the area Wednesday. Model
precipitation may be overzealous again for Wednesday in this post
frontal stable environment. We trended QPF and probabilities
downward to account for this but left low probabilities given a
northward trend noted with the upper low that continues to drift
toward the area. Some forcing and residual instability may be enough
for some convection in the southern portion of the Texas Panhandle
Wednesday. Dry weather is expected Thursday through at least
Saturday as the upper low moves across the state and further away
from us. Ridging will slowly build in and warmer temperatures will
return. The next chance of precipitation (albeit small chance) will
be Sunday as medium range models show ridge deamplifying some.

BRB

&&

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

&&

$$

03/06



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