Area Forecast Discussion
Issued by NWS Amarillo, TX

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593
FXUS64 KAMA 220235
AFDAMA

Area Forecast Discussion
National Weather Service Amarillo TX
935 PM CDT SAT MAY 21 2016

.Mesoscale Update...
00z sounding shows approximately 100 Joules of CIN at the base of a
residual EML. Further west, CIN from this warm layer near/just below
700 mb is probably weaker and this fits latest radar trends. The
storm north of Dalhart disipated as it moved toward the western
border of Potter and Randall counties. CIN should continue to grow
as the boundary layer gradually stabilizes and the severe threat is
expected to diminish later this evening. For the hour or two hail
will continue to be a threat with the ongoing storms in Deaf Smith
County. Additional development seems unlikely since this event
was primarily thermodynamically driven. We will make a last minute
call on whether or not to extend the Severe Thunderstorm Watch for a
small area, or to let it expire, based on trends over the next
several minutes.

BRB

&&

.Prev Discussion... /Issued 704 PM CDT SAT MAY 21 2016/

Aviation... /For the 00z TAFs/
Thunderstorms are near Dalhart now and these will push east of the
terminal within the next couple of hours. Other storms located west-
southwest of Amarillo may approach the terminal closer to 01z but
instability will be decreasing so storms may diminish before
impacting the terminal. Another storm nearing Guymon has shown a
downward trend but may still result in irradic wind gusts as it
passes over/near the terminal between 00 and 01z.

Otherwise, warm/moist southerly flow may result in MVFR or IFR
stratus at all sites later tonight, with Amarillo having the greatest
likelihood. Stratus should clear by mid morning. Thunderstorms will
redevelop tomorrow afternoon and could impact either of the three
terminals. Prob30 will suffice for now until timing can be better
resolved.

BRB

Prev Discussion... /Issued 529 PM CDT SAT MAY 21 2016/

Mesoscale Update...
Convection has developed late this afternoon in a band from near
Stratford to Dalhart to far western Deaf Smith County. This is ahead
of a surface trough/sharpening dryline west of the New Mexico state
line, on the western edge of low-level theta-e axis. Movement of
individual cells is northeast at 25 to 30 mph. Latest RAP sounding
for KHDT needed little/no modification based on nearby surface obs.
Deep mixing has occurred with MLCAPE approaching 1,000 J/KG and
300-500 J/KG of CAPE in the hail growth zone. With the absence of
large CAPE in the hail growth zone, significant (2"+) hail sizes may
be difficult to achieve. Nevertheless, sufficient instability is
present for marginally severe hail in the strongest storms. Effective
Bulk Shear of around 35 knots is supportive of organized/persistent
updrafts and at least transient supercell characteristics. Radar has
shown the deepest cores indicitive of the strongest updrafts have not
sustained for long.

No significant trends upward are expected this evening. Eventually
isollobarically forced low level backing and decreased mixing will
lead to a surge of better moisture northwestward, but by then
diabatic cooling will be underway and the surface based instability
will lessen with a downward trend in convection expected. Until then
(probably around 9 or 10 PM) a severe hail/wind threat should
persist. We will evaluate new guidance and observational trends, the
potential for storms to sustain into the night and/or redevelop with
warm advection process. This seems unlikely at this time (see
previous discussion for reasoning).

BRB

Prev Discussion... /Issued 335 PM CDT SAT MAY 21 2016/

Discussion...
Thunderstorms that develop this afternoon across the western
Panhandles will move east this evening with at least a marginally
severe wind/hail threat persisting through late evening.
Deepening moisture and increasing precipitable water values per
short term guidance and trends in the upstream GPS PWAT sites,
combined with relatively slow storm motions are supportive of
locally heavy rainfall amounts and possibly flooding potential,
particularly later this evening in the southern Texas Panhandle. For
specifics on convective initiation and potential severe please see
the previously issued mesoscale discussion. Updates on mesoscale
evolution will be sent as needed through the afternoon and evening.

There is a decent signal in some of the models of warm/moist
advection process keeping convection going across the southern
portion of the Texas Panhandle through the night. Most of the
forecast soundings still show evidence of ridging/subsidence for
most of the night, but the eastward progression of the ridge may be
enough for some activity late especially in the southeast Texas
Panhandle where the WAA signal is maximized. Kept low probabilities
to account for this mainly focused on the southeastern Texas
Panhandle.

Modest ascent will overspread the area tomorrow in diffluent upper
flow regime. A sharpening dryline across the western Panhandles
should focus thunderstorm development during the afternoon in a
moderately unstable environment with MLCAPE of 2,000-2,500 J/KG. 0-6
km bulk shear of around 30 to 40 knots should be sufficient for
storm organization and supercells. Large hail and damaging winds
will be the primary threat although with relatively low LCL heights
generally less than 1,000m isolated tornadoes will be possible. The
best chance for a tornado would be during the evening as low level
jet strengthens causing low level shear to increase and before
significant boundary layer stabilization occurs.

Troughing to our west continues through mid-week before accelerating
eastward toward the Panhandles by the end of the week. Until then
mid-level momentum should allow the dryline to mix/sharpen across
the far eastern Panahandles and this convection should be limited to
this area. We will need to monitor trends in the short term guidance
as the time nears in case models are mixing the dryline too far east
as has been the case lately. This is a more synoptically active
scenario with fairly decent cross-boundary mean flow, thus the
reasoning for not adjusting westward at this time. If models trend
slower and more amplified with approaching truogh, we will likely
need to introduce at least low probabilities of convection in the
east portion of the Panhandles.

BRB

&&

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

&&

$$

3/14



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