Area Forecast Discussion
Issued by NWS Amarillo, TX
FXUS64 KAMA 221912
Area Forecast Discussion
National Weather Service Amarillo TX
212 PM CDT SUN MAY 22 2016
See previously issued Mesoscale Discussion below for details on
today`s severe weather threat. We will provide updates throughout the
afternoon based on trends in the observations and short term
Challenges for this forecast package will be how far east dryline
mixes each day through mid week and severe potential ahead of it.
Upstream soundings across Central and southern Texas are quite deep
with moisture and without significant mean southwesterly flow it may
be difficult for the dryline to mix very far east. Model guidance
has consistently struggled with this all season. Furthermore, and
with this particular model bias aside, they have shifted slowly west
with low-level theta-e ridging/dryline over the last couple of days.
We have shifted thunderstorm chances westward accordingly and are
currently on the western edge of guidance with this forecast cycle.
Deep layer shear values taken at face value are not very impressive,
generally less than 25 knots, but models are also veered in low
levels behind the sharpening dryline they depict too far east.
Backed winds at the low levels east of the dryline yield at least 40
knots of effective bulk shear. Abundant low level moisture should
contribute to a strongly unstable air mass ahead of the dryline
during the afternoon with MLCAPE at least 2,500 J/KG and probably
higher. All modes of severe are possible. Heavy rain should still be
Not much change was made to the forecast beyond Tuesday. Main upper
trough will approach Thursday and have added thunder to the far
eastern Panhandles. We may very well see a westward trend with low
level moisture/dryline again on Thursday putting more of the area at
risk, especially if the trough deepens/slows more than currently
depicted in the model guidance.
Mesoscale Update... /Issued 1213 PM CDT SUN MAY 22 2016/
..Severe weather expected today...
* Synoptic Overview: This morning an upper-level low pressure system
was spinning over southern Alberta and western Montana, with a
pronounced ridge of high pressure aloft extending from Texas
toward the Great Lakes. The Texas and Oklahoma Panhandles remain
beneath southwesterly flow aloft between these features and just on
the western periphery of the ridge. A northern stream jet maximum
extends from Utah to the Dakotas, while the southern stream jet
maximum is confined to northern Mexico and South Texas. The
Panhandles remain under an area of diffluence between the jets, but
300mb winds will be at a relative minimum across this region today.
Water vapor imagery showed the remains of yesterday`s convection
being swept eastward by that shortwave and hints of a few other
shortwaves rounding the upper low and traversing the Rockies. The
overall upper-level support will be somewhat limited today due to
the lack of direct influence from an upper-level jet and the fact
that passing shortwaves are not expected to be very deep or extend
very far southeast into our area. At the surface a surface low will
deepen over eastern Colorado, and a dryline will tighten up
extending to its south through the length of West Texas.
Thunderstorms (some of which will be severe) are expected to
develop along much of the dryline this afternoon and evening.
* Mesoscale: With the deepening surface low over Colorado, we expect
the dryline to hang back across far western portions of the Texas
and Oklahoma Panhandles - likely extending from near Boise City to
Hereford by the late afternoon. In response to the developing
surface low and dryline, expect low-level winds to back more from
the southeast as the afternoon progresses. This will aid in low-
level convergence near the dryline and keep low to mid 60s
dewpoints in place across most of the Panhandles. Low and mid-level
clouds are breaking up across the area, with temperatures quickly
climbing into the 80s. Model guidance suggests that a combination
of mid-80s temps and low-to-mid 60s dewpoints will lead to a narrow
corridor of MLCAPE values approaching 3000-4000 J/kg near and just
east of the dryline. Steep mid-level lapse rates of 8 to 9 C/km
also expected east of the dryline. Any thunderstorms developing
near this area will have the chance to rapidly intensify. Deep
layer shear will be on the marginal side (only around 30-35 kts of
0-6km shear) during the afternoon and evening but will be
perpendicular to the dryline, suggesting a weakly organized storm
mode with a few supercells possible. Increasing low-level wind
shear by late evening does indicate at least some threat for
isolated tornadoes, though lack of upper-level support means these
should be short lived. Storm motion should be to the northeast at
around 25 kts, though right-moving supercells would have a slower
ENE trajectory similar to yesterday`s storms.
* Threats: With such a high potential for instability, large hail to
the size of baseballs and damaging wind gusts will be the primary
hazards. Increasing low-level wind shear near sunset will also
allow for a brief window when isolated tornadoes will be possible.
Slow storm motions for the strongest storms and recent rainfall
over portions of the threat area mean that localized flooding and
flash flooding will be possible as well.
* Timing & Location: Though there is some slight uncertainty on just
how far east the dryline will develop this afternoon, confidence is
fairly high that it will set up between the TX/NM state line and an
Amarillo-to-Guymon line. The greatest threat for severe weather
will be for central portions of the Texas and Oklahoma Panhandles.
Timing for storm initiation is expected to be around 2 to 4 pm this
afternoon, with storm severity and coverage decreasing by midnight.
.Preliminary Point Temps/Pops...
Amarillo TX 65 87 60 89 57 / 60 30 20 20 20
Beaver OK 67 89 63 91 59 / 50 30 40 20 20
Boise City OK 58 85 53 86 52 / 30 10 10 10 5
Borger TX 68 89 63 91 60 / 60 30 30 20 20
Boys Ranch TX 63 89 58 91 56 / 50 20 20 20 10
Canyon TX 64 88 60 90 56 / 60 30 20 20 20
Clarendon TX 66 87 64 90 59 / 60 40 40 20 30
Dalhart TX 59 87 53 88 52 / 40 10 10 10 5
Guymon OK 64 87 58 90 55 / 60 20 20 10 10
Hereford TX 64 89 57 90 56 / 50 20 20 20 10
Lipscomb TX 67 87 65 90 61 / 40 40 40 20 20
Pampa TX 67 86 63 89 59 / 60 30 40 20 30
Shamrock TX 67 85 66 89 61 / 40 40 40 40 40
Wellington TX 68 87 66 90 62 / 40 40 40 40 40