Area Forecast Discussion
Issued by NWS Amarillo, TX
FXUS64 KAMA 230418
Area Forecast Discussion
National Weather Service Amarillo TX
1118 PM CDT SUN MAY 22 2016
Lots of uncertainty regarding timing overnight stratus development
and heights of cloud bases, owing to convective disruption. Low
levels remain quite moist, with ongoing warm air advection expected
to continue through the night. Stratus ceilings expected to
diminish by 16z Monday.
Uncertainty also regarding thunderstorm development on Monday. New
models suggest that moisture will be concentrated across southeast
and eastern part of forecast area, with instability axis east of
KAMA, with some moisture pooling attempting to advance into northern
sections in the afternoon.
.Prev Discussion... /Issued 1012 PM CDT SUN MAY 22 2016/
Have allowed Tornado Watch to expire on time at 10 PM, based on radar
trends and guidance from SPC. A few strong thunderstorms will likely
persist for a few hours in eastern sections. Will continue with
numerous to widespread thunderstorms with heavy rain in eastern
sections though 1 AM, with PoPs dropping notably thereafter. Updated
text products have been issued. Thanks for coordination, WFO DDC.
Prev Discussion... /Issued 652 PM CDT SUN MAY 22 2016/
Outflow boundary from thunderstorms over eastern parts of forecast moving
slowly westward. Expect this feature to reach KAMA shortly,
accompanied by southeast surface winds. Could see new thunderstorm
development along this boundary near KAMA and KGUY early this
evening. Otherwise, another round of stratus is forecast for KAMA
after midnight, with no low ceilings expected at northern terminals.
Will monitor as convection could disrupt stratus field. Expect
thunderstorms on Monday to develop mainly east of a line from KGUY to
Prev Discussion... /Issued 356 PM CDT SUN MAY 22 2016/
Severe weather expected today...
* Synoptic Overview: H5 center remains located across near the
Canada/MMontanaline, however broad troughing extends south across
the WRN US with SW flow aloft across the Panhandles. Models agree
in very modest large scale lift through 6z assoc w/ weak s/wvs in
this flow as seen in h7-h3 Q-Vector convergence. Jet level winds
will only be near 50 kts, however the flow will be somewhat
diffluent across the area between jet cores centered across desert
SW and NRN Mexico.
* Mesoscale: SFC Trough/dryline is setting up across WRN panhandle
counties and this boundary is expected to remain in WRN counties or
even near the NM border through the event. Initial convection
formed in highest moist axis just east of AMA where mid-upr 60s
dewpoints exist. This may lead to a somewhat disorganized pattern
to convective development as dryline storms were not the initial
storms to develop and also increases chances of storm/boundary
interactions. The area is experiencing the most moist low level
environment of the year given aforementioned high dewpoints and H7
dewpoints near 6 deg C. This value is AOA the climo max for the
area for this date. Not surprisingly, mixed layer capes are near
3000 J/KG and with 1200 J/KG in the hail growth zone. 18Z sounding
also shows good turning with deep layer shear, but effective bulk
shear values remain in the 20-30 range, however wind fields will
become increasingly favorable with 0-6 KM bulk shear values
forecast to increase to 30-50 kts (highest south) by 00Z per
WRF/NAM. 35-40 kt LLJ will also develop between 00-03Z leading to
0-1 km helicity around 200 and 0-3 km helicities of 200-400 by 3Z.
LCL values are likely maxing out now around 3000-6000 ft and are
forecast to drop below 2000 ft after 00z also leading to that
increase tornado potential in the 00z-03z timeframe.
* Threats: Scattered supercells storms with potential for very large
hail (baseball or larger) and damaging winds across the area with
an increasing threat for tornadoes between 23z and 3z assuming the
area is not completely worked over before that time-frame. High
moisture values could also lead to HP supercellsmaking spotting
challenging and also providing a flash flood threat in any areas
where more intense supercells form or training occurs given very
high rain rates.
* Timing & Location: Entire Panhandles area from now through evening
with increasing tornado threat in the evening time-frame.
Disorganized initiation well ahead of dry line makes it difficult
to more specifically pinpoint any east west timing with this event.
Prev Discussion... /Issued 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.