Area Forecast Discussion
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FXUS64 KLUB 220843
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
343 AM CDT SUN MAY 22 2016

.SHORT TERM...
The forecast today remains challenging but has the potential to
produce significant severe weather this afternoon and evening.

Southwesterly flow aloft will increase modestly today as the nearby
upper ridge continues to yield to the broad western trough that will
make slow but steady eastward progress. This will cause the deep
layer shear to increase a notch from Saturday, up from around 30
knots to 40+ knots by late this afternoon/evening. At the surface,
another day of southerly/southeasterly flow has pumped up the
dewpoints to juicy levels with 08Z observations showing values in
the mid-upper 60s quite common for the South Plains and Rollings
Plains. This rich moisture will remain in place in advance of the
dryline which is progged to advance out of New Mexico into the
western South Plains by peak heating late this afternoon. The main
question mark, and one that isn`t handled well by the recent
guidance, is how the current scattered convection translating slowly
eastward through our western zones will evolve the rest of the night
into Sunday morning. This elevated convection appears to be at least
partially tied to some weak upper support moving through the
southwesterly flow aloft. There are some indications this elevated
activity, in some form or another, could hang on through much of the
morning as it shifts into the Rolling Plains. Obviously, this could
have ramifications on afternoon destabilization and how things play
out later this afternoon.

Regardless, we would expect good heating to take place west of the
early day activity (after the stratus scatters out) with moderate to
strong instability developing immediately in advance of the dryline
likely located near or just east of the NM/TX line by late
afternoon. Deep mixing/forcing within the dryline zone should be
enough to initiate isolated to widely scattered convection late this
afternoon, with favorable shear/instability for supercell structures
capable of producing very large hail and damaging downburst winds.
Low-level shear/helicity isn`t expected to be too strong, but given
the magnitude of the instability along with low LCLs and LFCs, a few
tornadoes will be possible. The tornado window could actually peak
very late this afternoon into this evening as the LLJ increases and
raises 0-3 km helicity toward 300 m2/s2. In addition, we will have
to be alert for any residual boundaries from earlier day convection
which could locally enhance the low-level shear. Further east the
picture is even murkier, with the potential for elevated activity
much of the morning and early afternoon, but some of the NWP does
suggest for storms will gradually become surface based with
increasing threats for all hazards mentioned above. In addition to
the severe potential, slow storm motions and plenty of moisture will
support the threat for locally heavy rain and the risk of flooding
too. The convection may attempt to grow upscale into one or more
clusters tonight, though these details remain elusive. Regardless,
the overall severe weather threat should gradually wane late tonight
as the convection becomes increasingly elevated.

Temperatures will be seasonably warm today with highs mostly in the
80s, maybe pushing lower 90s west of the dryline near the NM line.
Another mild night will follow tonight with lows mostly in the 60s,
though the far northwest zones may loose the moisture which could
allow temperatures to fall well into the 50s.

.LONG TERM...
Moderately energetic southwest flow aloft will continue over West
Texas through the entire work week courtesy of a blocky upper-air
pattern over North America with long-waves troughs on both
coasts. Periodic small shortwaves embedded in the southwest flow
Monday and Tuesday will likely provide some large-scale ascent to
coincide with diurnal destabilization along and to the east of the
dryline. The big question is where will the dryline be located
around peak heating? Monday afternoon, the latest progs show the
dryline near or just east of the I-27/U.S. 87 corridor. Tuesday,
the dryline may set up in the vicinity of the Caprock escarpment.
Temps in the 80s to low 90s should support large potential
instability east of the dryline, moderate levels of deep-layer
shear, and relatively high LCLs. So, we would expect mainly
multi-cell storms with perhaps a supercell or two and large hail
and damaging wind threats the main threats in this environment.

Wednesday into Thursday, medium-range guidance is in decent
agreement that a small upper-low will open up as it swings from
vicinity of Las Vegas, NV to eastern Colo., where it may deepen
again east of the Rockies. It remains to be seen whether or not
deep enough moisture will hold in this pattern across the Rolling
Plains for any t-storm chances. Blended solutions confine chances
to a sliver in the southern Rolling Plains during this period,
with warm and dry conditions elsewhere.

Dry, westerly flow should follow the trough on Friday. Then for
Memorial Day weekend, we will focus back to the west where a very
large upper low is expected to develop - covering much of the
Great Basin. This pattern will likely allow deep moisture to
return to West Texas and support a period of t-storm chances once
upper-level divergence begins to spread downstream of the low.
Right now it appears that this could happen by late Sunday or Monday,
although at 7-8 days out the details will almost certainly
change.

&&

.LUB Watches/Warnings/Advisories...
None.
&&

$$

23/33



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