Area Forecast Discussion
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090
FXUS64 KLUB 212325 AAA
AFDLUB

Area Forecast Discussion...UPDATED
National Weather Service Lubbock TX
625 PM CDT SAT MAY 21 2016

.AVIATION...
VFR conditions are in place at all three TAF sites currently.
Expect MVFR to IFR conditions again overnight tonight as moisture
continues to push into the area. Biggest uncertainty is about
strong thunderstorms possibly impacting KLBB and KCDS later
tonight. Confidence is very low in the forecast for storms however
and will leave out of the TAFs for now. MVFR/IFR conditions will
remain in place through late Sunday morning before going VFR and
there will be a possibility for severe thunderstorms at KLBB/KPVW
again tomorrow afternoon and evening. Again, confidence is too low
to include in the TAFS at this point.

Jordan

&&

.PREV DISCUSSION... /issued 243 PM CDT SAT MAY 21 2016/

SHORT TERM...
Low stratus has given way to sunshine once again as clouds continue
to scatter out from west to east. This has allowed surface temps to
rise across the FA particularly across our western zones. Dewpoints
remain in the upper 50s/low 60s. The bit forecast issue for today
will be the possibility of convection the afternoon and evening.
Tomorrow is a whole different monster that we will attempt tackle in
just a bit.

Current surface obs show the dryline to be well into NM near
Roswell. The dryline has begun to mix with dewpoints from Roswell to
Carlsbad having dropped from the low 60s this morning to the upper
40s currently. The dryline should continue mixing eastward through
the afternoon. A broken line of CU has begun to develop in the far
eastern counties of NM as surface convergence increases. Of note on
radar related to surface convergence is a boundary feature currently
moving westward across our northwestern zones. Winds have backed on
the east side of the boundary as it passes through and will likely
enhance surface convergence along the boundary once it reaches it.
This will allow for convective development. When this will happen is
a big question. Hi-res short term models seem to have a consensus on
convection developing along the dryline around the 20-22z time frame
while larger scale models convect several hours later. The latest is
the GFS which doesn`t convect until near 03z and does so near the
edge of the caprock. Being the biggest outlier it will have the
lowest consideration in the forecast. The 18z HRRR seems to be the
most ambitious with convection by developing a scattered line along
the TX/NM state line and holds it together for a few hours. Even
this is a bit more pessimistic than its previous runs which developed
an MCS by later in the evening as it progressed eastward across the
South Plains. It is possible that the models are picking up more on
the lack of upper level support in terms of lift. WV imagery as well
as 12z analysis shows a 50+ knot upper level jet to our south with
another one passing over the Baja peninsula. There is some speed
divergence overhead but nothing you can shake a stick at. The jet
over the Baja would provide sufficient storm top divergence, but it
won`t arrive here until sometime this evening at its current speed.
Below H300 there are no significant indicators of lift until you get
to the low levels. With that the forecast will reflect higher PoPs
after 00z with just a mention of scattered thunderstorms along the
TX/NM state line before then. Storm mode will likely start out as
individual cells before morphing into a line. With sufficient dry
air at the mid to upper levels large hail and damaging winds will
certainly be a threat. Bulk shear is marginal, approximately 30-40
knots (40 being on the high side). Heavy rain will also be possible
as PWATs will be well over an inch and storms will be moving at a
relatively slow pace.

Now for tomorrow. Precip should begin to diminish by the morning
hours with some showers and thunderstorms lingering across the
eastern half of the FA. Another round of fog will be possible in the
morning, but that will be if the precip coverage is not widespread.
The NAM and GFS keep a complex of convection ongoing to our south
and east tomorrow morning into the early afternoon. This could set
the way for differential heating and an increase in CAPE across our
western zones and the skies will clear out much faster there. The
dryline will have already retreated back into NM by this point. It
should begin an eastward jog during the afternoon at which time
convection should begin to initiate. 0-6km shear should be greater
tomorrow afternoon (45-50 knots) as the upper low currently sitting
over OR/NV will be closer. This will allow for a greater severe
threat tomorrow afternoon across the FA with large hail being the
main threat followed by damaging winds. A few tornadoes could also
be possible. The setup for tomorrow afternoon should become more
clear by the morning when we will be able to see how the overnight
convection evolves. Aldrich

LONG TERM...
Not a whole lot has changed for the first part of the coming week
as upper level low pressure lifts out into southern Canada, low
pressure starts to reload along the west coast, and a series of
impulses continue overhead in southwest flow. Sunday night most
wave energy will steer by far to the north, but we should have
enough weak forcing aloft combined with upper difluence overhead
for a decent shot at severe thunderstorms. A dryline seems a good
possibility to activate again over the western south plains and
panhandle with good convergence along the dry line and increasing
low level flow owing to surface pressure falls. Anticipate
convective energy levels will be on the order of 1500 to 2000
joules per kilogram and with the improved upper level flow we
expect bulk shear values between 45 and 50 knots, or more than
sufficient to support super cell thunderstorms with outflow pools
pushing activity eastward into the evening. And we agree that
there should be an improved tornado threat into Sunday evening
compared with this evening.

On Monday, deep flow will have turned slightly more southwest and
drying should push most moisture off the caprock. But its not a
clear dry push by any means. And we expect moisture to return
early Monday again into at least the southern South Plains. The
Day 3 outlook from the Storm Prediction Center maintains a Slight
risk of severe for the Rolling Plains into the southern South
Plains, with marginal over almost the entire remainder of the
area. This differs markedly from our current solutions which favor
activity mostly off the caprock, and also our blends which are
similar. We have edged thunder mention a bit further onto the
caprock mainly southern areas for late Monday but not as far west
as the SPC outlook at this point, but are in decent agreement with
other NWS offices in this area.

Drier southwest flow should prevail Tuesday through Thursday.
Difficult to rule out dryline activation at almost any point over
parts of the Rolling Plains, but we have only minimal mention
with precise positioning and means of activation difficult to
count on at this distance. The next upper level low pressure
expected to roll across the four-corners and into the central high
plains next Friday has deepened in latest runs and will make it a
bit more difficult to hold moisture into the area with increasing
southwest flow. Once again superblends for next weekend are quite
rich and cannot be used for this area with a climatological
preference instead. RMcQueen

&&

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

$$

14/93/14



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