Area Forecast Discussion
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FXUS64 KLUB 281730 AAB
AFDLUB

Area Forecast Discussion...UPDATED
National Weather Service Lubbock TX
1230 PM CDT Tue Mar 28 2017

.AVIATION...
LIFR to VLIFR conditions in place at KPVW and occasionally at KCDS
but will see conditions improve shortly at KLBB to VFR/MVFR.
Approaching storm system will continue to generate thunderstorms
at all the terminals through this evening, some of which will be
severe. Storms will be slow to clear but will start to move east
through the afternoon. A cold front will push through the TAF
sites Wednesday morning which could generate another round of
precipitation but uncertainty is too high to include at this time.

Jordan

&&

.UPDATE...
Brief update as storms already firing just east of the dryline
and ahead of a strong band of mid-level drying as seen on WV
imagery. Instability is rapidly increasing as low level moisture
feed ahead of the surface low which appears to be developing
across the southwestern portions of the forecast area. Biggest
question remains how far east the dryline will push across the
southern South Plains and where the thunderstorm threat will end.
Lubbock may be on the edge as storms have already started to fire
southwest of the city with the biggest concern remaining the
Rolling Plains where backing winds will increase storm-relative
helicities through the afternoon. High-res models continue to
struggle with the dryline location with the majority keeping it
over the city of Lubbock which would prolong the potential for
additional severe storms. Further north, still have some question
as to how long it will take storms to connect to the boundary
layer rather than being elevated as they have been all morning
north of the clearing line. Still feel the biggest threat of
severe weather will remain over the Rolling Plains through tonight
but enough uncertainty exists back into the South Plains that
everyone should keep an eye on the forecast through tonight.

Jordan

&&

.PREV DISCUSSION... /issued 643 AM CDT Tue Mar 28 2017/

AVIATION...
Immediate issue is low clouds spreading into the area, initially
IFR to MVFR, but dropping ceilings and visibilities as moisture
increases this morning. Also expecting showers to break out
shortly. A dry punch is most likely to impact KLBB early to mid
afternoon, although there is a chance still that low level flow
will remain backed longer. Otherwise retained mostly MVFR
conditions this afternoon at KPVW and KCDS, with chance of
thunderstorms later today. Some risk of severe thunderstorms will
need to be monitored. RMcQueen

PREV DISCUSSION... /issued 438 AM CDT Tue Mar 28 2017/

SHORT TERM...
Where the dryline will be later today remains a bit unknown, so
calls for imprecision with details. Generally we believe the Dryline
should lie somewhere from near Friona to near or just east of
Lubbock and then to Justiceburg. But could easily adjust east or
west by a county. That explains some of the flex in the thunderstorm
chances, still holding on to low mention vicinity central and even
parts of the southwestern South Plains later today.

Not much in the large scale is different this morning. The upper low
over eastern Arizona will shift into central New Mexico later today,
then wobble close to the northwestern South Plains or southwest
Panhandle by daybreak Wednesday. A weak impulse will lift across the
area later this morning, along with a decent moist and warm low
level push, and will give opportunity for showers and thunder. Cap
this morning may be prohibitive, but should it break anywhere storms
could rapidly intensify. This will become more plausible as we
approach midday. Low level moisture will surge into the area mid to
late morning, with solutions indicating near surface saturation and
potential for fog. Showers and fog may co-exist so could make it
difficult for widespread sharply reduced visibilities. But at least
local restrictions are possible. A warm front lifting northward may
stall over the western end intersecting the surface low over the
western South Plains. There is potential for fog to persist into the
afternoon north of the warm front. West of the dryline, deep mixing
will develop late morning and continue into the afternoon as surface
pressure falls spread into the western South Plains. Wind speeds may
approach Wind Advisory levels, but our current forecast is just shy.

How the lead impulse disturbs low level conditions for later today
is part of the uncertainty. But a sharper part of the upper trough
will swing across the Pecos along with a speed max and give
potential for intensification of thunder later today. Convectively
available potential energy that may actually be realized appears in
the 1500 to 2500 joules per kilogram range, with Bulk Shear values
as high as 50 to 60 knots. Low level hodographs will remain curved
near and east of the dryline/warm front with lifted condensation
levels mostly 4000 feet or lower. This gives rise to supercell risk
with the full gamut of outcomes from large hail to heavy rain and
tornadoes. Solutions at the moment still favor from the eastern
South Plains through the Rolling Plains, and points south and
east, for greatest severe potential from afternoon through evening.
The bulk of severe activity is expected to spread east of the area
around or after midnight. Drier air will follow though mid level
cooling will be underway. We have mostly removed shower mention
after midnight. RMcQueen

LONG TERM...
The center of an upper level low will move directly across the South
Plains and Rolling Plains during the day on Wednesday following
Tuesday`s fire weather and convection. This will bring an additional
risk for shower and thunderstorm development to much of the region
underneath the core and on the back side of the upper low. Cooling
mid level temperatures will lead to some elevated instability
although only on the order of a few hundred J/kg. At the same time
on Wednesday, a cold front will be moving through adding some
frontogenetical forcing in the mix. There will be no shortage of mid
and upper level moisture which may bring additional precipitation.
Also with the front, sustained winds in excess of 30 mph may be seen
in the extreme southwestern Texas Panhandle on Wednesday afternoon.
Subsidence will swing into the region as short wave ridging moves
overhead.

Models are still in good agreement in bringing another progressive
trough through the southern Rockies early this weekend but continue
to diverge past this point. The ECMWF solution has slowed down a bit
closer to the GFS solution with additional troughing moving onshore
on the west coast late in the weekend. A slower on shore trough
would mean a slower ejection of the southern Rockies low over the
weekend. Given the continued model inconsistency, confidence in the
forecast is low for this time, except for fire weather concerns.
This approaching upper low will create a surface response with a
deepening surface cyclone in eastern New Mexico on Friday and
Saturday. Strong southwesterly surface winds will likely return
these afternoons and with warm temperatures will elevate fire
weather concerns.

FIRE WEATHER...
Uncertainty regarding the location of the dryline later today,
but we are issuing a Red Flag Warning for the southwest into the
central South Plains. Lubbock county in particular appears to be
at the dividing line, but wherever it occurs will have a sharp
delineation from moist and backed flow to warm dry deeply mixed
conditions and gusty winds. Also, we are expecting quite a bit of
low level moisture early today along with a reasonable chance for
fog, showers, and thunder that could ease fire spread risks
especially central areas. Some adjustment in the Warning area is
possible today. RMcQueen

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM CDT this evening for TXZ027-028-
033>035-039>041.

&&

$$



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