Area Forecast Discussion
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FXUS64 KLUB 251725
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
1225 PM CDT WED MAY 25 2016

.AVIATION...
Have issued a precip-free and VFR forecast for the period. A
couple of possiblities in how that could be disrupted. Low level
moisture return back into the forecast is possible, despite the
dryline shifting to the east of the region this afternoon. That
could result in some stratus at KLBB and possible KPVW toward
sunrise Thursday. The other is the outside chance at isolated TS
late tonight that would also possibly affect KLBB and KPVW.

&&

.PREV DISCUSSION... /issued 625 AM CDT WED MAY 25 2016/

AVIATION...
VFR conditions in place at both KCDS and KPVW, however KLBB is
already starting to see rapid low cloud and fog development.
Ceilings are bouncing around in the 700 to 1200 foot range and
Gaines County Airport is down into MVFR range visibility wise.
Expect to see MVFR conditions in place right at or shortly before
the 12Z taf issuance goes into effect. Whether or not low clouds
or fog can develop to near Plainview remains highly uncertain and
KCDS should remain clear. Any low clouds and fog will take a while
to burn off but expect to VFR conditions to return by mid-day
today. Then...VFR conditions expected to remain in place until
about the same time tomorrow.

Jordan

PREV DISCUSSION... /issued 331 AM CDT WED MAY 25 2016/

SHORT TERM...
The dryline has once again sloshed back west early this morning and
was roughly located along a Tatum, NM to Tulia, TX line and was
continuing to slowly mix westward through the first part of our
graveyard shift.  Aloft, 00 UTC Upper-Air analysis shows that we
remain near a strong subtropical jet with 100 knot winds at 250 hPa.
A closed low was initialized well in the 00 UTC models compared to
the hand analysis location, with both showing a closed low over the
west central California Coast.  Water vapor satellite imagery shows
the forecast area being on the northern side of a mid-level moisture
stream associated with the subtropical jet and the 850 hPa analysis
shows the best moisture plume has shifted east across North Texas
with a pretty significant dry punch shown on the Midland sounding.

With the thermal ridge located over the area yesterday, the forecast
area was pretty much shut down for convection save one storm up in
the northeastern part of the forecast area.  The models once again
keep the thermal ridge at 850 hPa centered over the area although
temperatures are forecast to be about 2-4 degrees cooler than
compared to yesterday at the same time.  Winds aloft are also
forecast to remain out of the southwest on the Caprock which should
allow the dryline to once again mix east fairly rapidly through the
day and stall out along or just east of the edge of the Caprock.
Even with weak diffluence flow at the jet level, very little in the
way of synoptic-scale lift will be present over the area and model
soundings for the area around Childress show that strong subsidence
will take place in the mid levels of the atmosphere.  Models keep a
small sliver of SBCAPE values around 2000 J/kg near Childress
down to Aspermont but subsidence and fairly deep mixing should
keep convection at bay again this afternoon. Have opted to keep
rain chances out of the forecast for today and tonight even though
the GFS is hinting at a weak shortwave trying to initiate
convection over the Trans-Pecos and slide it northeast into the
southern Rolling Plains overnight into early Thursday morning.

Only other forecast challenge will be high temperatures today.  With
the dryline pushing east and deep mixing taking place, we could see
some of the warmest temperatures since the first part of May.
Subsidence indicated in the models and a dry airmass on the Caprock
should help to bump highs into the mid to upper 90s for the southern
Rolling Plains. Temperatures in the Rolling Plains will be tricky
as the dryline position will help or hurt temperatures from
warming up depending on how much moisture remains east of the
dryline zone. There could also be a bit of compressional/downslope
warming along/behind the dryline respectively giving a boost to
temperatures. Highs today in the Rolling Plains are also forecast
to be in the mid to upper 90s with the warmest temps in the
southern Rolling Plains. Low temperatures Thursday morning will be
on the mild side once again as the dryline sloshes back west and
low-level moisture helps to keep temps up. Low clouds may also try
to develop as the low-level jet sets up across the eastern half of
the forecast area but how far west any low clouds can develop
remains highly uncertain.

LONG TERM...
The upper low now approaching the southern California coast is on
track to translate across the Four Corners tomorrow before emerging
over the central High Plains Friday. Southwesterly flow aloft will
gradually back and strengthen on Thursday as the low approaches
while surface cyclogenesis occurs across southeast Colorado. An
attendant dryline trailing southward will likely be the focus for
robust convective development Thursday afternoon, though an early
day subtropical disturbance passing to our south through the central
part of the state could provide a period of subsidence and limit
storm coverage. The question then becomes where will the dryline
will reside by late afternoon? The latest NAM and GFS now favor a
more eastern solution near or just east of our eastern CWA
boundary as dry and gusty southwesterly winds overspread most of
the FA. This could happen, but with decent pressure falls to our
northwest it would not be surprising if the dryline were to hold a
little further west than currently progged (as has been the case
with the dryline the past couple of afternoons). Given this we
have maintained low storm chances roughly east of a Memphis to
Spur to Lake Alan Henry line Thursday afternoon. If storms can
form along/east of the dryline, strong instability and good deep
layer shear would definitely support storm organization and a
severe weather threat. Storms chances should briefly expand back
westward toward or even up onto the Caprock Thursday evening/night
as the dryline retreats before it encounters a Pacific front and
increasing upper support.

Breezy and dry west-southwesterly winds will then quickly spread
across the South Plains early Friday with the better storm chances
quickly shifting into the Rolling Plains and then points east.
However, as the upper low passes by to the north we will have to
watch and see if a little high-based convection developing across
northeast New Mexico can make a run toward the western Texas
Panhandle within developing northwest flow aloft. Current mixed
signals in the NWP combined with the very deep and dry sub-cloud
that will be present do not warrant more than about 10 percent
PoPs ATTM.

Weak shortwave ridging aloft will follow on Saturday and with the
deeper moisture likely relegated to our south and east West Texas
should experience a warm and dry day. The pattern is then forecast
to quickly transition back toward an unsettled one as low-level
moisture rapidly returns Saturday night and the western trough
reloads and provides periodic disturbances within renewed southwest
flow aloft. This will set the stage for improving shower and
thunderstorm chances from Sunday through the middle part of next
week. Relatively modest mid-upper level flow may tend to limit storm
organization through much of this stretch, but fairly strong
instability will likely still support some severe storms during
the afternoon and evening hours, while the weaker steering motion
and good moisture levels could lead to locally heavy rainfall.

Regarding temperatures, gusty downsloping winds (sustained at
15-30 mph) will help provide a warm Thursday with highs several
degrees above average. The UA trough passage will bring slight
cooling to close out the week before a quick jump back above
average to start the holiday weekend. Cooler temperatures will
follow through much of the remainder of the extended as increased
cloud cover and rain chances temper readings back toward or even a
little below average.

&&

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

$$

07


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