Area Forecast Discussion
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FXUS64 KLUB 201140

Area Forecast Discussion
National Weather Service Lubbock TX
640 AM CDT Fri Apr 20 2018

A strong SSE LLJ continues to advect gradually improving moisture
northward. In addition to creating LLWS at KLBB and KPVW early
this morning, the moisture flux will bring the risk for cigs in
the low VFR to high MVFR range through much of the day today. In
addition, weak elevated convection could affect the terminals this
afternoon. However, more widespread and robust convection is
expected this evening into the overnight hours as lift from a
potent upper low currently approaching the Four Corners
overspreads the area. Ceilings may eventually lower to MVFR or
even IFR late tonight. Before then, gusty southeasterly winds will
prevail at the terminals through much of the day today.


.PREV DISCUSSION... /issued 358 AM CDT Fri Apr 20 2018/

Observational data early Friday morning shows a dynamic upper-low
centered over Utah, with periodic lightning activity embedded
within t-storms just to the east and northeast of the 4-corners
in an zone of strong large-scale ascent. Synoptic-scale guidance
has come into very good agreement showing this system moving
slowly eastward to southeast Colorado by Saturday morning.

Mass response downstream of this system has resulted in
strengthening southeasterly low-level flow and elevated moisture
advection across West Texas. Surface moisture return will lag
behind as the front earlier this week drove the deep moisture into
the GOM, with 60 degree dewpoints just now returning into Deep
South Texas along the stalled front. Isentropic ascent and
increasing deep lift spreading east-northeast across New Mexico
may support some weak elevated shower and t-storm activity this
morning across the western Panhandle, and possibly into the
western portions of the South Plains.

By afternoon, west winds behind a Pacific-type front moving
across NM will intercept the southeast flow across West Texas and
result in dryline development somewhere near or just west of the
Texas- New Mexico state line. Strong convergence and moisture
pooling along the dryline with destabilization aloft is expected
to result in convective development mid to late afternoon as
suggested by most of the convective-allowing model guidance. As
the strongest synoptic-scale lift will be directed across the
north, and lower farther south, the coverage of storms may also
tend to be greater across the north, with less coverage south. The
environment in which the storms develop will generally be one of
high-shear and low CAPE. A strongly veering wind profile will be
supportive of supercells. However, modest expected CAPE values of
around 500-1000 J/kg and the strong forcing for ascent suggest
that it may be difficult to sustain individual storm updrafts.
Cloud cover and it`s impact on surface-based instability is a big
fly in the ointment. If the cloud cover is thicker and more
extensive over the dryline, storms may struggle to form/maintain
themselves. On the other hand, we`ll have to watch for any areas
out west where there is less cloud cover and more heating, leading
to greater instability. This may be more likely to occur from the
southwest South Plains or even in southeast NM or the western
Permian Basin. Storms that develop in those areas could have a
better potential for sustained rotation and then could move
northeast into the southwest or western South Plains. Large hail
and damaging winds will be possible with the thunderstorms. In
fact, owing mainly to the strong shear, there is some indication
of a small tornado threat both with the initial activity Friday
afternoon near the state line, and perhaps another window Friday
evening across the western and southern South Plains as moisture
levels continue to rise and LCLs lower. The latter potential may
be tied to the development of a QLCS and smaller spin-ups on any
bowing segments. The SPC HREF shows this potential with high
values of 0-1 km SRH and STP.

The dryline should move very little through the evening hours,
and the scattered thunderstorm activity should advance east-
northeast across the forecast area. As it does, it will encounter
a cooler, less unstable environment and should gradually weaken,
although with the strong lift and shear we can`t completely rule
out some strong or isolated marginally severe storms (likely
elevated) as the activity moves east into the Rolling Plains
Friday night.

As the upper low moves into the plains Saturday, and the surface
low drops southeast through Texas, a cold front will move south
through the forecast area and keep the rain chances going much of
the day, mainly across northern and eastern areas. Some thunder
will be possible as well due to instability associated with the
cold pocket aloft, but drier and cooler air will keep activity
weak and scattered. High`s Saturday will be in the 50s north to
around 70 south, with gradual moderation Sunday into Monday as we
remain under north or northwest flow aloft and ridging at the

Another cold front is due into the area late Tuesday as an upper
low swings across the Midwest. Medium-range guidance suggests that
there will be some jet energy moving through the northwest flow
aloft to combine with frontal ascent for some rain chances late
Tuesday into Wednesday. Warmer temperatures expected Thursday into
Friday underneath shortwave ridging downstream of the next upper-
level system moving across the west, which could affect the area
next weekend.




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