National Weather Service Raw Text Product

144 
FXUS64 KLUB 201140
AFDLUB

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

.AVIATION...
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/ 

DISCUSSION...
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 
surface.

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. 

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

33/23