Area Forecast Discussion
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FXUS64 KLUB 310910

Area Forecast Discussion
National Weather Service Lubbock TX
410 AM CDT TUE MAY 31 2016

Once again, thunderstorms late last night and earlier this morning
have dissipated leaving behind an airmass that has been pretty well
worked over.  The upper-level low continues to spin over southern
California keeping us under southwesterly flow aloft which is
helping remnant high clouds move off to the northeast. A moist
airmass is in place across the area with the sounding from Amarillo
with 0.79 inches precipitable water and Midland with 1.28 inches.
Averaging between the two for Lubbock will be right around one inch
which is still well above normal for this time of year.  At the
surface, dewpoints are in the low to mid 50s with low to mid 60s
just south of the forecast area.  A south to southeast wind through
the day should help to keep decent boundary layer moisture flowing
back into the region as the upstream airmass was not impacted by

The biggest forecast issues will once again revolve around the
aerial coverage and timing of thunderstorm chances across the
region.  Models continue to struggle with these features and are
pretty different in how things may unfold for today.  All of the
models have new convection developing by late morning with a general
agreement that this activity will remain over the South Plains.
Coverage decreases a bit in the early afternoon before taking off
again in the afternoon and evening hours.  The NAM and ARW are
developing an MCS in the afternoon with the ARW the earliest with
this feature while the GFS and TTU WRF hold off until later in the
evening.  Current radar mosaic shows storms already moving out of
Mexico into far West Texas from El Paso down into the Big Bend
indicating another weak shortwave could impact the area.  Right now
the track of these looks go south of the forecast area but may be
what the models are picking up on for storm chances this morning.

With all the differences, believe that the best thing to do is keep
low pops this morning and then ramp them up in the afternoon as
whatever heating we can receive helps to increase potential for good
surface-based instability/MLCAPE values. Forecast hodographs look
once again to favor stronger left mover/anticyclonic storms or slow
moving cyclonically rotating storms.  If storms can become anchored
on any outflow boundaries or interact with other storms, cannot rule
out some large hail like we saw last night. Only other concern is
heavy rainfall potential as slow storm motions should allow for
isolated areas to see some pretty significant rainfall rates.
Conditions are ripe for heavy rainfall however the amount of
coverage remains highly uncertain and will hold off with any flood
or flash flood watches for now, but day shift may have to reconsider
with the 12Z data when it arrives.  High temperatures today will be
fairly close to yesterday with the western South Plains being the
warmest thanks to a bit more sunshine than the eastern two thirds
which will likely be cloudy for a better part of the day.

Lastly, a cold front should move across the area late tonight into
early Wednesday morning but the frontal signal is getting masked by
convective outflow in the models. This could help refocus another
round of widespread precipitation after midnight so kept PoPs in the
likely range and added mention of locally heavy rainfall.  Min temps
will remain in the upper 50s to mid 60s from west to east
respectively as ample low level moisture keeps mild conditions in


Behind tonight`s cold front, surface ridging will exert greater
influence over the region throughout the day on Wednesday before
peaking in strength on Thursday. Although low level moisture
deficits will steadily increase during this time, Wednesday will
still feature a wealth of moisture aloft and broad lift as the
upper low to our southwest phases with a northern trough.
Markedly less flow within this trough axis could breed some slow
moving storms with heavy rain episodes on Wednesday especially
given PWATs at or above 1 inch area wide. Confidence in both the
coverage and duration of precip are low at this time and WPC`s 06Z
QPF is not supportive of a flooding threat at this time, so will
keep heavy rain mention out of the grids for the time being. The
06Z NAM`s QPF is not trusted as it develops noisy MCVs that
contaminate the overall larger picture. Although the environment
could support MCVs, the NAM has a long history of being too
bullish with such features.

Precip chances will dwindle from NW-SE on Thursday as the Desert SW
low tracks east to the Hill Country by Thursday night ahead of stout
height rises and subsidence. In concert with boundary layer drying,
feel this drying aloft should be enough to restore dry conditions
by Friday for all but our far southeast counties where lingering
saturated layers and weak lift reside nearest the low/trough axis.
Upstream, sharp upper ridging from a 594 decameter high near the
Four Corners should direct a stout 700 millibar N-S baroclinic zone
across our western zones. Baroclinic zones around this layer often
serve as a good source for warm season storm development and
nocturnal MCS tracks. However, with mean subsidence still intact
behind the departing low it appears that any north or northwest flow
storm potential may be too hard to come by. Rather than blanket
daily slight chance POPs from Sat-Tue, will defer to later forecasts
to isolate which of these days offers better precip potential.
Regardless, high temps will return to seasonal levels by late week
after the mellow 70s of Wednesday and Thursday.


.LUB Watches/Warnings/Advisories...


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