Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Lubbock Texas
1159 PM CDT Friday Apr 18 2014

Aviation...
light south winds overnight will become slightly breezy tomorrow
middle-morning through the afternoon /aoa 16 kts/. An approaching
upper level disturbance from the west will aid in the development
of -shra/-tsra initially well west of both terminals early
Saturday morning...but the precipitation activity is anticipated
to spread eastward throughout the day. The system is expected to
move relatively slowly and this reflected in computer model/S
timing of the spread of precipitation...as precipitation nears
klbb at or above 20/00z and kcds just after this taf cycle. Will maintain a
prob30 at klbb for this possibility as well as a vcsh at kcds
at this time. If trends are quicker than expected will of course amend as
necessary.

&&

Previous discussion... /issued 352 PM CDT Friday Apr 18 2014/

Short term...
no real significant changes made in the short term through tomorrow
evening. WV continues to show a comma head low over so-cal drawing
in plenty of tropical moisture from the lower latitudes of the
Pacific. The closed low is expected to open as it progresses
eastward and increase in forward speed. Models continue to disagree
on the handling of the low as it approaches the region. The GFS and
the NAM continue to push precipitation from the SW to NE across the area
with a shortwave ahead of the main wave. The GFS is quicker to move
the precipitation into the forecast area but both seem to favor our SW zones for the
highest chances of precipitation. The NAM is more aggressive with coverage
with supplying the most lift as the short wave passes through. The
majority of the lift will be dynamic as cape appears to be marginal
at best and lapse rates are anything but steep. Cloud cover ahead of
the trough will prevent much if any daytime heating. Moisture should
not be too much of an issue especially in the upper levels as the
low will continue to tap Pacific tropical moisture. Southeast winds
at the surface will help draw up moisture from the Gulf. For now I
have kept probability of precipitation mostly unchanged from the previous forecast as
nothing at the moment indicates any change is needed. I have kept
the heaviest precipitation coverage over our west and southwest zones with
probability of precipitation around 40 scattered. Showers and thunderstorms will move into
the area in the late morning to early afternoon. Aldrich

Long term...
we expect a batch of showers and thunderstorms to be moving across the
area Sat evening...but are still somewhat uncertain of the
coverage and location of this activity...so have kept probability of precipitation fairly
broadly painated. As the primary lift with the upper wave
approaches on Saturday night...we may see some lingering activity
through the overnight and early morning hours.
For Sunday...there is still some uncertainty on where where the
surface features will be located and where low-level moisture and lift
may best match up with upper-lift...which will be shifting to the
east. Latest indications are that we will see some drying working
in from the west...while moisture will hold in across the rolling
plains. We have made some minor adjustments to expand and raise
probability of precipitation...concentrating on the east. Guidance suggests that surface-based
convective available potential energy could run near 1000 j/kg in the east...depending on the
impact of cloud cover on temperatures...while deep layer shear will be
marginal for storm organization...likely somewhat better in the
south that north. We think this environment may support a few
stronger cells...and possibly a storm or two that is briefly
severe. The wave will move off to the east Sunday night...with
rain chances diminishing. A weak front moves through on Monday and
there is a hint that some shower activity may develop in the Post-
frontal upslope regime aided by some weak lift in northwest flow
aloft...mainly to our north and west. We think this activity will
have a tough time surviving off of the higher terrain and we/ve
kept probability of precipitation silent for now. Shortwave ridging Tuesday will quickly
transition to SW flow as the next trough moves across the inter-
mountain west. The latest GFS and European model (ecmwf) both advect moisture
quickly back into the County Warning Area on the low-level jet Wednesday morning and then
develop convection east of a dryline late Wednesday afternoon and evening. We/ve
added a slight chance mention in the rolling plains for this
possibility...while it should be very warm and dry up on The
Caprock. And...if the 12 UTC GFS and European model (ecmwf) are latching on to
something...a full-latitude trough taking shape across the west by
next weekend may bring a good setup for precipitation chances across the
County Warning Area.

&&

Preliminary point temps/pops...
Friona 49 74 49 75 49 / 0 30 40 20 10
Tulia 51 74 53 76 50 / 0 20 30 20 20
Plainview 52 74 53 77 52 / 0 30 30 30 20
Levelland 53 74 51 78 52 / 0 30 40 20 10
Lubbock 53 76 55 79 54 / 0 30 40 30 20
Denver City 55 73 52 79 53 / 10 40 40 20 10
Brownfield 54 73 52 79 54 / 10 30 40 20 10
Childress 52 78 58 78 55 / 0 10 20 40 30
spur 53 77 55 81 58 / 0 20 30 30 30
Aspermont 55 77 58 81 60 / 0 10 30 40 30

&&

Lub watches/warnings/advisories...
none.
&&

$$

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