Area Forecast Discussion
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FXUS64 KLUB 291126
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
626 AM CDT Sat Apr 29 2017

.AVIATION...
Low level moisture filling in behind a cold front will allow MVFR
and patchy IFR CIGS to continue at all TAF sites through the day
today along with strong northerly winds. A strong upper level
system approaching the area may bring rain showers and possibly isolated
thunderstorms to all TAF sites this afternoon and evening. A
return to VFR CIGS will not likely occur until early Sunday
morning as the upper level storm system moves east of the area.

&&

.PREV DISCUSSION... /issued 453 AM CDT Sat Apr 29 2017/

ALL PERIODS...
Almost all weather of concern will occur over the next 48 hours.
A highly unseasonably strong and southward extending upper level
low will traverse southeast from it`s current location near the
4-corners, through central New Mexico today, then curling back
northeast across our far northwest zones into the Texas Panhandle
tonight. This low will then continue heading northeast into the
central plain late Sunday, and further into the western Great
Lakes Monday. Solutions in good overall agreement on strength,
path, and timing. This low pressure, and associated cold airmass,
is around 3.5 to 4.5 Standard Deviations from normal, with a
return rate on the order of 30+ years in this area, for the very
end of April. This raises potential for some unusual concerns,
including snowfall in our favored northwest snow belt in
particular, but also a good possibility of a late season
widespread freeze affecting areas mainly on the Caprock tonight
and early Sunday morning. Note that much of this region hasn`t
experienced a freeze in 7 or more weeks. And with several decent
rain events, growing season has been well underway for some time.

In the immediate short-term, a cold front has pressed far south of
the area, with the majority of solutions maintaining cold surface
ridging throughout the day along with plentiful low clouds. Given
the pressure gradient and gusty winds, today will be chilly and
blustery. The GFS is still trying to edge a warm front northward
near our southern border this afternoon, but at least has backed
off some from previous attempts. This would be an abnormal event,
and is largely ignored. Other solutions are far more believable.

Upper flow was backing, and an upper impulse was attempting to
eject to our east this morning. But new thunderstorms continued
to erupt on the west end where the upper divergence remained over
the Rolling Plains. These storms were all elevated above the cold
dome, of course, but have been intense enough for several severe
thunderstorms showing large hail earlier in the night from the
central South Plains into the Rolling Plains. We have increased
thunder chances this morning across our eastern zones. A dry punch
through the mid levels of the atmosphere was gradually edging
east across the region and RADAR was not showing significant
renewed precipitation yet to our immediate west.

But, as the upper low edges east later today, we will see strong
height falls and differential vorticity advection. Solutions are
not showing significant instability later today but we wouldn`t be
surprised yet to see a few pockets of thunder approaching the
state line. Another impulse ejecting just in advance through the
Trans Pecos and Rolling Plains later today is showing mixed
ability to generate precipitation, especially given limited
instability. But, this looks like a valid chance of showers by
later today spreading back across most of the area. And dynamic
cooling will team with the low level cold advection to turn
soundings increasingly towards a snow or rain/snow mix initially
near the state line this afternoon, but spreading perhaps as far
east as the central South Plains this evening. Model precipitation
output doesn`t appear significant, with totals mostly under
0.20". The earlier turn over to snow in the northwest, which will
be under the track of the upper low and also near the deformation
axis early Sunday morning, still gives rise to potential for
around an inch of snow in our northwest corner. Will defer any
winter weather highlights to the next shift. The ground should
mostly be too warm for significant accumulation on pavement.

Low temperature guidance for early Sunday is mixed, with some
output trending even colder than previous, while other guidance
trending the other way. We have retained similar low temperature
forecast, close to the lower end of guidance, and thus have issued
a Freeze Watch for areas on the Caprock especially north and west
of Lubbock. But the watch will include a buffer of near freezing
potential over the southern and eastern South Plains including
Lubbock.

On Sunday as the upper low spins away, tight northwest height and
pressure gradients will give rise to stiff northwest winds and
potential for a Wind Advisory across our northeast 1/2 of the
area. Little change on this from previous forecast. Winds will
taper off Sunday evening and even though warm advection will be
underway just off the surface, there still could be a small risk
for local near-freezing around the area.

Upper flow will veer early next week with a quick warmup. A
fairly sharp upper trough is still expected to dip southeast
through the area late Wednesday which will see temperatures fall
again but limited moisture for significant precipitation. Then,
significant warming will follow to close out the week with an
upper Ridge moving overhead. Return moisture flow may develop into
the southern Rockies but uncertain if capable of thunder chances
late next Saturday or Sunday. More on this later. RMcQueen

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
Freeze Watch from this evening through Sunday morning for
TXZ021>024-027>030-033>035-039-040.

&&

$$

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