Area Forecast Discussion
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FXUS64 KLUB 221806

Area Forecast Discussion
National Weather Service Lubbock TX
106 PM CDT Fri Sep 22 2017

A moist low level southerly flow will continue through tonight
into Saturday with a moderate strength surface low pressure
trough near the New Mexico-Texas border. A low level jet on the
order of 35 to 40 knots is expected to develop during the evening
and may lead to a low level wind shear remark. But expectations
are for surface flow to remain fairly strong through the overnight
hours, at least somewhat mixing the lower atmosphere. An MFR low
cloud layer is expected to develop tonight, most likely spreading
into our area between 06Z and 12Z, though precise timing is still
a bit uncertain. Chose 08Z to 09Z for not at KLBB and KPVW based
on latest short trends, and closer to 12Z for KCDS, though still a
little less certain here. Clouds may be near the IFR range when
they develop - so some adjustments on ceiling height certainly are
possible. Clouds should gradually lift mid to late Saturday
morning, and could also trend to break up - but uncertain when
this may occur. Thunder chances will remain to our west, mainly
near the New Mexico line (near the surface trough) or even into
eastern New Mexico through the period. RMcQueen


.PREV DISCUSSION... /issued 632 AM CDT Fri Sep 22 2017/

Patches of MVFR cigs moving northwest through the Concho Valley
into the eastern Permian Basin and western Big Country early this
morning will most likely come up short of the terminals before
lifting to VFR levels later this morning. Aside from this, VFR
should prevail through most of the period, though low clouds make
make a stronger run at the terminals toward the very end of the
TAF cycle (toward 12Z Saturday). Any afternoon and
evening/overnight convection should remain well west of the
terminals near the TX/NM line. Otherwise, light southerly winds
will quickly increase to breezy levels by 14-15Z.

PREV DISCUSSION... /issued 447 AM CDT Fri Sep 22 2017/

Overnight NWP output in reasonable agreement through the next
several days with respect to evolution of weather pattern over the
western and central US. Mid/Upper level longwave trough over the
northwestern US will deepen and progress slowly eastward across
the Great Basin/Desert Southwest before deamplifying and lifting
northeast by the middle of next week. This will help bring the
first decent cold front of the fall southward into the region
sometime Tuesday. ECMWF is faster with the front clearing most of
the area by Tuesday afternoon while GFS suggests front may not
clear the area until late Tuesday night/early Wednesday. This is
where the medium range models sufficiently diverge enough to lower
confidence in the latter portions of the forecast. Speed of cold
front and progression of drier airmass in its wake will determine
the diminishing precipitation chances and daytime temperature

In the meantime, gradual approach of longwave trough from the
west will strengthen and maintain lee trough, drawing plenty of
low-level moisture northwest across the region. Additionally, the
longwave trough is expected to bring an increase of mid/upper
level moisture. Therefore, chance of showers and thunderstorms
will increase from west to east through the weekend and become
more widespread. Precipitable water values above 1.5 inches and
approaching 2 inches will be realized across much of the region by
Saturday afternoon and persisting for several days will bring an
increased threat of heavy rain. And combined with a slow-moving
cold front situated in a somewhat southwest-to-northeast
orientation across our forecast area, persistent heavy rain along
and just northwest of the front will result in a flooding threat.
However, it is still too early to reliably pinpoint timing and
location of heaviest rainfall, but latest NWP guidance suggests it
will be across the southeastern half of the forecast area. JH




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