Area Forecast Discussion
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FXUS64 KLUB 220947

Area Forecast Discussion
National Weather Service Lubbock TX
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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