Area Forecast Discussion
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FXUS64 KLUB 181733

Area Forecast Discussion
National Weather Service Lubbock TX
1233 PM CDT Thu May 18 2017

Windy conditions will persist at all TAF sites this afternoon as a
strong upper level storm system churns across the central Rockies.
Thunderstorms are expected to be near KCDS but most likely chances
will be far enough east of the terminal that a mention in the TAF
is not needed.


PREV DISCUSSION... /issued 418 AM CDT Thu May 18 2017/

The leading edge of strong moisture advection continued unimpeded
before daybreak and was found extending from Throckmorton SW to
Ozona at 4 AM. This moisture should expand to occupy roughly the
eastern half of the CWA by mid morning complete with some low
clouds. As a slow-moving upper low tracks from Salt Lake City this
morning to Grand Junction by sunset, SW flow above the TX South
Plains will amplify and trend more cyclonic through the day.
However, this appears to be a moot point for us as an approaching
surface trough and strong LL thermal ridge shunt rich Gulf moisture
largely out of our Rolling Plains` counties by mid-afternoon.
Model agreement is strong enough that we have trimmed PoPs back
to just slight chance in these areas - mostly to account for the
usual easterly bias of progged drylines. Should any storms
initiate from Childress to Aspermont before the dryline departs,
environment is sufficient for some low-end severe hail until
storms encounter extreme CAPE values farther downstream. West of
the dryline, deep mixing withing the thermal ridge looks
reasonable for some 25 mph SW winds by peak heating, with some
blowing dust expected yet again near the usual dust source

A modest dryline retreat is likely tonight with the only factor
limiting its return to the Caprock being a stubborn surface
low/wave anchored over the SE Panhandle with no net pressure
falls farther west. Otherwise, a weak cold front progged to enter
the Panhandle (via a vort lobe pivoting out of the base of the
upper low) should stall and mix out across our northern zones Fri
morning, before receiving a strong southward push Fri night as the
low departs east of the Rockies. Similar to today, Friday`s PoPs
are conditional and restricted to the dryline in our eastern
zones before this boundary mixes farther east during the day. The
only glimmer of hope for sustained rain chances unfolds Fri night
as the stronger cold front focuses moisture convergence along the
retreating dryline, possibly as far west as Lubbock. PoPs were
boosted Fri night mainly in our SE zones where moisture woes are
the lowest, and some severe events there certainly appear

By Saturday, modified but unseasonably cool cP air will drain over
the region on northerly winds. Opted to leave a sliver of rain
chances in our SE zones for forecast collaboration, but the
overall trend is clearly toward progressive drying of the column
from N-S through the day despite a lingering upper trough lagging
Friday`s upper low. Steady return flow beginning Sunday should
allow the establishment of modified Gulf moisture across the
region. This process will be critical in determining rain chances
for Mon and Tue as broad and deep cyclonic NW flow emerges
complete with another cP front. GEFS members along with
operational models agree well in delivering the best rain chances
late Mon with the arrival of the upper trough axis and cold front,
before moisture is scoured out late Tue and Wed behind the front.




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