Area Forecast Discussion
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FXUS64 KLUB 240844

Area Forecast Discussion
National Weather Service Lubbock TX
344 AM CDT Tue Apr 24 2018

The question of the day is whether or not we will issue our first
severe thunderstorm warning of the year (and first since October 21,
2017...over a half a year ago)?

07Z surface observations show dewpoints only in the 30s and lower
40s across the CWA, but continued southerly breezes in advance of a
cold front promise to boost dewpoints to around 50 degrees by peak
heating in the "moist" portion of the warm sector. By this time, a
cold front should have moved into the northwest 1/3 to 1/2 of the FA
as a surface low sags southward into southeast NM. Confluence along
the front, surface trough extending ENE from the NM low, and a
diffuse dryline combined with strong heating and weakening CIN
should be sufficient to initiate isolated to scattered convection by
mid to late afternoon. A majority of the NWP suggest CI somewhere
near Lubbock (give or take a county or so, depending on the exact
timing and placement of said features by 21-22Z), with the
initial activity quickly moving eastward and expanding as it
encounters better moisture and instability. Although moisture will
be modest at best, steep mid-level lapse rates should still
garner 1000-1500 J/kg of CAPE. This instability when coupled with
35-40 knots of deep layer shear will lend to some updraft
organization, and with effective straight-line hodographs,
splitting storms will be possible. This will promote a risk of
large hail production, while a hot and deeply mixed boundary layer
(highs near 90 degrees) will raise the threat of strong downburst
winds. Given these factors, there appears a pretty good chance we
will issue our first severe thunderstorm warning of the year
later today, and we have included a severe mention in the grids
this afternoon and evening for locations roughly along and east of
the I-27/US-87 corridor.

Additional convection may develop along the advancing cold front
across the southern zones into the evening hours before gusty and
cooler post-frontal northeasterly winds invade. The tight pressure
may even push wind speeds toward or above advisory levels across the
western zones tonight, though we will defer this headline decision
to the next shift. Isentropic upglide will then increase well behind
the front as the upper trough currently visiting the northern
Rockies and High Plains sinks southeastward. This should effectively
expanded shower coverage (and isolated elevated thunderstorms) over
much of the region late this evening into early Wednesday. It
appears the eastern/northeastern half of the FA, where moisture and
lift will be deeper, will be most favored to see additional light
rain. However, even on the Caprock light showers and sprinkles will
be possible. Large scale support and shower chances will dwindle
from northwest to southeast through the day Wednesday, with dry
conditions region wide by Wednesday evening. The moist and cloudy
start to the day will help keep temperatures down with highs likely
only in the upper 50s to lower 60s.

A quick return of southerly breezes before our next cold front and
passing upper level disturbance late Thursday will allow
temperatures to recover close to average after starting out the day
in the upper 30s and lower 40s. The passing front/trough late
Thursday could spark a little weak convection though meager low-
level moisture (except according to the GFS which appears to be
overdone) should limit both precipitation coverage and amounts.
The front will knock temperatures back to around 10 degrees below
average to close out the workweek.

A progressive upper ridge and return to southerly low-level flow
will provide more seasonal warmth this weekend. In addition, as
the ridge begins to break down and shift east and moisture
gradually improves we could see low thunder chances return to the
western zones by Sunday afternoon and evening. After that, the
weather could turn even more interesting as there is general
agreement that a western trough will begin edging eastward, though
many of the smaller (and important) details will still have to be
hashed out. At this point there does appear a decent shot for
convection in or near the area on Monday, and perhaps beyond that,
though much uncertainty enters the picture. For now, we have
maintained a slight chance of thunder for most of the area Monday
with temperatures rising to or slightly above average to close out




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