Area Forecast Discussion
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FXUS64 KLUB 210417

Area Forecast Discussion
National Weather Service Lubbock TX
1117 PM CDT FRI MAY 20 2016

Low ceilings, largely MVFR, should first develop at CDS in the
coming hours before expanding westward to LBB and PVW before
daybreak. Fog chances still look marginal, though some mist/light
fog could occur at times.

After MVFR ceilings exit toward noon, a dryline near the TX and
NM border will help focus isolated TS development by mid-afternoon.
There are better indications that these storms should expand in
coverage as they crawl eastward, so have inserted PROB30s at LBB
and PVW beginning at 23Z.


.PREV DISCUSSION... /issued 329 PM CDT FRI MAY 20 2016/

After several days of mostly cloudy to full overcast skies the
sun has finally prevailed. Some clouds still remain across our
eastern zones but are starting to thin out as well. Currently the
"dryline" is along the TX/NM state line. This should pose little
threat in the way of convection this afternoon/evening as surface
convergence will be lacking. This is shown fairly well looking at
surface observations. The best surface convergence is over Parmer
and Bailey county where some unauthorized CU has developed. CU
development along the dryline will be possible into the evening
but should be isolated in nature and should not gain much in the
way of vertical development due to lack of lift at all levels. Low
clouds and fog will be possible again tonight, mainly after
midnight, as winds back to the southeast again allowing more rich
moisture to push in to the FA.

Skies should clear out again late tomorrow morning which will allow
surface heating to commence before the festivities of evening
convection begin. The dryline, which will be in eastern NM early
tomorrow afternoon, will begin an eastward push by the late
afternoon. CAPE buildup ahead of the dryline will be fairly
impressive with the NAM showing MUCAPE upwards of 3000 J/kg. While
the more realistic value may be more around 2000 J/kg given the
NAM`s tendency to be more moist this should still be more than
enough energy for convective development. HiRes models such as the
TTU-WRF and the NAM show convective initiation between 18z and 22Z
across our northwestern zones. The initial batch of storms during
this time frame has the potential to be severe, but the better risk
for severe storms will come later in the evening as the dryline
pushes towards higher moisture. The highest severe potential will be
later in the day beyond the short term and will be discussed below
in the long term. Aldrich

Starting Saturday evening, todays solutions have shown a bit
stronger wave ejecting northeast across the area with likewise
better upper divergence and minimal capping inversion. This should
increase the chance of a push eastward of the dryline activity
with possibility as well of some amount of cool outflow push.
Given the large positive area and CAPE potentially available on
soundings over the central and western South Plains and southwest
Panhandle, we have added a mention for severe thunderstorm
potential Saturday evening. This threat is consistent with the SPC
day 2 outlook and also with the St. Louis University CIPS Analog
database for this pattern. Activity may not survive east through
all the area but we will maintain chance through the night for
eastern zones in particular.

Sunday is part II with the upper ridge aligning a little further
east as a stronger impulse lifts out through the Rockies and
additional energy as well between the polar and subtropical jet
branch flowing over our area. Potential energy levels may be somewhat
dependent on exactly how much overturning results Saturday night
perhaps affecting moisture quality, but as it appears now there is
certainly potential for at least as much energy as Saturday
evening while bulk shear levels should be improved with the
stronger flow aloft. All indications therefore for another round
of severe thunderstorm potential, probably slightly further east
than Saturday, but that is hardly set in stone. Also, we already
are seeing some solutions generate a dryline bulge which could
locally enhance the lower inflow part of the hodographs and lead
to more spinning. For both Saturday and Sunday we have gone
slightly higher with thunder mention, but otherwise the forecast
appears similar to previously. We did not yet add an explicit
severe mention for Sunday except in the hazardous outlook.

Deeper moisture is likely to be more scoured to the east by late
Monday, but still at least a low potential for thunder through the
Rolling Plains. And beyond Monday we may enter several days with
dry, warm, and breezy dominating, and plants to respond to all
the moisture in recent days. Solutions do agree that another well
defined upper trough will eject not far to the north through the
Rockies, but that moisture will have trouble staying deep enough
for a significant mention of thunder chances.

By late in the week and next weekend, the main model camps appear
totally out of phase. Our Superblend solution which indicated a
certainty for thunder in our eastern areas next Saturday was thus
discounted to only a climatological mention. RMcQueen


.LUB Watches/Warnings/Advisories...


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