Area Forecast Discussion
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FXUS64 KLUB 250855

Area Forecast Discussion
National Weather Service Lubbock TX
355 AM CDT Mon Sep 25 2017

...The potential for heavy rain and possible flooding remains a
concern the next few days...

The moisture is palpable to anyone who steps outside early this
morning. This is backed up by 08Z observations that show surface
dewpoints generally sitting in the middle 60s, which is impressive
for West Texas any time of year. The low-level moisture was
supporting precipitable water values well above 1 inch (Midland`s
00Z sounding integrated 1.38 inches of H2O) with the TPW
satellite product indicating PWATs of 170 to 190 percent of
normal. So the moisture is definitely in place. The trickier part
is determining the forcing mechanisms that will effectively make
use of the moist atmosphere in place. Some form of southwesterly
flow aloft will persist through much of the week as a broad trough
remains anchored over the western states. One center of
circulation within the trough currently spinning over Wyoming will
open and lift into southern Canada during the next two days.
However, additional energy diving into the base of the trough will
form another closed low that will take up residence over the
Desert Southwest Tuesday and Wednesday before lifting northward
and opening up late week as the flow begins to flatten across the

As the initial upper low departs it will reanimate the quasi-
stationary front currently stretching from far southeast Colorado
into central Kansas. This front will move from northwest to
southeast across the CWA late tonight and Tuesday morning, perhaps
not clearing the southeast zones until Tuesday afternoon. This front
combined with perturbed southwest flow aloft will support areas of
showers and thunderstorms, with the greatest focus shifting to the
southeast zones by Tuesday afternoon as cooler and drier air
advects in behind the front. Before then, in the shorter term, we
have only seen isolated convection locally early this morning,
with greater coverage over northeast New Mexico as well as Far
West Texas and over parts of the Edwards Plateau. Given favorable
upper level divergence situated over the region today and slight
lift grazing the region from the ejecting upper low well to our
north, most NWP does suggest one or two rounds of convection will
develop and spread from southwest to northeast across much of the
CWA today. The moist environment will support efficient rainers
which could cause minor flooding, though the progressive nature of
the convection should tend to mitigate a more widespread flooding
threat. Hence, we have chosen not to issue any flood highlights
ATTM, though we have added a heavy rain mention to the grids.
Overall, it appears many spots could get a quick 1/2 to 1 inch of
rain with localized 2 to 3 inch amounts through the course of the
day today. There may be a bit of a lull this evening, though the
approaching front should then temporarily renew shower and
thunderstorm coverage and intensity.

There could be another lull in activity Tuesday evening/night as the
cooler/drier post-frontal air briefly wins out. However it currently
appear the developing closed low well to our west will propel
tropical moisture off of Tropical Storm Pilar northward up and over
the frontal zone by Wednesday. Now well post-frontal, rain rates
locally my be reduced, but more widespread light to moderate rain
would overspread the South Plains. The tropical fetch should
gradually fade Thursday and Friday, but southwesterly flow atop the
cooler surface ridging will keep at least low rain chances in the
forecast. What remains of the western storm system will then eject
into the center of the nation at the end of the week or over the
weekend. As it does so, one last shot of lift could bring one more
chance of a few showers or thunderstorms.

Thus, all said, we have some form of mentionable PoPs in the entire
7 day forecast, with the highest values today through Wednesday
when locally heavy rainfall will be possible. As instability wanes
behind the front we have limited the thunder mention mid- to late
week. Aside from the rain chances, considerable cloud cover (and
the wet conditions) will mute the diurnal temperature range, with
highs well below average (mostly in the 60s and 70s) and lows
fairly close to average.




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