Area Forecast Discussion
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FXUS64 KLUB 282042

Area Forecast Discussion
National Weather Service Lubbock TX
342 PM CDT Fri Apr 28 2017

Cool northerly surface flow from earlier today has since veered S-SE
in response to pressure falls/thermal troughing focusing across
eastern NM. This process is serving to draw the back edge of Gulf
moisture westward across NW Texas, and after sunset dewpoints near
60F should occupy our eastern column of counties from continued
easterly winds. Farther west, aforementioned surface troughing will
edge east ahead of weak height falls preceding a closed upper low
now nearing the Four Corners. With steady top-down moistening
already underway from central NM into the western TX Panhandle, this
precipitation should improve markedly tonight mainly to our north
where isentropic ascent is maximized behind a cold front. As this
front spills south after sunset, a window for severe storms should
open primarily near the Highway 83 corridor near the deeper
moisture. Ample elevated CAPE of 2000-3500 J/kg looks quite
favorable for severe hail from any storms that realize this
instability. Given this environment and fair agreement among high
resolution models, have inserted large hail in the forecast for
these areas after midnight. Precip chances elsewhere are much more
conditional as vast moisture deficits rule the lowest 6-10k feet,
and shallow frontal forcing will not improve this situation any.

By the time post-frontal low clouds arrive after midnight, mid-level
saturation aloft will be drying out as dry slotting expands out of
northern Chihuahua. This ill-timed low level moistening looks to
keep much of the region dry Saturday morning, with the main
exception being in our far NW zones closer to a warm conveyor belt
of precip immediately east of the upper low. Dry slot vigor may be
too resilient for additional PoPs elsewhere on Saturday afternoon
even as a stout cold pocket (-25C at 500mb) rotates east with the
upper low. Opted to shave afternoon PoPs back to slight chance over
all but our NW zones as models are simply trending drier. Still,
some shallow convective rain showers could materialize along the
leading edge of the cold pocket, but diurnal heating and subsequent
destabilization will be minimal under what looks to be persistent
stratus and cold advection. GFS seems overly bullish in retreating
the front across our SW zones by midday ahead of warm, gusty SW
winds, so we continue to favor the colder NAM and short blended
guidance. High temps on Saturday will likely occur overnight as cold
air only gains more ground and depth region wide throughout the
daytime on brisk northerly winds.

Last but not least, prospects for rain changing to snow remain in
the offing for Parmer and surrounding counties, especially late in
the afternoon. Presence of the stout cold pocket does garner some
weak instability per forecast soundings at Clovis, but marginal
temps near the surface should keep accumulations slim to none until
the evening as discussed in the long term section below.

Guidance is in relatively good agreement with regard to the
positioning of the upper level storm system that will bring this
weekend`s cool snap--that is to say, the low should be centered
around KTCC.  As Sunday progresses, the low should swing eastward
into western Oklahoma before lifting northward into KS.  The GFS
exhibits more northward movement than the slower ECM.  Northwesterly
flow aloft will persist on Monday behind the exiting system with an
embedded disturbance (of a series) during the day on Tuesday.  A
sharper trough comes Wednesday before ridging sets up for the end of
the work week.

Breezy and chilly northerly winds are expected Saturday evening
along with post-frontal shower activity particularly in the
northwest.  The core of the low looks to remain just north of the
area. However, the core should be just close enough to keep a risk
of precip much of the night in our top row though some risk
remains further south. Precip phase looks to be mainly snow
Saturday evening/overnight in the NW South Plains and SE Panhandle
where light accumulations still look feasible. The surface flow
remains northwesterly until early Monday morning becoming
southwesterly for a brief spell then back to westerly. Another
modest front eeks in Tuesday morning followed by a somewhat
stronger front on Wednesday with a secondary surge on Wednesday
night which keeps us in northerly flow til Friday.




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