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Area forecast discussion
National Weather Service Lubbock Texas
1044 PM CDT Fri Apr 28 2017

Update...
products have been updated to reflect the Severe Thunderstorm
Watch now in effect for Childress and Cottle counties until 6 am.
It may take another hour or two until storms really get going in
the watch but the threat for elevated hailers will quickly
increase around or after midnight. The forecast has this well in
hand and no additional updates have been made at this time.

&&

Previous discussion... /issued 922 PM CDT Fri Apr 28 2017/

Update...
outflow aided front continues to March southward...stretching
roughly from Memphis to Abernathy to Tokio at 02z. Northerly winds
gusting to 40 to 45 mph are advecting in much colder air behind
the front with temperatures rapidly dropping from the 70s into the
40s and 50s. This front was a little ahead of schedule and
adjusted the grids to account for this. Steady moistening and lift
spreading in from the west has supplied plenty of cloud cover and
even a few sprinkles and light showers locally, though the bulk
of the activity to this point has remained to our north and
west...from central nm into the panhandles and southwest Kansas.
Short-range high-resolution nwp does suggest an uptick in shower
and thunderstorm activity locally by late evening after 04-05z. As
the lift spreads off The Caprock it will encounter improving
moisture/instability levels and this should lead to more robust
convection late tonight (after midnight). A few of these elevated
storm could become strong to severe with the potential of large
hail. It appears the southeast Texas Panhandle into the northern
rolling plains will have the best shot of seeing an overnight
severe storm, and we have maintained the severe mention in the
grids for this area from 06-12z. A few stronger storms may even
try to develop further southward over the rolling plains before
the better moisture, instability and lift quickly shift east of
the area around or shortly after daybreak Saturday. Saturday will
be cool/raw and breezy/windy though the chances for measurable
precipitation will likely be fairly low through much of the day
as drier air aloft spreads over the cool and moist low-level air
in place. This could change by later half of the afternoon into
Saturday evening when the approach of the cold core low may renew
precipitation chances, particularly across the northwest zones
where the rain could mix with and/or change over to snow for a
period.

Previous discussion... /issued 654 PM CDT Fri Apr 28 2017/

Aviation...
an outflow aided/enhanced front was seen on the Amarillo WSR-88D
advancing southward through the southern Texas Panhandle. Given
its current speed it should move through kpvw around 0130z, then
through klbb and kcds from 03-05z. Gusty northerly winds and
cooler air will quickly move in behind the front, with low clouds
(mvfr to IFR cigs) likely developing a few hours (give or take an
hour or two) after the frontal passage. The low clouds and gusty northerly
winds will persist through the day Saturday. In addition to the
clouds and winds, areas of showers were already affecting much of
the panhandles while trying to develop into the northern South
Plains. Any of the terminals could see a high-based shower
through the evening hours with even some thunder not out of the
question. The best shot for more robust elevated thunderstorms
will be around kcds around/after midnight and a tempo group was
included to reflect this threat. Shower/storm chances will then
likely be on the low side through much of Saturday morning before
renewing Saturday afternoon or evening.

Previous discussion... /issued 342 PM CDT Fri Apr 28 2017/

Short term...
cool northerly surface flow from earlier today has since veered S-southeast
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 northwest 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 Texas 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 northwest 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 northwest 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.

Long term...
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 Kansas. 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 northwest South Plains and southeast 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.

&&

Lub watches/warnings/advisories...
none.
&&

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