Lubbock, Texas

New SHORT TERM, LONG TERM, AVIATION

• Additional fog development, some of which could be dense, is possible tonight. The best chance for fog is on the Caprock.
• Storm chances return Sunday night, primarily to the northern South Plains and southwest Texas Panhandle. Storms could be strong to severe.
• Breezy westerly winds are expected on Monday, with gusts generally 35 to 45 mph, but a few gusts as high as 50 mph are possible.

It was another damp morning across west Texas, with low stratus (less than 1kft AGL), drizzle, and patchy fog. Forecast soundings suggest some breaks in the low-level cloud deck by mid-to-late afternoon, but additional high cirrus clouds will be streaming in from the west in advance of the next low pressure system, so expect at least partly cloudy, if not mostly cloudy, skies to persist through today. The continued cloud cover will help keep temps relatively steady for Halloween evening, in the upper 50s to mid 60s.

Forecast soundings depict an inversion present around 800mb today, which will keep low-level moisture in place and set the stage for another round of stratus development tonight into Sun AM, and perhaps patchy dense fog and drizzle as well. Several CAMs depict areas of dense fog developing on the Caprock Sun AM, and the REFS probability of vis below 1 mile is greater than 50% on the Caprock between about 5-9 AM. Those forecast soundings show a positive hydrolapse rate present into Sun AM (an increase in specific humidity with height), which is favorable for fog development and lends credence to the CAM output.

During the course of the day on Sunday, a deep upper trough will be moving from the west Coast towards the Four Corners, resulting in increasing high clouds overspreading the region. Additionally, the continued presence of that inversion layer should keep low clouds in place for much of the day (especially given limited diurnally-driven heating due to the increasingly thick high clouds). This favors lowering the high temperatures a bit. Aside from any drizzle with the fog Sunday morning, precipitation is not expected through Sunday evening.

As the aforementioned deep upper trough emerges onto the South Plains into Monday, a sfc low will develop over eastern CO and strengthen to near 990-mb as it moves onto the north-central Plains on Monday.

• STORM CHANCES *

Storm chances return to the forecast area Sunday night, expected to form initially along a dry line over eastern NM and sweep east during the overnight hours. Instability will be limited as mid-level and low-level lapse rates appear quite weak, but a few hundred J/kg of MUCAPE should still be present. Despite the weak instability, dynamic wind fields will result in strong shear supporting at least some severe potential Sun night (850mb winds approaching 50 kts). Downdrafts transporting strong winds to the sfc will be the main severe hazard, but there is non-zero tornado potential. Some supporting factors for the tornado potential include moist low- levels and the strong low-level wind shear (30+ kts in the lowest kilometer), but the diurnal timing is unfavorable, a small inversion lingers near 850mb, and the 0-3 km shear vectors are nearly parallel to the boundary (all of which lower the tornado potential). The storm chances Sunday night are mainly focused across the southwest TX Panhandle and the northern South Plains.

That dryline quickly progresses east on Monday. Much of the area will be capped to sfc-based convection through early afternoon, but a few storms could fire over the eastern Rolling Plains during the afternoon. A conditional severe threat exists Monday afternoon, dependent upon the storms actually forming in our area. However, most guidance favors storms forming just to the east of our forecast area, and the NBM had just 10% PoPs over our eastern counties Mon PM.

• BREEZY WINDS MONDAY *

Following the dryline passage, boundary layer mixing deepens considerably to as high as 700mb on Monday, allowing strong low-level winds to mix to the sfc. ECMWF Ens members are coming into better agreement on the max gusts, with most members showing 35-40 mph at Lubbock, and slightly higher as you go north towards Plainview (40- 45 mph). Forecast soundings suggest these values may even be a tad underdone, showing wind speeds of 45-55 mph within the 700-800mb layer (upper portion of the PBL). With that in mind, used the NBM 90th percentile to boost the wind gust forecast higher than the original model blend. The breezy winds persist on Tuesday, but aren`t expected to be as strong as Monday.

Winds on Monday will generally be out of the west-southwest, but a cold frontal passage Mon night will swing the winds to north-northwesterly for Mon night and Tuesday. This post-frontal airmass will offer some cooler nights, with lows in the low 40s on the Caprock each night Tues-Thurs, but a freeze appears unlikely over the next week (less than a 10% chance per the NBM). The typical first freeze is right around November 1st. The upper pattern remains progressive, so we`ll be keeping an eye on additional disturbances bringing more rain chances late week into next weekend.

Trends suggest that IFR conditions should lift/scatter to MVFR by mid afternoon with some potential for a brief VFR window for a few hours after sunset before conditions deteriorate again overnight. There is a real threat for below minimums flight conditions especially after 01/10Z. Substantial uncertainty resides in the timing of flight category changes. Conditions will probably start to improve late Sunday morning.

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