Area Forecast Discussion
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Issued by NWS
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996 FXUS64 KLUB 152341 AFDLUB Area Forecast Discussion National Weather Service Lubbock TX 641 PM CDT Sat Jun 15 2024 ...New AVIATION... .SHORT TERM... (This evening through Sunday) Issued at 220 PM CDT Sat Jun 15 2024 Mid-level subsidence was noted over the entire forecast area this afternoon on the heels of a shortwave trough shifting east of Highway 83 in westerly flow. Despite this less than stellar theme aloft, the low levels remain rather moist ahead of a surface trough in eastern NM. West Texas mesonets have been sampling a corridor of consistently breezier S-SE winds over the SW South Plains in response to a mesolow near the Guadalupe Mountains. This locally backed and breezier flow should aid with speed convergence and eventually some storms late this afternoon and evening near the TX- NM border provided convective temps in the mid 90s are realized. Most recent HRRR runs have dialed back CI and overall coverage this evening across our western zones, yet this is suspect in light of ample heating, deeper mixing, modest CIN, and expanding cu field. Unlike last evening, storms this evening will exhibit a better E-SE push thanks to 30-35 knots of 0-6km shear. Inverted-V soundings with around 1500 J/kg of MLCAPE and similar amounts of DCAPE favor severe winds before activity declines overnight. Opted to keep NBM`s 20-30 PoPs largely intact on the Caprock as pros for CI outweigh the cons at this time. Moist southerlies stay with us on Father`s Day, yet chances for more storms trend toward zero under weak anticyclonic flow and rising thicknesses. && .LONG TERM... (Sunday night through next Friday) Issued at 220 PM CDT Sat Jun 15 2024 The mid/upper-level pattern will feature the amplification of a large-scale, positively-tilted trough over the western U.S. as a well-defined vorticity lobe rotates into the northern Great Basin early Monday, effectively shunting the subtropical ridge over the northeastern Pacific Basin southward. Farther east, a 596 dam, mid/upper-level ridge will continue to wobble over the eastern tranche of the U.S. as the belt of 250 mb flow between 90-100 kt becomes increasingly meridional over the central and northern Rocky Mountains, resulting in the CWA being positioned within the inflection point of these features. A secondary, more-zonal 250 mb jet streak is forecast to become coupled to the amplified flow over the Great Basin, with the nose of the former 250 mb jet streak emerging into western Texas and becoming increasingly difluent along the apex of the flattening ridge over Mexico. At the surface, lee cyclogenesis of a sub-990 mb low is expected to occur across eastern Colorado in response to the geopotential height falls and related DPVA, with a sharpened dryline extending southward along the TX/NM state line by the afternoon hours Monday. The CWA will be enveloped within the moist sector, where leeward pressure falls associated with the deepening cyclone to the north generate an isallobaric response that will cause winds to accelerate to 20+ mph with gusts near the 30-35 mph range amidst intense heating. Temperatures are forecast to reach the upper 90s across most of the CWA amidst a plume of dewpoints potentially in excess of 60 degrees extending to the west of the I-27/HWY-87 corridors. A conditionally-unstable airmass is expected to develop as the geopotential height falls and westerly, mid/upper-level flow facilitate maintenance of the elevated mixed layer (EML) atop the southerly low-level flow. The majority of the CWA will be capped, especially in the Rolling Plains, and the dry and hot forecast has been maintained across those locales as 700 mb flow remains veered to the southwest. Intense, diabatic heating; confluent flow nearest the dryline; and the advection of high theta-e air will act to enhance localized areas of convergence along the dryline and erode the strong MLCINH, which should allow parcels to maintain enough residence time to overcome the deleterious effects of entrainment and reach the LFC and result in the initiation of thunderstorms. Low, mentionable PoPs (<15 percent) have been introduced for Monday afternoon and evening across most locations west of the I-27/HWY-87 corridors. Coverage of storms should be widely-scattered at best, with the thinking of cells remaining isolated given the potential for multi-cellular splits early on in the convective stage and weak forcing for ascent aloft. The magnitude of the storm-relative inflow developing by the late-afternoon hours, in addition to the moist boundary-layer (e.g., lower 100 mb mean mixing ratios near 14-15 g/kg), should also support updrafts wide enough to become sustained for a few hours with supercell wind profiles present. The sizable EML indicated on point and area-averaged soundings leads towards the potential for rapid development; however, warm-cloud depths approaching 13 kft AGL should temper the threat for large hail with a focus towards damaging downdrafts and torrential rainfall. The potential for severe-caliber convection will wane after dark as diabatic stabilization occurs despite southerly winds remaining near 20 mph heading into the overnight hours. Broadly cyclonic flow will continue to eclipse the CWA on Tuesday; however, the primary cyclone associated with the mid/upper-level troughing to the west is forecast to rotate into north-central Canada, governing a poleward response to the ridging over the Gulf of Mexico with a slight increase in geopotential heights occurring. Hot and dry weather is expected area-wide on Tuesday as the airmass will be strongly capped beneath the large EML aloft; however, the presence of the EML remaining over the CWA will have implications for the remainder of the forecast period. Thunderstorm chances are forecast to improve across the entire CWA as southwesterly flow aloft remains intact atop the reservoir of subtropical moisture originating from the Gulf of Mexico. There are some differences among the global NWP guidance on the position of the stalling front to the north of the CWA on Wednesday as the aforementioned cyclone in north-central Canada rotates into the Hudson Bay, but there exists a consensus that the front will stall in the vicinity of the OK/TX PH; and the thinking leans towards this scenario given the proximity of the barotropic airmass spread across the region. NAEFS and ENS guidance are indicating precipitable water (PWAT) content rising to nearly two standard deviations above normal Wednesday night into Thursday. Interpolation of the 20-21/00Z sounding climatology from WFO MAF indicates that the forecast PWAT content will be near or exceeding the 99th percentile across the CWA during this time. This points towards the potential for heavy rain across portions of the Caprock and Rolling Plains by the middle and end of next week; however, specificity of where heavy rainfall occurs remains nebulous owing to the limited predictability in the potential placement of thunderstorms. The blended PoPs have been maintained, and it is possible that PoPs may be increased in forthcoming cycles. Cooler temperatures are also forecast by Wednesday onward as southeasterly low-level flow remains intact beneath thickening cloud debris from the daily rounds convection. Sincavage && .AVIATION... (00Z TAFS) Issued at 632 PM CDT Sat Jun 15 2024 There is a window for ISO-SCT TS to pass in the vicinity of KLBB between 01 and 05 UTC, with a lower potential for the same at KPVW. Included a VCTS at KLBB but not at KPVW where confidence is low. There is also a small potential for low CIGS around KLBB Sunday morning, but confidence is too low to add to the TAF. Outside of any low stratus and thunderstorm activity, VFR conditions will prevail with modest S to SE breezes, which will increase late in the day Sunday. && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...93 LONG TERM....09 AVIATION...33