Area Forecast Discussion
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Issued by NWS
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874 FXUS64 KLUB 281916 AFDLUB Area Forecast Discussion National Weather Service Lubbock TX 216 PM CDT Fri Jun 28 2024 ...New SHORT TERM, LONG TERM... .SHORT TERM... (This evening through Saturday) Issued at 216 PM CDT Fri Jun 28 2024 The core of the upper level ridge remains over central TX early this afternoon with a belt of stronger midlevel flow aloft associated with a modest shortwave confined well to our north over SE CO and SW KS. Relatively deep surface troughing has expanded over most of the OK/TX Panhandles in response to this feature, resulting in breezy southwest surface flow across most of our area. Strong diurnal heating associated with this downslope flow should allow convective temperatures to easily be reached across the South Plains region which combined with a bit of residual midlevel moisture may allow an isolated thundershower or two to develop through this evening. Given the warm mid/upper level temperatures present, instability remains quite low and no more than a few updrafts are expected to develop and persist, but very high cloud bases will support a downburst threat with any storms that do develop. Surface winds will gradually back more south-southeasterly tonight, with SE return flow continuing through most of the day Saturday ahead of a cold front marching slowly southward over northern portions of the TX Panhandle. Surface dewpoints will consequently increase and are expected to remain above 60F off the Caprock through Saturday afternoon. With ridging aloft still in place overhead and highs in the upper 90s and low 100s, heat advisory criteria is expected to be met once again over the eastern Rolling Plains and far SE TX Panhandle on Saturday afternoon. The aforementioned cold front will likely remain near or just south of I-40 through the second half of the day on Saturday, but a relatively moist boundary layer, subtle pre-frontal surface troughing, and a weakness along the western edge of the upper ridge should all combine to support the development of a few thunderstorms by late Saturday afternoon over the SW TX Panhandle and NW portions of the South Plains. Coverage of this activity will still be relatively sparse, with much better storm chances confined to our north in closer proximity to the front. && .LONG TERM... (Saturday night through next Thursday) Issued at 216 PM CDT Fri Jun 28 2024 Isolated-to-widely-scattered thunderstorms may be ongoing across the extreme southern Texas Panhandle and portions of the northwestern South Plains on Saturday evening, with the best coverage forecast to be across the extreme southwestern Texas Panhandle. At the beginning of the period, the mid/upper-level pattern will feature a dampened, subtropical ridge stretching over the entire State of Texas due to an amplified shortwave trough digging into the Great Lakes region. The CWA will be located on the western periphery of this 596 dam ridge, with southwest-to-northeast-oriented steering flow becoming established aloft by Saturday night. At the surface, a stalling cold front should be located near the I-40 corridor as it moves beneath the barotropic airmass, where moist, southeasterly flow will be intact across the entire CWA after 30/00Z. Substantial adjustments to PoPs have been made for the start of the period into Sunday, with the chance PoP contour delineated across the extreme southwestern Texas Panhandle while the slight chance contour was shifted farther west and north compared to the blended initialization. These changes were made due to the expectation for the stalled front to remain north of the CWA; however, in the event a southward-surge of the front occurs along the edge of the Mescalero Escarpment via reinforcement from convective outflow, then chances for storms would improve across the northwestern zones. The thinking is leaning towards lower-bound PoPs/more-isolated coverage of storms compared to areas north and west of the CWA. The primary storm mode will be high-based, multi-cellular clusters with warm-cloud depths near 15 kft AGL, facilitating the potential for locally damaging wind gusts and brief downpours on Saturday night into early Sunday morning. Very warm temperatures are forecast heading into Sunday morning due to near-neutral to slightly positive geopotential height tendencies atop the return flow. Convective cloud/anvil debris should be limited to the western South Plains and extreme southern TX PH due to the southwesterly flow in the upper-levels with low temperatures ranging from the lower 70s near the TX/NM state line to near 80 degrees along the 100th meridian, the latter adding to heat stress on infrastructure and vegetation. Thunderstorm chances will be confined to the extreme southern TX PH through late Sunday morning with most of the convection occurring well to the north of the CWA, though it is possible that residual outflows propagate southward into the CWA. Such occurrence of this mesoscale phenom may result in cooler temperatures than what is currently forecast across the extreme southern TX PH. It is counterintuitive to forecast cooler temperatures with slightly positive geopotential height tendencies; however, the core of the subtropical ridge will shift over North Texas by Sunday with easterly, mid-level flow advecting into the Rolling Plains. Temperatures will still be hot but are forecast to remain below 100 degrees across most of the CWA with the exception of locales nearest the 100th meridian on Sunday. Amplification of the subtropical ridge is forecast to occur by early next week as it wobbles eastward across North Texas and into the Mississippi Alluvial Plain. Hot, dry, and breezy conditions are expected area-wide on Monday as surface troughing sharpens across the High Plains in response to lee cyclogenesis associated with another shortwave trough pivoting over the northern Rocky Mountains. The deeply-mixed boundary and dewpoints in the middle-upper 50s will keep heat indices in check; however, temperatures in excess of 100 degrees are forecast for portions of the Rolling Plains while remaining in the middle-upper 90s across the Caprock. High temperatures will also vary by a couple of degrees each afternoon as broadly cyclonic flow eclipses the region, with Tuesday potentially being the hottest day of the week as temperatures soar near or into Heat Advisory criteria (i.e., heat index values or temperatures between 105-109 degrees) across the Rolling Plains. All suites of global NWP guidance are in agreement with the subtropical ridge shifting farther east into the Deep South as the aforementioned shortwave trough ejects over the northern Great Plains. The CWA will be under the glancing influence of this trough and also within the inflection point of the stout ridging to the east. The position of these synoptic features will govern some strengthening to the southwesterly flow aloft, with the CWA being positioned within close proximity to the right entrance-region to the 250 mb jet streak as it translates across the Great Plains. Diurnally-driven, late-day thunderstorms continue to be forecast each day Tuesday through Friday as broad troughing persists across the northern U.S. due to an amplifying, mid/upper-level ridge over the northeastern Pacific Ocean. The blended PoPs have been maintained for this stage of the forecast period, with the best potential for thunderstorms across portions of the Caprock as the monsoonal fetch slowly shifts eastward towards the CWA. Sincavage && .AVIATION... (18Z TAFS) Issued at 1218 PM CDT Fri Jun 28 2024 VFR will continue through this TAF period with breezy SSW surface flow persisting through this evening. Some isolated high-based TS may develop late this afternoon through early evening in the vicinity of LBB and PVW, however coverage is expected to be very low and will omit TAF mention at this issuance. Nevertheless, potential for downburst winds will be high near any convection which does develop. Check density altitude due to hot surface temperatures this afternoon. && .LUB WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM CDT this evening for TXZ025-026-031-032- 037-038-042>044. Heat Advisory from 1 PM to 8 PM CDT Saturday for TXZ026-032-038- 044. && $$ SHORT TERM...30 LONG TERM....09 AVIATION...30