Area Forecast Discussion
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Issued by NWS
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694 FXUS64 KLUB 282313 AFDLUB Area Forecast Discussion National Weather Service Lubbock TX 613 PM CDT Sun Apr 28 2024 ...New AVIATION... .SHORT TERM... (This evening through Monday) Issued at 217 PM CDT Sun Apr 28 2024 Quiet weather will persist tonight as the upper-level low slowly shifts into the upper Midwest. A weak shortwave will slide across the forecast area tonight although moisture associated with this system will be shallow as dry air remains at the surface. This will increase mid-level cloud cover across the far southern Texas Panhandle into the northern South Plains and could lead to a few virga showers which would cause gusty and erratic winds similar to what happened last evening. We will be located on the subsident side of the shortwave on Monday which will allow for mostly sunny skies. A weak surface trough will slide east through the forecast area during the day which will shift winds to the southwest behind it while ahead of it winds will become southeasterly however wind speeds will remain around 10-15 mph. This will help to bump temperatures back above average into the mid 80s for most locations. /WI && .LONG TERM... (Monday night through next Saturday) Issued at 217 PM CDT Sun Apr 28 2024 The upper air pattern on Tuesday will feature a split in the belt of high-level flow, with the CWA positioned beneath the bifurcation of the 250 mb subtropical and polar jet streaks. Broadly cyclonic flow in the mid-levels will continue to envelope the region along the southern periphery of a larger-scale gyre located over the northern Rocky Mountains, and into western and central Canada, where several vorticity lobes and other smaller-scale perturbations will rotate about the gyre. The primary shortwave trough is expected to eject into the north-central Great Plains on Tuesday afternoon; however, despite the dampened, deep-layer flow, the left-exit region of the subtropical jet streak is forecast to emerge over the Big Bend region and eclipse the CWA during the afternoon hours. Large-scale, geostrophic deformation will also be maintained by the presence of the broadly cyclonic flow over the central and southern Great Plains. At the surface, lee cyclogenesis will be ongoing across western Kansas in response to the ejecting shortwave trough over the north-central Great Plains, with a sharp, well-defined dryline extending south-southwestward into the CWA. Strong, mixed-layer theta-e advection will be ongoing during the morning and into the afternoon hours despite the attenuated 700-500 mb flow where an elevated mixed layer (EML) will already exist in the morning hours. Intense, diabatic surface heating is expected by mid-day with temperatures breaching 90 degrees across the dry and moist sectors as the dryline remains stalled near the vicinity of the edge of the Caprock Escarpment. (LBB is forecast to reach 92 degrees, which is shy of the record of 94 degrees set in 2013.) Already weak MLCINH will erode quickly across the moist sector with superadiabatic lapse rates developing west of the dryline, where an EML characterized by MLCAPE values potentially in excess of 2,500 J/kg evolves across the east and southeastern Rolling Plains amidst relatively straight hodographs and weak, effective shear magnitudes of about 30 kt. Prospects for supercells remain low owing to a number of reasons, including: the position of the dryline, veered/parallel flow along the dryline, and parcel residence time along the respective circulation amidst a well-mixed (Inverted-V) boundary-layer profile as MLCINH erodes from the intense heating. Slight chance PoPs have been maintained across the east/southeastern Rolling Plains for late Tuesday afternoon and evening as the thinking of a cell or two forming remains intact, and would pose a threat for large hail as the orientation of the deep-layer flow favors storm-splitting with updrafts attain modest, mid-level rotation. The best window for thunderstorm initiation will be as the dryline begins to translate westward, resulting in an improvement of low-level confluence before nocturnal stabilization occurs. Return flow is forecast to intensify area-wide heading into Wednesday morning as lee cyclogenesis of a 992-996 mb surface low occurs near the Raton Mesa ahead of a positively-tilted shortwave trough digging into the central Rocky Mountains. Breezy, southerly winds will develop during this time as the translates towards the Texas/New Mexico state line before propagating eastward once again across the South Plains after sunrise, and perhaps stalling near the I-27/HWY-87 corridors. Thunderstorm chances improve on Wednesday with the potential for scattered convection to develop amidst a very unstable moist sector as mid-level cooling from gradual geopotential height falls bolsters strong instability with MLCAPE values >=3,000 J/kg developing by late afternoon. Marginal improvements to the effective shear magnitudes to around 35 kt should occur as divergent flow increases along the nose of the left-exit region of the 250 mb jet streak that becomes more-cyclonic as the northern-stream trough digs into the central Rocky Mountains. Severe thunderstorms will be possible with supercell wind profiles expected via cross-boundary shear vectors and relatively straight hodographs, which will once again favor storm-splitting and potentially sustaining of mid-level mesocyclones. The best storm chances remain in the Rolling Plains on Wednesday, but the slight chance PoP extends as far as the HWY-385 corridor across the South Plains. The tail-end of mesoscale guidance and area-averaged forecast soundings support this prognostication in addition to the general synoptic-scale pattern. Heavy rainfall will accompany severe-caliber storms, and this has been reflected in the official forecast for Wednesday evening across the Rolling Plains. Predictability of the upper air pattern towards the latter half of the week becomes convoluted owing to significant discrepancies among the global NWP guidance on the position and amplitude of the shortwave trough as it ejects into the Great Plains. Differences greater than 400 miles on where the base of the trough is located exists among the deterministic suites, whereas the ensemble and cluster indicate a lower-amplitude trough compared to the other amplified solutions. Irrespective of these differences, continuity remains with southwesterly flow remaining intact over the CWA as broadly cyclonic flow persists at the very least. Due to the limitations in the state of the synoptic-scale evolution otherwise, the blended PoPs have maintained through Friday and into the weekend, and future adjustments to PoPs may be necessary as NWP guidance begins to converge in time. This will also dictate the timing of when the cold front associated with the shortwave trough moves through the CWA, which is currently late Thursday. Cooler, though still warm, temperatures will follow as the cold front eventually passes through the region with renewed chances for thunderstorms possible area-wide through the end of the period. Sincavage && .AVIATION... (00Z TAFS) Issued at 613 PM CDT Sun Apr 28 2024 Continued VFR with light winds through Monday afternoon. && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...58 LONG TERM....09 AVIATION...93