Area Forecast Discussion
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Issued by NWS
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117 FXUS64 KLUB 161128 AFDLUB Area Forecast Discussion National Weather Service Lubbock TX 628 AM CDT Mon Sep 16 2024 ...New AVIATION... .SHORT TERM... (Today and tonight) Issued at 311 AM CDT Mon Sep 16 2024 As of 1AM CDT, mid-level satellite water vapor imagery and upper air RAP analysis has the low across northern Cali before it is expected to dive south into central Cali by this afternoon and then swing eastward tonight over Nevada. Meanwhile, a broader low across the southeast will remain stationary with a ridge sprawled over the Mid- Atlantic/New England states blocking any forward progression. Weak ridging will be in place over the Southern Great Plains today; however, weak west-southwesterly flow will begin to meander into West Texas with the incoming trough axis. Increased mid-level Pacific moisture is present this morning across the Desert Southwest with convection already developing. Storms are expected to continue across western New Mexico and into Colorado today, with this convection to remain west of the forecast area. Height falls this afternoon with weak lee troughing across eastern Colorado will give way to breezy southerly winds, especially along the Caprock. Additionally, a weak stationary front will be draped along a line from roughly Vigo Park to Jayton (nearly along the Caprock Escarpment). Isolated 10 PoPs were added for the potential of a storm or two developing. Dewpoints will be in the lower 60s east of this boundary coupled with hot temperatures in the lower 90s. Lift along the stationary boundary may help to initiate convection with instability parameters supportive of an isolated storm or two, similar to yesterday afternoon. Though unlikely, a strong storm cannot be ruled out with MLCAPE values of less than 1000 J/kg and bulk shear of 20-30 knots. Any storms that develops will be short- lived with chances coming to an end after sunset as there remains little to no forcing aloft with the weak ridging. Winds will diminish tonight after midnight, with above normal low temperatures mostly in the 60s and a few lower 70s across the Rolling Plains by early tomorrow morning. && .LONG TERM... (Tuesday through Sunday) Issued at 311 AM CDT Mon Sep 16 2024 The potential for thunderstorms remains intact for the upcoming week and into next weekend as a progressive, northern-stream pattern results in the formation of a cyclonic gyre over the western U.S. as the synoptic-scale blocking across the eastern seaboard is slow to erode. At the beginning of the period, the mid/upper-levels will feature a southern-stream, neutrally-tilting trough with a 250 mb jet streak approaching 100 kt rounding its base as it pivots over the southern Great Basin. This trough is forecast to have a closed, mid- and high-level low embedded within as it ejects northeastward towards the central Rocky Mountains and becomes negatively-tilted by Tuesday afternoon. The 250 mb jet streak will emerge over the southern Rocky Mountains and nose into West Texas by the evening hours, resulting in a significant increase in upper-level divergence coupled with strongly difluent flow. Geopotential height falls will be only slightly negative as the vertically-stacking cyclone associated with the negatively-tilting trough is displaced nearly 800 tangential miles to the north-northwest of the CWA (e.g., over the State of Wyoming) while the northern apex of the subtropical ridge remains positioned over the Permian Basin. At the surface, the CWA will be enveloped within a broad, open moist sector as the synoptic cold front moves across the southern Rocky Mountains and begins to stall as it enters the High Plains during the afternoon hours Tuesday. Southerly winds will become breezy as a result of the strong, leeward pressure falls associated with the stacking cyclone well to the north of the CWA, as winds will become coupled to the strengthening low-level jet stream throughout the course of the day. Winds were raised a couple of kt from the blended initialization due to indications of the lee cyclone deepening to near 992 mb on Tuesday afternoon. The highest wind speeds will occur across the Caprock with gusts to 30 mph expected in the afternoon as vertical mixing heights peak in depth, and winds should also back to the southeast towards the evening hours while continuing to advect a plume of lower 60 degree dewpoints across most of the CWA. Despite the weak, geopotential height falls, southwesterly flow in the mid-levels that gradually veers with height will maintain the elevated mixed layer (EML) atop Inverted-V boundary-layer profiles. The EML is forecast to be characterized by MLCAPE values >500 J/kg with most-unstable parcels yielding nearly 1,000 J/kg by the late- afternoon hours, particularly across the western and northwestern zones where geopotential height tendencies begin to increase and cooling in the mid-levels is greatest. Large-scale forcing for ascent will moderate with southward extent from the core of the negatively-tilting trough; however, numerous thunderstorms are forecast to unzip along the north-south-oriented cold front as it enters the Pecos River Valle by late Tuesday afternoon. PoPs were raised into the likely category (i.e., 60-percent) for Tuesday evening across the western South Plains and the far southwestern Texas Panhandle given the expectation for storms to linearize along and ahead of the cold front. The well-mixed boundary-layer will garner the potential for strong wind gusts in excess of 50 mph across the western zones before convection becomes more-tempered in intensity following the loss of diurnal heating and as the surface cold front lingers west of the New Mexico state line. Convective coverage is forecast to become more-scattered with eastward extent towards the I-27 and HWY-87 corridors, with low chances lingering throughout the nighttime hours as the once-high-based storms become rooted above the decoupling boundary-layer (i.e., transitioning into elevated convection). Low PoPs were, therefore, expanded from the NBM across portions of the Caprock and Rolling Plains through sunrise Wednesday, with the best potential across the far southern TX PH as upper-level divergence intensifies with northward extent. There is excellent agreement among the global NWP guidance for a synoptic-scale gyre to evolve by mid-week across the western half of the U.S., resulting in some deamplification of the flow over the CWA. The Rex Block should begin to collapse by this point as a barotropic low (currently Potential Tropical Cyclone Eight) begins its post-tropical transition within the dampened field of synoptic flow across the eastern seaboard, maintaining a blocking pattern at the very least. The position of these large-scale features should keep the stalling front near the TX/NM state line on Wednesday and allow the subtropical ridge over central Mexico to shift northward. Low PoPs were introduced across the Rolling Plains on Wednesday evening as the EML, albeit tall and skinny, remains intact amidst persistent, although weakening, moist ascent within the mid-level theta surfaces. Convective coverage is forecast to be isolated at this time, though a brief period of widely-scattered storms will be possible across the Rolling Plains on Wednesday evening. Increasing geopotential heights as the subtropical ridge sloshes northward on Thursday will nix any thunderstorm potential; however, additional chances for thunderstorms remain in the forecast from Friday and through this weekend as a positively-tilted trough within the southwestern tranche of the cyclonic gyre digs into the Great Basin. Blended PoPs were maintained through the end of the period given considerable agreement among the global NWP guidance suites for a more-progressive troughing pattern to develop following the erosion of the gyre to the west of the region. Sincavage && .AVIATION... (12Z TAFS) Issued at 602 AM CDT Mon Sep 16 2024 VFR conditions are expected through the period at all three TAF sites. There is a low potential for an isolated shower or storm near PVW/CDS this afternoon and evening, thus no mention was included in this TAF issuance. Otherwise light and variable winds will become predominantly south-southeasterly through the day and increase to around 10 to 15 knots. Winds will taper late tonight, but remain south-southeasterly through the end of the period. && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...11 LONG TERM....09 AVIATION...11