Area Forecast Discussion
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Issued by NWS
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101 FXUS64 KLUB 170817 AFDLUB Area Forecast Discussion National Weather Service Lubbock TX 317 AM CDT Tue Sep 17 2024 ...New SHORT TERM, LONG TERM... .SHORT TERM... (Today and tonight) Issued at 317 AM CDT Tue Sep 17 2024 As of 2AM CDT, the upper low can be seen spinning over Nevada on mid- level satellite water vapor imagery, along with another upper low spinning over the Carolinas with weak ridging between the two systems. As the western low ejects northeastward today, several waves of mid-level Pacific moisture will traverse the Rockies. An initial wave of convection is ongoing across northeast New Mexico early this morning and is expected to remain north of the forecast area. The best chances for precipitation today will be this afternoon along surface troughing across eastern New Mexico. The line of storms that develops this afternoon will push east-northeast into West Texas early this evening. There remains some uncertainty with how far south the line of storms will extend in coverage with the best chances expected across the far southwest Texas Panhandle and northern Rolling Plains. With the incoming trough axis and 30-40 knot jet aloft, large scale ascent will help to drive convection coupled with the increased mid-level moisture. However, much of the better forcing will clip our far western zones as the negatively tilted trough axis swings into the central Rockies. Lee troughing will strengthen across eastern Colorado with breezy southerly surface winds and warm, above normal temperatures in the upper 80s to lower 90s. The warmest temperatures will keep off the Caprock where skies may stay a bit sunnier and winds will be slightly less breezy. Afternoon instability parameters near the New Mexico and Texas state line will feature MLCAPE values of less than 1000 J/kg and most likely closer to 500 J/kg. With the approaching upper jet and increased southwesterly flow aloft, 0-6 km bulk shear values will be around 30 to 40 knots. Throw it all together and there is a potential for a few strong to severe storms in the line as it pushes east across the state line. The main threats will be damaging wind gusts up to 60 mph, small hail and localized flooding with heavy rainfall. PWATs will approach 1"-1.25", which is near the 90th percentile for climatology and supports moderate to heavy rainfall. As the evening progresses, the line of storms will continue to push eastward across the forecast area. Once again, there remains uncertainty in the how far south the line of storms will develop and persist through the late evening hours tonight. Once again the best chance for continued showers and storms will be across the far southern Texas Panhandle and northern portions of the South and Rolling Plains. As the sun sets this evening and surface temperatures cool, storms will become elevated with MUCAPE around 1000 J/kg or less. The low level jet will ramp up late tonight to around 20-30 knots with bulk shear values remaining around 30-40 knots. The threat for strong to severe storms will diminish as the line pushes eastward tonight, but the environment will still be capable of maintaining storms with gusty winds, small hail and brief downpours. Shower and thunderstorm activity should wane overnight tonight into the early morning hours tomorrow. Temperatures will remain 5 to 10 degrees above normal in the 60s along the Caprock and lower 70s off the Caprock. Childress Airport has the potential to tie or break the record for warmest low on September 18th, which is currently at 72 degrees (set back in 2013). && .LONG TERM... (Wednesday through Monday) Issued at 317 AM CDT Tue Sep 17 2024 Isolated-to-widely-scattered thunderstorms are forecast to affect portions of the Caprock and Rolling Plains on Wednesday, with additional storm chances remaining in the forecast heading into the weekend. In the mid/upper-levels, a cyclonic gyre will have become established across the western U.S., featuring a vertically-stacking low associated with a negatively-tilted trough over the Yellowstone River Valley; and another amplifying, positively-tilted trough digging southward offshore the Klamath Mountains and Redwood Coast of California. The Rex Block over the eastern U.S. should dissipate by this point as a well-defined cyclone rotating over the Carolinas becomes absorbed into the slow-moving, opening trough. This will maintain the channel of broadly cyclonic flow over the CWA with the left-exit region of the 250 mb jet streak gradually shifting northward as the subtropical ridge centered over central Mexico continues to amplify. Smaller-scale perturbations are expected to translate through the belt of broadly cyclonic flow on Wednesday as the CWA will be otherwise bereft of any significant vorticity anomalies. At the surface, lee cyclogenesis will be ongoing across eastern Colorado with a 998-1000 mb low forecast to develop by the afternoon hours Wednesday. This cyclone will be embedded along the stalling Pacific cold front that branches southward from the occluding cyclone in the northwestern Great Plains, with a secondary surface low forecast to develop across southeastern New Mexico. The dryline will branch southward from this secondary low while the stalled front bends farther to the southwest into southern New Mexico. Leeward pressure falls will also begin to slacken compared to the prior day, though the breezy, southerly fetch will remain intact with winds between 10-20 mph amidst the plume of lower-middle 60 degree dewpoints advecting across the moist sector. A narrow corridor of strong theta-e advection is forecast to become established by the early-afternoon hours across the Caprock, and to the east of the dryline and cold front intersection, with an expectation for a well-mixed boundary-layer to evolve with PBL heights ascending to near 700 mb coupled with Inverted-V profiles. Full insolation and deep mixing will cause temperatures to breach 90 degrees area-wide, though the southerly fetch will mitigate further effects of adiabatic compression, so temperatures were tweaked slightly to align with the 00Z MOS guidance. The elevated mixed layer will remain intact as flow throughout the steering layer remains oriented out of the southwest, with individual and area-averaged forecast soundings continuing to indicate MLCAPE values between 750-1,000 J/kg and most-unstable parcel trajectories yielding <1,500 J/kg of CAPE. The arrival of a ribbon of high-altitude cirrus advecting overhead from the southwest will serve as a source of large-scale lift atop an increase in low- level confluence. Surface convergence will maximize in proximity to the diffuse dryline, with isolated-to-widely-scattered storms forecast to develop during the afternoon and evening hours across portions of the Caprock and Rolling Plains. Low PoPs were once again added across a large portion of the CWA on Wednesday compared to the dry NBM, but were capped 20-percent for now. Initial cells will split given the nearly linear orientation of hodographs throughout the mean cloud-layer, but the dampened, mid-level flow and high LCLs will favor the merging of cold pools as the evening progresses. It is possible that a slow-moving, loosely-organized line of storms develops, before succumbing to the effects of nocturnal cooling and decoupling of the boundary-layer. Warm and muggy conditions will follow heading into Thursday morning area-wide as the dryline remains stalled near the TX/NM state line. The negatively-tilted trough will cross north of the 49th parallel heading into Thursday and become absorbed into a northern-stream trough over far northwestern Canada, allowing the positively-tilted trough digging into the western U.S. coast to pivot inland over the Sierra Nevada Mountains. Geopotential height tendencies will become positive as the subtropical ridge over central Mexico continues to amplify and shift farther north, resulting in hot and dry weather area-wide on Thursday. The synoptic-scale gyre is forecast to erode by the end of the week following the absorption of the stacked low and further amplification of the subtropical ridge, with global NWP remaining in agreement of the southern-stream trough attaining a neutral-tilt late Friday into Saturday. High-level divergence will be most significant to the west of the CWA on Friday as a 250 mb jet streak near 100-kt rounds the base of the neutrally-tilting trough, with scattered storms forecast to remain most west of the TX/NM state line; however, a few storms may clip the western zones late Friday night. Storm chances are forecast to expand eastward across most of the Caprock and Rolling Plains heading into Saturday as the trough ejects over the central Rocky Mountains while potentially becoming negatively-tilted. However, there remains discrepancies among the guidance with respect to the amplitude and timing of the trough ejection. PoPs remain low (e.g., isolated-to-widely-scattered) for Saturday, and further adjustments will be required in forthcoming forecast cycles until guidance begins to converge on the evolution of the latter uncertainty. A dry and warm forecast continues to be advertised thereafter and through the end of the period as the mid/upper-level pattern should begin to deamplify. Sincavage && .AVIATION... (06Z TAFS) Issued at 1231 AM CDT Tue Sep 17 2024 VFR conditions with southerly winds increasing to near 15 to 20 knots through the afternoon hours today. A line of storms will approach PVW late tonight around 03z-06z tonight, but coverage remains uncertain. Confidence is low that the line of storms extends south towards LBB, thus no mention was given at this time. && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...11 LONG TERM....09 AVIATION...11