Area Forecast Discussion
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Issued by NWS
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573 FXUS64 KLUB 071753 AFDLUB Area Forecast Discussion National Weather Service Lubbock TX 1253 PM CDT Sun Jul 7 2024 ...New AVIATION... .SHORT TERM... (Today and tonight) Issued at 313 AM CDT Sun Jul 7 2024 06Z upper air analysis reveals a shortwave trough pivoting across the central Great Plains with a small, vertically-stacking low located over the MN/ND border. Several other smaller-scale perturbations were also evident on water-vapor imagery as the broadened waveguide of the trough extends from the northern Rocky Mountains into the Great Lakes region, with an elongated ribbon of vorticity emanating from the apex of the subtropical ridge that is centered over the Sacramento Valley. The mid-level cold front associated with the stacking low branched southward into western Kansas before it becomes increasingly ill-defined aloft with southward extent into the TX PH. Subsidence continues to advect overhead this morning as the CWA remains within the inflection point of the broad trough and the subtropical ridge to the west, with this distinct subsidence layer observed by the 07/00Z RAOB from WFO ABQ. The orientation of the synoptic-scale flow and related subsidence over the CWA will continue to shunt the upper-level outflow channel from T.C. Beryl to the southeast and east of the CWA. The tropical system will not have an influence on the thunderstorm potential later today and into Monday as the right entrance-region to the 250 mb jet streak remains superposed over the region through end of the short-term period owing to the blocking of the subtropical ridges over the western U.S. and eastern Atlantic Basin. At the surface, a fairly active pattern has been analyzed with a double cold front structure evident in the central and southern Great Plains, both of which are currently north of the CWA. Multiple surface troughs were also evident on recent METAR and West Texas Mesonet (WTM) data, with WTM data delineating a surface trough west of the edge of the Mescalero Escarpment, another one located east of the 100th meridian; and a convectively-contaminated, pre-frontal surface trough located near the OK PH. Two lee cyclones were also located near the Raton Mesa and the other in north-central Kansas. The deepening of these lee cyclones, in addition to the slightly negative geopotential height falls, has resulted in southerly winds increasing to the 15-25 mph, particularly across the Caprock, as per recent WTM data. Breezy, southerly winds are expected to remain intact through sunrise before gradually veering southwestward later this morning as the lee cyclone that is currently near the Raton Mesa rotates eastward into the TX PH and its annexed surface trough translates towards the NM/TX state line. Veering of the surface flow will enhance the effects of adiabatic compression amidst intense heating from full insolation, and temperatures are forecast to near 100 degrees this afternoon while the 65 degree isodrosotherm lingers across the Rolling Plains as winds remain backed to the south ahead of the surface trough. As the southwest-to-northeast-oriented surface trough sloshes into West Texas this afternoon, surface and low-level convergence will begin to increase considerably along and northeast of the I-27 corridor as convective temperatures are reached. The superposition of the right entrance-region to the 250 mb jet streak will also provide enough large-scale forcing for ascent during the early and mid-afternoon hours (i.e., a few cirrus bands will likely be observed advecting in from the northwest as the ribbon of increasing DCVA approaches the CWA). Similar to what was observed last evening by the neighboring 00Z RAOBs, a deeply-mixed boundary-layer is expected with LCLs near 700 mb. Initial attempts at thunderstorm initiation will be isolated-to-widely-scattered after 18Z, though steep, mid-level hydrolapses ahead of the convectively-reinforced, southward-surging cold fronts should keep storms cellular with the possibility of semi-discrete propagation during the mid-afternoon hours. More-scattered to potentially widespread convection is forecast to develop later this evening as the cold front arrives, with the highest potential for heavy rain and severe-caliber wind gusts occurring across the Rolling Plains. Precipitable water (PWAT) content near 1.5" in the open warm sector and warm-cloud depths nearing 14 kft AGL beneath the right-entrance region to the 250 mb jet streak will galvanize the potential for heavy rain across the Rolling Plains. The progressiveness of the cold front and misalignment of the Corfidi vectors for upwind propagation will temper a more-significant flooding risk; however, rain rates as high as 2"/hr will accompany the deepest cores across the Rolling Plains. PoPs were once again raised from the blended initialization for locales in the Rolling Plains (i.e., 80 percent in the official forecast), with storm chances diminishing onto the Caprock while a dry forecast maintained west of the I-27/HWY-87 corridors. Reinforcement via convective outflow may cause the cold front to accelerate in forward-speed, with the MCS exiting the CWA perhaps as early as 08/05Z (midnight CDT) tonight. Renewed chances for showers and thunderstorms will follow after the passage of the initial MCS/cold front as the 250 mb jet streak near 70 kt that was analyzed on the 07/00Z upper air map data digs into the southern Rocky Mountains, and as the upstream jet streak amplifies as another well-defined shortwave trough digs into the north-central Great Plains. The net increase in moist, isentropic ascent; and associated DCVA at the base of the sharpening trough, should result in at least scattered showers and thunderstorms heading towards sunrise Monday with the reservoir of PWATs potentially being convectively-augmented by the prior MCS as easterly, upslope flow develops in the wake of the cold front. Heavy rainfall will be possible, particularly with bands of post-frontal, elevated thunderstorms that become organized as warm-cloud depths remain near 13 kft AGL up onto the Caprock Escarpment towards sunrise on Monday. Sincavage && .LONG TERM... (Monday through Saturday) Issued at 313 AM CDT Sun Jul 7 2024 A broad shield of rain is forecast to linger over portions of the CWA after sunrise on Monday, with rainfall coverage and intensity gradually dissipating by the late-afternoon hours as the base of the mid/upper-level trough begins to move east of the CWA. Easterly flow will remain intact throughout the course of the day, further aiding in adiabatic expansion and moist, isentropic ascent to maintain at least light rain showers through the evening. Subsident warming of the mid-levels will also gradually erode the depth of the elevated mixed layer, with most-unstable parcels yielding less than 750 J/kg by Monday evening across portions of the Caprock and Rolling Plains. Total rainfall accumulations will vary immensely across the CWA, with the lowest amounts forecast across the southwestern South Plains compared to areas farther east and northeast. The dense overcast and rain-cooled airmass will also keep high temperatures in the middle 70s across most of the CWA with the exception of locations near the 100th meridian where lower 80s are forecast. Coverage of thunderstorms will become more-isolated after sunset Monday, with convection ending altogether before daybreak Tuesday. The subtropical ridge to the west of the region is forecast to amplify on Tuesday as it drifts eastward over the Great Basin. Temperatures will warm into the upper 80s as the dense overcast erodes and advects eastward entirely, and winds will be light and variable as the weak surface anticyclone remains anchored across the southern Great Plains. Northwesterly flow will persist aloft on Tuesday and Wednesday, with diurnally-driven thunderstorms forecast to occur each day across eastern NM. The cells may propagate near or into the western zones each evening, but confidence in this remains low as the magnitude of the steering flow remains dampened and similar to what has been observed in prior days (e.g., near 15 kt). The blended PoPs were trimmed to the west of the HWY-385 corridor for Tuesday evening while being maintained across most of the Caprock for Wednesday evening. Temperatures will continue to steadily warm throughout the week as well as the center of the subtropical ridge rotates eastward towards the Four Corners, resulting in a gradual increase in geopotential heights with the forecast remaining dry heading into next weekend. Sincavage && .AVIATION... (18Z TAFS) Issued at 1245 PM CDT Sun Jul 7 2024 VFR conditions will continue this afternoon ahead of an approaching cold front. Thunderstorms are expected to develop early this evening near LBB and PVW, with thunderstorms slowly spreading eastward late tonight. Confidence on a direct impact at the three TAF sites remains too low at this time to include a prevailing mention. A cold front will sweep south early Monday morning with an additional round of thunderstorms expected along with the potential for IFR ceilings. Confidence in thunderstorms with this second round is highest in CDS however LBB and PVW may be clipped by the thunderstorm activity as well. Low ceilings should persist for a few hours tomorrow morning at all three TAF sites. && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...09 LONG TERM....09 AVIATION...58