Area Forecast Discussion
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Issued by NWS
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757 FXUS64 KLUB 011557 AFDLUB Area Forecast Discussion National Weather Service Lubbock TX 1057 AM CDT Wed May 1 2024 ...New MESOSCALE UPDATE... .MESOSCALE UPDATE FOR AFTERNOON SEVERE STORMS... Issued at 1057 AM CDT Wed May 1 2024 Upper air analysis this late morning depicts a shortwave trough digging into the north-central Rocky Mountains, with a well-defined vorticity lobe rounding the base of the trough and beginning to eject into the west-central Great Plains. Further south, a subtle, shortwave perturbation was analyzed over northern Mexico, and was steadily moving northeastward towards the Big Bend region while the mid/upper-levels are otherwise bereft of any noticeable feature on the water vapor bands. The 12Z objectively analyzed upper air data depicted the left-exit region of the 250 mb jet eclipsing southern New Mexico, evident by a 50 kt wind maximum observed on the EPZ RAOB this morning while the primary jet streak near 80 kt was located further south per the MMCU RAOB (Chihuahua International Airport). Upstream RAOBs from ABQ and EPZ also indicated a substantial elevated mixed layer (EML), and the 12Z AMA RAOB also sampled the EML as the balloon was launched within the dryline circulation. Meanwhile, the 12Z RAOB from WFO MAF sampled a large EML atop a strong cap with mixed-layer parcels yielding >2,500 J/kg CAPE amidst a very moist, yet shallow, boundary-layer, characterized by T/Td spreads of only 6 degrees and a dewpoint of 67 degrees. This airmass was, and continues, to advect northward where LIDAR data out of LBB continues to detect the dispersion of a strong low-level jet (LLJ) with a speed now <=30 kt compared to the near-50 kt LLJ sampled earlier this morning. At the surface, a lee cyclone with a minimum pressure of 1008 mb was analyzed over the OK PH, particularly GUY, with a sharpening dryline extending southwestward across the TX PH and into the extreme southwestern TX PH as per recent West Texas Mesonet (WTM) and METAR data. A reservoir of 60+ degree dewpoints exists to the east of the dryline, with the 65 degree isodrosotherm delineated generally along the I-27/HWY-87 corridor per WTM data. Dewpoints were approaching 70 degrees across the Rolling Plains as well, with a corridor of very high theta-e air (e.g, 350-355 K) spread across the Caprock and Rolling Plains this morning. Visible satellite imagery and webcams reveal a shallow, low-level stratus deck anchored across the eastern Rolling Plains with evidence of billows across the Rolling Plains while a shallow cu field continues to develop and advect northward from the Permian Basin and into the CWA. The billows have been convectively reinforced by outflow from severe convection last night, though the increase in pressure tendencies following the passage of the initial gravity waves were negligible and pressure tendencies have since stabilized. Differential heating along the edge of the stratus deck was most pronounced across the far southeastern TX PH where current temperatures are in the upper 60s while increasing into the middle 70s where the billow field is located. Deepening of the lee cyclone to the north will continue throughout the rest of the day beneath the glancing influence of the shortwave trough ejecting into the west-central Great Plains today, with most guidance indicating gradual pressure falls of 10 mb/12 hr through 00Z this evening. The pressure falls associated with this deepening cyclone will generate an isallobaric response such that the southeasterly winds within the moist sector accelerate to 15-25 mph with gusts to 35 mph this afternoon and evening. The dryline bulge remains positioned to the north of the CWA at this time, and the combination of intense, diabatic surface heating as temperatures breach 90 degrees along the I-27/HWY-87 corridors and into the upper 80s in the Rolling Plains; intensifying low-level storm-relative inflow, and the continued advection of high theta-e air, will serve as a focus for the initiation of a discrete supercell or two in close proximity to the extreme southeastern TX PH and northern Rolling Plains. VWP data from the KFDR WSR-88D (despite the lapse in data from maintenance) continues to observe a substantial component of streamwise vorticity in the 0-1-km layer where storm-relative helicity values are approaching 400 J/kg as of 1518Z. A tornado threat is forecast to focus in proximity to the extreme southeastern Texas Panhandle, including the City of Childress, late this afternoon as convection unzips to the south in the form of a broken MCS as CINH erodes from intense heating in congruence with the belt of weakened mid-level flow. The best timing for this scenario is 5-8 PM CDT (22Z-01Z) as discrete propagation, particularly with a rightward-moving supercell, will be <=10 kt to the southeast in environment of buoyant and unimpeded storm-relative inflow, especially if the full component of the right-moving storm motion vector is realized. Deviant tornado movement can be expected in a situation such as described above, and with high relative humidity within from the surface-to-700 mb layer, in addition to the dampened storm-relative flow at anvil-level, hydrometeor loading of updrafts will occur with HP supercells expected and would lead to cyclic behavior of discrete/semi-discrete storms before upscale growth occurs. Large, bulbous, rear-flank downdrafts would also enhance the potential for wind-damage and further enhance deviant tornado movement during the occlusion process. The slow storm motion associated with right-moving supercells and excessive hydrometeor loading also points towards both the potential for very large hail near baseball size and/or a accumulating hail event as wet-bulb zero heights were objectively analyzed near 8 kft AGL. An additional discussion involving the forecast for the rest of the CWA will be issued with the primary package this early afternoon as the expectation for a broken line/MCS remains intact. Sincavage && .SHORT TERM... (Today and tonight) Issued at 311 AM CDT Wed May 1 2024 In classic West Texas fashion, the first day of May should hit the ground running with dryline storms later today and especially by this evening. Early morning water vapor imagery showed gravity waves rolling west over the region courtesy of two MCSs in OK, but otherwise our W-SW flow aloft was devoid of any meaningful features. This will change later this morning as SW winds aloft pick up some steam ahead of an elongated trough overspreading the Intermountain West. At the surface meanwhile, a dryline roughly from Dora-Dimmitt- Amarillo at 2 AM is expected to retreat another 60 miles or so ahead of increasingly moist southerlies and eventually some low clouds by daybreak. Eastward mixing of the dryline this afternoon doesn`t appear particularly aggressive thanks to the deepening moisture and more importantly a diffuse surface low drifting from eastern NM into southeast CO by this evening. By peak heating, most high res guidance paints the dryline along a line from Silverton southwest to Lubbock and Brownfield which seems reasonable. East of the dryline, MLCAPEs should soar to 2500-3500 J/kg with modest CIN overall and 30-35 knots of deep layer shear. Marginal CIN and poor anvil-level SR flow would tend to favor a shorter window for supercells early on, before ample DCAPE near the dryline raises the chances of storm modes becoming increasingly messy and linear. On that note, several models (CAMs and globals) depict a H7 trough currently along the Sierra Madres that lifts northeast through the day before triggering dryline storms over the western Permian Basin around 21Z and growing quickly upscale thereafter. Given large DCAPE along the dryline and straight hodographs, there is a growing signal from CAMs that this initially supercellular convection could be quite efficient with downbursts and more importantly left movers that race north and into our southern South Plains this evening complete with damaging winds and blowing dust. Past events such as this often accelerate the dryline`s evening retreat and expand chances for additional storms. NBM`s westward extent of PoPs on the Caprock look good for this setup, but its values were raised considerably off the Caprock by this evening as a linear MCS is likely to evolve with wind and heavy rain the greatest threats. A second and more conditional area for storm initiation later today could involve an outflow boundary currently loitering over our northeastern counties from nocturnal storms in southwest OK. This boundary appears rather diffuse overall and will more than likely wash out through the day given how much modification will ensue in the next 12+ hours. Convection should depart our eastern zones toward midnight all the while the dryline returns to NM and a cold front works its way south across the western TX Panhandle. NBM temps today and tonight needed no change. && .LONG TERM... (Thursday through Tuesday) Issued at 311 AM CDT Wed May 1 2024 A generally quieter weather day is expected on Thursday as an early- day cold front passes southward through the region. The front itself will not be particularly strong or quick-moving as upstream pressure rises remain modest and deepening surface troughing over eastern NM and the Permian Basin slow its southward progression. Even behind the front temperatures will still warm well into the 80s with the more notable post-frontal change being a reduction in near-surface moisture and relative lack of cloud cover given the drier upstream airmass. Some models still depict isolated convection on Thursday in the vicinity of a remnant dryline, but this should be well to our east and will therefore carry a dry forecast over the entire forecast area Thursday through early Friday. Guidance is in good agreement that low level moisture will increase once again beginning on Friday as surface flow obtains a stronger easterly component, which will also result in high temperatures falling back near seasonal averages. Thunderstorm potential on Friday is a bit more unclear as some models hint at scattered storms firing within the moist upslope regime, but large-scale forcing will still be quite weak with only a very modest midlevel wave progged to approach the region during the evening with inhibition also appearing fairly significant due to a strong capping inversion. Still, the uncertainty and increased moisture does support maintaining low PoPs off the Caprock Friday afternoon and evening. An additional cold front will pass through the region on Saturday, with flow aloft also progged to strengthen through the day as well. A majority of model guidance still points to the late Saturday through early Sunday period as most favorable for potential widespread rainfall as a more significant upper level disturbance transits overhead within the stronger southwest flow aloft. Specifics are uncertain at this range, but ensemble consensus suggests that most of the region has a good chance (50-80%) of receiving one tenth of an inch of rain or more over the weekend. Early next week, a much deeper upper trough is progged to develop over the western CONUS, but at this point its projected evolution would bring a return of dry and breezy conditions to our area Monday through Tuesday. && .AVIATION... (12Z TAFS) Issued at 615 AM CDT Wed May 1 2024 Beginning to see MVFR visbys and lower CIGs develop from CDS on north behind an outflow boundary, although it`s unclear if these conditions will become prevailing or not. Satellite and models suggest VFR is more likely to win out overall at CDS and also at LBB where a second layer of stratus could threaten around sunrise. Toward this evening, ISO TS should develop near LBB and grow in coverage as they shift E-NE toward CDS. However, this threat is still 12+ hours out and not worthy of a TS mention at the moment. && .FIRE WEATHER... Issued at 311 AM CDT Wed May 1 2024 Dry and breezy conditions are likely this afternoon across the far southwest Texas Panhandle and northwest South Plains behind a dryline. Fuels in these areas are more receptive to fire spread and when combined with southwest winds of 15 to 20 mph and RHs falling to around 10 percent, a Rangeland Fire Danger statement is justified for Parmer and Bailey Counties from 1 PM until 8 PM. Farther east, thunderstorms (some severe) will increase in coverage by this evening with heavy rainfall possible off the Caprock. && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ MESOSCALE UPDATE...09 SHORT TERM...93 LONG TERM....30 AVIATION...93