Area Forecast Discussion
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Issued by NWS
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212 FXUS64 KLUB 220801 AFDLUB Area Forecast Discussion National Weather Service Lubbock TX 301 AM CDT Wed May 22 2024 ...New SHORT TERM, LONG TERM... .SHORT TERM... (Today and tonight) Issued at 301 AM CDT Wed May 22 2024 A surface cold front, as of 2 am, was located near I-40 and quickly moving south. This front is expected to clear our forecast area by 8 am and bring cooler temperatures to the region for today. Northerly winds will also increase behind the front with sustained winds around 20 mph and gusts up to 35 mph for much of the morning. While this front will stabilize the lowest levels of the atmosphere steep mid-level lapse rates will keep MUCAPE around 2500 J/Kg in place across the southeastern Rolling Plains. Upper-level lift will be rather meager today although a slight ripple in the flow combined with increasing 850 mb flow may be enough for some thunderstorm development where elevated instability remains behind the front. Bulk shear values around 60 kts would be supportive of elevated supercells and with straight hodographs, splitting supercells would be possible. Fortunately, the better instability will remain south and east of our forecast area which is where the best chances for seeing severe weather will be today. As mentioned previously, temperatures will also be cooler today in the wake of the cold front with high temperatures only warming into the upper 70s to lower 80s. Winds will slowly diminish this afternoon and become more easterly as we go into the evening and then southerly overnight. This will advect low-level moisture into the forecast area with a blossoming of low-level clouds expected after midnight for much of the forecast area. This cloud cover will keep overnight low temperatures a few degrees warmer than this morning with temperatures dropping into the mid 50s to mid 60s by Thursday morning. /WI && .LONG TERM... (Thursday through Tuesday) Issued at 301 AM CDT Wed May 22 2024 The mid/upper-level pattern on Thursday will continue to feature a broad, synoptic-scale trough enveloping the central and western U.S., with a well-defined gyre centered over the northern U.S. and into west-central Canada. Maintenance of this gyre will stem from reamplification of the subtropical ridge across the northeastern waters of the Pacific Ocean, and a shortwave trough within the southern tranche of the gyre is forecast to pivot over the northern Rocky Mountains on Thursday. The CWA will remain within the broadly cyclonic flow field associated with the larger-scale troughing, with an expectation for smaller-scale, mid-level perturbations to translate over the region and beneath a quasi-zonal, subtropical, 250 mb jet streak approaching 100 kt. At the surface, the warm front will have lifted northeast of the CWA shortly after sunrise with post-frontal, low stratus gradually eroding as diabatic heating intensifies and the low-level jet veers southwestward. The dryline will initially be positioned near the TX/NM state line on Thursday morning, but will mix eastward across the Caprock (perhaps rapidly) and into the Rolling Plains by the early afternoon hours. Intense dry-bulbing will occur following the passage of the dryline as mixing heights soar into the mid-levels, with the potential for superadiabatic lapse rates to evolve within the surface-to-3-km layer. Temperatures will reach the lower-middle 90s across the dry sector and into the middle 90s in the moist sector/east of the dryline as well, resulting in a substantial zone of differential vertical mixing as convective inhibition (CINH) weakens in the moist sector. Blustery, southwesterly flow will develop across the Caprock and into the western Rolling Plains in response to a lee cyclone deepening to near 994 mb near the CO/KS state line during the afternoon hours. This will cause the dryline sharpen with a dewpoint gradient of 30-40 degrees across 30 miles or less possible as surface winds remain backed to the south, enhancing the magnitude of confluence along the sharp, well-defined boundary. Elevated to critical fire weather conditions are forecast to develop west of the I-27/HWY-87 corridors during the afternoon hours Thursday. Advection of an elevated mixed layer (EML) will have already occurred over the previous 24+ hours. Although geopotential height tendencies will be near-neutral, a strong-to-extremely unstable airmass will be intact across the moist sector with surface-based parcels garnering 2,500+ J/kg of CAPE and MUCAPE values near 4,500 J/kg amidst long, relatively straight hodographs. Despite the presence of broadly cyclonic flow aloft, and the base of the aforementioned shortwave trough pivoting over 500 miles north of the CWA, deep- and cloud-layer shear magnitudes will be near or in excess of 60 kt due to the contribution of the 250 mb jet streak. Weakening CINH from the intense heating and steep, mid-level lapse rates approaching 8 deg C/km, in addition to strong-extreme instability, will promote the potential for explosive thunderstorm development in the eastern Rolling Plains on Thursday with splitting supercells expected as the primary storm mode. Coverage will be isolated due to the weak, large-scale forcing for ascent; however, storms can rapidly become severe in a pristine airmass such as this (e.g., less than 30 minutes after initiation) with classic supercell structures evolving given anvil-level storm-relative flow >=50 kt. Should storms become supercellular within the eastern Rolling Plains, a threat for extremely large hail will exist as wet-bulb zero heights lower below 8,500 ft AGL and strong, mid-level mesocyclones evolve atop a large region of upward-forced, stable air (e.g., LCL-LFC separations of nearly 100 mb). Damaging downdrafts will also accompany the supercell(s) with gusts in excess of 70 mph possible due to Inverted-V profiles beneath cloud base. However, the residence time of supercells in the eastern Rolling Plains should be short-lived as the dryline will be in close proximity to the 100th meridian. Slight chance PoPs (>=10 percent) were drawn westward from the blended initialization to include Childress County southward to Stonewall County as recent mesoscale guidance has come into better agreement with the position of the dryline. The potential for severe-caliber convection will end prior to sunset as cells that do develop move east out of the CWA. Thereafter, the dryline is forecast to remain stalled in the Rolling Plains ahead of a southward-moving cold front generated by the passage of the shortwave trough to the north of the CWA. The cold front is forecast to arrive in the extreme southern TX PH by Friday morning, though a faster time-of-arrival will be possible due to the potential for the front to be reinforced by convective outflow. Cooler, though still hot, temperatures are forecast on Friday with highs ranging from the upper 80s to lower 90s from the extreme southern TX PH into the South and Rolling Plains, respectively. Return flow should become established heading into Friday night as the expansive, but weak, surface anticyclone shifts east out of the Great Plains. All suites of the global NWP guidance spectra maintain broadly cyclonic flow and the gyre across the central and western U.S. as anomalously strong ridging persists over the northeastern Pacific Ocean. Hot, dry, and breezy weather is expected this weekend and into early next week, though the near-neutral geopotential height tendencies should act to prevent widespread, triple-digit temperatures from coming to fruition. Elevated fire weather conditions will be possible this weekend across portions of the Caprock Escarpment. The persistence of the large-scale gyre over the northern U.S. and west-central Canada will continue to facilitate a progressive wave train into early next week, with another shortwave trough forecast to eject over the north-central Great Plains, sending a weakening cold front into the CWA on Monday. This front should also be bereft of thunderstorms; however, cooler temperatures will follow once again with highs remaining within the upper 80s to lower 90s range. Global NWP guidance is in modest agreement with shifting the mid/upper-level ridge over the Rocky Mountains by mid-week, though discrepancies remain regarding its amplitude and geometry. Blended PoPs were maintained across portions of the CWA for the end of the period as there remains enough evidence of shortwave perturbations to translate through the ridge, regardless of its amplitude, in congruence with a belt of northwesterly flow aloft. Sincavage && .AVIATION... (06Z TAFS) Issued at 1255 AM CDT Wed May 22 2024 A cold front is currently moving through the northern Texas Panhandle as of the start of this TAF period. This front should move through the TAF sites between 09z and 12z with a northerly wind shift. Winds will also quickly ramp up in the wake of the front with sustained northerly winds around 20 kts. These winds will slowly diminish through the afternoon hours. There is also a chance for some showers and thunderstorms this morning and afternoon south and east of the TAF sites. && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...58 LONG TERM....09 AVIATION...58