Area Forecast Discussion
Issued by NWS Hastings, NE
Issued by NWS Hastings, NE
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219 FXUS63 KGID 160637 AFDGID Area Forecast Discussion National Weather Service Hastings NE 137 AM CDT Sun Jun 16 2024 ...Aviation Update... .KEY MESSAGES... - Main concern shifts to heat for Sunday and Monday with highs well into the 90s and heat indices 100-105F in spots. There will at least be some wind for "relief" - gusting up to 40 MPH on Monday. - Record-warm LOW TEMPERATURES possible for Monday (June 17) at Grand Island/Hastings airports (see separate CLIMATE section below). - Thunderstorm chances Sun-Mon are low and isolated, but better chances for frequent rounds of storms arrives for the Tue-Thu time frame. Some storms could be strong to severe, but the main hazard may shift to heavy rain and localized flooding. && .UPDATE... Issued at 658 PM CDT Sat Jun 15 2024 ***The Tornado Watch is CANCELLED for south central Nebraska as of 7PM.*** Visible satellite trends show a distinct decrease in agitated cumulus over the past hour, and the upper level shortwave responsible for the current convection continues to lift E/NE. An isolated storm may redevelop prior to sunset (~20% chance), but additional severe weather is not expected. Thunderstorms currently over the High Plains are forecast to dissipate as they shift east after sunset, thanks to increasing convective inhibition. && .DISCUSSION... Issued at 515 PM CDT Sat Jun 15 2024 Rest of today into tonight: A weak surface boundary, reinforced by last night/early AM convection, and currently residing from roughly Grand Island to Hebron, will continue to shift E/NE through the remainder of the daytime hours. The first storm developed around 20Z in Mitchell Co, likely in an area of reduced CINH on nose of very steep low level lapse rate plume (as evidenced by multiple severe wind gusts with convection in central KS), and has quickly shifted NE. This storm has shown signs of organization and potential hail core, at times, but several negative factors to deep severe convection are working against it: poor mid level lapse rates (~6.5 C/km), weak 0-6km bulk shear (~25kt), and poor mid to upper level storm relative flow. This basically just leaves the strong instability (MLCAPE 2000-3000 J/kg) and low level helicity (0-3km SRH 200-300 M2/S2) as ingredients favorable to severe wx. Furthermore, what weak mid-level troughing remains is quickly shifting E/NE with subtle height rises expected for central/western zones through the evening. Thus, the window for severe weather in the E will be limited to next few hrs (perhaps even less). Unsure if we`ll get anything to fill the gap between BVN and HJH along the retreating boundary and within axis of strong instability as sfc convergence seems weaker. If we do, large hail up to around 1.25-1.5" (limited by the weak shear and poor lapse rates), damaging wet microburst, and perhaps a tornado would be the main threats. At least iso convection is trying to develop along another instability gradient along Hwy 183/283 corridors in Phillips and Rooks Counties, but upper support is even worse out there. Additional convection over the NE Panhandle within deep mixing and along sfc trough will likely weaken by the time it arrives in our area due to capping. Sunday - Monday: Main story will be heat, though a non-zero chance for an isolated storm exists in parts of the area, as well. A cold front will attempt to push into the area Sun AM, but likely stall out and even lift back to the N/NW as a warm front during the afternoon. It will become hot S of the front thanks to breezy Srly winds, deep mixing and mostly sunny skies. In fact, areas near/S of the state line could push triple digits on air temps. Humidity will decr some compared to today owing to the deeper mixing, but still be enough to produce some heat indices 100-105F. Opted against an advisory on this shift as this heat event appears somewhat marginal for us given we well into June now, its fairly short-lived at 2, maybe 3, days, and we have wind during the hottest temps. Speaking of wind, rather unusual strong gradient winds by June standards are forecast for Monday in which gusts may reach 40-45 MPH. Fortunately many areas saw a nice rainfall Fri night as things are going to dry out quickly with that kind of heat/wind and strong sunshine. Some model guidance hints at iso storm development near a sfc low/triple point in far W zones Sun aftn, within area of intense mixing that may erode an otherwise seasonably strong cap. If convection indeed forms, its likely going to take every bit of heating and sfc convergence as the broader mid to upper level pattern will be pretty hostile. Moderate to strong instability and modest deep layer shear support a conditional risk of severe hail/wind, and this is handled well in the SPC Day 2 outlook. Convective chances appear even more isolated/conditional on Mon given very warm mid level temps 15-17C and the primary sfc front even a bit further N. Rest of the forecast: Not a lot has changed to overall thinking during this period as ridging intensifies over the NE CONUS and a trough works its way through the Great Basin/N Rockies and into the N Plains Mon night into Tue. This will result in SW upper flow and a plethora of weak perturbations, along with cooler mid level temps and weaker capping. In addition, models continue to show a persistent plume of moisture with tropical origins/source wrapping around the eastern ridge in a "ring of fire" type effect. The N Plains trough will help to force a frontal zone into the region either later on Tue or into Wed and combine with the aforementioned factors to produce repeated rounds of convection for much of the second half of the work week. Severe weather potential is pretty uncertain, locally, as we`ll be on the SE fringes of stronger mid/upper level flow/shear. More confidently, however, will be the risk for heavy rainfall and at least localized flooding. PWATs consistently AOA 1.5" (1.5 to 2 standard deviations above normal), deep layer flow potentially parallel to sfc front/low level baroclinic zone, and multiple rounds is a setup that will almost always present increased risk of flooding in mid to late June. With that said, details will be important, so too soon to go into even modestly specific amounts or local areas of concern. Temperatures will depend on rain/clouds and sfc front position, but in general will be quite a bit cooler than early week. Ensembles have been hitting on Wed being particularly cool in the upper 60s to 70s for most of our Neb zones. Increasingly zonal upper flow could keep the active weather going into next weekend before perhaps some ridging returns around the 23rd or 24th. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 135 AM CDT Sun Jun 16 2024 For KGRI/KEAR Airports: - General overview: Confidence is overall-high in VFR ceiling/visibility and also rain/thunderstorm-free conditions through the period, although there is admittedly a very small chance for a brief shower/thunderstorm both early this morning, and then again late afternoon-evening (deemed around 10% or less). However, the main story of the period will be winds, and in particular two separate periods of low level wind shear (LLWS)...the latter more intense than the former. - Ceiling/visibility/rain and thunderstorm potential details: Confidence is very high in VFR ceiling/visibility through the period, with perhaps a scattered lower-VFR cumulus field developing during the daytime hours, but otherwise any clouds mainly near-to-above 10K ft. As for shower/thunderstorm potential, odds appear to strongly favor the entire period staying dry (90% chance). However, there is also an outside chance that a shower/weak storm could pass through early this morning, and a similar outside chance that a stronger thunderstorm could flare up late this afternoon-evening. However, with both of these chances deemed to only be around 10%, and with better chances for the later afternoon-evening storms to focus at least slightly off to the north, will forego any formal inclusion of rain/thunderstorm chances. - Winds: - Surface winds: Although a bit breezy/gusty at times, overall surface winds will not be a significant issue. The majority of the period (but especially the first and final several hours will feature a prevailing southeast/southerly direction, with sustained speeds commonly 10-15KT and gusts into the 20-25KT range. However, particularly between 13-18Z, direction could honestly be quite variable as a weak front stalls in the area before lifting back north. - Low level wind shear (LLWS): There are two distinct periods of mentionable LLWS during the period, with the second one overall-stronger than the first: 1) Right away this morning through around 13Z, southwesterly winds within roughly the 1,500 ft. AGL will top out around 45KT, creating roughly 30-35KT of shear magnitude between the surface and this level. 2) This evening (02Z onward), a very strong southerly low level jet will kick in, with speeds within roughly the lowest 1.500 ft. AGL accelerating to around 50KT, creating fairly strong shear magnitude around 40KT between the surface and this level. && .CLIMATE... Issued at 530 PM CDT Sat Jun 15 2024 -- Regarding possible RECORD WARM LOW TEMPS on Monday (June 17th): Both Sunday night-Monday morning and Monday night-Tues morning are expected to remain very warm, with most of our CWA not dropping below the low-mid 70s. As a result, calendar day (midnight-to-midnight) records for warmest low temperature could be threatened at Grand Island/Hastings airports (the 2 sites for which we issue formal Record Event Reports/RERs). Any such records are most likely to be threatened on Monday the 17th, because a cold front arriving Tuesday the 18th is currently expected to drop temps safely below record territory by midnight that night. - GRAND ISLAND Record Warm Low Latest Forecast Monday June 17th 74 (1906) 73 - HASTINGS Record Warm Low Latest Forecast Monday June 17th 72 (2020/2014/1946) 73 NOTE/REMINDER: in order for a new record warm low/minimum temperature to become official it has to "survive" the entire 24-hour calendar day (in other words, it is not always based solely on the early-AM low temp). && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ UPDATE...Thies DISCUSSION...Thies AVIATION...Pfannkuch CLIMATE...Pfannkuch