Area Forecast Discussion
Issued by NWS Hastings, NE
Issued by NWS Hastings, NE
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246 FXUS63 KGID 211008 AFDGID Area Forecast Discussion National Weather Service Hastings NE 508 AM CDT Sat Sep 21 2024 .KEY MESSAGES... - A seasonably-strong cold front arrives today (marked by rather gusty north winds), but despite this most areas will see one more day of above-average warmth...especially the southeast 1/3 of our coverage area (CWA) where upper 80s to around 90 are likely. - Although very spotty showers/storms are possible during the daytime today (mainly this afternoon and mainly in KS), it`s increasingly-clear that MOST of our CWA will get through sunset dry, with higher/more widespread chances for rain/embedded thunder arriving later this evening-overnight (overall severe threat low). - While at least portions of some counties especially along/south of the KS border are still expected to pick up 1-2" of rain this weekend, expected total rainfall (QPF) for MOST of our CWA continues to trend down, with especially counties along/north of I-80 now looking at less than 0.50" (and our far north around Ord/Greeley unfortunately struggling to see 0.10"). Suspect more folks will be disappointed than pleased across our CWA as a whole. - Once the last showers depart Sunday afternoon-evening, the Mon-Fri time frame currently features a dry forecast. - Temperature-wise: lovers of early-fall weather (highs mainly 70s/lows mainly 40s-50s) should really enjoy next week! Sun night should be overall-coolest with parts of especially Valley/Sherman/Dawson counties possibly dropping into the upper 30s. && .DISCUSSION... Issued at 507 AM CDT Sat Sep 21 2024 -- PRIMARY CHANGES WITH THIS 7-DAY FORECAST VERSUS THE PREVIOUS ONE ISSUED FRI AFTERNOON: - Chances for measurable rain (PoPs) have continued to nudge downward for the daytime today, with especially our Nebraska CWA expected to remain largely dry until at least sunset. None of our CWA features "likely" (60+%) PoPs until later evening. - As hit on above, total weekend rain totals (QPF) continue to trend down especially for the northern half of our area (most places 0.50" at most), and while our south half should see more overall, anything in excess of 1.50" will likely be a very localized exception. Minimal concern for anything more than very minor/nuisance flooding at worst. - As touched on above, low temps for Sun night have have trended down very slightly, and IF they trend down much more some patchy frost could MAYBE even come into play for a few of our far north-northwest counties (currently not in official forecast). - High temps for especially Sun-Wed have trended up a few degrees. However, Sunday is clearly still the coolest day of the next week with at least spotty lingering rain/widespread clouds holding highs down mainly a few degrees either side of 60 most places. -- 7-DAY FORECAST CHRONOLOGICAL DETAILS: - UP-FRONT ADMIN NOTE: now that our roughly 30-hours of various comms issues (due to a fiber cut) are behind us, it`s back to "business as usual"...one more big thanks to OAX for helping us out with product issuance, radar watch, etc.! - CURRENT/RECENT WEATHER SCENE AS OF 4 AM: Following a brief flare-up of spotty storms in our far southeast zones Friday evening (including a radar-indicated marginally- severe storm in Mitchell County KS), the remainder of the overnight has been quiet/dry and unseasonably warm. In the big picture of the mid-upper levels, we reside under broad southwesterly flow...downstream from a strong/large scale closed low currently churning across the CA/AZ border. At the surface, weak low pressure is centered over the NE/CO/KS border area, with a weak boundary extending off to its northeast separating modest southerly breezes and warmer/humid air (over our CWA) from the leading edge of a strong cold front that is currently diving southeastward through northwest NE. Just within mainly the last hour, some high-based showers/perhaps a thunderstorm have developed just outside the extreme southeast corner of our CWA within a zone of low-mid level warm air/moisture advection. overnight low temps are on track to range from around 60 far northwest...to mid-upper 60s central...to upper 60s-low 70s southeast. Early morning dewpoints have risen into the low-mid 60s most places. - TODAY-EARLY EVENING (through around sunset/9 PM): In the mid-upper levels, the aforementioned strong upper low over the Desert will trudge northeast...centered over the Four Corners by sunset. Meanwhile, lower amplitude disturbances out ahead of it will stream into the Central Plains from the southwest, providing the necessary lift for at least spotty showers/thunderstorms as the day wears on (especially in our south). That being said, higher-res models (HRRR/NAMNest) clearly show that any showers/storms this morning should mainly favor our extreme southeast counties, with at least scattered activity eventually becoming a bit more widespread toward late afternoon-early evening especially near/south of the KS border. At the surface, the cold front is clearly the "story of the day", with its passage marked by an abrupt transition to northerly winds generally sustained 15-25 MPH/gusts 25-35 MPH. The leading edge of this front will enter our far northwest shortly after sunrise, be roughly halfway through our CWA by Noon, and then slow a bit as it finally reaches our extreme southeast CWA by late afternoon-early evening. Although not likely, there appears to be a brief window for a strong to marginally-severe storm to develop along/just behind this front mainly between 5-8 PM and mainly in our far southeast KS counties (Osborne/Mitchell/Jewell), with latest RAP depicting around 1500 J/kg mixed-layer CAPE/around 30KT of deep layer shear. Interestingly, SPC has not included this portion of our CWA in its initial Day 1 Marginal Risk area, but should it be expanded in later issuances it might include this area. Overall though, the vast majority of our CWA is not expected to have any severe threat. Last but not least, both high temperatures and hourly temperature trends will be a bit tricky today given the cold frontal passage and a gradual increase in clouds this afternoon...with a good 15-degree difference/gradient expected across our CWA. Leaned heavily on a multi-model blend, which if anything nudged highs up 1-2 degrees from previous, but ranging from only mid 70s far northwest, to upper 70s-low 80s central (Tri Cities area), to upper 80s-around 90 southeast where the front arrives last (especially Hebron to Beloit areas). - LATER THIS EVENING-OVERNIGHT (post-sunset/after 9 PM): While any possible/brief severe storm threat in our far southeast should be on the wane, chances for increasingly- widespread showers with embedded thunderstorms (a few possibly strong enough to produce small hail) will expand northward to include the majority of our CWA...in response to increasing mid- level convergence (especially around 700 millibars) out ahead of the main/parent upper low that will still be out to our west over CO through the night. As already hit on above, while most all of our CWA should see at least minimal rain, the most concentrated heavier showers/downpours will surely favor our south more than our north...as increasingly-dry low level air with surface dewpoints falling into the 40s will help to "eat away" at the northern edges of steady rain. Also at the surface, steady north-northeast breezes at least 10-15 MPH with gusts around 20+ MPH will persist overnight. Low temps were actually nudged up very slightly given the expectation of widespread clouds, with most of the CWA aimed fairly uniformly between 51-55. - SUNDAY DAYTIME-NIGHT: Over the course of these 24 hours, the main upper low initially over CO will gradually track east-northeast over the heart of our CWA, opening up/weakening slightly as it does so. However, forcing will remain sufficient for scattered to numerous showers and perhaps a few weak thunderstorms especially during the morning-mid afternoon hours, with activity becoming increasingly spotty during the late afternoon-evening while also departing from west-to-east with the upper wave. At the surface, it will remain a bit breezy through the day with northerly sustained speeds generally 10-15 MPH/gusts 15-20 MPH. Under cloudy/mostly cloudy skies, high temperatures will easily be the coolest of the next many days, with highs currently aimed mainly a few degrees either side of 60 (warmest north where rain/showers should be least prevalent and clouds not as deep). Sunday night, skies should slowly/gradually clear from northwest-to-southeast, and winds will become very light as surface high pressure moves in. There are still some question marks regarding exactly how fast clouds vacate, but assuming they do vacate efficiently, this is on track to be a legitimately cool night for late-September, and have lows aimed from upper 30s far north/west central (Ord/Gothenburg areas), to low-mid 40s central (Tri Cities) to mid-upper 40s southeast. As already hit on, IF temps trend a few degrees colder in our north/west-central Nebraska zones, then at least limited/patchy frost COULD come into play, but this is still considered a low probability scenario. - MONDAY-TUESDAY: Various models are in agreement that at least the vast majority of our CWA remains dry, as we initially reside in the wake of the departing weekend system, before another disturbance drops down into our region out of the north-northwest. There are hints that especially some western counties could see some light showers/sprinkles mainly Tues AM from this second wave, but am okay letting our CWA-wide dry forecast ride for now. Overall, these look like two seasonably pleasant days. High temps have trended up generally 1-4 degrees from previous for both days, with Monday now aimed mainly 67-70 and Tuesday low-mid 70s. Overnight lows will also nudge upward...mainly mid 40s Mon night and mid-upper 40s Tues night. - WEDNESDAY-FRIDAY: At least for now, our forecast remains dry CWA-wide, with overall-high confidence in seasonably-pleasant high temps mid- upper 70s and lows a few degrees either side of 50. That being said, latest ECMWF/GFS really start to diverge with their depiction of the upper air pattern in the wake of Tuesday`s disturbance. In short, the ECMWF cuts off a very slow moving low pressure system somewhere between north TX and southern KS, while the GFS keeps any possible closed upper low well to our east with more prominent upper ridging over our region. Either way though, both primary models currently favor mainly (if not completely) dry conditions. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 101 AM CDT Sat Sep 21 2024 For KGRI/KEAR Airports: - Ceiling/visibility/precipitation/thunderstorm potential: High confidence in VFR ceiling/visibility through at least the vast majority of the period, with the only foreseeable possible "catch" being an outside chance of brief sub-VFR visibility if any heavier showers/thunderstorms happen to pass directly overhead late in the period Saturday evening. Otherwise, most of the period will feature only varying degrees of high cirrus, before a lower (but still VFR) ceiling roughly around 8K ft. becomes more probable Saturday evening. As for the aforementioned shower/thunderstorm potential, largely maintained continuity with previous TAFs by starting a mention at 23Z, but did go with "vicinity thunderstorm" (VCTS) instead of VCSH as there will be enough elevated instability for a few non-severe storms. - Winds: This is actually the "main story" of the period, as a well- defined cold front will slice into the area Saturday daytime and result in a pronounced directional switch to northerly and an uptick in speeds. Starting out early this morning, sustained southerlies around 10KT will prevail. Then, after sunrise direction will briefly turn westerly before the main frontal surge arrives (currently aimed around 15Z), switching winds northerly with sustained speeds commonly around 20KT/gusts 25-30KT through much of the day. Saturday evening, northerly speeds will slacken some what, but gust potential to around 20KT will remain. One last wind-related note: There could be a brief (2-3 hour) period of marginally-strong low level wind shear (LLWS) early this morning (mainly 07-10Z), but have deemed this too brief in nature/too marginal in magnitude for formal TAF inclusion. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ DISCUSSION...Pfannkuch AVIATION...Pfannkuch