Area Forecast Discussion
Issued by NWS Hastings, NE
Issued by NWS Hastings, NE
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
569 FXUS63 KGID 221155 AFDGID Area Forecast Discussion National Weather Service Hastings NE 655 AM CDT Sun Sep 22 2024 ...Aviation Update... .KEY MESSAGES... - While this weekend`s "rain event" will surely end up being a disappointing dud for the vast majority of our coverage area (CWA) with MOST places unlikely to exceed 0.10-0.20" (instead of the widespread 1-3" potential it appeared to carry a few days ago!), there was already one "surprising stripe" with embedded 0.25-0.75+" amounts overnight, so this thing can`t be totally written off yet for all. - Once the rain from this system departs tonight, the vast majority of the next 7 days appear dry, although there are hints of least spotty rain chances centered on Tuesday and perhaps toward next weekend (although the latter is of very low confidence). - A few of our far northern/northwest counties (especially Valley/western Dawson) could actually flirt with brief/patchy frost potential very late tonight/early Mon AM as temps could drop into the upper 30s, but current thinking it should remain JUST warm enough to keep frost at bay. - Temperature-wise, this next week will feature what most folks will probably consider a pretty darn pleasant/comfortable stretch of early fall weather, with daily high temps mainly 70s and overnight lows mainly 40s/50s. - That being said, medium range models are currently exhibiting an unusually large spread (high uncertainty) in both the upper air/low level pattern for especially Thurs onward...with at least some chance that Thurs-Sat end up being warmer than currently forecast. && .DISCUSSION... Issued at 526 AM CDT Sun Sep 22 2024 -- PRIMARY CHANGES/UNCERTAINTIES/WEAKNESSES WITH THIS 7-DAY FORECAST PACKAGE: - Unfortunately, expected cumulative weekend rainfall amounts (QPF) have continued to "free fall" after peaking as high as 1-3" just a few days ago (this forecaster honestly can`t remember the last time a larger scale rain event fizzled this drastically). It now appears that MOST places will be lucky to pick up more than 0.10-0.20" (if hardly a drop in several counties especially north of I-80). That being said, as mentioned above we will likely continue to see some very narrow/localized bands that "overachieve" the dwindling expectations and give some lucky folks at least 0.25-0.75". - Although not a "high impact" uncertainty, by far the biggest uncertainty apparent over the next 7 days are temperature trends for Thurs-Sat. Will hit on this more below, but in short our official forecast falls more in line with the cooler ECMWF solution (highs in the 70s), while the GFS suggests a more marked warm-up with highs climbing back well into the 80s to maybe even around 90. These trends bear watching, as this is a pretty notable spread even by Day 5-7 standards. - A bit closer in time, one of the possible weaknesses with our going official forecast is a lack of at least a low-end rain chance in most areas for late Mon night into Tuesday daytime, and it`s quite possible that later forecasts will at least need to expand/introduce some small chances/PoPs. -- 7-DAY FORECAST CHRONOLOGICAL DETAILS: - CURRENT/RECENT WEATHER SCENE AS OF 4 AM: In the big picture of the mid-upper levels, water vapor satellite and short term model data clearly reveal a fairly strong low pressure system centered over CO, with various smaller pieces of energy streaming out ahead of this main low and extending over our CWA and points east. Meanwhile at the surface, the seasonably-strong cold front that passed through yesterday is now well south into OK/TX, with breezy (but not overly-strong) north winds in place over our CWA (sustained speeds mainly 10-15 MPH/gusts 15-20+ MPH). While a good chunk of our CWA (especially KS zones and also several counties north of I-80) have had a dry/mostly dry night, in contrast, many places within counties especially along the I-80 and Hwy 6 corridors (along with Polk County north of I-80) have seen the development of scattered to numerous rain showers...with this generally west-southeast to east-northeast oriented swath of precip apparently tied to a zone of concentrated mid level convergence/saturation (somewhat evident at 700 millibars). As of this writing, the main "rain winners" overnight have been within a roughly 10-15 mile band extending roughly from Holdrege-Kearney-Grand Island-Osceola...with some personal weather stations in this band (along with Grand Island airport) reporting at least 0.25-0.75". Overnight low temps are on track to bottom out somewhere in the 50s most all areas...ranging from low 50s north to upper 50s southeast. - TODAY (daylight hours): Although amounts will not be nearly what was once anticipated for most areas, today still features decent chances for scattered to numerous showers...particularly for counties south of I-80 and into our KS zones. In the mid-upper levels, the aforementioned "parent" upper low currently over CO will gradually slide eastward to over the heart of our CWA by late afternoon/early evening, but likely in a somewhat weakening phase at it "shears out" somewhat (this weakening trend, along with the invasion of drier air from the north with dewpoints mainly only 40s are the basic/primary reasons for the overall "rain event" falling short). Leaning on higher-res shorter term models such as HRRR/NAMnest, it`s quite clear that the vast majority of scattered to numerous rain showers today will focus within counties south of I-80 down into KS...within the main mid level convergence/lift zone associated with the upper wave. MOST places will likely receive no more than 0.10-0.20" of rain, BUT as evidenced by what`s already happened tonight there could be localized/luckier exceptions that could continue to sneak into at least 0.25-0.75" territory. Unfortunately for most areas near/especially north of I-80 (except for those limited places that already saw rain overnight), little to no rain is anticipated. As for the rain itself, have characterized it as simply "showers" in the official forecast, as while a very rogue rumble or two of thunder is not out of the question, convective instability appears quite meager and unworthy of a formal thunder mention. In other departments today, temperature-wise there is ZERO doubt that this will be coolest day of these next 7, BUT high temps continue to nudge slightly upward given the expectation of rain showers to diminish in coverage through the mid-late afternoon hours, along with possibly some limited/filtered sunshine breaking through especially in our far northern counties. The net result is highs aimed mainly low-mid 60s south to more solidly mid 60s north. North winds will gradually/slowly ease as the day wears on, but most of the day will generally feature 10-15 MPH with occasional gusts 15-20. -THIS EVENING-OVERNIGHT (sunset onward): It will take most of the night to actually get the heart of the upper level low east of our CWA as it slowly passes overhead. That being said, mid level saturation/lift will be on a steady decrease. Although most models suggest it will be an almost totally dry night (especially post-midnight), especially the ECMWF hints at some "sneaky" lingering showers (at least sprinkles if not spotty measurable rain) especially in some of our eastern counties overnight, and thus have lingered/expanded some slight Pops (20% chances) well into the night. Really, the biggest question mark overnight involves how efficiently/quickly clouds clear and thus how chilly temps can manage to get. While would not be surprised to see clouds linger a bit stubbornly especially in our southern/eastern zones with the upper wave still passing overhead, most models are fairly insistent that especially our northwest half will clear pretty efficiently post-midnight. This clearing, in the presence of very light winds thanks to dominant surface high pressure, will likely set the stage for the coolest night our CWA has seen so far this late summer/early fall. Currently have lows for most of the CWA aimed from low-mid 40s northwest to mid-upper 40s southeast. HOWEVER, especially parts of Valley/Greeley/Sherman/western Dawson counties could perhaps drop into the upper 30s (currently have as cold as 37-39). This puts these areas perilously close to possible frost formation, but current thinking is that they will remain "safe" by a few degrees, especially given the expected very limited time duration of temps under 40. Something to watch though. - MONDAY-MON NIGHT: The daytime hours appear very seasonably-pleasant, as skies will be sunny/mostly sunny as we reside "in between" the aforementioned departing system and another one dropping in from the north through the Dakotas. Breezes will start out very light, but gradually pick up a bit from the south in the afternoon, albeit only around 10 MPH and gusts mainly under 15 MPH. High temps were raised a decent 3-4 degrees from previous forecast, as despite the chilly start to the morning afternoon readings should reach 71-73. Monday night, high confidence that most of the night stays dry (especially pre-midnight). However, especially the latest NAM/ECMWF suggest that we may need to add a chance for light showers/sprinkles to the late-night hours as the aforementioned disturbance drops down from the north. Temp-wise, it will not be quite as chilly as tonight, with lows aimed mainly 46-49. - TUESDAY-TUES NIGHT: In suit with the preceding Monday night paragraph, it`s starting to look like later forecasts very well might need to increase/expand at least slight rain chances into especially Tues AM, as the upper wave dropping down from the north appears to be fairly potent. Amounts would likely be minimal (no more than a few hundredths), but again the potential is seemingly increasing. This wave will also send another weak cold front across the area, flipping breezes to northerly. That being said, temps are actually expected to be slightly warmer than Monday...most of the CWA aimed 74-77. Lows Tues night again mainly mid-upper 40s. - WEDNESDAY-WED NIGHT: High confidence in our going dry forecast here, as the Tuesday disturbance departs to our southeast/east. Thus another seasonably-pleasant day with highs mid-upper 70s and lows upper 40s to around 50. - THURSDAY-SATURDAY: Honestly, this is where things get unusually uncertain in the model world. While confidence is reasonably high that most of our CWA will remain dry most of this time (especially Thurs), our official forecast features some small rain chances mainly in our eastern counties Fri-Sat, which is a nod toward the latest ECMWF solution. In short, the 00Z ECMWF solution shows a quasi- stationary/cutoff upper low generally centered over MO/AR throughout this time frame, with our CWA perhaps catching some showers along its western periphery Fri-Sat. The ECMWF also supports our going forecast high temps in the mid-upper 70s. However, in start contrast, the 00Z GFS solution does NOT cut off an upper low just to our east, but instead moves it well east and allows widespread ridging to dominate the Central/Southern Plains. Although not reflected in our current forecast, IF this scenario plays out, then Thurs-Sat could easily trend 10-15 degrees warmer than currently advertised (more 80s to possibly near-90). So plenty of uncertainty here on the large-scale pattern and the ultimate evolution of any larger scale trough/low over the central/eastern United States...perhaps also influenced by possible tropical development in the Gulf. && .AVIATION /12Z TAFS THROUGH 12Z MONDAY/... Issued at 655 AM CDT Sun Sep 22 2024 For KGRI/KEAR Airports: - Ceiling/visibility/precipitation: High confidence in VFR ceiling/visibility throughout, with the only possible "catch" being the possibility of brief MVFR visibility at some point these first 12 hours IF a steadier rain shower happens to pass through. Speaking of which, although KGRI/KEAR will likely remain just north of the primary area of scattered/numerous rain showers in southern NE today, felt enough potential still exists to maintain a basic vicinity shower (VCSH) inclusion through 00Z (lesser chance of rain beyond that, albeit probably not truly zero chance until closer to 03Z). As for ceiling, today into this evening will likely feature a mid-level VFR ceiling mainly 7-10K ft., with scattering/clearing increasingly likely as the night wears on. - Winds: The overall-strongest northerly breezes of the period will focus these first 9 hours through around 21Z (sustained around 10-12KT/gusts up to around 17KT). Thereafter, speeds will decrease to under 5KT this-evening overnight with a somewhat variable direction, but probably favoring some semblance of westerly. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ DISCUSSION...Pfannkuch AVIATION...Pfannkuch