Area Forecast Discussion
Issued by NWS Hastings, NE
Issued by NWS Hastings, NE
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635 FXUS63 KGID 291155 AFDGID Area Forecast Discussion National Weather Service Hastings NE 655 AM CDT Mon Apr 29 2024 ...Aviation and Short Term Update... .KEY MESSAGES... - Although cannot 100% guarantee that a few rogue/high-based showers won`t try drifting over mainly our KS zones late this afternoon-evening, this is UNDOUBTEDLY a dry, tranquil and mostly sunny/clear 24 hours for the vast majority of our coverage area (CWA), with the only mentionable hazard (for plants that is) being the ongoing Frost Advisory through 9 AM for much of the western 2/3 of our coverage area (CWA). - Take advantage of today`s quiet/pleasant weather, because especially the Tues afternoon-Thurs AM time frame already brings back two separate chances for thunderstorms (some potentially severe), although plenty of question marks abound with both of these. - Beyond Wed night-early Thurs AM, there are no "obvious" severe storm threats through the rest of the 7-day, but the upper level pattern remains active with various disturbances passing by and keeping our forecast "littered" with several/low- confidence chances for showers and/or storms. - Temperature-wise: a fairly typical regime for late- April/early-May prevails, with highs on most days in the 60s/70s and lows on most nights in the 40s/50s. The best chance for 80s looks to be Tues mainly south and southeast of the Tri Cities. && .UPDATE... Issued at 655 AM CDT Mon Apr 29 2024 - Update regarding recent fog development mainly in our western Platte valley area: Although not expecting to be long-lasting (only a few hours at most), airport obs and NDOT cams clearly reveal that varying degrees of fog have materialized in the Platte River valley/I-80 corridor of primarily Dawson and western Buffalo counties (this is usually one of our most favored areas for "sneaky fog" when 99% of our CWA remains fog-free. Anyway, have added a stripe of basic "patchy fog" to the official forecast for the next few hours, but again this issue should be too fleeting in both areal coverage and duration to warrant a formal Advisory. && .DISCUSSION... Issued at 525 AM CDT Mon Apr 29 2024 -- PRIMARY CHANGES TO THIS 7-DAY FORECAST PACKAGE VERSUS THE PREVIOUS ONE (issued Sun afternoon): - If anything, added quite a bit of attempted detail to our Hazardous Weather Outlook (HWOGID) for the separate storm/possible severe weather chances between Tues afternoon- Thurs AM, but even so there are still plenty of unresolved details to sort through (see below for more). - Temperature-wise: although not monumental changes by any means: 1) highs for Wed have trended down around 5 degrees especially in our south (a possible sign that the main warm front might struggle to lift north?) 2) Highs Friday have trended up around 5-degrees area wide, with less of a cool push evident in the wake of Thursday`s cold front. -- 7-DAY FORECAST DETAILS (heavily focused on the first 3 days): - CURRENT/RECENT WEATHER SCENE AS OF 4 AM: Ahhh, what a refreshing break to catch a brief respite from ongoing or imminent thunderstorms/severe weather threats (as brief as it may be). Speaking of refreshing, confidence is fairly high that this ongoing night/early morning will be the overall-chilliest one of the next week (except for perhaps Thurs night?). Thanks to a relatively ideal radiational cooling setup (skies now almost totally clear and light breezes ranging from near-calm to 7 MPH most places, morning lows are on track to bottom out between 33-39 degrees across most of our CWA. While at least brief/patchy frost cannot be ruled out within pockets of many counties (especially sheltered/low-lying places), our official Frost Advisory remains in effect for most counties along/west of Highway 281, which are overall most favored to see somewhat more widespread frost development particularly between 5-7 AM. In the mid-upper levels, water vapor satellite imagery and short term model data clearly show our latest departing upper low churning across the SD/MN border, while we are in the midst of likely at least 30+ hours of overall-quiet weather before our next disturbance visible off the Pacific Northwest coast comes into play. - TODAY-THIS EVENING: Other than perhaps some scattered "fair weather" cumulus expected this afternoon, this will surely be no worse than a mostly sunny and seasonably-pleasant day CWA-wide, and also likely a dry day- evening for the vast majority of our area as transient/low amplitude upper ridging prevails aloft. The only possible "catch" is that some models (especially NAM-based) generate a few spotty, high based sprinkles/showers late this afternoon- evening primarily in our KS zones where some weak/elevated instability interacts with an initially weak low level jet. Next few shifts will need to keep an eye on this in case some small rain chances (PoPs) need introduced/re- introduced to our forecast in this area, but consensus of most models either develop nothing or keep it slightly south of our CWA. But other than this one possible "catch", it`s hard to beat today`s weather, as winds will be seasonably-light from mainly a west- southwesterly direction, with speeds (including gusts) mainly just 5-15 MPH. Afternoon high temps most areas will improve by a good 10-15 degrees versus yesterday, and made little change with most areas aimed a few degrees either side of 70, and mid to even a few upper 70s most prevalent in KS zones. - OVERNIGHT: Like late this afternoon-evening, cannot completely rule out a few rogue sprinkles/light showers passing through here or there, but not enough of a signal to "ruin" our going dry forecast as slightly better chances for this should reside to our east and also northwest. However, we will likely at least see a gradual increase in mid-high level clouds, which combined with slowly- increasing southerly winds (10-15 MPH toward sunrise) will keep temperatures tonight considerably milder, with lows aimed between 48-54 most places. - TUESDAY DAYTIME-NIGHT: Most importantly, a POSSIBLE severe storm risk returns, but latest trends point toward a more brief-in-nature threat within our particular CWA (especially our far east), with a more concerning/higher-confidence risk instead taking aim mainly on the OAX/TOP/ICT counties just to our east-through-southeast. Will break this period down by topic: 1) Basic upper air/surface situation (including temps): Aloft, a fairly vigorous, open shortwave trough will quickly zip from the Central Rockies to the Great Lakes over these 24 hours, sending a fairly quick-moving surface cold front across our CWA from west-to-east over the course of the day. The day will start with breezy south winds area-wide (gusts easily 20-30 MPH), but as the day wears on this front will pass through from west-to- east, turning breezes westerly and northwesterly (also breezy behind the front with gusts 25-35 MPH likely). Ahead of the front, the southerly winds will draw low level moisture back northward with dewpoints of at least mid 50s likely (maybe upper 50s?) Among more pressing issues, high temps will depend on the exact timing of the frontal passage, but have highs aimed from mid-upper 70s in roughly our northwest half (including Tri Cities) to low-mid 80s especially in our southeast 1/3. 2) Rain/Severe storm prospects: Already in the morning, small chances for showers/weak storms return to mainly our north-northeast zones. However, the million dollar question is clearly: where exactly do vigorous storms fire along the front in the afternoon? Consensus of several models (including a few new 06Z runs) are honing in on a little faster frontal passage, which would be nothing but good news for our CWA. Latest higher-res HRRR/NAMNest fire up storms very near our eastern fringes (Hwy 81 corridor) around 3-5 PM, but then quickly move them off to the east-southeast of our CWA by very late afternoon-evening. That being said, a few 00Z model runs reflected a slower front with storms perhaps initiating as far west as around Highway 281...putting more of our CWA under the gun. Given these timing uncertainties, can`t blame SPC for keeping the west edge of the Day 2 Marginal Risk near Hwy 281, but if latest trends/consensus holds this could be trimmed east a bit in later updates. No matter whether storms affect our CWA or not, they could become severe quickly with healthy mixed- layer CAPE of 1500-2500 J/kg in the presence of around 40KT of deep layer shear. There could initially be a few discrete supercells capable of producing mainly large hail (at least golf ball size), and if storms congeal quickly into at least a broken line then damaging winds are on the table too. Given the relatively high-based nature of storms, the tornado threat could be muted somewhat, but it`s non-zero for us and a little higher just to our east. IN SUMMARY: we have a highly conditional threat for severe storms Tues afternoon in especially our eastern zones, but it`s also possible we could be spared completely. Once storms move out of our area by early evening (if they ever affect our CWA to begin with), MOST of our CWA will probably remain dry through the late nigh hours. That being said, especially southern zones could see some some mainly elevated convection (perhaps strong?) toward sunrise Wed as a low level jet kick in. - WEDNESDAY DAYTIME-OVERNIGHT (through Thurs AM): At least "on paper" this time frame looks to carry higher- confidence chances for more widepsread storms and quite possibly a severe threat...particularly near/south of the KS border where SPC has focused it`s Day 3 Slight Risk. Aloft, the next in our parade of upper systems gradually approaches from the Rockies during the day, with a strong surface low developing in southwest KS. One of the biggest question marks for our CWA is whether we see mainly elevated instability north of the main warm front which is currently projected to reside near or even south of our far southern CWA through late afternoon, or whether this front can lift north closer to the NE border during the evening, making surface-based storms and even a possible tornado threat more realistic. For what it`s worth, we just had a situation a few days ago (Saturday), when the main surface front failed to surge north into our CWA and muted a higher-end severe threat, but no guarantees that this happens this time around. There are a lot of things to sort out before this threat arrives over 48 hours from now, but particularly the NAM paints a concerning picture into especially our KS zones with perhaps 3000 J/kg mixed-layer CAPE, around 40KT of deep layer shear and increasing low level shear as the evening wears on and the low level jet cranks up. Whether or not we have a tornado threat depends so much on how far north this front can make, but with healthy elevated instability extending well north into our Nebraska counties, at least a large hail threat could extend up through most of our CWA. Not to be overlooked, this could also be a good setup for a decent swath of heavy rains, and although not reflected this high in our official QPF forecasts (which often under-do localized convective maximums), parts of our CWA could easily see 1-3". Fortunately, most areas will have had several days to dry out by then, but at least localized flooding/flash flooding is on the table (WPC Excessive Rain Outlook has a good chunk of our CWA in a Slight Risk). On less-impactful notes, much of Wednesday daytime could simply be cool and perhaps even drizzly to the north of the front in KS in an easterly wind regime, and we could end up with more of of north-south temperature gradient than currently reflected (currently aimed from 60s most of Nebraska zones to 70s in KS. -THURSDAY-FRIDAY: In the wake of the passing cold front Wed night, Thursday should be a mainly dry and moderately-windy day with northwesterly gusts likely 30+ MPH. Latest deterministic models suggest Friday should be mainly dry as winds flip back around to southerly, but timing uncertainty at that range keeps low-confidence chances for rain in our forecast. -SATURDAY-SUNDAY: Needless to say, confidence in details are VERY low by this time frame, as general model consensus is for active west- southwesterly flow to continue, bringing almost impossible-to- time shower/thunderstorm chances through our area (and it could easily remain mostly dry too for some or most places). We have a lot of days to get through before we can fine tune our going low-confidence weekend PoPs with any degree of certainty. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 655 AM CDT Mon Apr 29 2024 - General overview for KGRI/KEAR: For the most part, this will be a "quiet"/uneventful aviation period, with the main exception being the development of moderately-strong low level wind shear (LLWS) very late in the period (early Tues AM). There is high confidence in VFR ceiling/visibility throughout, and for the majority of the period winds will be seasonably-light (even gusts mainly under 15KT). - Wind details: - Surface winds: Breezes today will average sustained around 10KT/gusts up to around 15KT out of a mainly westerly direction. This evening, there will be a brief period of variable direction/very light speeds before a gradual increase out of the south- southeast occurs mainly post-midnight (gusts perhaps 15+KT very late in the period). - Low level wind shear (LLWS): Introduced a formal LLWS group very late in this period (starting 09Z) as a strong south-southwesterly low level jet cranks up, with winds in the 1-2K ft. AGL layer accelerating to at least 40-45KT. This results in at least 30-35KT of shear magnitude between the surface and this level...plenty worthy of TAF inclusion. && .GID WATCHES/WARNINGS/ADVISORIES... NE...Frost Advisory until 9 AM CDT this morning for NEZ039-040-046- 047-060>062-072>075-082>085. KS...Frost Advisory until 9 AM CDT this morning for KSZ005-006. && $$ UPDATE...Pfannkuch DISCUSSION...Pfannkuch AVIATION...Pfannkuch