Area Forecast Discussion
Issued by NWS Hastings, NE
Issued by NWS Hastings, NE
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751 FXUS63 KGID 161206 AFDGID Area Forecast Discussion National Weather Service Hastings NE 706 AM CDT Sun Jun 16 2024 ...Aviation Update... .KEY MESSAGES... - Like yesterday, the late afternoon-evening hours hold VERY CONDITIONAL potential for popping off up to a few severe storms (kind of an "all or nothing" scenario depending on whether or not the cap can hold). Main threat would be our northern/western counties. - Both today and Monday will be plenty hot, with actual high temperatures well into the 90s most places and flirting with 100 especially in parts of KS. However, factoring in humidity, wind speeds etc., today is likely the worst of the two days, with widespread peak heat index of 100-104 across especially the southeast 2/3rd of our coverage area (CWA). In other words, JUST short of official Advisory criteria. - Overnight lows also quite warm these next 2 nights (most areas dropping no lower than low-mid 70s). Potential record- warm lows (through the full calendar day) could be in play at Grand Island/Hastings airports on Monday (June 17). See separate CLIMATE section below for details. - Monday afternoon-night will be quite windy by mid-June standards, with sustained southerly speeds commonly 25-35 MPH and gusts up to around 45 MPH. - Rain/thunderstorm chances Mon-Sat: each and every day/night forecast period features at least small/iffy chances somewhere in our area, but by far the highest chances for the most WIDESPREAD activity looks to focus between Tues afternoon-Wed night as a cold front enters and stalls over our region (at least limited chances for both severe storms and heavy rains/localized flooding). && .DISCUSSION... Issued at 550 AM CDT Sun Jun 16 2024 -- PRIMARY CHANGES TO THIS 7-DAY FORECAST PACKAGE VERSUS THE PREVIOUS ONE (issued Sat afternoon): - Honestly, no changes of major significance. While confidence is lower-than-average regarding thunderstorm chances (or lack thereof?) these next few days, confidence is high in various other aspects including: the heat today-Monday, seasonably- strong winds Monday afternoon-night, decent rain chances Tues- Wed and that Wed should be the overall-coolest day of the week. -- 7-DAY FORECAST OVERVIEW/HIGHLIGHTS (heavily focused on the first 48 hours): - CURRENT/RECENT WEATHER SITUATION AS OF 5 AM: Briefly looking back at yesterday afternoon-early evening: our CWA indeed got fairly lucky in terms of potential severe storm threat. While we did issue a couple of Severe Thunderstorm Warnings for mainly the Thayer County area (and a few other semi-strong storms developed in our KS zones), as was expected, the VAST MAJORITY of severe storms (and even some tornadic activity) focused mainly slightly east-northeast of our CWA within the OAX coverage area (our area largely spared by being JUST behind the passing mid level trough axis by peak heating). Turning to the current and more recent weather scene, since nightfall last evening we had a few weak storms brush into both our extreme southeast (Thayer County) and also our extreme west-northwest (Dawson/Valley counties), but this activity has long since moved out (east) or dissipated (west), leaving us dry CWA-wide at this time under mainly clear skies. In the mid-upper levels, water vapor imagery and short term model data reveal the since-departed mid level shortwave trough axis centered from IA to eastern KS, with our CWA under subtle ridging in its wake. At the surface, the main feature on the regional map is a roughly 998 millibar low pressure center over the eastern Dakotas, with a trough axis/weak cold front trailing southwestward from this low through north central/western NE. However, our entire CWA remains in the warm sector to the south-southeast of this boundary, with early-AM breezes generally 10-20 MPH out of the south (some higher gusts especially east). These breezes, in tandem with dewpoints well into the 60s, has low temps on track to bottom out between 66-70 most areas. - TODAY-TONIGHT: We are truly dealing with two primary concerns...one of one high-confidence (near-Advisory level heat) and one of lower confidence (will any spotty storms...possibly severe...form later this afternoon-evening?). In the big picture of the mid-upper levels, our flow aloft will turn more west-southwesterly as various/subtle disturbances kick into our region well-downstream from a larger-scale trough over the far northwest CONUS. Compared to yesterday (and perhaps a big factor later today), mid-level temps have warmed a bit, with 700 millibar readings now 12-14C over most of our CWA. At the surface, the situation is a touch complex today, as the aforementioned trough axis/weak cold front currently just to our northwest will work southward into especially the northern 1/3 of our CWA today, before stalling out this afternoon ROUGHLY near I-80 and then lifting back north this afternoon as a warm front. This will result in a varied wind regime today, with breezier south winds prevailing in our southern zones today (gusts at least 25-30 MPH especially in KS), while lighter breezes prevail especially in our north from a variety of directions (including northerly/easterly) as the front stalls out. Temperature-wise, the vast majority of our CWA should soar into the mid-upper 90s (with 100 possible mainly in KS), but the presence of the stalling front should keep roughly our northwest 1/4 (mainly north of a Lexington-Fullerton line) a bit cooler in the upper 80s-low 90s. However, some areas near the boundary could also see the highest humidity levels with dewpoints most favored to be in the upper 60s to around 70 at peak heating. The net result will be widespread heat index readings of upper 90s to around 104 across most of the southeastern 3/4ths of our CWA. This puts us VERY close to official Advisory criteria, but for many of the same reasons given by previous forecaster (and also the fact we`ve already had a few pretty hot days recently so this is not a "totally new" thing this season), have opted against issuing one. Turning to thunderstorm potential, this is admittedly a frustrating, type of "all or nothing" forecast. Leaning on higher-res CAM models as usual in the very short term, on one hand recent HRRR runs have the capping (warm air aloft) winning out and keeping our entire CWA storm-free through the evening. However, other models including the often-over-aggressive NAMNest (but also deterministic NAM/GFS/ECMWF runs) suggest that at least isolated/spotty storms could erupt along the aforementioned surface front anytime from around 4 PM into the evening. A perusal of both plan-view and forecast sounding data reveals that this will clearly be one our first truly "huge instability/CAPE days" of the year, with considerable mixed- layer CAPE around 4000 J/kg possible near the front during peak heating. The bottom line is that IF the cap is breached a few storms could become severe quickly, with the saving grace that deep-layer shear appears to be fairly weak (20-30KT). Even so, given that much instability, hail to at least golf ball size and some damaging winds cannot be ruled out. Overall agree with SPC on keeping it "only" a Marginal Risk categorically (level 1 of 5) especially given the conditional nature of the threat, but IF storms go it could get active quickly. No matter what does/doesn`t happen late this afternoon-evening, especially post-midnight the vast majority of active/possibly severe convection should focus at least slightly north of our CWA into northern NE/southern SD within the exit region of a powerful low level jet. That being said, at least spotty/weak elevated convection could from within this low level jet axis especially within our western zones and am carrying some low chances/PoPs to cover this. - MONDAY-MONDAY NIGHT: Although at least spotty/weak elevated showers/storms cannot be ruled out especially during the morning, compared to today, there is overall-less concern about potentially severe storms developing overhead during the later afternoon-evening, as that focus should clearly reside to our north as the surface front will have surged north of our entire CWA by then. Even so, will carry some slight chances for storms mainly far north in the evening, just in case. Overall though, the big stories Monday- Monday night will be more heat, but this time with more wind...in fact quite a bit of wind by mid-June standards. Actual high temps will be fairly similar to today most areas solidly 90s), but with dewpoints expected to "mix out" a bit more, heat index readings should MOSTLY top out slightly under 100 degrees. Wind-wise, have nudged up wind speed for the afternoon-overnight hours, with sustained southerlies of 25-35 MPH and gusts of 40-45 MPH looking increasingly likely as seasonably-strong low pressure deepens to around 990 millibars over western NE. - TUES-TUES NIGHT: Various models are in excellent agreement that a decent cold front will arrive during the day, turning winds northerly and beginning a cool-down, and also likely sparking at least a narrow corridor of afternoon storms along the front. Tues evening-overnight, more widespread convection will likely blossom across the area as forcing increases north of the surface boundary, with at least limited severe storm potential in play (SPC Marginal Risk) along with heavy rainfall/localized flooding potential (currently a WPC Slight Risk for excessive rain). - WED-THURS: Healthy rain chances continue especially Wed-Wed night, as Wed clearly looks to be the coolest day of the week and has trended a few degrees cooler yet (highs most places aimed mid 60s to upper 70s). However, winds turn southerly again Thurs and allow another warm up to begin (highs mainly 80s). - FRI-SAT: Admittedly spent VERY little effort looking at these days, but a quick glance at latest ECMWF/GFS suggests Friday should be mainly dry and breezy from the south (highs well into 80s to around 90 again), with a possible disturbance bringing back increasing storm chances for Sat and probably more so Sat night. && .AVIATION /12Z TAFS THROUGH 12Z MONDAY/... Issued at 705 AM CDT Sun Jun 16 2024 For KGRI/KEAR Airports: - General overview: Confidence is medium-high in VFR ceiling/visibility and also rain/thunderstorm-free conditions through the period, although there is at least some concern (low probability...around 20%) that a robust/perhaps severe storm could rapidly develop in the general area late this afternoon-evening near a weak surface boundary (this bears close watching). However, of high confidence is that the the main story of the period will be winds, and in particular separate periods of low level wind shear (LLWS)...the latter more intense than the former. - Ceiling/visibility/rain and thunderstorm potential details: Confidence is high in VFR ceiling/visibility through the period, with perhaps a scattered lower-VFR cumulus field developing this afternoon, but otherwise any clouds mainly near-to-above 10K ft. As for shower/thunderstorm potential, odds still appear to favor the entire period staying dry (80-90% chance). However, in the slight chance (10-20%) that thunderstorms DO manage to develop late this afternoon (mainly after 21Z), they could quickly intensify in the vicinity of the terminals (probably favoring KEAR more so than KGRI), so short-term trends bear close watching. Considered introducing a low-confidence VCTS to mainly KEAR with these TAFS, but with any possible thunderstorm threat beyond the first 6 hours opted to hold off and let later issuances assess further. - Winds: - Surface winds: Much of the period will be fairly breezy, but particularly right away this morning (mainly KGRI) and then again later this afternoon into tonight at both sites. While direction will prevail southerly to southeasterly the vast majority of the time, the presence of a stalling front will probably result in variable directions at times especially between 14-20Z (but also lighter speeds). The overall-strongest speeds will focus later this evening-overnight (sustained 15+KT/gusts around 25KT). - Low level wind shear (LLWS): There are two distinct periods of mentionable LLWS during the period, with the second one overall-stronger and much longer lasting than the first: 1) Right away this morning through around 14Z, southwesterly winds within roughly the 1,500 ft. AGL will continue around 40KT, creating marginally TAF-worthy shear magnitude around 30KT between the surface and this level. 2) This evening-overnight (starting 03Z but really ramping up by 06Z), 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 550 AM CDT Sun Jun 16 2024 -- Regarding possible RECORD WARM LOW TEMPS on Monday (June 17th): Both tonight-Monday morning and Monday night-Tues morning are expected to remain very warm, with most of our CWA not dropping any cooler than 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, because a cold front arriving Tuesday 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) 71 - 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. && $$ DISCUSSION...Pfannkuch AVIATION...Pfannkuch CLIMATE...Pfannkuch