Area Forecast Discussion
Issued by NWS Hastings, NE
Issued by NWS Hastings, NE
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158 FXUS63 KGID 172147 AFDGID Area Forecast Discussion National Weather Service Hastings NE 447 PM CDT Fri May 17 2024 .KEY MESSAGES... - Although a rogue, high-based shower or a few passing sprinkles cannot be totally ruled out in VERY limited spots late this afternoon into Sat AM, for sure the vast majority of our coverage area (CWA) will stay dry/storm-free until late Sat night-early AM. - Particularly late Sat night through Tues, we enter a very unsettled pattern with several chances for showers/thunderstorms, some of which will likely be severe...particularly Sunday-Monday...although we want to make it very clear that DETAILS ARE STILL MURKY. - Additional, intermittent shower/thunderstorm chances exist Wed-Fri, but overall these chances appear to be less widespread/spotty than Sun-Tues, and with an overall-lower severe risk (especially Wed). - Temperature-wise: certainly nothing out of the ordinary by mid-late May standards, with highs most days somewhere between the upper 60s-low 80s, and lows most nights somewhere between the upper 40s-low 60s. && .DISCUSSION... Issued at 445 PM CDT Fri May 17 2024 -- PRIMARY CHANGES TO THIS 7-DAY FORECAST PACKAGE VERSUS THE PREVIOUS ONE ISSUED FRI AM: Nothing major of note, but at least in the shorter term: - nudged up winds (mainly gusts) a few MPH mainly for Sat AM behind the cold front (gusts around 30 MPH likely for at least a few hours). - Delayed any mentionable (15+ percent) chances for thunderstorms Saturday night to AFTER midnight based on consensus of most models (including HREF) -- 7-DAY FORECAST OVERVIEW/HIGHLIGHTS (heavily focused on the first 3 days): - CURRENT/RECENT WEATHER SCENE AS OF 4 PM: Overall, today has turned out very much as expected. Although this will indeed likely end up being the warmest day most places will see for at least the next week, if anything official highs are on track to fall JUST short of this forecaster`s expectations from this morning in some spots, with most places likely topping out 85-89, and a few places mainly in our far western counties most favored to tag 90. As expected, it`s been a very breezy to somewhat-windy day, with southerly speeds commonly sustained 15-25 MPH/gusts 25-35 MPH (overall stronger in Nebraska zones than KS). Skies have been very sunny, except for a smattering of high-based cumulus along a weak surface trough axis in our far western counties. In the big picture aloft, water vapor satellite and short term model data confirm rather benign west-northwesterly flow aloft, as we are well downstream from a vigorous shortwave trough churning eastward across western MT. - LATE THIS AFTERNOON-OVERNIGHT: This forecaster is "100% confident that at least 98% of our CWA remains void of rain"...especially of the measurable variety. That being said, there is a very low chance (probably 5-10%) that a rogue/high-based shower/non-severe thunderstorm MIGHT try popping up mainly in our extreme northern zones between 5-9 PM (corresponding to just after peak heating). However forcing is meager and the best lower-level convergence looks to focus up closer to the SD border, so have left our official forecast dry/storm-free for now. Otherwise tonight, aloft the aforementioned MT disturbance will drive east into ND by sunrise. Our area will remain plenty far south/removed from this for any truly active weather, but at the very least a batch of mid-level clouds will drift in from the west, with an outside chance that a few very late night-early AM sprinkles could also try falling. However, with any such activity so high-based and meager in nature, felt it was not "ruining" our going dry forecast for. At the surface, the vast majority of the night will feature continued steady southerly breezes, with sustained speeds staying up 10-15+ MPH. However, toward sunrise the leading edges of a cold front will enter far northern/western zones, turning direction northwesterly. Low temps tonight will hold up at least 3-8 degrees warmer than last night most areas, with most places aimed 58-62. - SATURDAY DAYTIME-EVENING (through midnight): Unless some rogue sprinkles do indeed graze our southeast zones between sunrise and mid-morning, this should remain a dry time frame with departing mid level clouds giving way to abundant sunshine. By far the main feature will be a period of breezy to moderately-windy conditions behind the passing cold front, with the leading edges of this front through all but our far southeast counties by 10 AM, and through all areas by Noon. In the wake of the front, north winds will be sustained at least 15-20 MPH/gust 25-30 MPH for at least a few hours. However, speeds will steadily diminish in the afternoon while slowly turning more northeasterly, making for what will honestly be another rather pleasant mid-late afternoon time frame. Temp- wise, this front is rather weak, and while most areas will be 5-10 degrees cooler than today, highs are still aimed into the upper 70s-low 80s in our Nebraska zones, and low-mid 80s KS. During the late afternoon-evening, some storms (possibly strong) could try to fire along the cold front to our south- southeast, but any such activity should remain 50+ miles south- southeast of our domain. - LATE SAT NIGHT-SUNDAY MORNING: This is where things abruptly turn more active. As the first in a series of low amplitude disturbances arrives in west-southwest flow aloft, low level moisture will return northward as a southerly low-level jet ramps up. Confidence is fairly high that at least scattered (if not more widespread) thunderstorms will blossom between midnight and sunrise, and track from west to east across parts of our area, although exact north vs. south placement is somewhat in question. While this activity should be elevated, enough elevated instability/CAPE and sufficient shear should exist to promote a few strong to marginally-severe storm, mainly with a hail (to around quarter size) and brief heavy rain threat (damaging winds less likely given time of day). The majority of this activity should "clear" our eastern zones by mid-late Sunday morning. - SUNDAY AFTERNOON-EVENING: This is where A LOT OF QUESTION MARKS BEGIN. The real million dollar question is: will our airmass destabilize sufficiently to to realize potentially robust late afternoon-evening storm development (which if so could easily be severe), or will the morning activity and or also lingering cloud cover really hold down instability and "mute" our severe threat? These things are yet to be pinned down, but for what it`s worth the latest 18Z NAMNest would target our KS zones more so than our Neb zones for a severe threat. The bottom line: nearly our entire CWA is under a Slight Risk (level 2 of 5) from SPC for good reason, with perhaps both a morning and late afternoon-severe threat on the table. In other departments, for some of the same reasons above (possible lingering clouds), confidence in high temps for Sunday is not overly-high, and if anything have nudged most placed down slightly, now aimed mainly upper 70s to around 80 in Neb, and better odds for widespread 80s in KS. - MONDAY-MONDAY NIGHT: As if Sunday doesn`t still hold enough uncertainty regarding a severe threat, the uncertainty only grows for Monday. Sticking to only GENERAL model trends, it appears much of the daytime hours could be fairly quiet/dry as we reside "in between" the parade of low amplitude upper waves, but with the evening- overnight hours holding another uptick in convection and possible severe potential. That being said, it is starting to look like most of our CWA (except may KS zones) will likely remain north of the main west-east frontal boundary and resultant highest instability (especially low-level instability), which could also mute our severe threat somewhat here (although large hail/heavy rain north of the boundary could still be very well on the table). A lot to sort out here, but cannot disagree with the SPC Day 4 severe risk area for now. - TUESDAY-WEDNESDAY: While fairly widespread rain and mainly weaker thunderstorm activity could linger into especially Tues daytime, the general expectation per latest ECMWF/GFS is that MOST of this time frame will be overall-drier and less active as instability gets shunted south. In fact, Wed looks to be the overall-coolest day of the week with highs only upper 60s-low 70s most areas, and also the least likely day of the week to carry a severe storm threat (as supported by CSU Machine Learning progs). - THURSDAY-FRIDAY: By this time, primary models start to diverge even on the bigger picture aloft, with the latest ECMWF a bit faster than GFS bringing in another wave around Thurs night-Fri. For now, our forecast simply continues to carry various, low-confidence chances in intermittent showers/storms. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1259 PM CDT Fri May 17 2024 - General overview for KGRI/KEAR: Very high confidence in VFR ceiling/visibility throughout, and high confidence in dry/thunderstorm-free conditions. That clearly leaves winds as the primary aviation concern, as not only will this period feature a pronounced frontal passage and directional change (with moderately-windy conditions both ahead and behind it), but also several hours of moderately-strong low level wind shear (LLWS) overnight into early Sat AM. - Ceiling/visibility/precipitation details: Although a few-to-scattered clouds mainly at-or-above 8K ft. are likely at times, confidence is high in VFR conditions. As for precipitation/thunderstorm potential, have left out any formal inclusion, but that being said, there is the slightest chance (only 5-10%) of a rogue, high-based shower passing through late this afternoon and perhaps a sprinkle sometime early Saturday morning. - Winds: Surface winds: The overall-strongest winds of the period will focus this afternoon into early this evening, and then again late in the period behind a passing cold front. This afternoon into early evening, southerly speeds will be sustained mainly 15-20KT/gusts 25-30KT. Overnight, speeds will gradually relax ahead of the approaching cold front. Although not reflected in current TAFs (too far out in time to include such detail), there will probably be a 2-3 hour period (probably centered 10-13Z) with a fairly light speed/perhaps variable direction. Then, around 13-14Z, the main frontal passage will occur, with north winds quickly ramping up sustained around 20KT/gusts 25+KT. - Low level wind shear (LLWS): Have attempted to add some greater detail here, as now have two LLWS groups to the overnight period to account for a directional shift in the low level jet. First, from mainly 04-08Z, winds within the lowest 1,500 ft. AGL will ramp up to around 45KT out of the south-southwest. Then, from 08Z-11Z KEAR/08-12Z KGRI, have introduced a separate group to account for a more "true" southwesterly (possibly even west-southwesterly) directional component. During this entire time, however, shear magnitude between the surface and this level will be moderately-strong at 30-35KT. Any notable LLWS concerns will abate once the cold front arrives. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ DISCUSSION...Pfannkuch AVIATION...Pfannkuch