Sunrise 6:34 AM   Sunset 8:27 PM Moonrise 11:48 PM   Moonset 7:32 AM

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FXUS63 KGID 270621 AFDGID

Area Forecast Discussion National Weather Service Hastings NE 121 AM CDT Sat Apr 27 2024

Aviation Update

KEY MESSAGES

- Ongoing lingering shower/storm activity will continue into the early-mid evening hours, but is expected to end for most areas by midnight, with the rest of the overnight hours dry.

- The break from thunderstorm chances is short-lived, with the next round expected to develop mid-afternoon Saturday along an northward pushing warm front. Large hail/damaging winds are the main threat, but cannot rule out the threat for tornadoes.

- The next main upper low moves through the area on Sunday, keeping precipitation chances in the forecast. While the SPC Day 3 risk areas are currently focused east of the forecast area, any slowdown of the system and accompanying surface boundaries would bring that risk back west into our area.

DISCUSSION
Issued at 510 PM CDT Fri Apr 26 2024

Currently through tonight...

Been a very busy day today, mainly from late morning on through mid-afternoon, as a strong low pressure system sliding east through the Central Plains drove the development of thunderstorms along a northward arcing warm front. The strongest storms extended from northern Buffalo County northeastward into Greeley County, and a few tornadoes did touch down. Damage survey is ongoing and will continue into tomorrow. Late this afternoon, the main focusing surface features have shifted just to the east of the forecast area, but scattered thunderstorms continue as the upper low continues to cross the region. Can't rule out some of these storms being on the strong side through this evening, but better instability/shear parameters are also focused east, so additional severe weather is not anticipated.

Activity is expected to wane in coverage/intensity as we get further into the evening hours, with models in pretty good agreement drying things out after midnight. At the surface, expecting winds to also taper off, as the pattern influence transitions from the departing low to the east and another gradually deepening to our southwest. Overnight lows tonight are expected to drop into the 40s.

Saturday and Sunday...

Unfortunately, the break from thunderstorm chances coming in tonight is a short-lived one, lasting only into the morning and early morning hours on Saturday. At 12Z Saturday, models show the forecast area sitting under upper level shortwave ridging, set up between the system driving today's weather (which will have moved into the western Great Lakes/MN area) and the next low pressure system, which is expected to be in the Four Corners region. Also start of the day between areas of surface low pressure, keeping winds on the lighter side. Through the day, the main upper low sill continue pushing east, ending up over eastern CO by early evening. In response to this next approaching upper low, surface low pressure is expected to deepen over southeastern CO, resulting in a strengthening of the eastward extending warm front...which by midday models show being anywhere from across our southern forecast area counties to closer to I-70. Through the afternoon hours, this warm front is expected to lift north...with some uncertainty with just how far north it gets by mid-late afternoon, but could be roughly along the NE/KS state line. Today's system isn't bringing a strong cold front through the area to 'clean things out' (instability/dewpoints) for Saturday...current dewpoints are still mid-50s for much of the area, so areas especially along/south of that warm front will have sufficient instability to work with, and deeper layer shear remains strong...so severe weather will again be a concern. The southeastern 1/3rd of the forecast area is included in the SPC Day 2 Enhanced Risk, with the Slight Risk northward roughly to a Arapahoe-Osceola line.
All modes of severe weather will be a concern, mainly from mid- afternoon through the evening hours.

Shower/thunderstorm chances continue on into Sunday, as the main upper level low looks to push northeast...models showing the general path going through eastern CO/western KS/western NE.
The current SPC Day 3 risk areas are just off to the east of the forecast area...but similar to today's system, we'll be at the mercy of the timing of the upper low and accompanying surface features. Any slow down and strong/severe storm concern will increase.

Monday and beyond...

Honestly, spent little time on this time frame. Dry conditions are expected to settle in late Sunday night into Monday, as we sit in the wake of this weekend system. Further into the work week, models showing an overall zonal pattern with periodic shortwave disturbances, so precipitation chances return Tuesday- Thursday. Forecast highs through the new work week are in the 60s-70s.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
Issued at 120 AM CDT Sat Apr 27 2024

- General overview for KGRI/KEAR: While there is high confidence in VFR conditions through at least the first 6-9 hours and high confidence in dry/thunderstorm-free weather through at least the first 15 hours, anything beyond those respective timeframes brings increasing chances for sub-VFR ceiling and thunderstorms. Aside from any possible thunderstorm-related enhancement, winds will not be a major issue, although gusts around 25+KT will be likely by later in the period especially Saturday evening.

- Ceiling/visibility/precipitation (thunderstorm) details: Starting with ceiling trends: confidence in VFR and mainly clear skies these first 6-9 hours, although a few fleeting patches of MVFR stratus could pass through. However, already by as early as 15-18Z chances for MVFR ceiling will start to increase, but just how quickly this happens is still in question. For now, have introduced scattered MVFR mention at 15Z, but do not indicate prevailing MVFR ceiling until 18Z (stay tuned for adjustments here). Once showers/thunderstorms arrive by late afternoon/early evening, in theory there should be a better chance of a more solid/persistent MVFR ceiling (perhaps even IFR at some point?), but have seen many instances where convective activity keeps the low levels "mixy" and at least delays onset of sub-VFR ceiling.
Again something to watch.

Shower/thunderstorm trends (strong storm potential): Other than maybe a few rogue sprinkles before then, confidence is high in dry/thunderstorm-free weather until roughly 23Z. From that point onward, fairly widespread thunderstorm activity could persist at least in the general area through the remainder of the period. Although KGRI/KEAR will reside slightly north of the main severe storm threat area, storms could easily pose at least a small hail/gusty wind threat. Given these convective chances are still well beyond the first 12 hours, have simply maintained a generic "vicinity thunderstorm" VCTS for now.

- Wind details (not accounting for possible convective influences late in the period): The very lightest winds of the period (mainly at-or-below 10KT)
will occur these first 6-9 hours as direction shifts from westerly to northerly. Then, during the daytime hours and into the evening, winds will gradually increase out of the northeast, with sustained speeds commonly 15-20KT/gusts around 25+KT.

GID WATCHES/WARNINGS/ADVISORIES
NE...None.
KS...None.

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