Sunrise 6:14 AM   Sunset 8:51 PM Moonrise 3:18 PM   Moonset 2:58 AM

  Print   HELP   Reset   Save   Recall  New

FXUS63 KGID 181913 AFDGID

Area Forecast Discussion National Weather Service Hastings NE 213 PM CDT Sat May 18 2024

KEY MESSAGES

- Scattered showers and thunderstorms move in late tonight and continue into Sun AM. Most likely non-severe, but small hail and gusty winds will be possible in strongest cores.

- Off and on thunderstorms are expected Sun PM through Tue, some of which could be strong to severe and pose risks for all severe hazards. However, confidence on details is only low to medium as each round will have significant impact on subsequent rounds' severity, timing, and placement.

- Cold front sweeps through the area and brings somewhat cooler and less active weather for Tue night into Thu.

- Temperatures most days will peak in the 70s-80s, though mainly mid 60s-70s are expected Tue-Wed. Lows will be mainly 50s- 60s, except for cooler 40s Tue/Wed nights.

DISCUSSION
Issued at 208 PM CDT Sat May 18 2024

Expect increasingly pleasant conditions late this aftn and into the evening as wind speeds gradually decr and temps remain mild. Short term CAMs are in pretty good agreement that elevated convection will develop over the central High Plains 03-06Z as 45kt LLJ noses into the region, then shift E/NE into our area 06-09Z. Peak MUCAPE will increase to around 1500-2000 J/kg for parcels lifted from H7-H8 amidst steep mid level lapse rates. However, the bulk of the veering in the wind profile is below the MUCAPE layer, so effective shear is rather marginal at mainly 25-30kt. This could yield some "pulsey" elevated hailers, generally of the low-end variety (penny to half dollar size), and perhaps some gusty winds around 40-50 MPH. Recent HRRR runs and HRRR seem to focus the majority of the activity along and S of the Platte River, which is a bit of southward shift from where previous forecast placed the highest PoPs. Seems probable (60- 70%) that at least scattered activity will persist into the mid to late AM hrs Sunday as the LLJ slowly veers and weakens, though the lingering activity will probably have a lesser hail risk.

Pattern recognition and general model guidance would suggest a dry period, or at least a lull in coverage/intensity, from around midday Sunday through AT LEAST mid aftn. Thereafter, details for additional convection become quite a bit more murky owing to uncertainties left by the earlier round, such as location of outflow boundaries, cloud cover that will affect ability to destabilize, and quality/depth of BL moisture. The overall upper pattern will feature only modest height falls, but most guidance has several weak disturbances in moderately fast SWrly mid-upper flow, and the AM round may actually help to suppress the strongest mid level capping to our S. As it stands now, there appears to be two scenarios of convective potential:

1) Seems plausible that enough recovery will occur to allow for a narrow window of sfc based development along lingering outflow boundary that will probably be located somewhere between the NE/KS border and I-70 corridor around 22Z-02Z. After that, cooling BL will probably become capped along this boundary in the absence of stronger forcing. It is a highly conditional, and probably isolated, threat...but if something does pop up, it will likely be supercellular with all modes of severe possible - including tornadoes - given tendency for backed low level flow and perhaps some pooling moisture. Worth noting, however, that forecast soundings suggest moisture quality/depth will not be great during the late aftn/early eve period and subject to mixing out - so would really need some pooling and backed flow to get low enough LCLs for tors. Greatest risk would likely be large to very large hail given very steep mid level lapse rates and bulk shear values of 40-50kt in the presence of clockwise curved hodographs, along with damaging wind gusts.

2) The other scenario - which is more probable and likely more impactful because of coverage - will be for tstms to develop along a N-S corridor along the High Plains from the NE Panhandle southward to TX/OK Panhandles within warm/hot, deeply mixed environment with little to no capping and beneath slightly stronger height falls.
This activity would have a tendency to become outflow dominate given inverted-V thermodynamic profiles and more forward propagating due straighter hodographs. Since it's developing further W, this threat would likely be a bit later, generally after 00Z, but severe will still be a risk as this activity will actually be moving into pool of greater instability, and LLJ again increases to 40-50+kt. Would tend to favor W/S zones the most, but if a mature MCV develops then local dynamical forcing could overcome incr capping after 03Z to persist the severe threat longer and further E. Heavy rain is not a concern attm given isolated/conditional nature of scenario 1, and likely progressive nature of scenario 2.

Thunderstorms remain possible into Monday, and the entire area is outlooked in either a Marginal or Slight Risk of severe weather (levels 1 and 2 on a scale of 5) on SPC Day 3 outlook. As there are uncertainties on Sun due to earlier convection, the uncertainties are even higher on Monday. In general, upper troughing still resides to the W and we'll remain in diffluent (but kinda weak) SWrly upper flow. At least one or two upper waves will likely be ejecting NE out of the broader trough, which could enhance the upper flow late in the day and moreso into Mon night. Sfc mass fields suggest a triple point over central KS, with previous outflow boundaries possibly augmenting and/or narrowing the primary instability axis to the E of this triple point and southward trailing dry line. I have a tendency to doubt we'll have much sfc-based activity in our CWA prior to sunset as mid level temps appear to be 1-2 deg warmer, though mesoscale details will be important. Would think the later arrival of upper support would favor activity moving off the High Plains after sunset and/or new development ahead of possible northward moving warm front in response to incr LLJ. This would provide more of a wind/hail threat and lesser of a tornado threat, but again, plenty of details to work out.

Trough moves through on Tuesday, and timing will be key for severe weather chances in our area. At this time, appears it will be just fast enough to keep primary risk to our E/SE, but any slowing trend and our chcs will incr. Continued cloud cover and shwr chcs behind departing system amidst NWrly low level flow will likely keep temps considerably colder in the 60s, esp N/W of the Tri-Cities. Flow turns more zonal late in the week and into the start of the holiday weekend, which should support seasonable temperatures and off and on pcpn chances.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
Issued at 1248 PM CDT Sat May 18 2024

Significant weather: Elevated thunderstorms possible late tonight.

Rest of today and into the evening will be SKC with gradually decr wind speeds/gusts. In fact, by ~22Z expect sustained winds only 7-11kt with no more gusts. Direction will gradually veer from N to NE/ENE this evening. Confidence: High.

Mid to high clds will increase towards 06Z as elevated shwrs and tstms approach from the SW. Have introduced VCTS 08-09Z and seems like model guidance is in good enough agreement to go with a few hrs of prevailing -TSRA in the 10-14Z time frame. This activity probably won't be severe, but can't rule out some small hail and gusty winds. This activity should weaken and shift E/SE by mid to late AM as overall pcpn chcs decr to 20-40%. Should remain VFR tonight thru Sun AM (outside of brief reductions in VSBYs in heaviest rn) with most CIGs above 5-8k ft. Winds will turn SErly around dawn and bec brzy late AM into the aftn.
Confidence: Medium.

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

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

Grand Island, NE,