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Area Forecast Discussion
Issued by NWS North Platte, NE
Issued by NWS North Platte, NE
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820 FXUS63 KLBF 102117 AFDLBF Area Forecast Discussion National Weather Service North Platte NE 417 PM CDT Sat Aug 10 2024 .KEY MESSAGES... - Scattered showers and storms tonight with a marginal threat of severe weather in the panhandle due to hail and wind. - Additional thunderstorms expected tomorrow afternoon and evening, especially across the Sandhills, also with a hail and wind threat. - Virtually daily thunder chances through the week as temperatures gradually climb to near normal levels by late week. && .SYNOPSIS... Issued at 417 PM CDT Sat Aug 10 2024 Nebraska lies on the periphery of a transient upper ridge along the spine of the Rockies, while a deep closed upper low continues to spin just north of the Great Lakes. Thick cloud cover and well below normal temperatures accompany broad northwest flow aloft. Toward the surface, high pressure is centered over Kansas, which places most of the forecast area in southerly return flow. A low near the Laramie Range extends a weak trough across the northern Sandhills and a quasi-warm front south along the lee of the CO Rockies. Temperatures as of 20z range from the lower 60s in the Platte River Valley to around 70F along the SoDak border. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 417 PM CDT Sat Aug 10 2024 This evening into tonight... A fairly substantial mid-level shortwave begins to enter northwest Neb, while the surface trough lifts north into So.Dak and the main front reaches the Neb. panhandle. Despite the strong forcing aloft, the bulk of the surface driven lift will be focused away from the heart of the forecast area. Isentropic analysis also reflects this, with the steepest gradients occurring either north of the state line or above 305K. South/southeast near surface winds will help keep dew points steady in the mid to upper 50s, but overall moisture advection appears negligible. Confidence is not the greatest in widespread or organized activity, but CAMS still suggest scattered showers and storms coming in a couple different waves. One would be existing activity from Wyoming and Colorado during the late evening, then perhaps new development overnight closer to the area. Overall, limited PoP to 40% throughout the night to message the scattered coverage and conditionality of the event. As for the current convection to the west that may enter the panhandle, a minor wind and hail threat exists. Instability is weak overall, however an axis of slightly greater MUCAPE values of 500+ j/kg stretches along Hwy 61. Deep layer shear is the main component as values reach 50 kts. For min temps, stayed near the NBM mean. Strengthening southerly flow at H85 helps lead to modest warm air advection, and generous low cloud cover should limit boundary layer decoupling. Forecast values range from mid to upper 50s. Tomorrow... An active day could be on tap for western Nebraska as a few synoptic features come together over the region. The aforementioned mid-level shortwave crosses the Sandhills, following the tail of a local H3 jet maximum. The surface low pushes toward the NE/KS/CO border and extends the front through the heart of the forecast area. A few items are at play, which would determine the overall thunderstorm (and severe) threat. Any lingering rain showers from overnight could be moving through north central Neb until midday. The accompanying stratus deck may be pretty thick and only slowly erode to the Hwy 61 corridor by mid-afternoon. These factors would likely lead to another very mild day, especially east of Hwy 83 where forecast highs reflect the 25%ile of NBM, equating to lower/mid 70s. Instability will be limited once again for areas east of Hwy 83 with MUCAPE values generally held to 500 j/kg, perhaps 1000. However, farther west toward Hwy 61, additional clearing and a big warmup to around 80F closer to the surface low will create a steep gradient of convective parameters. A ribbon of greater instability in the form of 2000 j/kg MUCAPE and 7-8 C/km mid-level lapse rates will complement strong deep layer shear around 50 kts. CAMS seem to support a couple focus areas for thunderstorm development, with one being in So.Dak north of the warm front and more aligned with the upper forcing, and one being directed toward Kansas ahead of the surface low. Most of the activity in our CWA will likely be derived from the northern setup. Forecast soundings suggest the bulk of the CAPE east of Hwy 83 occurring above H7, but plenty of low level veering. Initial storm mode may very well be supercellular before cold pooling takes over and storms evolve into clusters or perhaps a QLCS. Agree with the sentiment of MRGL risk by SPC, but would not be surprised to see an upgrade to SLGT north of Hwy 2 should later model trends point toward greater instability. The threat of severe wind and hail certainly exist, but may be more of a widespread low-end event more than a localized significant severe threat. Most guidance pinpoints mid-afternoon (~21z) for far northern Neb between GRN and VTN, early evening (~00z) from ANW to BBW, and mostly exiting to the east by 03z or so. && .LONG TERM /MONDAY THROUGH SATURDAY/... Issued at 417 PM CDT Sat Aug 10 2024 The subtle upper ridge over the Western US shifts east onto the Plains and builds midweek, with the axis bisecting the Sandhills on Tuesday. The pattern turns progressive later in the week as a trough pushes through on Thursday and then a more amplified ridge building into the weekend. Nearby surface features also promote periodic precipitation chances, especially the first half of the week. Southwest Nebraska may receive a couple more rounds of wetting rain Monday and Tuesday as storms originating from upslope flow spread east off the mountains. As for temperatures, they should finally warm up with the help of the upper ridge and breaks in cloud cover. Guidance continues to support a gradual rise from 70s to 80s over the next few days and potentially reaching 90F on Wednesday. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1242 PM CDT Sat Aug 10 2024 Stratus continues to be present across western and north central Nebraska. Model guidance is struggling to catch on to the redevelopment of lower ceilings, which is being observed on satellite. Tended to the more aggressive solutions on ceilings, as MVFR to VFR conditions persist this afternoon and evening. Overnight ceilings should remain VFR, with a drop to IFR and LIFR ceilings along and south of Highway 2 tomorrow morning. As thunderstorms track in from the west this evening and overnight, they are expected to weaken and bring periods of showers around both terminals. Though the winds are expected to remain fairly light, decaying thunderstorms and showers may introduce some briefly erratic winds. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Snively SHORT TERM...Snively LONG TERM...Snively AVIATION...Richie