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Displaying AFOS PIL: AFDLBF Received: 2024-04-23 11:11 UTC
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540 FXUS63 KLBF 231111 AFDLBF Area Forecast Discussion National Weather Service North Platte NE 611 AM CDT Tue Apr 23 2024 .KEY MESSAGES... - Breezy at times today and again on Wednesday with isolated showers possible across portions of the area each night. - Seasonal temperatures continue through the week with highs generally in the 60s to lower 70s, trending cooler for Saturday and Sunday. - Unsettled weather conditions likely for Thursday into the weekend with multiple rounds of rain showers and thunderstorms. Widespread accumulating rain is likely (>70% chance for total rainfall of 0.50" or more) across western and north central Nebraska during this timeframe. - A Marginal Risk (1/5) for isolated strong to severe thunderstorms capable of producing large hail and severe wind gusts exists across much of the area for Thursday. The severe threat for Friday into this weekend remains uncertain at this time. && .SYNOPSIS... Issued at 400 AM CDT Tue Apr 23 2024 Recent GOES-16 WV imagery and RAP 500-mb analysis showed a deep trough of low pressure centered over the Hudson Bay with a northern stream shortwave cantered near North Dakota/Canada border, tracking southeast into the Upper Midwest and Upper Great Lakes. An upper- level low pressure system was centered over the Pacific, approximately 600 miles off the California coast. At the surface, low pressure was noted over the Upper Midwest/Great Lakes region with an attendant cold front extending southwest into the Iowa/Missouri/Nebraska/Kansas borders to another area of low pressure located over southwest Kansas. Surface high pressure across the northern Rockies was beginning to nudge into the northern Plains. The previously mentioned upper-level shortwave and convergence behind the surface cold front has provided a focus for light rain showers and isolated thunderstorms across portions of the state. The bulk of the activity occurred to the south and east of the forecast area earlier tonight with even some small hail reported over Beatrice in southeast Nebraska. While early morning radar shows some returns across portions of the local area, believe a lot of this is in the form of virga given drier air moving southward. Any rain that is reaching the ground will be very light and quick hitting through around sunrise. && .SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 400 AM CDT Tue Apr 23 2024 Today and Tonight...Generally dry and quiet conditions are expected during the day today, though breezy at times due to a tightened surface pressure gradient (SPG). Northwest winds gusting 15 to 25 mph will be common for most locations with the strongest gusts up to 35 mph expected across north central Nebraska where the SPG is more compact. These breezy winds will quickly diminish heading into the evening as the SPG relaxes and surface high pressure takes hold over the area. Daytime temperatures will be a few degrees cooler than yesterday,though still in the seasonal range, generally in the 60s. An upper-level shortwave over the Idaho Panhandle/western Montana will continue southeast into portions of the northern Plains today, providing another quick-hitting chance for precipitation tonight for the southern Panhandle/southwest Nebraska. Confidence continues to remain rather low on the potential for precipitation due limited moisture and weak forcing across the area. Temperatures tonight will fall into the mid 30s to low 40s with winds veering towards the south on the backside of the departing surface high pressure. Wednesday and Wednesday Night...Upper-level ridging will build back into the central CONUS with the upper-level low continuing to deepen off the coast of California. High temperature warm back into the at to slightly above normal range in the mid 60s to lower 70s. The SPG will tighten again between developing surface low pressure systems to the west and strong surface high pressure holding strong over the Great Lakes and Mississippi Valley. South-southeasterly winds will strengthen during the day as a result with wind gusts of 15 to 25 mph for most locations, though the strongest gusts up to 35 mph will be felt for areas west of Highway 83. As the upper-level trough begins to move further inland across southern California Wednesday afternoon/evening, lee-cyclogenesis will begin to organize across far southeast Colorado, driven by mid-level height falls and upper- level divergence under the left exit region of the 250mb jet streak. At the same time, a weak leading shortwave will eject eastward out of the central Rockies into the area, with a strong (40kts+) southerly low-level jet (LLJ) ramping up over the northern Plains. Not only will the LLJ support continued breezy winds through the night, it will also provide a focus for another round of isolated to scattered precipitation chances early Wednesday evening into the overnight as warm air and moisture begins to advect across the area. Not much in the way of moisture return quite yet with dew points generally in the 40s, lowering overall forecaster confidence on precipitation during this period. && .LONG TERM /THURSDAY THROUGH MONDAY/... Issued at 400 AM CDT Tue Apr 23 2024 The flow aloft will transition to southwesterly on Thursday as the the first of two upper-level trough tracks into the Four Corners region. As the southern California upper-level trough approaches the Front Range late Thursday afternoon, the lee cyclone will deepen even further across southeast Colorado, moving northeastward toward northeast Kansas and southwest Nebraska by Friday morning. Continued low-level southeasterly flow will support modest moisture return across the area, highlighted by both the NAEFS and ENS ensembles, suggesting that the mean PWAT will meet or exceed the 90th percentile. An attendant warm front will move northward across the central Plains during the day with some thunderstorm development possible near and to the cool side of the effective warm front during the afternoon/evening. While deep layer shear will be rather weak, steep mid-level lapse rates (8+ C/km) and increasing instability (MLCAPE ~500-1,500+ J/kg) will create an environment supportive of isolated thunderstorm development capable of producing large hail. A lot can change from now to Thursday, so will need to closely monitor the severe threat as we head into the near-term and details become more fine scale. With the first upper-level low moving northeast across Nebraska into Minnesota on Friday, another upper-level shortwave will develop across the Desert Southwest, pushing into the central Plains Saturday evening into Sunday. While this second system will be similar to the first, it appears the track of the surface low will be further to the south and east of us. Despite this, the system will provide another optimal shot at widespread precipitation across western and north central Nebraska. There will certainly be some breaks in the precipitation during this period, though there continues to be quite a bit of spread amongst models on exact timing of each of the individual disturbances. Although questions remain, confidence continues to grow on the potential for widespread wetting rain Thursday into the weekend. NBM Probabilities indicate an overwhelming 90% chance or greater for 72 hour 0.25"+ liquid equivalent precipitation across all of western and north central Nebraska. When looking at the potential for 1.0"+, probabilities become a lot more sporadic, though generally a 30 to 60% chance exists across the area. When looking at the ECMWF EFI (Extreme Forecast Index), it has begun to suggest increased confidence of an anomalous event on Friday into Saturday, such that the SoT (Shift of Tails) is greater than 0 across portions of the Panhandle into the Sandhills. While the severe threat remains uncertain beyond Thursday, thunderstorms are entirely possible which would result in locally higher rain rates and amounts. Precipitation will begin to taper off late Sunday as the second system continues northeastward into the Upper Midwest. Ensemble and deterministic model solutions are in general agreement that upper-level ridging will reestablish itself across the central CONUS at the beginning of next week. This will bring the return of above normal temperatures in the 70s. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 607 AM CDT Tue Apr 23 2024 VFR conditions prevail across western and north central Nebraska through the period. Winds strengthen out of the north-northwest mid-morning with widespread gusts of 20 to 30 kts. These gusty winds begin to diminish through the early evening hours, becoming light and variable overnight. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Viken SHORT TERM...Viken LONG TERM...Viken AVIATION...Viken