Area Forecast Discussion
Issued by NWS North Platte, NE
Issued by NWS North Platte, NE
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630 FXUS63 KLBF 230557 AFDLBF Area Forecast Discussion National Weather Service North Platte NE 1257 AM CDT Thu May 23 2024 .KEY MESSAGES... - A strong cool front will dive into the area Thursday and bring the threat for severe thunderstorms, locally heavy rain, and strong winds behind it late Thursday afternoon into Thursday night. - Thunderstorms chances increase Saturday afternoon through Sunday during the Memorial Day holiday as temperatures range near to slightly below normal. && .SHORT TERM /THROUGH FRIDAY/... Issued at 322 PM CDT Wed May 22 2024 On Thursday, a positively tilted upper trough will move across Montana and Wyoming. Surface low pressure will deepen ahead of the upper trough to near 995mb, becoming positioned from central South Dakota through the western Sandhills into eastern Colorado. Increasing southerly winds ahead of this feature will bring dewpoints into the mid 50s and SBCAPEs to 1500-2000 J/KG as highs reach near 80, with near 85 far southwest. The focus for thunderstorms to initiate will be along the advancing cold front across the northwest Sandhills and also a distinct dryline located near Ogallala through Benkelman soon after 20Z. Ahead of the dryline, surface winds will tend to be more backed to the southeast across southwest Nebraska. Aloft, H7 to H5 lapse rates will steepen to 8.5 to 9C/KM. The location favoring discrete supercells will be near the dryline northward to the intersection of the cold front and dryline, possibly over Keith county. As surface convergence increases along the cold front and dryline, scattered thunderstorms are expected to develop by late afternoon within an environment supportive of organized severe weather given a moderately unstable environment and deep layer shear near 40kts. Coverage of thunderstorms is expected to increase significantly east of Highway 83 where PoPs increase to as high as 80-90%. The Storm Prediction Center (SPC) has a Slight Risk (Level 2 of 5) for areas east of a Crookston through Hayes Center line and an Enhanced Risk (Level 3 of 5) over central Nebraska, east of a Eustis to Arnold and Brewster line. Forecast soundings depict clockwise curving hodographs, favorable for a brief tornado by early evening. Isolated very large hail to 2 inches in diameter is also possible. As storms congeal along the advancing cold front, a severe MCS is likely to develop into central Nebraska during the evening hours. Large hail and damaging wind gusts up to 80 mph may occur. With the progressive nature of the frontal boundary, expect the main line of storms to exit southeastern zones by 06Z. While not overly significant, rainfall amounts up to 1.25" is possible near and east of Ainsworth through Broken Bow. With recent rainfall, this may present at least a localized flooding risk. Winds behind the cold front may gust up to 35 mph Thursday night, as 3 hr pressure rises reach up to 6 to 9mb. Lows fall to the upper 30s to mid 40s, aided by winds keeping the surface mixed. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Issued at 322 PM CDT Wed May 22 2024 On Friday, strong northwesterly winds will continue through Friday morning with gusts up to 35 mph, lessening in the afternoon. Weak cold air advection will keep afternoon highs on the cooler side from near 65 to 70. Saturday and beyond...active weather is expected Saturday afternoon through Sunday. An upper trough over the Great Basin will cross the region Saturday afternoon trough Sunday evening. This will bring another good chance for showers and thunderstorms. Highs range in the 70s Saturday and upper 60s to low 70s Sunday. The main frontal boundary during this time will be draped across southern and eastern Kansas during this time. The severe weather risk remain uncertain at this time. Northwest flow aloft Monday through Wednesday, with as slight chance for showers and a few thunderstorms Monday across north central Nebraska, then dry conditions Tuesday and Wednesday with highs warming into the upper 70s to low 80s. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1255 AM CDT Thu May 23 2024 VFR conditions expected at TAF sites through at least the first part of the TAF period, but expect significant impacts to aircraft operations from low level wind shear, gusty surface winds, and potentially severe thunderstorms. Will be dealing with significant low level wind shear across central and western Nebraska early in this TAF period as a robust low level jet becomes established. There may be enough mixing to get some gusts to the surface before daybreak, but winds aloft will generally be 45 to 50kt form the south. Once diurnal heating mixes the boundary layer after daybreak the low level jet will diminish but surface winds will become gusty with 25 to 30kt expected into the afternoon. Currently there appears to be potential for 2 separate triggers for convection, first with a dryline and then with a cold front. Any storms with the dryline will have potential to be discrete, individual cells with very large hail and strong gusty winds. As the cold front overtakes the dryline and becomes the dominant driver of convection, storms are expected to develop into a linear complex that may produce very strong winds and large hail as it moves from central into eastern Nebraska. Storm initiation may occur along or just west of Highway 83, though confidence in exact timing and locations is not high. Will use VCTS at KVTN for the 3 hour period where thunderstorms are most likely, and will use 2 separate periods for VCTS at KLBF to indicate periods of best potential for thunderstorms with the dryline followed by thunderstorms along/ahead of the approaching cold front. All convection with a return to VFR looks like a good bet by the end of the valid period as convection pushes off to the east and southeast. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Roberg LONG TERM...Roberg AVIATION...MBS