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Area Forecast Discussion
Issued by NWS North Platte, NE
Issued by NWS North Platte, NE
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662 FXUS63 KLBF 172050 AFDLBF Area Forecast Discussion National Weather Service North Platte NE 350 PM CDT Fri May 17 2024 .KEY MESSAGES... - Fairly warm and dry to begin the weekend, then storms overspread the area late Saturday and persist through at least Tuesday - Severe weather possible Sunday (hail and wind main threats), then significant rainfall possible Monday into Tuesday - Relatively big cooldown for Tuesday before temperatures rebound to seasonable levels for the rest of the week && .SYNOPSIS... Issued at 349 PM CDT Fri May 17 2024 Quasi-zonal flow aloft is the regime for Nebraska today as an upper low swings through the southern Plains and a more significant trough digs into the Inland Northwest. At the surface, a low centered near the MT/ND border pulls not only a cold front back toward the Great Basin but also a subtle trough down the Hwy 83 corridor. Somewhat gusty southerly winds exist in central Nebraska this afternoon and slightly warmer breezy west winds in the panhandle and western Sandhills. Some of the warmest air of the season (outside a short spell in mid-April) is the story for today as highs approach 90 across the area. && .SHORT TERM /THROUGH SATURDAY NIGHT/... Issued at 349 PM CDT Fri May 17 2024 This evening into tonight... The aforementioned cool front quickly drops south through the Plains, approaching our northern border by 06z and nearly exits our south/east borders by 12z. Introduced a schc PoP (<20%) for the northwest half of the CWA, roughly OGA-ANW and points west with its passage. A potent mid-level shortwave accompanies the surface front, adding to the deep layer forcing. Low level moisture will be the main limiting factor, partly told by afternoon dew point depressions around 40F. A ribbon of moisture at H5-7 and the strong forcing may be able to overcome the dry layer in spots. Used the more aggressive CAMS solutions (mainly HRRR) for coverage and timing should isolated showers develop. Otherwise, most of the CWA should experience a rapid wind shift to northwesterly overnight and newly arriving cool air, especially in the panhandle. Forecast min temps range from mid 40s near the Pine Ridge to around 50 along Hwy 83 to mid 50s central Neb. Tomorrow and tomorrow night... The Dakotas take the brunt of the northern US trough, keeping Nebraska in quasi-zonal flow aloft. Toward the surface, high pressure briefly settles into the Sandhills in the wake of the cool front. Northerly low level flow starts the day, then transitions to south/southeasterly return flow by sunset. Notable cold air advection occurs at H85 with 24 hr temp changes of around -8C. With forecast sounding suggesting a mixed layer to H7, max temps should generally range in the 70s across the area (lower to the north, upper south). Depending on the timing of the returning south winds and continued sunshine, the western and southern portions of the CWA may be a tad cool. The higher end of the NBM envelope (75%ile) suggests lower 80s. Going into the evening, and especially nighttime hours, low level moisture advection kicks into high gear. Dew points in the 30s are replaced by the 40s and even lower 50s (far south). Strong isentropic upglide is noted around 300- 305K, corresponding with a warm front lifting north. Scattered showers and storms should develop in the southern panhandle or northeast CO after sunset and spread into the Sandhills overnight. The increasing cloud cover and persistent south/southeast winds should hold min temps in the lower/mid 50s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Issued at 349 PM CDT Fri May 17 2024 The active synoptic pattern for next week is still on track with one large upper trough is quickly replaced by another. Details for Sunday have grown a bit fuzzier regarding the severe potential for western Nebraska, seeming to shift away from a greater tornado threat to more of hail and wind. Convective mode and location may be messy due to existing morning precip as well. A couple trains of thought... a more pessimistic route involving increased cloud cover through midday and stabilization, or breaks of sunshine later on to help redevelopment along several little boundaries. Overall, still think the risk of severe exists even with quite a large spread in parameters or precip coverage in model guidance. Forecast soundings suggest drier air in the low levels Sunday afternoon, showing more of an inverted-V profile at times, versus more of a loaded gun with yesterday`s guidance. Deep layer shear appears slightly weaker overall, but veering still occurs in the first 3km, encouraging supercells at onset. The mid/upper levels grow more unidirectional and hodographs take on a longer profile at 6+ km, which is more indicative of large hail. Abundant CAPE, including in the hail growth zone, still appears likely east of Hwy 83, along with very steep mid-level lapse rates of 8+ C/km. A cool front Sunday night clears out whatever convection occurs, also leaving a lull in action early Monday. The next wave of precip arrives later Monday and continues into Tuesday as the Western US upper trough digs further into the Four Corners. A deep surface low cuts up the central Plains while broad southwesterly flow aloft is supported by a stout H3 jet. This wave does not appear as conducive for severe storms (for western Nebraska), as the brunt of the energy is shifted toward eastern half of the state. Deep layer shear will be plentiful with 0- 6km values of 50+ kts, but instability is limited and lapse rates go back below 7 C/km. However, the risk of heavy rainfall will need to be monitored. NAEFS ensembles suggest PWAT values around 90%ile of climo, and the NBM envelope and WPC guidance suggest widespread 1"+ amounts. Most of the activity wanes on Tuesday, but low end chances continue through the end of the week. As for temps, highs begin to take a hit on Monday in the northwest and Tuesday for everywhere, when forecast values range form mid 50s (northwest) to around 70F (far south). Milder air arrives again Wednesday as low level flow transitions to southerly and helps push highs into the 70s. The risk of frost appears low at this time, but will need to watch Wednesday morning as some min temps brush the upper 30s in the panhandle. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1226 PM CDT Fri May 17 2024 VFR conditions are expected to continue through tomorrow afternoon across western and north central Nebraska. Forecast soundings suggest strong mixing will be possible this afternoon and again tomorrow morning, which will lead to periods of gusty winds. Skies will remain relatively clear, though passing high clouds will be possible. Winds will shift overnight from westerly to northerly following the passage of a cold front across the region. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Snively SHORT TERM...Snively LONG TERM...Snively AVIATION...Richie