129 FXUS63 KLBF 291138 AFDLBF Area Forecast Discussion National Weather Service North Platte NE 638 AM CDT Thu Aug 29 2019 .SHORT TERM...(Today through Friday) Issued at 355 AM CDT Thu Aug 29 2019 Main concerns in the forecast period continue to be the threat for strong to severe thunderstorms this afternoon and evening. The Central Plains finds itself in general northwest flow as modest ridging is occurring across the west and a large-scale trough sits across southeast Canada, stretching down along the Appalachian Mountains. Surface analysis depicts a cool front dropping south and east through South Dakota early this morning. This feature is associated with a clipper-like system diving southeast out of the Canadian prairies into the upper Midwest and Great Lakes region later this morning. Satellite imagery shows little cloud-cover associated with this boundary and the expectation is for it to move into the local area later this morning, splitting the area by midday. No precipitation is expected as moisture is scant and temperatures between h85-h7 are running warm which should keep the area capped and quiet. With morning frontal passage, areas generally north of Highway 2 will see winds turn to the northeast quickly which will help usher in cooler and drier air. Expect highs to hold onto the upper 70s with breezy northeast winds. South of this boundary will see east to southeasterly winds which will help to push in more moisture and set the stage for the threat of strong to severe thunderstorms. Highs will once again push well into the 80s for a few locations south of Highway 23 making a run at 90. Surface front will slow enough this afternoon to allow areas ahead to develop strong instability as temperatures climb and dew points approach the upper 60s to near 70. Highest confidence continues to be for areas south of Interstate 80 to see strong to severe thunderstorms develop as MLCAPE values look to exceed 3000 j/kg according to the NAM. Expect storm development to occur in the vicinity of the triple point around the 21-23z timeframe across southwest Nebraska as a mid-level short wave moves in from Wyoming. Mid-level flow will remain fairly strong with h5 winds in the 25 to 35 knot range leading to deep layer shear values sufficient for multicell clusters. Discrete development and briefly supercellular structure may be possible for the first hour or two after initiation, however, shear vectors are largely parallel to the firing boundary and so storms should grow upscale quickly. Mid-level lapse rates will be steep, on the order of 7.5-8.5 C/km, leading to the threat of large hail, especially if storms can remain discrete. Point soundings show inverted-v profiles with large DCAPE and delta theta-e values, leading to the additional threat of damaging wind gusts. Believe as storms merge together, the main threat will transition to mainly wind gusts before activity exits the area. Believe there to be a threat for localized heavy rainfall as well, but the combination of frontal motion and storm motions will keep storms from sitting over any one location too long before thunderstorms clear the area by late tonight. Winds will turn to the east for late tonight as the frontal boundary shifts farther south into Kansas. Skies will begin mostly clear before cloud cover increases late in the overnight. Temperatures will fall in the upper 50s south of Interstate 80 to low to mid 50s for points north. Precipitation chances return to the area after midday Friday as the next mid-level shortwave moves overhead, sparking scattered rain and thunderstorms during the afternoon. Instability will be greatly limited as cloud cover will remain heavy and moisture quality reduced. SPC covers the western tier of counties with a Marginal Risk in their DY2 SWO. Think any threat for a strong storm will be low and largely tied to the developing low- level jet. Shear will again be sufficient, but instability greatly limited so thinking any potential for a strong storm to be quite low and very isolated if it occurs. Highs on Friday will be much cooler than Thursday with values generally in the upper 60s to low 70s. Rain and thunderstorm chances increase for the overnight Friday into Saturday owing to the aforementioned low-level jet and additional shortwaves moving into the area. Timing appears to favor after midnight for arrival and after coordination with neighbors, have lowered PoPs for the evening. Cloud cover will remain in place, however, leading to mostly dry but dreary conditions for Friday night activities. Given the cloudier conditions expected, lows will remain in the 50s to near 60 for all across much of western Nebraska. .LONG TERM...(Friday night through Wednesday) Issued at 355 AM CDT Thu Aug 29 2019 Beginning 12z Saturday. Dry conditions look to return to the area by Saturday afternoon as the h5 trough axis clears the area to the east. Moisture isn't likely to be diminished much, leaving dew point values in the 60s as highs only climb into the 70s under mostly cloudy skies. Clouds will eventually begin to clear for the evening leading to pleasant conditions. Some signs, most notably from the NAM, point towards the development of isolated showers Saturday evening as another low-level jet noses into the local area. This prediction doesn't have much backing as the GFS, ECMWF, and SREF guidance focus the low-level jet elsewhere and keep the period dry so will hedge towards the consensus for now. Upper-level ridging is still expected to strengthen across the Four Corners region for the start of next week. With height rises signifying mid-level warming and the lack of any appreciable shortwave in the area, confidence is fairly high that we should see at least a couple days of dry weather for Sunday, Monday, and possibly most of Tuesday. Attention turns to the evolution of both the approaching Pacific Northwest trough. The GFS had been the outlier regarding the Pac NW trough, but has now come into better agreement with the ECMWF which phases the system back into the upper- level flow on Monday and carries the remnants east across the northern Rockies. Temporal and spatial discrepancies remain for when the remnants of this system eject onto the plains. The ECMWF favors further north while the GFS targets South Dakota into northern Nebraska. This will play a big role in precipitation chances for mid- week and beyond so stay tuned. The Four Corners ridge will slowly drift east over the southern plains towards mid-week and will keep the local area under its influence through the extended outlook. This will keep the area in relatively zonal to slightly northwest flow aloft with warmer temperatures to the southwest and cooler to the northeast. Quick moving systems may dart across the local area but the threat of any significant system impacting the area appears low for the time being with temperatures running closer to normal. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) Issued at 618 AM CDT Thu Aug 29 2019 Latest satellite imagery and surface obs show clear skies overhead though a few obs have reported restrictions to visibility attributable to widely patchy fog (KTIF, KOGA, and KONL). The risk for patchy fog will continue into early morning across parts of western NEB, especially across climo-prone and low-lying areas. Thinking restrictions will be primarily MVFR and short-lived in nature. Otherwise, concerns turn to thunderstorms late this afternoon into evening with main threat along and south of the I-80 corridor with isolated to widely scattered thunderstorms possible. Possible impacts at KLBF so continued mention but confidence remains low given uncertainty in coverage and initiation there thus the PROB30. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Jurgensen LONG TERM...Jurgensen AVIATION...ET