813 FXUS63 KLBF 082003 AFDLBF Area Forecast Discussion National Weather Service North Platte NE 303 PM CDT Fri Oct 8 2021 .SHORT TERM...(This evening through Saturday night) Issued at 302 PM CDT Fri Oct 8 2021 Forecast concerns focus on an increasingly active weather pattern expected to arrive next week. Details pertaining to this can be found in the Long Term discussion below. Slight chances for light rain will also exist primarily Saturday for portions of the area. Afternoon satellite analysis depicts a departing trough across the Great Lakes region with low-amplitude ridging over southern Texas. To the west, another approaching longwave trough will bring about precipitation chances and cooler weather mainly for Day 4 and beyond. For tonight, will watch as a modest low-level jet develops ahead of the next mid-level disturbance to approach the region. This will usher in warmer, more humid air into the area. This will lead to increasing cloud cover tonight and keep overnight lows in the 50s to low 60s. The previously mentioned longwave trough to the west will lead to a modest disturbance ejecting onto the Central to Northern High Plains late tonight into early Saturday. This will lead to the development of a surface low across western South Dakota which will drag a cool front into the area during the day Saturday. Modest height falls along with rather nebulous frontogenesis should be enough to allow isolated showers to develop late tonight through Saturday morning...mainly for areas along and north of Highway 20. Cannot completely rule out a few rumbles of thunder as point forecast soundings indicate some elevated instability, but thinking this will be rather limited in scope. Latest hi-res guidance are fairly aggressive in southward extent of shower activity. Am hesitant to buy into this given copious dry air in the lowest levels. That said, these frontal boundary tend to "over-produce" and so will need to monitor this potential in later forecast packages. This frontal boundary will likely split the area around midday Saturday with gusty west winds in its wake across the Sandhills and south to southwesterly winds ahead of it. Did boost temperatures slightly to account for some downsloping winds in addition to compressional warming from the advancing front. This puts the area in the 70s northwest to low 80s south and east. Depending on progression of the frontal boundary, will need to watch for redeveloping showers and thunderstorms along this feature during the afternoon and early evening. Big proponents of this potential are the RAP and HRRR with the HRRR even advertising a few more robust storms in the area. Shear would be adequate with effective bulk shear of 35 to 45 knots but instability is sorely lacking with MUCAPE values < 500 j/kg. SPC maintains a Day 2 SWO up in South Dakota and though I think it would be premature to draw this further south, this idea will need to be investigated further later on. Following fropa and an invading drier air mass, expect another cool night Saturday into early Sunday with lows falling into the low 40s west of Highway 61 to low 50s east of Highway 183. Even so, this remains nearly 10 to 15 degrees above normal low temperatures for early to middle October. Expect a breezy start to the day Sunday with northwest gusts approaching 30 to 35 mph. .LONG TERM...(Sunday through Friday) Issued at 302 PM CDT Fri Oct 8 2021 Beginning 12z Sunday. A lot to talk about in the extended forecast period with an increasingly active weather pattern setting up leading to increasing chances for precipitation and an appreciable cooldown expected towards the end of the forecast period. The period begins with a complicated upper-flow pattern. A longwave trough the was approaching the area on the day Saturday will fracture with two prominent systems emerging. The first of these will be across the Northern Plains where a strong surface low- pressure system will take shape early Sunday morning. This will track a cold front through the area bringing an appreciable cooldown to the area with highs only reaching the 60s to low 70s. Moisture availability will be rather limited with considerable dry air throughout the profile therefore little to no precipitation is expected with this. The lone advocate for precipitation early Sunday is the Euro with support from its ensemble where enough wrap around moisture may approach from the north to bring light rain showers to portions of the Sandhills. Will maintain a slight chance mention to account for this but any precipitation amounts should remain fairly light. A fairly compact surface pressure gradient with strong CAA will combine to produce gusty winds as well during this period. Peak timing of these features will limit greatest gusts to late morning and early afternoon as the gradient relaxes in latter half of the day with dry conditions expected. The second shortwave of prominence will track across the Southern Plains along the baroclinic zone in proximity of the aforementioned cold front which will have stalled across Oklahoma by this time. A second surface low will take shape in the Texas and Oklahoma panhandles and track east through the late afternoon and evening into early Monday morning. At this time, it is believed the precipitation associated with this system will remain south of the area with little in the way of sensible weather in the local area. After a brief return to dry weather for the daytime Monday with a slight warmup thanks to shortwave ridging, attention then turns to the next longwave trough as it approaches from the west late Monday. A large, digging trough will dive southward along the west coast and begin to cutoff by early Monday. As with most cutoff systems, details remain murky at this range but fairly consistent model consensus depicts this feature ejecting as a negative tilt trough in the Tuesday/Wednesday timeframe. Precipitation looks to begin as early as Tuesday in the form of WAA showers before better upper- level dynamics arrive by early morning Wednesday. Latest trends have boosted warm air in the system and thus decreased confidence in much if any snow in the area. The large player in this is the absence of cold air in the wake of a lead impulse. Thermal profiles across the area appear to be unfavorable for much more than a few wet snowflakes across portions of the Nebraska Panhandle, therefore, thinking remains steadfast that this event will be a rain event for the entire forecast area. Regarding the potential for thunderstorms...strong low-level moisture advection will precede the deepening low and will push surface dew points into the upper 50s to low 60s across mainly our eastern zones. Though some modest mid- level lapse rates may exist, spatial coverage of these may be limited which in turn will limit overall scope of instability in place. Ensemble guidance paints a picture where instability should remain fairly weak with less than 20% probability of seeing CAPE values exceeding 1000 j/kg. Given this, believe the threat for strong to severe thunderstorms to be fairly low this far north even with strong shear in place. Regarding forecast precipitation amounts...given strong lift do anticipate widespread wetting precipitation with even the NBM 25th percentile showing much of the area seeing at least a tenth of an inch of water. Latest guidance from WPC suggests anywhere from a half an inch in the south to nearly two inches in the north of liquid equivalent precipitation. This will likely be refined in the coming days but expect locally heavy rain in spots. Though some timing discrepancies remain, confidence is medium in greatest window for precipitation, high in being primarily a rain event, and high regarding the potential for strong winds to accompany the system. Given anticipated rapid deepening of the surface low on Wednesday, low-level mass field response will ramp up considerably. Utilizing the model blend, the gust forecast calls for many locations to see 30 knot plus wind gusts late Wednesday and again Thursday. Do believe this may be a bit conservative with some guidance advertising potential for some High Wind Warning criteria being met (sustained > 40 mph for at least one hour or any gusts exceeding 58 mph). This is far from a slam dunk so continue to monitor the forecast if susceptible to strong winds. Temperatures for Tuesday and Wednesday remain in flux, largely due to discrepancies in timing of the system. For now, can expect to see a mild day Tuesday with much cooler temperatures Wednesday...likely a 10-15 degree drop day-to-day...with high temperatures running below normal for Wednesday and Thursday. Lows may fall into the low 30s for west of Highway 83 on Wednesday and for the entire area on Thursday so the frost potential will need to be monitored as well. High pressure will work in Friday into the weekend which should bring about a return to dry weather but will also set us up for more Fall-like temperatures with highs in the 50s-60s and lows in the 30s. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1221 PM CDT Fri Oct 8 2021 VFR is expected throughout wrn and ncntl Nebraska this afternoon, tonight and Saturday. Isolated showers and thunderstorms are possible along and north of highway 20 tonight and Saturday morning. Otherwise, upper level moisture will continue to produce widespread mid and high level cloudiness across the region. The risk of low clouds leading to MVFR/IFR conditions is low. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...NMJ LONG TERM...NMJ AVIATION...CDC