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Area Forecast Discussion
Issued by NWS North Platte, NE
Issued by NWS North Platte, NE
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846 FXUS63 KLBF 110900 AFDLBF Area Forecast Discussion National Weather Service North Platte NE 400 AM CDT Sun Aug 11 2024 .KEY MESSAGES... - Strong to severe thunderstorms are again possible today with large hail, damaging winds, locally heavy rain, and a tornado or two possible. - Near-daily rain and thunderstorm chances will persist through the extended forecast as temperatures look to return to normal by the middle of the week. - The recurring rain and thunderstorm chances may allow for appreciable rain amounts for some. && .SHORT TERM /THROUGH TONIGHT/... Issued at 358 AM CDT Sun Aug 11 2024 Modest northwest flow once again has entrenched itself across much of the central Plains. This is as deep troughing continues to drift into southeast Canada and broad ridging remains in place across much of the southern half of CONUS. Morning satellite analysis depicts another slug of mid-level moisture slowly departing the central Rockies and tracking onto the High Plains over much of Nebraska, Kansas, and portions of Oklahoma. Observations show fairly widespread low-stratus moving into southwest Nebraska. This is coincident with some isolated light rain and patchy fog, both of which should prevail through sunrise mainly for areas along and south of Highway 2. For Sunday...expect this plume of moisture to continue to be shunted east in the moderately strong mid-level flow. As it does, a modest increase in WAA both at h85 and h7 should support reinvigorated showers with a few embedded weak thunderstorms. While the majority of this activity will wane after sunrise, areas of north central Nebraska could see new development as forcing for ascent increases along and ahead of a subtle h7 warm front. HREF ensemble mean guidance picks up on this with a splattering of light QPF between 12-18z. Recent runs of the HRRR have shown a notable trend towards this outcome, so will keep Slight Chance (< 20%) PoPs to cover this. Reasoning for capping at such a low value is dry low-level air necessary to overcome. NWP forecast soundings depict cloud bases nearing 3km and limited convective elements owing to poor mid-level lapse rates. After morning showers depart around midday, expecting a decent break before the next wave of thunderstorms arrives from the northwest. Recent performance of NWP guidance on high temperatures has been poor, and little evidence exists to suggest we`ll break the mold today. Surface high pressure will maintain an influence locally as it remains situated just east of here. Though broad southerly flow will develop, advection will remain modest and favor the early part of the day before tapering off. With stubborn cloud cover and h85 temperatures continuing to remain on the cooler side of climatology, expecting another well below-normal day for much of the area. Many locations may struggle to reach 70 degF and all locations are likely to remain below 80 degF. Values such as these are roughly 10-15 degF below normal for early to mid August. Confidence continues to increase with respect to the development of strong to severe thunderstorms across central and southern South Dakota, quickly tracking southeast into the local area. Given previously mentioned cooler temperatures, instability values will be fairly limited. Even so, near steady to slightly increasing low- level moisture with steep lapse rates overhead should support modest instability, favoring our western zones. As a mid-level speed max remains centered along and near the I-80 corridor, deep layer shear will be strong with southerly surface flow quickly veering to just north of due west around h7. This limits greatest curvature in forecast hodographs to the lowest 2km with mainly speed shear above that. Latest CAMs output, particularly consecutive runs of the HRRR, advertise a plethora of semi-discrete supercells developing near the I-90 corridor of South Dakota and quickly tracking south and east. HREF output showcases high neighborhood probabilities of updraft helicity values exceeding 75 m2/s2 with multiple swaths depicted in paintball output, including in a second area centered around the Cheyenne Ridge across the southern Panhandle. This suggests not only supercellular storm structure but also the potential for extended life storms. While the tornado potential appears somewhat limited, its hard to completely rule one out with expected storm mode and a surface boundary draped in the area. Fortunately, storm motion versus boundary orientation may preclude greater concerns. Otherwise, the main concerns will be large hail approaching golf ball size and damaging wind gusts of 70 mph. Storms will eventually cross the boundary into more stable air and this should lead to a fairly rapid weakening with southeastward extent. Even so, locally heavy rain will remain a threat. Latest QPF values top out near 1.0" for north central Nebraska. This generally lines up with the HREF probability-matched mean output but do believe a few locations may top 1.5" before all is said and done. Precipitation should depart the area to the east by sunrise Monday. && .LONG TERM /MONDAY THROUGH SATURDAY/... Issued at 358 AM CDT Sun Aug 11 2024 Overall thinking for the extended forecast hasn`t changed much in the past 24 hours. Ridging will build north into the Great Basin early in the week with the ridge axis expected to push onto the High Plains by late morning into Tuesday. With the lack of any appreciable disturbance tracking around the northern periphery of the main high pressure, little will be done to scour out local moisture. With steady south to southeasterly flow through the forecast period, rain and thunderstorm chances will return daily as convection fires off the Front Range and tracks east to east- southeast into the local area. Latest NBM probabilities suggest Monday night into Tuesday and again Tuesday night into Wednesday as the favored periods for appreciable rainfall at this time. In both instances, the greatest probabilities focus across southwest Nebraska which lines up well with some of the greatest Drought intensities in the area. Overall, total QPF through next week may surpass 0.50" for many and 2.0" for some. This is highly dependent on placement of thunderstorms so continue to check back for more precise details. Temperatures, as ridging arrives around the middle of the week, will moderate through that time but then look to resemble a persistence forecast thereafter. This means a return to 80s for all and possibly low 90s for some. These values are right near climatology for mid-August. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 104 AM CDT Sun Aug 11 2024 Isolated rain showers will continue to move into southwest Nebraska and the Sandhills over the next several hours. Some of these showers could have an embedded thunderstorm or two, but should not be severe. Regardless, reduced visibilities due to falling rain as well as erratic winds may be possible. A brief break returns by mid morning before a better chance of stronger storms arrives by late afternoon and into the evening. These storms could become severe with large hail along with strong, erratic winds and heavy rainfall all being possible. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...NMJ LONG TERM...NMJ AVIATION...Kulik