Area Forecast Discussion
Issued by NWS North Platte, NE
Issued by NWS North Platte, NE
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144 FXUS63 KLBF 191719 AFDLBF Area Forecast Discussion National Weather Service North Platte NE 1219 PM CDT Sun May 19 2024 .KEY MESSAGES... - The Storm Prediction Center has maintained a Slight Risk (level 2 of 5) for western Nebraska Sunday, mainly for areas west of Highway 83 with large hail and damaging winds the main concerns. - Additional strong to severe thunderstorms are possible on Monday though the main concern is likely to be the threat of heavy rain Monday night into Tuesday. - Cooler temperatures arrive around the middle of the week. Confidence in seeing a frost or freeze event remains low. - A return to normal temperatures with active weather is expected for the latter half of the upcoming week. && .SHORT TERM /THROUGH TONIGHT/... Issued at 407 AM CDT Sun May 19 2024 Early morning radar and satellite analysis depict a broad area of moderate to heavy rainfall lifting north and east out of western Kansas into far southwest and south central Nebraska. This activity is largely being driven by a modest shortwave ejecting ahead of larger scale troughing taking shape across the western CONUS. DCVA and WAA in the low-levels are helping provide broad ascent across the local area. Though instability declines quickly with northward extent, non-zero MUCAPE values and values reaching as high as 1000- 1500 j/kg have reached the Nebraska/Kansas border and will continue to translate north through the morning. This should allow for a continuation of rain and thunderstorm chances this morning. Given the magnitude of instability and deep-layer shear exceeding 35 knots, cannot completely rule out stronger storms capable of at least small hail during the late morning, mainly for areas east of Highway 83. Lift is expected to wane by early afternoon as the main shortwave departs to the north and east. This should lead to an appreciable break during the day with dry conditions likely for at least the majority of the early afternoon. Residual cloud cover as well as rain will likely hamper diurnal temperatures during the day. NWP model spread for high temperatures today vary widely for central Nebraska with discrepancies nearing 10 degF. Higher resolution guidance is more bullish on afternoon high temperatures. This is largely due to quicker departure of rain/clouds as well as continued strong southerly flow in the lower levels which will support advection of warmer air into the area. Afternoon dew points will steadily climb with many locations climbing into the middle to upper 50s and even a few locations potentially seeing values in the lower 60s. While confidence is fairly limited for the immediate short range, the going forecast calls for afternoon highs in the middle 70s to middle 80s east to west. With the expected overlap of greatest surface temperatures and greatest low-level moisture, moderate instability will develop as west-southwesterly flow aloft will advect a stout EML over the region. This will yield moderate to strong instability immediately east of a sharpening dryline that will stretch from the Black Hills south into far northeast Colorado. With adequate deep layer shear already in place, organized severe convection is appearing more likely. The latest SPC Day 1 Outlook has expanded the pre-existing Slight Risk (level 2 of 5) north and east with the coverage now including most if not all locations between the Highway 385 and Highway 83 corridors. Forecast soundings, while depicting fairly strong capping that will need to be overcome, show long/straight hodographs above 1km with the majority of the instability located within and above the hail growth zone. With non-zero SCP values and moderate storm relative inflow at the surface, believe hail up to golf ball size will be possible with discrete convection early on. Gradually, upscale growth due to merging cold pools in an area of 1000+ j/kg DCAPE and delta theta-e values falling below -20 degC should support more of a damaging wind threat. This will likely persist into the evening as rich theta-e air continues to be advected into what will likely be a maturing MCS. Only when this system begins to encounter recycled air originating from strong convection across Kansas will a weakening trend become likely. This will generally be around Midnight with the majority of activity likely having exited the local area by then. Precipitation amounts from this activity will be fairly variable. While a few localized areas may see 1.00" or more, most locations will likely remain in the 0.25-0.50" range. && .LONG TERM /MONDAY THROUGH SATURDAY/... Issued at 407 AM CDT Sun May 19 2024 Monday and Tuesday...Largely expect Monday to begin fairly quiet as the area is caught between the smaller scale system departing to the east and approaching large scale trough from the west. Deepening trough to the west will begin to approach the central CONUS by early morning Monday. Height falls are unlikely to increase markedly until the latter half of the day though which should limit the arrival of the greatest rain chances. Opted to decrease PoPs during the day as a result. This was done by blending in SREF/HREF PoPs. As a result, only Slight Chance PoPs (< 20%) exist for the early afternoon with only a slight increase of up to 35% (Chance category) expected by late afternoon for the eastern Panhandle. PoPs will maximize Monday evening into early Tuesday as the main PV anomaly overspreads the area. An attendant surface low lifting southwest to northeast across central Kansas will help promote strong lift within a anomalously moist environment where PWATs will likely exceed 1.00" in the pre- convective environment. PoPs overnight Monday into Tuesday will likely near 100% for most locations in the local forecast area, as confidence remains high in a noteworthy rainfall event. The ECMWF Extreme Forecast Index (EFI) continues to highlight this with values exceeding 0.8 and Shift of Tails values of 0-2, suggesting the extreme values of the ensemble suite exceed the 90th percentile in the model climatology. Both EPS and GEFS ensemble products show increased probabilities of exceeding 1.00" total QPF for Monday night through Tuesday afternoon with the EPS the more bullish solution of the two. The 24-hour mean values from both ensemble suites exceed 1.00" in the maxima with the EPS nearing 1.75" for mean QPF. Deterministic solutions show widespread 1.00-2.00" rainfall with localized amounts closer to 3.50". It`s important to note that unlike typical convective heavy rainfall scenarios, these amounts are being achieved in closer to 6 hour timeframe versus shorter periods. This should limit, but not negate, the threat for flash flooding. As the main trough aloft lifts north and east into the upper Mississippi Valley, precipitation will wind down and likely end by late in the day Tuesday. The PoPs inherited from the NBM maintain Slight Chance and Chance categories right through Tuesday evening and into Wednesday but deterministic solutions suggest there should be a notable break for the latter half of the daytime Tuesday so expecting these to be cleaned up with later forecasts. Temperatures will be trending cooler with a values falling into the 60s to low 70s Monday and 50s-60s by Tuesday. A fairly active pattern will persist through the middle of next week as a stalled out upper-low allows smaller scale disturbances to pivot through the area. While day-to-day predictability remains fairly low confidence for now, ensemble signals point to Friday into early Saturday as the next appreciable chance in the local area. This will be attributed to a stronger cold front expected to dive south through the area. For now, precipitation chances will favor eastern Nebraska with decreasing probabilities as one goes west. That said, finer details like timing and placement of key features are unlikely to be confidently located until we`re closer to 48-72 hours out so expect the forecast to waver somewhat in the coming days. Ahead of this, temperatures will recover to seasonable values for Thursday and possibly Friday before falling once again in the wake of the front. The exact magnitude of cold air moving in remains to be seen but a brief cooldown is likely and the current forecast highs for Friday and Saturday include temperatures falling to around 10 degrees below normal. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1219 PM CDT Sun May 19 2024 Multiple aviation weather concerns exist this forecast period, including gusty winds, thunderstorms, and low ceilings. First, southerly winds will continue to gust 20+ kts through the rest of the afternoon. Current scattered storms over central Neb (BBW to ONL) will gradually taper through mid afternoon (19/21z), then new development will take place in the panhandle. Those storms are expected to overspread the Sandhills this evening and present a large hail and strong wind threat. Most likely timing for LBF to VTN for wind, visby, cig impacts will be around 20/00z to 20/02z. Behind those storms, winds will switch around to north/northwest overnight and strengthen again toward sunrise. A low stratus cloud ddeck may build into the region as well, resulting in MVFR conditions. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...NMJ LONG TERM...NMJ AVIATION...Snively