Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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112 FXUS63 KOAX 300250 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 950 PM CDT Sat Jun 29 2024 .KEY MESSAGES... - Seasonally pleasant weather through sunset on Sunday. - Flooding continues on the Missouri River below Decatur through the coming week. - Sunday through Tuesday will feature multiple rounds of thunderstorms. Severe thunderstorms are possible, particularly Monday afternoon through Tuesday evening, with very heavy rain possible during this time frame as well. - Thunderstorms are possible on Independence Day, but overall confidence is low, and thunderstorm potential may change based on minor changes with speed of the storm system. && .DISCUSSION... Issued at 303 PM CDT Sat Jun 29 2024 The last two days of June, on a weekend nonetheless, are an absolute delight in terms of weather. High pressure is building into the region behind yesterday`s cold front with below normal temperatures under mostly sunny skies. A northerly breeze has been a bit gusty today, but we can expect decreased winds this evening, and generally light winds through Sunday...just enough to keep the seasonally pleasant air moving during the afternoon hours. Overnight lows tonight will be in the 50s...with highs Sunday in the 70s...and lows Sunday night in the lower 60s. For some of us, windows-open weather has returned! While there may be a passing sprinkle or light rain shower on Sunday, even these will be light, and moving along at a good enough pace such that they won`t linger long over any given location. After an extremely busy April, May, and June, it is just nice to be able to write this paragraph and look forward to enjoying a couple of peaceful weather days across eastern Nebraska and western Iowa. Now...on to the rest of the forecast for Sunday night through the end of next week... Sunday Night into Monday Morning: Yesterday`s cold front has indeed pushed well south of the area, but the extremely moist and warm airmass still exists south of the front in Oklahoma and southern Kansas. As we move into late Sunday, a longer wave trough will build on to the west coast and northern Rockies with an upper ridge centered over Texarkana. An intensifying upper level southwesterly jet will develop over Wyoming with lee cyclogenesis over WY/MT. A lead short wave trough will ride up and over the ridge on Sunday night, with height falls extending across our region. These features will help to pull the frontal boundary back north as a warm front, with a good amount of heat and moisture riding northeast of the front into the local area on the low level jet as early as Sunday night. This will set up a favorable scenario for widespread rain and thunderstorms associated with the short wave trough passage. Currently expect elevated parcel MUCAPE into the 1000-1500 J/kg range, but effective shear may struggle to support much storm organization. Also, there will be good moisture return with this system, but it also appears somewhat progressive and scattered...so for now it appears that the severe and hydro threats for Sunday night into Monday morning are fairly low. Late Monday into Monday Night: Another subtle short wave trough focused a bit farther south within the flow pattern will cross into the Plains by late on Monday. Expect a surface low to develop over southwest NE and another over northeast WY. These should be quite effective in surging the frontal warm sector north into Nebraska and eventually northeast into the NWS Omaha coverage area by late afternoon into the evening. This will be a mobile warm sector, at least initially, characterized by 1500+ J/kg of MLCAPE, but most forecast soundings have a pretty stout cap in place. Hodographs, particularly on the leading edge of the warm sector, feature large cyclonic shear in the low levels. The main question, it appears, is if that cap can be broken for surface based thunderstorm development. If so, it would appear that supercells would be the primary storm mode, with ample low level shear available. For now, this is worth carefully monitoring, especially west of a Falls City to Fremont to Neligh line. As the evening progresses, see an increasing likelihood for strong to severe elevated convection. Mid level lapse rates will be steep, with a very impressive amount of moisture transport on the LLJ focused into our region. Layer PWAT in the 2 to 2.4 inch range along with a focused zone for moisture convergence and ample instability points to the potential for very intense rainfall rates on Monday night. And, while storms should be at least somewhat progressive, any locations experiencing multiple rounds of storms or periods of backbuilding will quickly see flash flood potential increase given the intense rates. Some of this heavier rain may also fall into already swollen or flooded rivers, worsening existing flooding...but specific locations are yet to be identified and at this time the main takeaway is that the ingredients for very heavy rain will be present. Tuesday into Tuesday Night: The front sags back south and lays out across the region for late Tuesday. Instability will likely be impressive south of the front with mid 70s dewpoints and hot temperatures wherever clouds break. Deep layer shear will again be quite strong, although with less low-level turning than on Monday. The shear vectors are also likely to be more parallel with the frontal boundary than on Monday which tends to result in clusters or more linear storm mode, although probably with embedded supercells given the shear magnitude. Moisture content will again be very high with impressive rainfall rates in the storms, and with several hours of front-parallel flow, could easily result in some higher-end rainfall totals once again, along with the severe weather potential. Rest of the Week: Wednesday looks relatively quiet with the front south of our area, but it lifts back north for Independence day as the strongest of the short wave troughs crosses the northern Plains. Depending on system timing, the 4th may be rather stormy...with ingredients in place ahead of this storm system... but hesitate to go all-in on this for now, as a slightly faster system movement could make for a pretty clear evening. Definitely a period worth paying close attention to the forecast. Friday through the weekend, at least for now, look to be largely dominated by high pressure, and relatively dry. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 950 PM CDT Sat Jun 29 2024 VFR conditions expected through the period with passing mid level clouds Sunday. Light northeast winds overnight will become southeasterly Sunday morning, with speeds on either side of 10 kts. A few pieces of guidance hint at shower and storm development toward the very end of the period, but consensus is to hold off until after 06Z and possibly even 12Z Monday. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Barjenbruch AVIATION...CA