Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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179 FXUS63 KOAX 181650 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1150 AM CDT Wed Sep 18 2024 .KEY MESSAGES... - There is a 20-30% chance of storms late this afternoon into this evening, with a 5-15% chance of severe storms. Hail and damaging winds will be the primary threats, but a tornado cannot be ruled out (2% chance). - Additional isolated severe storms will be possible (5% chance) in far southeast NE and far southwest IA Thursday afternoon and evening. - Widespread rain chances arrive Friday evening and last into Monday, peaking Saturday into Sunday morning at 50-80%. Expect a widespread 1.5 to 2.5 inches of rainfall with this system. - Temperatures remain above average through the remainder of this week, with highs in the 80s to lower 90s. Cooler conditions are anticipated with and after the rain this weekend, with highs in the 60s and 70s from Sunday into next week. && .DISCUSSION... Issued at 348 AM CDT Wed Sep 18 2024 The main story early this morning was a band of showers and storms associated with low level moisture transport and some shortwave energy pushing east toward the area. Additionally, an associated outflow boundary was out in front firing some more storms in northeast NE. These could produce some small hail and gusty winds through the early morning hours, but severe weather is not expected. Guidance is in good agreement that the main band of storms will weaken as it pushes into our area, as moisture transport weakens through the morning. Still, could see a few light showers push toward and maybe slightly east of the MO River by late morning/early afternoon. Otherwise, despite having associated clouds to contend with, we`ll still warm up into the mid to upper 80s and possibly even 90 with decently strong southerly flow allowing us to do some good mixing. Attention then turns to strong to isolated severe storm chances late this afternoon through the evening. A cutoff low currently over the MT/WY border will continue pushing northeast today with a surface boundary sliding east into the area this afternoon. Ahead of this, dewpoints are progged to be in the mid to upper 60s with HREF mean SBCAPE approaching 2000 J/kg. Shear will be somewhat limited, but latest RAP guidance suggests 25 to 35 kts of 0-6 km shear edging into northeast NE. As a low level jet ramps up late this afternoon into this evening, low level shear will also increase, and resulting moisture transport should allow for storm development in vicinity of the boundary. There is some degree of low level hodograph curvature that could yield a small (2%) tornado chance, but the primary severe weather concerns will be hail and damaging winds, especially in northeast NE where deep layer shear will be strongest. The severe weather threat should taper off by 10 PM or so, but like past nights, expect at least spotty showers and storms to persist into the early morning hours Thursday with moisture transport continuing to point into the area. Clouds should then clear out by mid to late morning while a surface cool front starts to push through the area. Areas that remain ahead of the front through much of the day (likely southeast NE and far southwest IA) will see continued southwesterly flow, allowing temperatures to climb into the lower 90s, while areas behind the front "only" top out in the mid 80s. So quite warm for this time of year, but still several degrees short of record highs (97 for Omaha, 100 for Lincoln). Once again, expect some storm development in vicinity of the passing front by late afternoon/evening with decent instability progged to be in place ahead of it. Strongest shear looks to remain behind the front, but still could be just enough for storm organization, yielding another strong to isolated severe storm threat. The big question will be how far west/east storms go up, as a few pieces of guidance suggest they could go up east of us and we end up with nothing. As it stands, we`re looking at a 15-20% chance of storms in far southeast NE into southwest IA and a 5% chance of severe storms in those areas. Hail and damaging winds will once again be the primary threats, but a tornado cannot be completely ruled out. Then heading into Friday and the weekend, guidance continues to trend slower with a potent shortwave trough ejecting out of the Desert Southwest with an attendant surface low spinning up, pushing through KS, and bringing us widespread rain. Latest consensus only gives about a 15-25% chance of storms Friday evening, and anything that does develop would likely hold off until 10 PM or after when moisture transport starts to ramp up. Shower and storm chances quickly climb after that with 40 to 70% chances in place across the area through the day on Saturday and Sunday, highest at any given time near and south of I-80. Still some questions on exact track and timing of the system, but given its strength, will need to keep an eye on potential for severe weather. Instability will likely be quite limited with persistent rainfall/cloudcover, but if we get any breaks we could see a bit of a threat as the low pushes through (likely on Sunday). Also of note, current forecast calls for a widespread 1.5" to 2.5" of rainfall Friday evening through Sunday night. Locally higher amounts will certainly be possible, especially if we`re able to develop some instability. For what it`s worth, guidance suggests a 60 to 80% chance of at least 1" and a 40 to 60% chance of at least 2". So overall, relatively high confidence we`ll get some decent rain out of this system. Some precip could linger into Monday, especially if the slowing trend continues. As the system passes through and on the back side, we`ll see much cooler and more fall-like temperatures, with highs in the 60s and 70s Sunday through at least the middle of next week. We could also see additional spotty light precip through Wednesday as we remain under the influence of cyclonic flow aloft, though surface high pressure should limit that potential quite a bit. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1147 AM CDT Wed Sep 18 2024 VFR conditions are favored throughout the forecast period. Southerly winds will continue above 12 kts with gusts up to 22-28 kts possible through the afternoon. Winds will calm under 12 kts by 01-03Z. Isolated to scattered strong to severe thunderstorms will develop in northeast Nebraska this evening (00-04Z). Due to the scattered nature of these storms, have opted to leave out of the TAFs at this time. A similar situation is present with scattered showers expected Thursday morning (10-14Z). && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...CA AVIATION...Wood