Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
500 FXUS63 KOAX 070917 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 417 AM CDT Fri Jun 7 2024 .KEY MESSAGES... - Severe thunderstorms will develop (95% chance) in northern Nebraska by mid to late afternoon, and move across parts of eastern Nebraska and southwest Iowa through mid evening. - The strongest storms may produce areas of significant damaging wind and hail, flash flooding, and a lesser-but-non- zero chance for a tornado. The greatest potential for significant severe weather is southwest of a line from Niobrara to Norfolk to Omaha to Clarinda. - There is another chance for showers or a storm late Saturday, and a lesser chance on Sunday, with mostly dry conditions after that through the first half of the week. - The large scale weather pattern becomes increasingly favorable for a few rounds of strong to severe storms late next week into the weekend. && .DISCUSSION... Issued at 414 AM CDT Fri Jun 7 2024 Early Friday morning, conditions were quite comfortable across eastern NE and western IA. Temperatures were in the 50s and a few low 60s with light winds under high pressure. Most of the area will wake up to a calm, pleasant morning. Our benign early weather will not be a good indicator of what is to come late this afternoon and evening in the form of strong to severe storms. A long wave ridge axis from the Four Corners into Montana this morning has a strong upper jet and embedded short wave trough running over the ridge across the Rockies this morning. At the surface, pressure falls are ongoing this morning with the deepening surface low over eastern WY. Showers and a few storms have developed in the warm advection wing into southwest SD, and this activity will move east this morning, bringing showers and perhaps a storm across northeast NE. Looking farther south, there is a pool of decent boundary layer moisture as far north as extreme southwest KS. As the surface low continues to deepen, that moisture will be drawn north into north central NE by mid afternoon and an effective warm front will lift north into the local forecast area where it will orient itself from northwest to southeast by this afternoon. Thunderstorm development is likely in north central Nebraska by mid afternoon. One thing that we`ll need to watch closely is just how far north these storms will develop and how far north the boundary layer moisture and surface based instability will extend around the time of initiation. It would seem that the longer that convection is delayed, the farther north that the warm sector will extend, and the farther north and east that severe storm potential will extend. Wherever these storms do initiate, the warm sector in central NE will be characterized by 1000-2000 J/kg of MLCAPE. Farther east, the MLCAPE decreases sharply but still expect around 1000 J/kg to extend into a good portion of the forecast area and probably even extend into southwest Iowa. Those most unstable parcels should also be unstable enough that a healthy cold pool could lift into the LFC and support forward propagation...especially with westward extend in the forecast area. Deep layer wind shear is impressive in the near storm environment with some turning of winds in the low levels and an elongated hodograph through the mid and upper levels of the storm. So while CAPE is not particularly impressive, the shear profiles will strongly favor storm organization and intensity. This all favors an initial supercell storm mode transitioning toward forward propagating systems and probably with wind- driven hail being a concern during that transition period. So, initial hazards will be smaller pockets of intense wind and potential for some very large hail. This will transition toward wind-driven hail especially in large RFD regions of storms...and eventually toward a predominantly damaging wind and marginally severe hail hazard. The forward propagating Corfidi vectors are in the 70-90 kt range over southeast NE, and this alone suggest that significant wind gusts greater than 80 mph are possible assuming that this storm mode develops. There is also a non-zero tornado potential, especially in southeast Nebraska in the early evening hours where low level directional and speed shear will be maximized compared to the areas farther northeast. The peak severe weather time frame appears to be between 6 and 11 PM in the local forecast area, but again will need to watch initiation time to our west very closely...and a farther-north initiation would cause more of our area to be under the gun. As it stands, locations near/southwest of a line from Niobrara to Norfolk to Omaha to Clarinda seem to stand the best chance for severe weather. There is also potential for some heavy rain and flash flooding, despite the fast storm motion. Any flooding would be tied to training storms near the frontal boundary draped across the area, especially as the storm motion is pretty parallel to that boundary. If the whole front lights up in advance of the severe storms and these initial cells track along the front, then some areas could see isolated 3+ inch amounts of rain. This isn`t a guarantee, but a possibility. Northwest flow persists through the weekend with another short wave trough passage on Saturday bringing a chance for showers and storms, although these should not be strong. There is perhaps another lower chance for showers Sunday evening, but after that see a good chance for mostly dry weather through the first part of the week with highs in the 70s...and 80s by Wednesday. The upper air pattern flips by late in the week with a high likelihood of a large scale trough building into the western CONUS and a series of short wave troughs ejecting into the Plains. Boundary layer moisture will increase and this is a favorable setup for increasing potential for rounds of severe weather by next weekend into the following week. Most model guidance keeps the heart of the jet stream north of the local area, but embedded waves of enhanced mid/upper winds will drive severe potential. There is plenty of time to watch this unfold, but certainly appears to be a signal for an active weather period. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1143 PM CDT Thu Jun 6 2024 Calm winds (less than 5 knots) will become south/southeasterly, increasing to 10-15 knots by 17Z. Scattered showers and thunderstorms are expected to develop across eastern Nebraska (all TAF sites) by 22Z and slowly move to the east. Additional strong to severe thunderstorms will dive southeast across eastern Nebraska bringing the potential for severe hail and damaging winds up to 60 knots at all TAF sites sometime between 22Z and 03Z. Scattered showers and thunderstorms are expected to linger through the end of the forecast period across southeast Nebraska and southwest Iowa (KLNK and KOMA). The general time frame for thunderstorm potential has been delineated using a -RA FM group in TAFs. As this gets closer, will likely be converted to a convectively driven TEMPO as timing becomes more certain. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Barjenbruch AVIATION...Darrah