Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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
761 FXUS63 KDMX 191750 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1250 PM CDT Sun May 19 2024 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Active weather pattern for at least the next several days with varied intensity and severe weather potential - Tuesday most noteworthy severe weather potential with a widespread Enhanced Risk (3/5) - Seasonally warm temps through the period, with precip chances increasing again late in the week && .DISCUSSION... Issued at 410 AM CDT Sun May 19 2024 Our weather pattern will remain active through the period, especially into the start of the work week, with continued relatively progressive lower amplitude flow. There is little going on early this morning, but precip chances will increase somewhat later today as remnants of the approaching KS/NE MCS reach the state. There is little moisture and instability this far north and east at the moment, so it is expected to weaken and become more scattered with little severe weather potential through at least early afternoon. Better moisture and instability isn`t that far away to the south however with yesterday`s cool front still lingering across KS, MO, and IL per the 08z surface analysis. This is expected to begin advancing northward by afternoon in response to persistent SW flow aloft and short waves advancing out of the SW CONUS into the Plains. While the best severe weather parameter space should remain to our west toward the Day 1 Moderate Risk, the boundary may lead to some spotty development during peak heating across southern IA into IL with some severe potential as MLCAPEs reach ~2000 J/kg and deep shear increases: mainly hail and wind threats although a tornado cannot be ruled out. This may persist into the early evening, with potential farther north as well as Plains MCS remnants reach IA later into the night. The severe potential should diminish toward midnight, but a 40-50kt low level jet and persist support ahead of an approaching H85/H7 trough should drive scattered convection into the night with increasing moisture and warm cloud depths leading to the potential for isolated heavy rains of 1-2". Confidence drops into Monday with little consensus on how much precip potential there will be tomorrow during the day. Some guidance exits the overnight precip, while others fester throughout the day or redevelop again by peak heating. Chances do increase into Monday night however as the maturing Rockies long wave trough increases warm advection and moisture transport into the state along the advancing warm front. Much like later today, adequate deep shear and instability will be in place, with a bit of tornado potential in the vicinity of the warm front as well. Local heavy rains are again possible with EC ensemble low level moisture climatological percentiles into the upper 90s. This leads into Tuesday and the greatest severe weather potential. While this is somewhat conditional, with questions regarding recovery and how long the overnight MCS lingers, the signal of regeneration later in the day has been consistent with deterministic guidance pushing MLCAPEs to at least 2500 J/kg and strong deep shear (50+kts) easily supporting organized convection with noted wind and hail potential. The tornado potential is certainly there as well, but examination of forecast soundings varies quite a bit from backed low level flow and strong low level shear, SRH, and streamwise vorticity ingest, to broader SW low level flow in the warm sector and more linear hodographs. Correspondingly, 00z guidance does vary on the triple point placement and timing 18-00z. CSU machine learning guidance has been consistent in the past few days highlighting a considerable severe weather threat, which is paralleled by a widespread Day 3 Enhanced Risk, although the CSU output has been steadfast in highlighting areas just east of our forecast area, possibly hinting at a faster solution. Although storm motion should be quite fast, mean winds 50+kts and Bunkers supercell motions not far behind, locally heavy rains may again occur with any convection as the aforementioned EC ensemble specific humidity and water vapor transport approach extremes. It won`t last long, but intense rainfall rates are possible with the passage of the strong convection. This will certainly be a situation Tue that will continue to be monitored in the coming days. Most precip should exit the area later in the evening, leading to somewhat more tranquil weather for the middle to latter portions of the coming work week. The next appreciable precip cycle seems to be late in the week when another weaker wave traverses the MO Valley. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1245 PM CDT Sun May 19 2024 Main focus was timing best storm chances at area terminals thru this forecast cycle. Ongoing thunderstorm across central IA has missed TAF sites thus far, but still may clip KDSM yet thru 19z. Otherwise, uncertainty remains in how much thunderstorm coverage will redevelop this afternoon, which will depend on how much sun can get through thick mid/high-level cloud shield. Still think better chance for thunderstorms will be later this evening and overnight with the arrival of the primary storm system ejecting from the plains. Have trended TAFs to focus on the 04-13z time period for best thunderstorm coverage as a result. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Small AVIATION...Hahn