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
701 FXUS63 KDMX 150455 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1155 PM CDT Fri Jun 14 2024 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - Prolonged period of elevated heat and humidity Sunday through Tuesday. - Off and on chances for showers and storms this weekend into next week. Some chances for strong to severe storms and locally heavy rainfall Saturday mainly west/southwest during the late afternoon to evening. && .DISCUSSION... Issued at 335 PM CDT Fri Jun 14 2024 Rest of Today Through Sunday: The lower dew points and humidity levels of today will be short lived with a prolonged heat wave upcoming with upper-level ridging dominating the overall pattern today and again on Sunday into early next week. A shortwave lifting out of the southwest U.S. today will be our main disruption in the overarching pattern as it nears and crosses through the area early Saturday into Sunday. Initially this will be in the form of showers or weak storms starting overnight as theta-e advection increases west/southwest with general expectations and model trends suggesting any showers/storms to be on a weakening trend as they move eastward with time towards central Iowa during the morning hours Saturday. It will also take time for profiles to saturate with nearing 12kft of dry air in place prior to theta-e advection increasing tonight making it so rain could hold off until closer to early Saturday morning. Either way, instability remains very minimal overnight so while cannot completely rule out some lightning, not expecting anything in the way of severe storms overnight/early Saturday. Some CAMs kick off new storms on Saturday morning south behind the weakening first line which could potentially muck up storm potential late Saturday afternoon into evening in addition to how much clearing does or does not occur behind the first main line. However, moisture, instability, and heat should all be on the increase through the afternoon hours Saturday as a warm front lifts into the area ahead of the approaching wave. The question will be how much instability and will it be surfaced based. On the high end, MLCAPEs could reach 3000-4000J/kg which could easily help storms become severe. More likely instability might be closer to 1000-2000 J/kg of MLCAPE paired with the more marginal 25-35 knots of bulk shear. Soundings indicate steepening low level lapse rates, especially southwest on Saturday afternoon, with LCLs under 1000m, 0-1 SRH values near to over 200 m2/s2, which would keep some tornado and large hail potential with any initial supercells that are able to form, with some damaging wind potential if any storms can congeal. Details are highly dependent on morning activity and our degree of realized instability, but the SPC Day 2 Slight (Level 2 out of 5) captures the main threat area well. Although the severe threat wanes with time into the evening hours as storms move eastward, rain continues through the overnight into Sunday morning before ending in the east early Sunday. Will also have to monitor heavy rain amounts as pwats increase to be near to over 1.5-2" by 00Z Sunday (Saturday night) with warm cloud depths of 11-13kft. 24-hour HREF QPF Probability Matched Mean values ending 12Z Sunday (Sunday morning) indicate localized areas of 1-3" with isolated higher amounts possible. Highest QPF amounts look to be over southwest into western Iowa, with a secondary localized area over northern Iowa given the potential for repeated storms from activity Saturday morning and Saturday evening into Sunday morning. Some additional storms are possible on Sunday later in the day, especially far north to northwest, but otherwise main story Sunday will be the building heat and humidity as highs reach into the 90s with heat indices in the mid 90s to nearing 100 in parts of central to southern Iowa. Monday and Beyond: The new work week starts off with Iowa being sandwiched between an amplifying ridge over the eastern U.S. and a digging trough over the northwest U.S. keeping various degrees of ridging in place in the otherwise southwest flow. Although there may be periodic storm chances at times, conditions will remain hot and humid with highs near to in the 90s and some areas approaching the upper 90s on Monday. These hot temperatures will be paired with dew points in the 60s to maybe even low 70s at times sending the heat indicies to the upper 90s, nearing 100 in parts of central to southern Iowa, on Monday and Tuesday, with Monday being the hotter day. Little relief is expected at night with lows in the 70s and challenging some high minimum temperature records on Monday and Tuesday mornings. As mentioned in the previous discussion, although heat indices remain below heat advisory criteria, the duration of the heat event may lead to heat headlines at some point, something we will continue to monitor. On a positive note, the heat on Monday and Tuesday will be paired with breezy to gusty winds that will help mitigate some of how the heat feels. However, certainly prepare accordingly for the multi-day above-normal summer heat by staying hydrated, limiting outdoor activities in especially the heat of the day or by taking breaks in the shade, and never leave pets or kids in a vehicle unattended - look before you lock! Although the south to southwest flow remains in place with the otherwise eastern U.S. ridge and western U.S. trough dominating the upper-level pattern, uncertainty increases significantly on Wednesday and beyond in overall degree of heat remaining (whether it be 80s or 90s) with the Euro suite hotter and drier and the GFS suite slightly cooler and more active/wetter. One period of storm chances we`ll continue to monitor is Tuesday night into Wednesday though details remain sparse at this lead time. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1154 PM CDT Fri Jun 14 2024 Light winds out of the southeast expected tonight before picking up and becoming gusty through the day tomorrow. A few light showers will drift over northern Iowa this morning, before additional rainfall is expected later in the morning and into the afternoon. Low confidence in location of thunder this afternoon and evening, so have left out of TAFs at this time. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...KCM AVIATION...Dodson