Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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781 FXUS63 KDMX 112324 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 624 PM CDT Tue Jun 11 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Few isolated storms possible before sunset northeast, but severe threat remains low this afternoon/early evening. - Strong to severe storms possible Wednesday afternoon and evening especially north and east. - Additional storms, possibly severe, expected south Thursday as well. - Continued warming into midweek as highs reach into the 90s. - Slightly cooler/drier Friday but heat and storm chances return for the weekend. && .DISCUSSION... Issued at 354 PM CDT Tue Jun 11 2024 Rest of Today: Scattered showers this morning fizzled out by about midday leaving mostly clear skies through much of central Iowa except for some budding cu this afternoon. Surface boundary connected to the main trough over southern Canada continues to move through the area this afternoon into evening but overall chances for any isolated storm development remain fairly low, around 20% or less with dew points well into the 60sF as many models suggested not being realized. As of 3 PM, dew points were in the 50s to low 60sF at a few sites with temperatures in the 80s. These overall lower levels of moisture should continue to help limit any storm development, though won`t completely rule out an isolated storm with gusty winds or small hail mainly in the far northeast, but overall chances for any severe weather remain low this afternoon into early evening with any storm development chances waning completely by around sunset. Temperatures tonight will be warmer than this morning and generally in the upper 50s to 60s. Wednesday/Thursday: Wednesday will be noticeably warm and humid as warm air advection amplifies with the thermal ridge moving through the region and H850 temperatures nearing +20C or more by Wednesday afternoon. This heat will be paired with surging moisture as dew points reach towards or well into the 60sF which translates to high temperatures in the upper 80s to 90s and heat indices in the low to mid 90s for many. A few theta-e advection induced showers or storms are possible in the morning to early afternoon mainly north but moisture may once again be an issue with this early day activity with forecast soundings looking fairly dry. Attention then turns to the the main shortwave and associated frontal boundary that will be dropping south through MN through the day with storms, some severe, possible in two rounds Wednesday, the first in the later afternoon to evening, and the second close on the heels of the first, but in the later evening to early overnight. Some questions remain on the placement of the storms, especially in the coverage of storms to the south and west, but storm chances are highest, >60% chance, over northeast areas, as this is the most likely area to see storms given current CAM trends and overall parameter space. The extent of capping could be the limiting factor in portions of central and western Iowa where afternoon H700 temperatures look to be near +10 to +12C which can be tough to overcome. As noted in the previous discussion, the overall parameter space is pretty good with the warm, humid environment surging MLCAPE values into the 1000-2000+ J/kg range per NAM and RAP soundings in portions of northern Iowa with storm relative inflow around 25-35 knots and overall bulk shear of 30-40+ knots. Strong to severe storms are possible with damaging wind gusts (DCAPEs over 1000 J/kg with lower level dry air in soundings) and large hail (elongated hodographs) the primary threats. Won`t completely rule out the possibility of a tornado if everything can come together with boundary interactions given increasing helicity values into the early evening, but overall LCLs are high which would be a limiting factor. Heavy rain may also occur, especially in areas that see multiple rounds of storms like the northeast, where rain amounts may near 2-3+ inches, as noted in the 24 hour QPF HREF localized probability matched mean. Progressive nature of storms should overall limit hydro issues, but will certainly keep an eye on this with potential for higher rainfall rates. Although storms wane by the early overnight, additional showers are possible Thursday morning with the location of the front towards southern Iowa the location for new storm development on Thursday afternoon to evening in another warm, humid, and unstable environment as highs climb into the 80s to 90s with heat indices in the upper 90s over far southern Iowa. Storm threats will better be determined based on location of the front and timing, but severe storms may again be possible with wind hail, and will even need to watch the tornado potential depending on how the mesoscale details evolve. The overall take away for Wednesday and Thursday is to monitor the forecast for updates with a SPC Day 2 Slight Risk (Level 2 of 5) Wednesday north, with a Day 2 Marginal Risk (Level 1 of 5) extending through much of the rest of the area, and a Day 3 Marginal Risk (Level 1 of 5) over far southern Iowa on Thursday. Friday and Beyond: A small reprieve is expected on Friday with slightly cooler temperatures, though still in the 80s, and lower dew points. Additional storm chances return for the weekend with more building heat as temperatures climb into the upper 80s to 90s again on Sunday and Monday with upper 90s heat indices south. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 622 PM CDT Tue Jun 11 2024 VFR conditions currently prevail and are forecast through the TAF period. Forecast uncertainty increases after 18z Wednesday as model guidance suggests a complex of showers and storms will dive southeast out of Minnesota. Confidence is low wrt the track and timing of this thunderstorm activity, however the highest chances currently reside just north/east of our northern terminals KMCW and KALO. Opted to leave any mention out of their respective TAFs for now, however that will be closely monitored as additional guidance becomes available. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...KCM AVIATION...Martin