Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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233 FXUS63 KDMX 231801 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA Issued by National Weather Service Quad Cities IA IL 101 PM CDT Thu May 23 2024 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Another Round of Potential Severe Storms Late Tonight - Quieter Weather Returns Friday Afternoon and Saturday - Showers/Scattered Storms Sunday - Lower Confidence Forecast Day7 && .DISCUSSION... Issued at 335 AM CDT Thu May 23 2024 .Short Term /Today through Friday/... Confidence Short Term: Medium Active pattern ramping up again late tonight into early Friday with more severe potential overnight. Yesterdays storm now just southwest of Hudson Bay with weak westerly flow and high pressure over Iowa now at H850. Upstream already a rather potent spring system at H850 of 138dm is just entering northwest Wyoming. Farther south another area of low pressure is located in New Mexico. Flow ahead of this large western trough has turned back to the south over much of the lower Mississippi River Valley at 00z with a plume of +5C dew points already back into western Iowa; farther south +10C dew points are into southeast Kansas and not far behind a pool of +15C dew points extends across eastern Texas. Surface analysis at 04z shows low pressure beginning to organize over western South Dakota and Wyoming. Surface moisture return is slow, but dew points already in the mid 50s have entered southeast Kansas. The synoptic models show a double low structure approaching the Western Plains by 00z with increasing southerly flow over Iowa. This will aid in advecting a plume of 60 to 65F dew points into Iowa by 07z, focusing along a cool front associated with the elongated trough as it crosses the state. Instability will be ramping up through the late afternoon and evening, though no real forcing mechanism will be available until later in the evening as the trough/low approach. Today will see some mid and higher level clouds in response to the approaching moisture and warm air advection. Along with that, highs will likely reach the upper 70s to lower 80s over the area. By tonight, 0-6km wind shear will increase from 03z to 12z overnight to 35 to 50kts with ample MUCAPE of a conservative 500 to 1500 j/kg by 06z and continuing through 12z. Though there are some differences in strength of both thermal/forcing features between the NAM/Euro and GFS deterministic runs at 00z, the HRRR is supportive of the NAM/Euro in that convection is likely to break out in eastern/southeast Nebraska between 00 and 06z and then quickly grow upscale into an MCS/MCV bowing structure through Friday morning as it tracks east northeast. Currently the GFS is slightly weaker than the NAM/Euro suite. With support for decent H850 LLJ overnight and increasing shear aloft, we will likely see a bowing QLCS potential with possible damaging wind gusts and some brief tornados the main threats as the line tracks east overnight. There appears to be a warm front moving northeast with the warm air advection and this would be the likely axis of the bowing feature as it matures overnight. There remains some uncertainty as to how long the bowing structure will remain strong, though QLCS features sometimes increase in strength toward dawn as the H850 low level jet peaks. As for rainfall, PWATs are increasing to 1.5 inches along the boundaries overnight with warm cloud depths just above 10kft. This might lead to rainfall amounts up to 1.5 to 2.0 inches in a few spots, though the progressive nature of the line should mitigate any widespread additional hydro issues. Right now the 06z HRRR is showing the trailing southern edge of the QLCS along US30 to I80 east of I35 may see between 1.5 to 2.0 inches in a 3 to 4 hour period. If this type of scenario sets up, will need to monitor for some additional hydro issues during the event. As the mesoscale feature exits by mid to late Friday morning, we should be left with a relatively quiet afternoon through most of Saturday with a break in the action until later Saturday evening. Weak high pressure will build over the area Friday night into Saturday with seasonal highs and slightly cooler overnight lows Friday night. Highs tomorrow will reach the lower to mid 70s. .Long Term /Friday Night through Wednesday/... Confidence: Medium As we approach Saturday night, another area of low pressure will track into the Central Plains. The bulk of the energy is still forecast by the medium range models to be just southeast of Iowa, though the Euro does bring some slightly more unstable air into the southeast/south by 12z Sunday. Though severe storms are not expected, there may be a few stronger storms in far southeast and southern Iowa. Rainfall may be the bigger issue, with another half inch to inch across the south half of the state. Certainly not needed at this time. Lows Saturday night will be in the 50s to around 60 with highs Sunday in the 60s to lower 70s. As we round out the weekend, there is lower confidence heading into Monday as operational model runs diverge. The current EPS is more supportive of the operation GFS with the light rain lingering Sunday night into Monday over the region. This will likely keep the region cooler and somewhat cloudy/wet with highs in the 60s to lower 70s again. From Tuesday through Wednesday night, a break from the wet weather is expected. Highs should gradually warm back to the mid to upper 70s. By Thursday some scattered showers and storms are possible with cooler highs in the lower to mid 70s. We may need to make some temperature adjustments at that time. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1259 PM CDT Thu May 23 2024 VFR conditions with breezy south to southeasterly sfc winds through mid evening, then after midnight or even 3-4 AM CST there will still be the chance for a line of storms. This linear convection may include some bowing structures with damaging/high winds as it propagates eastward through the TAF network of Central Iowa through 13-14z. Most sites will see a 1-2 hour window of these strong storms with potential high gusts and made a TEMPO group window using a CAM ensemble blend. Also a chance 10-30% coverage of higher based/ elevated showers and storms developing ahead of the main line from 04z to 09z tonight, but these will be hard to pin-point for TAF occurrence or VCNTY wording. Cigs generally VFR, but may dip to MVFR levels with the storm line passage. Also, much guidance comes in with higher coverage MVFR stratocu in the wake of the main line Friday morning. VSBY also drops during the passing storms. Will have to keep in mind strong gusty south or southwesterly sfc winds caused by wake low pressure perturbation behind/west of the main storm line as it exits or decays. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...REV AVIATION...12