Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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958 FXUS63 KDVN 211111 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 611 AM CDT Fri Jun 21 2024 .KEY MESSAGES... - Another hot day expected today, with highs in the lower 90s along and south of Highway 30 - Increasing chances (20 to 50%) of showers and storms after midnight tonight, with an outside chance of a strong storm - More robust thunderstorms are expected Saturday afternoon and evening, with some strong to severe storms possible - Generally dry conditions return for Sunday through Thursday, with another round of convection Tuesday and Tuesday night && .SHORT TERM /THROUGH SATURDAY/... Issued at 356 AM CDT Fri Jun 21 2024 Things have calmed down quite a bit from yesterday evening`s convection, with largely dry conditions observed across the area. A low-level thermal inversion, which has developed across our far northern areas, has resulted in a low stratus deck, and some areas of fog will be possible early this morning along the Highway 20 corridor. The overall synoptic pattern hasn`t changed a whole lot over the last few day, with a large upper-level high anchored over the southern Great Plains region. We remain on the far northern side of the upper high, with a low-amplitude trough developing over the northwestern CONUS and an upper-level jet streak over the Dakotas into northern Minnesota. The heat dome continues to be strong, with temperatures expected to warm to the upper 80s north and the lower 90s south for highs. A warm frontal zone continues to be draped across far northern Iowa into southeastern SD, where a large complex of thunderstorms has developed early this morning, which should translate eastward. This complex, plus additional convection expected later on along the warm front, could graze our far northern areas later on, which would influence temperatures if they make it into our area. However, the CAPE gradient does appear to remain north of us, so the convection is likely to remain anchored along it and stay away from our region. Humidity today should be slightly lower compared to the last few days, so although it will be another hot day, heat indices should remain below 100 degrees, precluding the need for heat headlines. Shortwave ridging will become more likely in our region late tonight as mid-level shortwave impulses sink southward. This will support increasing chances (20 to 50%) of showers and storms. Both shear and instability appears to be pretty meager, with deep-layer shear less than 25 knots and most-unstable CAPE from the HREF less than 1000 J/kg, so more likely non-severe storms should result. Still, there is an outside chance of a strong storm, and SPC does have a Marginal Risk, or level 1 of 5, for areas along and north of a Freeport, IL to Van Horne, IA line. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Issued at 356 AM CDT Fri Jun 21 2024 As we go through the day Saturday, the aforementioned low-amplitude trough over the northwestern CONUS gradually moves eastward with time, and an attendant surface cold front will sweep through our area during the afternoon to evening time frame. Instability will increase to around 1500 to 2500 J/kg of surface-based CAPE per the HREF ensemble mean, and strengthening mid-level westerlies around 35 to 45 knots will result in deep-layer shear increasing to 30 to 40 knots, so more supportive of strong to severe convection. Low-level shear and mid-level lapse rates remains a bit more limited, but PWAT values near daily records (2+ inches) per the SPC sounding climatology for the Quad Cities area should help support strong, damaging wind gusts as the main hazard, with large hail and isolated tornadoes as secondary threats. As such, SPC has expanded the Slight Risk, or level 2 of 5, for areas along and northwest of a Keokuk, IA to Sterling, IL line, with Marginal Risk elsewhere. Timing of the front remains uncertain, given the differences among the CAM guidance, but confidence remains high for a Saturday afternoon arrival. After the front moves through late Saturday night, a much more pleasant day is expected Sunday, with lots of sunshine and more seasonal temperatures and humidity. Sunday is definitely looking like the pick day for the weekend! In fact, the large-scale pattern appears to support a period of mostly dry conditions through Thursday, thanks to upper-level ridging developing over the Intermountain West states and surface high pressure settling into the upper Midwest. The only other opportunity for showers and storms appears to be for Tuesday and Tuesday night, as yet another compact upper-level trough and attendant surface cold front crosses the area. The timing of the front per the latest global models does appear to be advantageous for more strong to severe storms, especially with the CSU ML severe probs suggesting strong to severe convection with a hot and humid air mass again in place, so we will need to watch Tuesday as well. && .AVIATION /12Z TAFS THROUGH 12Z SATURDAY/... Issued at 611 AM CDT Fri Jun 21 2024 MVFR to LIFR conditions were observed early in the TAF period at CID and DBQ, thanks to a low stratus deck and fog development. These conditions should improve fairly quickly around 13z or so, but IFR ceilings should linger for a time at DBQ. Some isolated showers and storms are possible later this afternoon and evening, but confidence is rather low on the coverage due to large differences among the high resolution models, so have continued to use PROB30 groups to highlight the most likely timing. A widespread cumulus field is expected late this morning through the afternoon, with ceilings generally around 4 to 5 kft. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...Schultz LONG TERM...Schultz AVIATION...Schultz