Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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211 FXUS63 KDVN 230308 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 1008 PM CDT Sat Jun 22 2024 .KEY MESSAGES... - Active weather today, as a cold front brings strong/severe storms this afternoon and evening. The SPC highlights our area in a Slight Risk (level 2/5) for Severe Weather, with winds and tornadoes being the main threats. - Unseasonably high PWATs will allow for heavy rainfall throughout the area, with a specific focus on areas along/north of Highway 30. This will result in a localized flash flood threat today. With this new rainfall, along with high regional rainfall, river flooding is expected for many area rivers over the next 1-2 weeks. - A Heat Advisory remains for areas along and south of Interstate 80, with heat index values between 90-100. The unseasonably warm conditions will continue through much of the long term forecast, with a couple days of relief in the mix. && .SHORT TERM /THROUGH SUNDAY/... Issued at 1249 PM CDT Sat Jun 22 2024 This Afternoon into Tonight... This will be the time period to keep an eye on, especially over the next 4-8 hours. A surface low will track just north of the area today, dragging a cold front through the area. This cold front will be the reason for rapid thunderstorm development this afternoon and evening, where some may be strong to severe. Currently, the SPC has highlighted our area in a Slight Risk (level 2/5) for Severe Weather throughout the whole area, with the main hazards being winds and tornadoes. The other hazard will be the potential for flash flooding today, where the WPC highlights much of our area in a Slight Risk for Excessive Rainfall. Both of these hazards will be discussed in more detail below. On top of theses hazards, we will see some excessive heat today as well, with heat index values between 90-100. A Heat Advisory is out for areas along/south of Interstate 80, highlighting this potential. First, we will dive into some severe parameters. Looking at the sounding analysis throughout the area, temperatures are expected to rise into the 90s, which will combine with dewpoints in the 70s to develop moderate instability. Currently, guidance ranges between 1500-3000 CAPE. This will combine with sufficient shear, generally ranging between 30-40 KTs. While this is not high shear, it should balance well with the instability for organized convection, some of which will be supercells. With shear just a bit off from being parallel to the boundary, this should aid in repeated storms early and allow for cold pool development. Thus, this favors the upscale growth, leading to a line of storms later in the afternoon. Lapse rates are quite low, especially in the midlevels, which also limits our widespread hail potential. Also, PWATs are unseasonably high, which will also limit hail growth. Thus, it will take a very robust updraft to get large hail. While not impossible, this is a lower-end risk, with the best chance to see hail in the earlier, semi-discrete supercells. Much of the shear will be in the LLVLs, which will result in spin in the low levels of the storms, favoring a tornado potential throughout the event. As was mentioned above, the wind threat will end up being the main threat, with DCAPE values around 1000+ favoring this. Secondly, we shall start with the severe weather threat. We are expecting rapid development of storms at/by mid afternoon today. This is a couple of hours sooner than the initial thoughts from overnight guidance. Thus, we can see showers and storms develop as early as 2/3pm for areas along and north of Highway 20. The initial storms that develop are looking to be more of a semi- discrete line of supercells. Thus, all hazards will be possible with these, with a particular focus on the tornado possibilities with these early storms. The SPC has noted an increase in the tornado threat last night, increasing it to a 5% chance along/north of Interstate 80. Not only will we be worried about the severe potential in these areas, but we will also have a flash flood threat. PWATs throughout the area are forecast to increase above 2.00". The initial storms that develop early in the event are not expected to move southeast that quick, with some repeating rounds of storms for area. This, along with the overnight/morning rainfall, will allow for a localized flash flood threat, with that increased threat seen down to Highway 30. Finally, these supercells are expected to pick up speed as the storms mature, growing upscale as we approach the late afternoon and evening. These early storms will push southeast with the front, bringing a line of organized convection southeast towards the Quad Cities area between 5-7pm. As we transition to a linear mode of convection, we will move to a severe wind threat, with embedded tornadoes along the line possible. This will be especially true if we get bowing segments along the line, then we will see that tornado threat increase. This line of storms will continue through the area during the remainder of the evening, with the severe threat decreasing after 10pm. Residual showers and storms will continue in our southeast after midnight, but much of the area should be dry by 3am locally. Behind the front, we will be left with temperatures in the low 70s and a light northwesterly breeze. -Gunkel Sunday... Sunday will be the pick day for the weekend, with much quieter conditions expected in the wake of tonight`s fropa. Models and ensembles are in good agreement with large upper-level ridging developing to our west and surface high pressure building across the western Great Lakes, leading to partly to mostly sunny skies. The NBM is keeping our area dry Sunday into Sunday night, despite an upper-level trough just grazing our northeastern areas late Sunday. -JTS && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... Issued at 1249 PM CDT Sat Jun 22 2024 Active pattern will largely continue through next week, with a few dry days in the mix. Upper level pattern transitions next week to a ridge over the Rockies and a trough east. This will allow bouts of energy to pass through the area periodically next week, bringing sporadic chances for precipitation. Some days, the moisture will be a concern, as is usually the case. Aside from Monday and Tuesday, temperatures will remain largely in the 80s. The next significant opportunity for showers and storms will be Tuesday and Tuesday night, as yet another cold front passes through the area. A look at the convective parameter space indicates instability to be rather high with a pretty strong signal for another hot and humid day, but the deep-layer shear values are pretty meager. The CSU ML severe probs remains bullish on severe potential for Tuesday, so we will have to keep an eye out for perhaps another bout of strong to severe storms then. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 659 PM CDT Sat Jun 22 2024 Scattered thunderstorms this evening ahead of a cold front. MVFR/lcl IFR conds in TSRA. Once the front passes northwest winds can be expected with areas of MVFR cigs. On Sunday, VFR conds with northwest winds 10-15 kts. && .HYDROLOGY... Issued at 959 PM CDT Sat Jun 22 2024 In the Cedar River basin, the most recent rain event underperformed significantly, particularly around the Shell Rock River. This coupled with more soil absorption than expected led to a decrease in flows on the Shell Rock River by as much as 5000 cubic feet per second. When this translated to the Cedar River, many forecasts became lower. Included in this is the Cedar River at Cedar Rapids forecast, which is still likely to reach Moderate flood stage. Some precipitation is still expected before the Cedar River crests towards the middle to end of this week, so we will continue to monitor and update. The Mississippi River is expected to reach flood stage at multiple locations, including the Rock Island gage, by the middle of this week. Long term we expect the Mississippi to reach Moderate and/or Major flood stages the week of the Fourth of July, with the crest at the Rock Island gage possibly reaching just over 18 feet early on the Fourth of July. However, a larger margin of error should be taken into consideration whe forecasting precipitation amounts and locations in the 7-10 day timescale. Watches are currently out for most of the Mississippi River and warnings will follow in the next few as a clearer picture is drawn on what precipitation and routed water we have coming downstream. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...Gunkel LONG TERM...Gunkel AVIATION...Haase HYDROLOGY...Wilson