Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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131 FXUS63 KDVN 190007 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 707 PM CDT Sat May 18 2024 .KEY MESSAGES... - Scattered showers and storms will wane after sunset tonight. There is a Marginal risk (level 1 of 5) of severe weather today west of the Mississippi River. - Boundary stalls south of the area as temperatures again reach well into the 80s as chances for thunderstorms return late. - Active pattern through the long term with chances of strong to severe storms through Tuesday. Tuesday is the best day for severe weather in the next 5 days. && .UPDATE... Issued at 705 PM CDT Sat May 18 2024 Cold front approaching the nw part of the forecast area had briefly flared up a few thunderstorms along the front, but since then they have weakened rapidly. The bulk of the thunderstorms, some severe, have been across Wisconsin and western Upper MI where the stronger shear/forcing exists. In our forecast area, the SPC mesoanalysis showed weak shear (<20 kt) along with weak forcing, while the SBCAPE was about 1500 J/kg. In addition, the 00z/19 DVN sounding showed a decent capping inversion above 800 mb. Being that we are past peak heating it appears that the threat for any severe storms has diminished. However, still can`t rule out an isolated storm or two this evening until the front moves through. && .SHORT TERM /THROUGH TONIGHT/... Issued at 109 PM CDT Sat May 18 2024 Temperatures well into the 80s today were found area-wide. Dewpoints in the upper 50s to low 60s made it feel somewhat nicer than the middle of July. To the west of the area, a cold front was located across the center of Iowa. A shortwave passing north of the area today will drag this front through the area this afternoon and into the evening. The boundary will then stall out across southern portions of the area. This boundary on Sunday will separate the higher moisture air from the drier air. Nonetheless, we will see highs again in the 80s, but with drier air than today. With that boundary in place across the south, we could see some thunderstorms redevelop along the front later in the day and move east towards us late. Most of the impactful weather will likely be ongoing at 00z tonight as the cold front moves through the area. Guidance has CAPE building ahead of the front to around 2000 J/kg this afternoon. Shear looks very weak, so updraft organization is not expected. Pulse like storms are expected if they develop. The main question today is forcing. The main upper level forcing is way north, so the front and daytime heating will be the main drivers for thunderstorm development. CAMs have either a broken line of storms or not much with the exception of the highway 20 corridor. Dprog/Dt of the HRRR shows run to run variability with some having convection down to highway 30 the rest further north. The NAMnest has convection all the way through the CWA. Think the best chance for storms is highway 20 north. In a nod to the NAMnest, did keep schc south through I80. Am not too big on severe today. Could see near severe wind gusts and hail, especially due to the steeper lapse rates, but don`t expect cells to have much longevity to really get going. && .LONG TERM /SUNDAY THROUGH SATURDAY/... Issued at 251 PM CDT Sat May 18 2024 Extremely active pattern with a mid-summer like pattern is expected to last through most of the period as a stalled out boundary resides just south of the CWA. This boundary will separate the area between Tds in the 50s, to the more robust deep moist Tds in the 60s and 70s to the south. A series of weak waves and possibly MCVs/convective induced waves/ move over the boundary later Sunday into Monday evening. A strong wave, with better shear is expected to approach the area into Tuesday. A deepening surface low with this wave will help to bring this boundary north as a warm front Tuesday. This will bring higher Tds into the area ahead of the wave and increased shear. Then the boundary is sent south again as a cold front later Tuesday. After this point, there are questions about where the boundary will be and additional chances for thunderstorms. Closer look at the guidance for Sunday evening suggests a MCV rolling into the area after 00z. The 12Z HRRR has convection firing with this wave like feature across the area. In fact, the HRRR suggests some of these storms could be supercellular in nature. As mentioned before, shear looks to be weak, however, if this truly is a MCV, then the shear may actually be stronger than forecast. With Tds lower tomorrow, think that these supercells would be hailers and possibly HP in nature and a wind threat. That said, other guidance keeps us clear. We will need to keep an eye on convection upstream to see if this forms. So there is a conditional risk for severe weather tomorrow afternoon and evening. Monday, another possible day with severe weather as the wave induces height falls and the sfc boundary moving north again. The NAMnest depicts yet another MCV moving through our area Monday with redevelopment of showers and storms in the afternoon. This is yet another potential case where we could see higher shear than forecast. With clouds possibly keeping Ts lower, our T/Td spread may be lower as well. Llvl winds looked back so if we develop afternoon showers and storms monday they could be severe as well. We currently have a mrgl for this day as well, but could see this day updated to a slight if the MCV comes true. So after the next two days with conditional severe weather outlooks we get to Tuesday when a better wave makes its way into the area. This one will bring better shear into the area Tuesday. Storm Mode: 0-6km shear vectors are perpendicular to the forcing and around 40kts. This would suggest supercells and they will likely form first west of the CWA. However, upper level flow is weak so expect convection to quickly become cold pool dominated. Expect a mature/ing bow to enter the area in late afternoon. Severe Hazards: 0-3km shear vectors of 40kts will help the production of mesovorts with localized higher wind gusts and possible tornadoes. The LLJ is impressive for the afternoon, and even more so after sunset, so this thing could really ramp up later in the evening. With weak upper-level flow, the overall system should not be moving all that fast. Some hail is possible early on, but think this is rain/strong wind/tornado event. Heavy Rain: In addition, some heavy rainfall will be possible with this event, with PWs around 1.5 to 1.7 inches, which would be above the 90th percentile for this time of year. Wednesday On...additional showers and storms will be possible late week. However, model timing differences in shortwaves moving through the flow precludes changing the PoPs, which are in the 15 to 30 percent range for each 6 hr period through Friday. There will be some dry hours, but when this will occur is still in question. Temperatures will return to more seasonable values by late week, with highs in the 70s and lows in the 40s. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 705 PM CDT Sat May 18 2024 VFR conds through this taf cycle. An isolated shower or storm is still possible along a cold front, but coverage too low to mention in the TAFs. Winds will turn northwest overnight then become northeast to east on Sunday. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ UPDATE...Haase SHORT TERM...Gibbs LONG TERM...Gibbs AVIATION...Haase