Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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734 FXUS63 KDVN 010752 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 252 AM CDT Mon Jul 1 2024 .KEY MESSAGES... - Beautiful day ahead of us, with temperatures in the 70s and increasing clouds. High pressure will slowly push east today, with increasing moisture ahead of the next wave. - Several rounds of showers and storms are expected from Tuesday night through Wednesday morning, with chances retuning again Wednesday night through Thursday. Severe weather and flash flooding are both possible with any storms, especially Tuesday PM, as repeating storms are expected. - Unfortunately, Independence Day is looking to be a wet day, as a warm front brings the potential for widespread showers and storms once again. Too soon to determine severe risk. - Moderate to Major River Flooding continues, with further changes to the forecast expected due to fluctuations in the QPF forecast. && .SHORT TERM /THROUGH TONIGHT/... Issued at 240 AM CDT Mon Jul 1 2024 High pressure will be the rule through the day, leaving us with another beautiful day, with temperatures in the 70s throughout. Today will be very similar to yesterday, with the main difference being an increase in cloud cover. This increase in cloud cover can be attributed to increasing moisture, as ridging builds overhead and LLVL southerly flow kicks in. The best of the moisture return will be west of the forecast area through the day, which is a good thing, as a large bout of energy pushes through the area today, as a wave develops over the Rockies. With such dry air in place today, we are not expecting any precipitation with this. Tonight, we start to see the moisture increase slowly from the west. The main focus for this moisture will be along our western border, especially in our northwest. In these areas, PWATs will quickly rise into the 1.75-2.00" range, favoring heavy rainfall in any storms that develop. Guidance does not have the best grip on when we will start to see precipitation, with the HREF being a good happy medium at the moment. Currently, the HREF starts to introduce measurable precipitation to our west around 09-12z tonight, which is about 4- 7am local time. Thus, this will be quite late, with chances increasing through the day tomorrow. This will be discussed more below. We are not expecting much on the side of excessive rainfall with any storms that we get tonight, as convection seems to be more scattered in nature, rather than widespread heavy rainfall. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Issued at 240 AM CDT Mon Jul 1 2024 Much of the forecast below is from the previous forecast package, as they covered this event very well. Some updates were made, resulting from latest trends in guidance, but the big picture largely remains the same. Up front, one of the more notable changes was the introduction of an Enhanced Risk (level 3/5) for Severe Weather in southeast Iowa, with all hazards in play. Also, with several chances for heavy rain this week, we may need to start considering headlines for the Flash Flood Potential, especially as we approach Tuesday night and then again Thursday. More widespread showers and storms are expected Tuesday afternoon into early Wednesday, as stronger synoptic forcing aided by a shortwave aloft and the right entrance region of a 100-120 kt 250 hPa jet steak overspread the Upper Midwest, while at the surface a cold front moves through. This will be especially true through the nighttime hours, which seem to be the best chance for widespread heavy rainfall. The primary concern for this period remains heavy rain and flash flooding. NAEFS and ENS continue to support PWATs climbing to 1.75 to around 2.00 inches by 00z Wednesday, which is 2 to 3 standard deviations above climatology and approaches the 99.5 percentile or is near max of their respective climatologies. Ensemble guidance shows high probabilities of at least 1.00 inch from Tuesday evening through Wednesday AM, especially across the northwest 2/3rds of the service area, with 60-90% favorability amongst guidance. However, given the convective nature and magnitude of the synoptic ascent doubling the PWAT would give a general idea of the higher limit, which in this case with PWATs around 2.00 inches would yield potentially higher amounts of around 4.00 inches. With rivers rising, we will be watching this heavy rain potential closely, as this will lead to fluctuations in the river forecast. In addition, the significant moisture advection (IVT) and a southwesterly LLJ of 40 kt could contribute to backbuilding and an elongated MCS, resulting in a risk of flash flooding. This flash flood threat looks to be highest especially across east-central and northeast Iowa, into northwest Illinois, where rainfall in the past week has accumulated 125-200+ percent of normal and soils are saturated. Severe weather potential may exist by Tuesday PM, as deep layer shear 0-6km increases to 35-45+ kts aided by the approaching shortwave trough. Models try to build in the instability during this time, especially west of the Mississippi River with MLCAPE increasing to 1000-2000+ j/kg. Initial supercell potential will exist before upscale growth into a line of storms, transitioning to a wind threat, provided sufficient destabilization occurs. As previous shift mentioned, one thing to watch for is any potential OFBs from Tuesday AM convection, which could serve as a focus for redevelopment and an earlier severe/flash flood threat Tuesday PM. Otherwise, Tuesday evening/night would be most favored for the severe. If rain/clouds persist for much of Tuesday, that could limit instability or keep the primary instability axis further west. Bottom line, extent of instability and initial placement and timing of the surface convergence will play a key role in how far east/south the severe threat reaches. A brief respite in the wet weather is expected Wednesday AM/PM, but the emphasis is on brief, as a surface warm front passes north into the area as early as late Wednesday night/early Thursday AM with convection potential increasing (30-60%) south of I-80. Then, the shower and storm potential increases over the rest of the area on the 4th of July into Thursday evening, as a vigorous shortwave trough evolves into a closed low while traversing near the international border to the north. Ensembles point to PWAT values of 2.00+ inches pooling near and south of the boundary supporting a heavy rain threat. The frontal location will be critical to where this heavy rain threat eventually sets up, and will bear watching in the coming days given the ongoing river flooding and saturated soils in some areas. With this forecast in mind, we may be preparing to see more of nature`s fireworks, rather than actual fireworks. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1224 AM CDT Mon Jul 1 2024 VFR conditions will prevail through the TAF period, with light southeast winds. No sig wx is expected at this time. && .HYDROLOGY... Issued at 1135 AM CDT Sun Jun 30 2024 New forecasts this morning for the tributary rivers have come in slightly lower for the Cedar River at Conesville, Iowa River at Wapello, and the Wapsipinicon River near De Witt. However, no changes to the expected flood category were made. The crest on the Cedar River has gone through Cedar Bluff and should reach Conesville by Monday morning. A return to an active weather pattern will bring a heavy rain risk Monday night through Wednesday that may result in renewed rises on many tributary rivers. Those with interests along the tribs should monitor future forecasts, especially Monday evening when the bulk of the 1-3 inch rainfall will be incorporated into the river model. On the mainstem Mississippi, no change to the expected flood categories with the new forecasts this morning. Broad crests are now shown from Dubuque to Fulton LD13 late in the 7 day forecast. A widespread heavy rain event (1-3" amounts across much of eastern IA into southern WI) is anticipated in the Monday evening through Wednesday time frame which may have an impact on expected rises and delay the crest downstream. Residents and interested individuals/businesses should monitor future forecasts for any changes to the river rises. && .CLIMATE... Issued at 145 PM CDT Sun Jun 30 2024 Record low temperatures for July 1 Burlington......51 in 1918 Cedar Rapids....43 in 1924 Dubuque.........47 in 1995 Moline..........48 in 1988 && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...Gunkel LONG TERM...Gunkel/McClure AVIATION...Gunkel HYDROLOGY...Gross CLIMATE...McClure