Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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959 FXUS63 KDVN 171736 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 1236 PM CDT Fri May 17 2024 .KEY MESSAGES... - Areas of fog, with some dense fog, will continue this morning generally along and east of the Mississippi River - Largely dry conditions expected for the reminder of the day through tonight - An active pattern returns next week, particularly for the Sunday night through Tuesday night time frame - There is now a Slight Risk of severe weather for Tuesday across the entire forecast area - Very warm this weekend, with more seasonal temperatures coming for the middle of next week && .SHORT TERM /THROUGH TONIGHT/... Issued at 404 AM CDT Fri May 17 2024 Areas of fog have developed early this morning, mainly for areas along and east of the Mississippi River. Latest observations reveal that dewpoint temperatures here have hovered in the upper 50s to lower 60s, compared to Tds in the lower 50s to the west. This is due to a surface front becoming stationary and bisecting our forecast area from southwest to northeast. We are now starting to see dense fog reported, with visibilities of 1/2 mile or less from Burlington, IA northeast towards Sterling/Rock Falls, IL. With that being said, we have issued a Dense Fog Advisory through 9 AM this morning to encompass the aforementioned areas. Use extra caution if travel this morning! Eventually, the fog will dissipate by mid-morning, leading to an overall dry period for the remainder of the day and tonight. Guidance indicates we will remain under a shallow mid-level shortwave trough, but given very dry air in the HREF ensemble soundings, most of the area will see sunny skies. The only exception we will need to watch will be over our extreme southeast in Hancock and McDonough counties in west-central Illinois, where some high-res models suggest surface temperatures warming to the convective temperature, which could spark off a few isolated showers, but chances of this happening are very low (less than 20%). Today`s highs should warm to the lower 80s. Tonight will be dry and quiet, as the aforementioned trough scoots off to the east. Lows should fall to the middle to upper 50s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Issued at 404 AM CDT Fri May 17 2024 The upcoming weekend will overall be dry and quiet, thanks to a dry air mass in place. Synoptically, we will be between a northern jet stream across the northwestern CONUS, and a sub-tropical jet to our south. A brief period of mid-level ridging will keep our conditions quiet Saturday before a weak surface cold front sweeps through Saturday evening. Confidence in showers and storms developing along the front is pretty low, given the amount of dry air in place, but there are some hints for at least slight chances (20 to 30 percent) for precipitation. Mixed-layer CAPE values progged around 1000 to 1500 J/kg could fuel some thunderstorms, but deep-layer shear appears to be quite meager, with values around 20 knots, so any organized convection should be hard to come by. A more active pattern then takes shape for Sunday night through Tuesday as the northern jet stream begins to amplify over the Intermountain West, while the southern stream jet lifts northward and strengthens as it meets the northern jet. A series of mid-level shortwave impulses will sweep through our region Sunday night through Tuesday night. With temperatures warming to the lower to middle 80s Monday and Tuesday, and dew point temperatures in the lower to middle 60s, instability values will be elevated. However, there are some differences on just how much, with the GEFS probabilities of CAPE 1000 J/kg or greater around 80 to 100 percent Tuesday, but the ECMWF were more around 40 to 70 percent for a similar threshold. The kinematics appear to be rather strong, with both the GEFS and ECMWF ensemble mean 500 mb jet magnitude of 50+ kts on Tuesday, nosing into central Iowa. Not only will the deep- layer shear be enhanced, but so will the low-level shear, given clockwise-curved hodographs from the various coarser-resolution ensembles (GEFS, ENS, GEPS). The most recent CSU machine-learning severe weather probs are painting some decently high values for Monday and Tuesday (especially Tuesday, which is when the better kinematics are expected). Additionally, the ECMWF EFI for the CAPE/Shear combination are showing values around 0.6 to 0.8 along and south of I-80 - additional evidence for a possible severe weather event Tuesday. Just before we sent this discussion, SPC introduced a Slight Risk (level 2 of 5) for severe weather across our area for Tuesday. Confidence on the exact timing of severe weather remains uncertain, but with this new outlook, the situation will need to be watched as we approach Tuesday as all hazards of severe weather appear possible. In addition, some heavy rainfall will be possible with this event, given Pwat values around 1.3 to 1.7 inches, which would be above the 90th percentile for DVN from the SPC sounding climatology. For Wednesday and Thursday, confidence in the forecast decreases as models aren`t in as much agreement. The NBM PoPs reflect this disagreement in the GEFS/ENS ensembles, with PoP values around 20 to 30 percent, despite a strong signal for rainfall Wednesday evening from the GFS deterministic model. It does appear that temperatures will return to more seasonal values by mid-week, however, with values in the lower to middle 70s. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1222 PM CDT Fri May 17 2024 High pressure will move across the area through the TAF period resulting in clear skies and VFR conditions. Southerly winds will begin to increase after 14 UTC on Saturday with speeds of 10 to 15 knots. && .HYDROLOGY... Issued at 1051 AM CDT Thu May 16 2024 Changes: None. Discussion... Most tributary rivers in eastern Iowa have crested and are slowly dropping. The exception is the lower Iowa River where the crest is currently working its way through Wapello and Oakville. On the Mississippi, Gladstone and Burlington will begin a broad crest just above flood stage that will continue through Friday. After a relatively dry weekend, the active weather pattern will return next week with the potential for several rounds of rain. While rainfall amounts continue to be somewhat uncertain, any heavy rainfall would prolong the high river levels on tributary rivers in eastern Iowa, northern Illinois and on the Mississippi River. The longer range outlook through the end of the month has a 40-42 percent probability of above normal rainfall. This outlook suggests the potential for additional improvement with the severe drought conditions across eastern Iowa. Unfortunately, this outlook would also suggest that river levels could remain higher than normal. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...Schultz LONG TERM...Schultz AVIATION...Cousins HYDROLOGY...08