Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
Issued by NWS Quad Cities, IA IL
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301 FXUS63 KDVN 180515 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 1215 AM CDT Sat May 18 2024 .KEY MESSAGES... - Isolated to scattered showers and storms are possible Saturday afternoon west of the Mississippi River. - An active pattern returns next week, particularly for the Sunday night through Tuesday night time frame. - There is 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 SUNDAY/... Issued at 158 PM CDT Fri May 17 2024 Mainly clear skies across the area this afternoon as high pressure sits across the area. Scattered showers and storms have remained to the southeast of the area. Temperatures at 2 PM ranged from 77 degrees at Freeport and Independence to 81 degrees at Macomb. Expect quiet weather across the area through Saturday morning as high pressure slowly shifts to the east. Low temperatures on Saturday morning will be in the upper 50s to around 60 degrees with light and variable winds. A weak shortwave is forecast to pass to our north Saturday afternoon and push a weak cold front into the area. Moisture is limited with some warmer air in place at 700 MB. The 12 UTC NAMNest continues to shows an isolated to scattered line of showers and storm developing in central Iowa and slowly moving into the area during the late afternoon. There is 1000 to 2000 J/KG of CAPE but shear is limited to around 20 knots. There is disagreement among the different models on the degree of instability tomorrow afternoon. However the Storm Prediction Center has a Marginal or level 1 out of 5 risk of severe storms for parts of the Highway 20 corridor but confidence is low in this occurring. If showers and storms do form do not think that they will last very long given the dry atmosphere and weak shear. High temperatures on Saturday will be in the mid 80s. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Issued at 158 PM CDT Fri May 17 2024 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 /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1206 AM CDT Sat May 18 2024 VFR conditions are expected through the TAF cycle. A weak cold front will track across Iowa this afternoon and evening, with scattered showers and isolated thunderstorms developing ahead of it. These storms are forecast to weaken before reaching eastern Iowa (around 00z at CID) and have left out mention for now due to low coverage. NBM probability of precip and thunder potential is currently less than 10%. Behind the cold front, winds will switch out of the northwest. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...Cousins LONG TERM...Schultz AVIATION...Gross