Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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023 FXUS63 KIWX 041736 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 136 PM EDT Sat May 4 2024 .KEY MESSAGES... - Active weather pattern for this week, with chances for showers and storms every day. The best chances will be Tuesday into Thursday when a stronger low pressure system moves through the area. A few strong to severe storms are possible Tuesday afternoon into Wednesday, but confidence is low at this time. - Temperatures linger in the 70s and low 80s through most of the week, except Sunday when highs north of US 24 will be in the 50s and 60s, coldest near Lake Michigan. Next weekend lows will be in the 60s. && .DISCUSSION... Issued at 458 AM EDT Sat May 4 2024 Mostly dry today as a weak surface high lingers in place, with mid level ridging breaking down somewhat late this afternoon thanks to an approaching trough. There is a stationary front settled just to the southeast of our CWA, oriented from roughly southern Ontario southwest towards Lima, OH and down into Saint Louis, MO. This will be a focus for shower activity, maybe a few storms, into the afternoon-with the best chances after 18z as we build up some instability. Going by the NAM, it looks like we`ll have around 500- 1000 J/kg of sfc based CAPE by 21z largely east of I 69 (more like 200-500 J/kg west), in addition to weak moisture advection from the southeast and mid level lapse rates of around 7 C/km. We have a subsidence inversion to overcome and weak forcing overall, but felt 20-30 percent pops were warranted for the east. Luckily the bulk effective shear for the afternoon time period is less than 20 knots, so if any storms develop, don`t expect much in the way of severe weather. Otherwise, expect partly to mostly sunny skies with increasing clouds towards the evening. Highs will be in the 70s. Late this afternoon into tonight, a surface low and mid level trough will move through, bringing better chances for rain and some storms that dwindle with eastward progression. SPC Day 1 outlook has all of our area in general thunder, with the marginal risk for severe weather to the west of our CWA associated with the system, where wind shear is more on the order of 25-35 knots and the cold front is moving through during more favorable time of day. For us, the shear weakens to about 20-30 knots, with waning instability-so while I have higher pops west tonight (40-60 percent) I dropped them off to 20-35 percent further east with lesser chances for thunder. Severe weather is not expected at this time. Lows will be in the 50s and 60s, warmest inland from Lake Michigan. Isolated/scattered showers & storms will persist east of I 69 through Sunday evening-largely associated with the slowly exiting cold front. Again, minimal shear with around 500-1000 J/kg of sfc based CAPE by Sunday afternoon in the east warrants 20-30 percent pops, however, severe weather is unlikely. Highs will be in the 50s and 60s north of US 24 (coldest near Lake MI) and the low to mid 70s south. Otherwise, expect partly to mostly sunny skies. For most areas, Sunday night into late Monday night will be dry thanks to an amplifying mid level ridge and an expansive surface high sprawling over the Great Lakes. A low pressure system approaching from the southwest Monday afternoon and evening will bring increasing chances for showers and maybe a few thunderstorms south of US 24, but confidence is low (it could miss us to the south all together). Highs will be in the upper 60s and low to mid 70s. Tuesday into Wednesday will be the best shot at more significant precipitation and even thunderstorm chances. An upper level low dives into the north central CONUS and develops a surface low somewhere over IA/MO/KS Tuesday afternoon, lifting it through the Great Lakes as it deepens. The low is forecast to reach southern Ontario roughly Wednesday evening. The warm front moves through Tuesday, followed by the cold front on Tue Night/Wed Am, with decent moisture transport out ahead of the low. Kept the 50-90 percent chances Tuesday into Tuesday night, with thunderstorms likely. I suspect that we have potential for severe weather if this pans out as the models currently suggest, with 40-65 knots of bulk effective shear and 500-1500 J/kg surface based cape by Tuesday afternoon/evening. At this time, we are in the 15 percent for the western half of the CWA for the Day 4 SPC outlook, and think it`s definitely worth monitoring. The upper low over the central CONUS will gradually migrate eastward into the Great Lakes by Friday afternoon, lingering through the weekend and bringing additional chances for showers and storms, particularly Thursday. A secondary low develops behind the Tue/Wed system in much the same location, drifting over the forecast area through the day and bringing potentially heavy rain-but too far out to add much detail at this point (we are in the WPC Excessive Rainfall Outlook Marginal Category for Wed/Thu). Temperatures linger in the 70s and low 80s until the weekend, when we cool into the 60s for highs (40s and 50s for lows). && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 133 PM EDT Sat May 4 2024 Two boundaries collocated with mid level vorticity and areas of low level convergence allow for times of cloud cover and rain between the start and end of this TAF period. A boundary pushed north and west this morning allowing cloud cover at FWA. CIGs rising from MVFR to VFR start this TAF period there as a result. Light rain and drizzle was observed under that cloud this morning, but with the raising ceilings expect to see less of that for the afternoon. Expect VFR conditions to continue into later portion of the overnight. On the other hand, an area of vorticity and surface convergence associated with a line of convective showers moving eastward from IL encroaches on SBN this evening. With much of the insolation staying west of IN-15 today, low level lapse rates steepen and instability increases ahead of the line. Even still models, dissipate it as it moves inland from Lake MI. Wouldn`t be surprised to see a brief increase of winds from the outflow boundary as well as some showers or perhaps a thunderstorm at SBN before it dissipates. Guidance indicates the cold pool associated with this may leave some MVFR CIGs behind at SBN for late tonight/early Sunday morning and perhaps FWA for Sunday morning. IFR CIGs may also be possible at SBN, but confidence on that is low at this time. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ DISCUSSION...MCD AVIATION...Roller