Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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353 FXUS63 KIWX 040711 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 311 AM EDT Thu Jul 4 2024 .KEY MESSAGES... - Chances for showers and thunderstorms will be possible today with the greatest chances mainly south of US-30. Additional chances for showers and storms occur on Friday with strong to perhaps severe weather possible. - The best day of this weekend looks to be Sunday with seasonable high temperatures in the low to mid 80s and a mix of sun and clouds. Some rain is possible on Saturday, especially the first half of the day, and temperatures look to be below normal. - Our next round of showers and storms looks to occur between Monday and Tuesday. && .DISCUSSION... Issued at 304 AM EDT Thu Jul 4 2024 Much of this period`s pattern will be shaped by a subtropical high in the Western CONUS and another in the Gulf States as well as a trough in the middle CONUS States. A Pacific upper jet within the mid to northern tier of the United States contains a deepening upper low that enters the northwestern Great Lakes tonight into Friday. Closer to the surface, a cold front pushed through the forecast area yesterday evening and now straddles the southern portion to just slightly south of the forecast area this morning and appears to wash out as the day goes on. As we head into the afternoon and evening hours, a low level jet encroaches on our southwestern areas, this brings additional moisture and better forcing to the area. Models indicate the better instability will be south of the front, but also that initial dry air may cut into the intensity of showers that try to approach from the southwest in the midday to early afternoon time frame. As a result, they would just be light showers or virga at the onset. One component of this setup that`s still without a lot of confidence is the placement of the warm front through the day today. Some models are still stalling it out in the same spot through the day today while others are allowing it push farther north. As a result, am more confident in chance PoPs south of US-30, but slight chance PoPs north. As these showers move in, models also are gutting instability until at least after midnight tonight. Sub 30 kt effective shear during this time frame will likely keep severe weather at bay, but given the moisture available, there could be ponding with training of storms over the same area, especially if that warm front stays stalled over the area today. At the very least, we can expect a cold front to push through, from west to east, from sunrise Friday morning through Friday afternoon. The greatest residence time of instability appears to reside east of I-69 and perhaps south of US-24. With some stronger shear in this bounded area, perhaps a few stronger to severe storms could form. At least by this point, models are bringing that potentially stalled warm front northward. Even still, model reflectivities are not forming strong storms. This will need to be watched going forward and wouldn`t be surprised to see a marginal risk of severe weather hoisted by SPC for Friday. Friday`s cold front looks to gut the humidity by Saturday. However, enough mid level moisture, cooled mid level temperatures, and forcing may still be around to provide some showers as vorticity wraps around the departing upper low. There`s little if any instability though so this would have limited convective enhancement, but it does look to have some large scale ascent to aid its QPF output. As a result, also expect below average temperatures for this time of year with highs in the mid to upper 70s. Sunday looks to be the better of the two weekend days with surface high pressure skating by in the early portion of the day and mid level ridging moving through providing dry weather and a return to more seasonable temperatures with highs in the low to mid 80s. Our next trough, which is slowly deepening, enters the Northern Plains on Monday and models indicate there will be an instability axis oriented such that Lake MI-adjacent counties are in around 1000 J/kg of MUCAPE as waves of vorticity on the weaker side of the scale move northeast into the Northern Great Lakes Monday morning. The base of the trough continues traversing eastward through the day so that a stronger area of vorticity reaches the area Monday night. While instability appears to wane at night without the diurnal influence, can`t totally rule out a convective influence and rain chances continuing into the night. Monday looks like the warmest day of the long term with highs in the mid to upper 80s and heat indices around 90 degrees. Additional afternoon chances for showers/storms will be possible Wednesday and Thursday as an upper low sets up to our north and spokes of vorticity pass through in the flow. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 150 AM EDT Thu Jul 4 2024 VFR Conditions are expected at the TAF sites for a majority of the period, with the exception of brief dips to MVFR this morning with any BR that develops. Calm winds, low level moisture, and a mix of clearing/clouds led to areas of BR and patchy FG. Most of the visibilities at the moment are in the 2-6SM range where BR has developed, with isolated spots less than 2 miles. Most of the guidance keeps both KFWA/KSBN VFR, but there are a few suggesting around 4-5SM for KFWA later this morning. Held of for KSBN at the moment given no drops in visibility yet and the guidance all showing VFR/P6SM tonight-but wouldn`t be surprised if I had to add in later. Have a tempo in at KFWA from 10-13z. Otherwise, variable winds will shift south-southwest and increase slightly through the afternoon. There are chances for showers at both terminals in the afternoon, but the better confidence is at KFWA so have a prob30 in there from 19-23z, then becoming a prevailing group after 00z. KSBN is dry for now. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ DISCUSSION...Roller AVIATION...MCD