Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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078 FXUS63 KIWX 081725 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 125 PM EDT Mon Jul 8 2024 .KEY MESSAGES... - Chances for showers and thunderstorms increase for NW IN/SW Lower Michigan today into tonight mainly west of I-69. - Remnants of tropical system Beryl will bring showers and thunderstorms to the area Tuesday afternoon through Thursday with heavy rain at times. - Warmest conditions this forecast period expected on Monday (mid 80s to around 90), and possibly again next weekend. && .UPDATE... Issued at 1045 AM EDT Mon Jul 8 2024 Showers have been slowly weakening as they have entered southern Lk MI with some light returns still back across central IL. Main focus for the afternoon will be a cluster of showers and storms near/south of St Louis, MO that will track NE. Several CAMs try to spark additional showers/storms, albeit isol to sct, from roughly White county NE across our office and to the NE from there. Will monitor trends, but may need to expand the slgt chc and chc pops further SE for later this afternoon into this evening. Still sorting through 12Z data for the remnants of Beryl and the potential impacts. Think axis of heavier rainfall may shift somewhat SE (not dramatically) and heavier rain arrive more in the late Tue night into early Wed period, but still lots to sort out with more details in the afternoon package. && .DISCUSSION... Issued at 333 AM EDT Mon Jul 8 2024 A mid level trough continues to be centered across the Northern Plains with its eastern periphery traversing through the Lake MI- adjacent counties of MI and IN. As of this writing, there`s still plenty of disagreement on handling of the weak shortwaves moving through this area. Some high res guidance wants to bring showers through this morning whereas others hold things off until this afternoon and evening when a stronger shortwave moves into the northwestern Great Lakes and grazes our northern and western zones. Have a little more confidence in carrying PoPs this afternoon and evening with the better forcing, but also because better instability is able to build in west of I-69. Even still will cap PoPs at low end chance still with us being far enough south of the forcing in some model solutions. As this area of vorticity advances eastward, expect the forcing to wash out and for the instability to wane beyond sunset so PoPs will diminish to slight chance overnight, never reaching the I-69 corridor. There appears to be some residual outflow boundary from the overnight activity that may serve as forcing for showers and storms that could initialize Tuesday morning as the sun comes up and instability begins to develop. The ECMWF increases sfc dew points Tuesday morning and that will make the atmospheric column more conducive to lift as the remnants of Beryl reach Arkansas and upper divergence (outflow) and moisture streams northward from it. As such, will allow chance PoPs to blossom and extend outward along a line from Grissom to Hillsdale. Highs today look to achieve the upper 80s in most places to around 90 degrees east of I-69. Highs Tuesday will be a little cooler as Beryl approaches with increased cloudiness, only achieving the upper 70s to mid 80s. As we head into Tuesday night, a ECMWF/NAM camp seems to bring better low level moisture into the area associated with the remnants of Beryl. 850 mb dew points increase to around 15C in these models, but sfc dew points drop below 70F. At the same time, this is also when the better large scale ascent makes it into the area and starts squeezing out this influx of moisture. A slight southward shift of the low pressure center in recent model runs has shifted precipitation totals slightly southward back to the US-24/I-69 corridor. Models have come into better agreement when compared to yesterday at this time, but there`s still some chance for shifting of rainfall axis up until probably Monday night/Tuesday. A statistical glance at the guidance (Model Certainty tool) for FWA indicates a 25th percentile around 1.6" whereas a 75th percentile resides around 2.15", which is right around where WPC`s storm total qpf winds up. Fort Wayne was already 2 inches below normal for June and is 0.5" below normal for July so there is some ground to make up before the ground can become saturated. It will likely require vigorous rain rates or stalled/training cells and this system does appear to be fairly progressive in nature on the GFS/ECMWF models so that`s not in its favor. Given the cloudiness and the location of the low pressure center, we`re likely also too far west to see any significant convective cells in a warm sector so that`ll keep rainfall totals down as well. Have the most confidence in saying some low-lying and normally flood prone areas could see standing water as a result of this time period. The coolest highs of this period will be observed on Wednesday with the most cloudiness and likely the heaviest rain observed, only achieving the mid 70s to around 80 degrees. This system begins to depart Thursday as the trough still stalled to our west since today finally pushes the system`s energy east. Vorticity within the base of the nearby trough and developing instability will at least require slight chance PoPs Thursday with the greatest chance during the afternoon. Mid level height rises take over behind Beryl and surface high pressure comes in so am skeptical of anything higher than slight chance PoPs for Thursday. The trough stalls out overhead through the weekend into next week so will at least keep a token slight chance PoP around during the afternoon Saturday within the diurnally forced instability. Temperatures look to slowly trend warmer, towards 90 degrees by the weekend or next Monday as the ridge that was in the west slowly trends eastward. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 119 PM EDT Mon Jul 8 2024 Beryl was still down in TX and was weakening as it was moving farther inland. Well ahead of this tropical system over northern Indiana, the atmosphere was destabilizing with surface based CAPEs over 1500 J/Kg per SPC meso. Included SBN with a VCTS mention in this more unstable air; otherwise, the showers and storms from Beryl should hold off until after the end of the TAF period. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ UPDATE...Fisher DISCUSSION...Roller AVIATION...Skipper