FXUS63 KIND 310501 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 101 AM EDT Thu Oct 31 2024 .KEY MESSAGES... - A warm and breezy night ahead. Lows in the lower to middle 60s. - Widespread rain, isolated thunderstorms, windy and warm on Halloween. - Rain ending by late afternoon and early evening on Thursday afternoon; Turning cooler. - Cooler and Dry early weekend and more rain chances and warmer late weekend into next week. && .FORECAST UPDATE... Issued at 934 PM EDT Wed Oct 30 2024 Going forecast is in excellent shape this evening. Breezy conditions and anomalously warm low temperatures are expected overnight. Gusts will be more sporadic than during the daytime as mixing decreases, but full decoupling of the boundary layer will be prevented by the continued strong pressure gradient and relatively strong flow just off the surface. This continued mixing and low level warm advection, along with increasing cloud cover, will keep temperatures up overnight - with lows in the mid 60s - above normal highs for the time of year, much less lows. Latest high resolution guidance brings the main pre-frontal band of precipitation into the area as early as 10-11Z in the northwest, which fits well with current grids. && .SHORT TERM (This evening through Thursday)... Issued at 238 PM EDT Wed Oct 30 2024 Synopsis: Surface analysis early this afternoon shows a strong pressure gradient in place over Central Indiana. This was allowing for a moderate southerly flow of warm air across our forecast area. This was due to a strong area of high pressure found over NC and a cold front a trough of low pressure stretching from Lake Superior to western IA and Central KS. Aloft, water vapor imagery showed a deep trough over the western CONUS and strong ridging in place over the eastern third of the CONUS. GOES16 shows high clouds streaming within the SW flow aloft over Indiana, mainly focused over IL/MO/WI. Temperatures remained quite warm, mainly in the lower 60s this morning. Dew points were unseasonably moist for this time of year, in the mid to upper 50s. Radar shows light showers over far western IL, while convection and thunderstorms were developing along the front over KS and NB. Tonight Quiet, breezy and warm weather is expected tonight. The strong ridging aloft is expected to depart to the east coast tonight, but it will take almost the entirety of the period to do so. Meanwhile the upper trough over the Rockies will push toward the Central Plains. During the overnight hours, little in the way of forcing is expected to pass across Central Indiana, however the southwest flow aloft will continue along with a continued flow of warm air. A strong LLJ, around 50 knots, is expected to advance into the area late overnight. This along with the strong surface pressure gradient will continue to allow for good mixing, and allow for a breezy warm night. Forecast soundings through much of the night remain dry for most of Central Indiana. Points in the west, near the Wabash, do shows hints of saturation as the cold front and LLJ arrive toward 12Z. Thus a dry evening will be expected and small chances for rain will be included across the western parts of the forecast area after 09Z. Given the expected increasing cloud cover and continued mixing of warm air, unseasonably warm low temperatures will be expected in the lower 60s. Halloween (Thursday) Get ready for a spooky weather day as the atmospheric ghouls stir! Models reveal that a menacing upper trough is lurking over the Plains, set to glide across the Great Lakes like a ghostly apparition. This ominous system will drive a cold front across the plains toward Indiana in the morning, creeping ominously into our state by the afternoon. A wisp of eerie mid-level moisture is expected to accompany the cold front, arriving in the west during the morning and gradually haunting Central Indiana throughout the day. By the witching hour of 21Z to 00Z, this moisture will have drifted southeast, with the best rain producing moisture lurking near the Ohio River. Forecast soundings reveal a saturated atmosphere enveloping Indianapolis around 18Z, but as the clock strikes 21Z, subsidence will creep in, drying the air out by 00Z. With these trends, expect a late afternoon filled with fleeting rain showers, fading into dry conditions as the darkness descends. The forecast reveals a peak precipitable water value of 1.62 inches (a rare and potent brew for this time of year) boosting our confidence for rain as these atmospheric forces pass. Near 100 percent chances of precipitation mean the ghosts of rain are likely to haunt us. However, while a rumble of thunder might echo in the distance, widespread storms seem unlikely. Given the encroaching clouds and the spectral showers, anticipate high temperatures in the upper 60s. A fitting backdrop for this Halloween haunt. As night falls, temperatures will drop to the lower 60s. This combined with a ghostly breeze howling at 10-20 mph may result in chills, making it feel even colder. So, don your raincoats during the day and afternoon and get your costumes ready by the evening and keep an eye out for those creeping clouds. && .LONG TERM (Thursday night through Wednesday)... Issued at 238 PM EDT Wed Oct 30 2024 A low-amplitude shortwave trough will be departing Thursday night and will temporarily nudge a cooler and drier continental air mass into Indiana. Sensible weather on Friday will be reminiscent of what we experienced this past weekend, and could actually be the coolest temperatures that we have experienced since the 16th. Medium-range deterministic and ensemble guidance agree on the retrograding and amplifying nature of the eastern mean ridge as stronger westerlies aloft shift poleward and western trough amplifies and moves slowly eastward. Deep/rich moisture is only relegated to near or just south of the Ohio River given the character and path of aforementioned departing shortwave trough, and should readily flow northward late Saturday into Sunday in response to the approaching west trough. There is a QPF signal in most models late Saturday night into Sunday that appears to be tied to broad weak isentropic ascent within an anomalously moist environment, and subtle lead shortwave perturbation. The ascent per deterministic model isentropic charts is most concentrated during a period of frontogenetical forcing along the advancing warm front, and may tapper off later on Sunday. But, the timing varies among the ensemble members. More members than not show the more concentrated ascent and probable warm advection- driven rain band to be early, while a smaller percentage of members lag. We will refine the timing but for now it appears slightly higher probabilities are needed early in the day with low-mid range probabilities late in the day into the evening. This latter period may actually be a lull in precipitation if the broader weak isentropic ascent weakens further and/or the aforementioned shortwave perturbation is less influential this far east. This will potentially have some impact on temperatures, but a blended approach will suffice for now until we can better refine precipitation timing. Sunday night into Monday, well be on the eastern periphery of a pronounced deep anomalous (>+3 sigma) moisture river with subtropical connections. While the stronger forcing for ascent will still be to our west, another shortwave perturbation augmented by, or originating from, Plains convection late Sunday will result in precipitation chances increasing again. Given the spread in the ensembles and sensitivity of compact convectively-induced impulses, we will not attempt to refine timing further at the moment and continue with a fairly broad mid-range probabilities Sunday night through Monday night. Throughout this period there is little to no conditional instability and thunder should be limited. Tuesday, there is noteworthy spread in the ensembles seen in spaghetti plots and clustering techniques. There seems to be a general convergence on ejecting and deamplifying shortwave trough bringing a period of stronger forcing into the established deep subtropical moisture ribbon. This would likely bring the best chance of precipitation of the long term period to Indiana during a roughly 6-9-hour period sometime on Tuesday. Specific timing and magnitude of the precipitation is in question given the ensemble spread. There is about a 1.00 inch spread among the 25th-75th percentile multi- model ensemble, and a mean of around 0.50-0.75 inches. Instability/thunder should again be limited by the misalignment of colder midlevel temperatures with the warmer/moist lower troposphere. The general synoptic pattern looks similar post-wave into Wednesday with temperatures returning to near climatology for early November, but not likely below given the amplitude and track of the shortwave trough and tendency for anomalous midlevel heights/ridging to quickly build back in. The Day 8-14 day period generally shows a warmer than typical pattern with at least normal if not above normal precipitation chances. But, confidence is not particularly high since some medium-range models show a transition to a less progressive (and less predictable) pattern with weakening subtropical jet and closed low over the Southwest or southern Plains. There are some variations with a potential eastern trough near/northeast of our region as well. && .AVIATION (06Z TAF Issuance)... Issued at 100 AM EDT Thu Oct 31 2024 Impacts: - LLWS through 12Z - Southerly wind gusts up to 35kts, more frequent gusts to 30kts after 12Z - Wind shift from south to west between 15Z and 18Z. - MVFR cigs/vsbys expected with showers from 12Z to 18Z, brief TSRA possible Discussion: LLWS will persist through the remainder of the overnight hours, ending as surface gusts increase after daybreak. Showers with embedded thunderstorms expected after 12Z with best chance for TSRA at HUF and BMG. Brief wind gusts to 35kts possible with more frequent gusts to 30kts with a gradual wind shift from the south to west between 15Z and 18Z. Vsbys will stay VFR outside of any showers with MVFR cigs persisting for a few hours after the end of precipitation. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Nield SHORT TERM...Puma LONG TERM...BRB AVIATION...White