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Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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476 FXUS63 KIND 040509 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 109 AM EDT Thu Jul 4 2024 .KEY MESSAGES... - Rain and storm chances Thursday morning and again late Thursday night into Friday - Expected lull in between rounds of storms during the afternoon and evening for 4th of July - Dry conditions and less humid late Friday through Sunday...highs around 80F on Saturday && .FORECAST UPDATE... Issued at 955 PM EDT Wed Jul 3 2024 Convection continues to impact southern Indiana while gradually shifting south as outflow boundaries are thrown out by the storms. The northern fringes of the rain have been grazing far southern portions of the forecast area at times since early this evening. Elsewhere it was dry but muggy. 0130Z temperatures ranged from the mid 70s to lower 80s with dewpoints into the 70s. The focus for convection since late afternoon as mentioned above has been over southern Indiana within a broad convergence zone and on the nose of the instability gradient. With sunset...convection has begun to decrease in coverage and intensity although a few showers may linger over far southern portions of the forecast area for the next few hours. Cannot rule out an isolated shower further north across central Indiana but overall trends are not terribly supportive at this point. An instability minima in the wake of the convection over southern Indiana lingers and will likely serve to maintain an overall lid on convection into the overnight. Most of the rest of the night will be quiet with a shift in focus to the west as convective development expected over the Missouri Valley overnight builds upscale into an MCS that is poised to impact the forecast area Thursday morning. Recent model trends have slowed the eastward progression of the complex to near or after 12Z into the Wabash Valley and pops have been updated to reflect those changes. There remains a low end wind threat with the storms over the region Thursday morning...but locally heavy rainfall is likely to be a greater impact with any outdoor activities through the first half of Thursday being impacted. Lows overnight will remain in the lower to mid 70s. Zone and grid updates out. && .SHORT TERM (This evening through Thursday)... Issued at 243 PM EDT Wed Jul 3 2024 Latest satellite imagery shows widespread high level cloud cover across the western and northern 2/3 of Central Indiana, greater coverage than what previous guidance has suggested. The SE quadrant of Central Indiana currently has a healthy cu field developing due to greater boundary layer heating and less upper level cloud cover. Current frontal boundary extends W-E across the state from around Danville, IL to Muncie with SW surface flow and dew points in the lower 70s south of the front. While high clouds have resulted in less boundary layer heating and subsequent destabilization, still expecting scattered showers and thunderstorms to develop later this afternoon and evening. Latest IND ACARs sounding does show weak capping in place and poor mid level lapse rates, which may limit the overall coverage of storms later. The best environment for stronger to potentially severe storms is across far SW and SE Indiana, where greater instability and steeper lower level lapse rates are present. The Louisville ACARs sounding is likely more indicative of the environment in Southern Indiana showing much steeper low level lapse rates near 7.0 C/km, CAPE over 1000j/kg and DCAPE values exceeding 800 j/kg. LLJ aloft is weakening with 0-3km shear at or under 25 kts across the state, not very supportive of sustained, and organized updrafts, but the thermodynamic profile does support an isolated damaging wind threat from wet microbursts. Expect scattered convection to initiate along and south of the I-70 corridor over the next few hours with the threat continuing through around 03z tonight. Later tonight, a secondary low from the SW will begin to develop, helping re-establish a moist warm sector over southern portions of the state. Depending on where the aforementioned frontal boundary sets up, potential is there for low clouds and patchy fog along and north of this boundary near dawn on Thursday. Best chance for lower clouds and patchy fog is along and north of I-70. Hi-res guidance does indicate an overnight complex of showers and storms developing in Missouri and pushing eastward into South Central Indiana around dawn as well. Confidence is low on this as guidance tends to poorly perform in scenarios where there are multiple rounds of showers and storms with weak synoptic scale forcing. Keeping highest PoPs overnight in Southern and SW Indiana for now, but will have to closely monitor upstream trends tonight. .Tomorrow... The first half of the holiday looks to be relatively cloudy, humid, and warm with the threat for showers and storms. Frontal boundary from the previous day remains draped across the region with the potential for a convective complex during the morning hours. Typically these are in a weakening phase as they approach Indiana; so confidence remains low in how widespread shower and storm activity will be around sunrise. Latest guidance does show the best chance for a morning round of precipitation along and south of the I- 70 corridor. The main threats with any morning convection will likely be heavy rain and flooding for areas that see repeated storms, especially as precipitable water values will be near or over 2.0 inches. Guidance indicates subtle ridging in the mid levels during the afternoon and evening hours ahead of an approaching low over the Upper Midwest. With this in mind, despite a frontal boundary near the Ohio River, mid level drying and subsidence may work to inhibit convective development during the latter half of the day tomorrow. Still expecting low and high level clouds to stick around through the day, with a few peaks of sun towards the evening hours. Confidence is lower if clouds will break up; so keeping forecast high temperatures below guidance in the lower 80s for Central and North Central Indiana and mid 80s for Southern Indiana closer to the front. Despite "below average" highs for the 4th of July, humidity will be rather oppressive, even for this time of year, with a tropical like airmass in place. && .LONG TERM (Thursday night through Wednesday)... Issued at 243 PM EDT Wed Jul 3 2024 Thursday Night through Friday night... Despite not having the greatest confidence in timing or location of any organized showers/t-storms Thursday night...latest guidance is indicating late Thursday`s modest ridging should continue through the evening hours, ahead of low pressure slowly approaching from the northwest. Suspect widely scattered showers to return later during the overnight, although modest CAPE and unimpressive mid-level lapse rates should prevent any severe weather. Any heavier rainfall in stronger showers/isolated t-storms is not expected to be widespread, although much of the area could see at least brief rain late Thursday night. Surface low pressure over the Upper Midwest will strengthen while slowly crossing the northern Great Lakes through the late week. The supporting upper wave should deepen while crossing the northern Mississippi Valley...with the whole system dragging its north-south cold front across central Indiana during the day Friday. So far appears moderate confidence that corresponding scattered showers and t-storms would be sub-severe Friday with better instability and deep moisture departing east just before better shear arrives with the upper wave. Post-frontal WSW breezes should gust to 20-25 mph, especially north of I-70...dropping humidity to more reasonable mid- summer levels by evening. Friday night will be dry with a return to seasonable temperatures as light to moderate breezes drop dewpoints towards 60F. Saturday through Monday... Overall lower heights across much of the CONUS are expected between short wave troughs over both the Great Lakes from the slowly- departing late-week system and a plunging short wave over the northern High Plains. In between weak yet broad surface high pressure will cross from the central High Plains to the Mid- Atlantic. Dry conditions and slightly lower dewpoints near 60-65F should therefore prevail over the region through Sunday...before more southwesterly flow around the Sunday night-Monday timeframe returns seasonably moderate humidity, clouds, and likely a few showers with perhaps isolated thunder. Saturday and Saturday night should be the mildest/coolest periods of the long term with readings about 5 degrees below normal...before seasonable warmth returns to start next week. Tuesday and Wednesday... A rather broad trough slowly crossing interior/northern North America will drag its southern portions into the Midwest for the mid- week. Modest westerly surface flow under lower heights and lower H850 temperatures should be the rule...along with a trend to lower rain chances as corresponding surface high pressure arrives from the north-central CONUS. Expect ample sunshine and limited cold air advection to bring near to slightly below normal temperatures, with widely scattered diurnal showers/storms possible from the passing wave`s weak forcing. The normal max/min at Indianapolis through the long term is 85/66. && .AVIATION (06Z TAF Issuance)... Issued at 109 AM EDT Thu Jul 4 2024 Impacts: - Widespread rain and thunderstorms arrive after daybreak - Isolated convection this afternoon but confidence is low - MVFR ceilings possible withing rain/storms Discussion: Overnight will be quiet although some localized shallow ground fog is possible mainly at KBMG. Confidence is growing in a developing convective cluster late tonight in the mid Mississippi Valley that will track E/NE into the region after daybreak Thursday. Expect a 3- 4 hour window late this morning through the early afternoon with restrictions in visibility and ceilings as rain and storms impact the terminals. Weak ridging develops in the wake of the morning storms for Thursday afternoon which will limit more widespread convective redevelopment through the evening. Storms should remain isolated in coverage with the remnant boundary lingering over the area. Light and variable winds early Thursday will eventually become southwest up to 10kts in the afternoon. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Ryan SHORT TERM...CM LONG TERM...AGM AVIATION...Updike