Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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273 FXUS63 KIND 220555 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 155 AM EDT Wed May 22 2024 .KEY MESSAGES... - Warm and humid through this evening. - Isolated severe storms possible late tonight and again Wednesday afternoon and evening. - Additional chances for rain and storms through early next week. && .FORECAST UPDATE... Issued at 1002 PM EDT Tue May 21 2024 Current surface analysis shows a strong low pressure system centered near eastern Minnesota with thunderstorms ongoing along an attendant cold front which stretches from the upper midwest to portions of AR/OK. Most CAMs suggest a weakening line of thunderstorms along the approaching front will move into central IN after midnight. Modest instability and deep-layer shear suggest loosely organized storms are possible, mainly across far western portions of the area. Isolated damaging wind gusts cannot be ruled out as these storms move in. Expect the line of storms to weaken as it progresses eastward and should move out before daybreak. POPs were slightly delayed since latest guidance shows precipitation moving in around 1am. Southerly flow and increased cloud cover will keep temperatures mild overnight in the upper 60s. && .SHORT TERM (This Evening through Wednesday)... Issued at 300 PM EDT Tue May 21 2024 This Evening and Tonight... Another hot and humid day across Central Indiana as the region is placed firmly within the warm sector of an area of low pressure moving NE through Iowa. Satellite imagery this afternoon shows a cu field over the whole state with widely scattered convective showers popping up in SE Indiana. IND ACARs sounding show deep mixing this afternoon up to 2km agl bringing gusty winds to 25 mph down to the surface. Low to mid level moisture advection evident on regional soundings has inhibited dry air from mixing down to the surface with observations reporting dew points in the low to mid 60s. Focus shifts to the storm threat tonight into the early morning hours Wednesday as a weakening line of storms approaches Indiana from the north and west in the 03-08z timeframe. The main area of low pressure is forecast to eject NE into northern Minnesota tonight while the main upper level jet energy holds back in the Central Plains. With the best forcing for ascent and dynamics well to the west, it is likely that this line of storms will be in a weakening phase as it crosses the state. Despite a strengthening 45-55kt low level jet over the region, waning low level instability and lack of upper level support do not make for a favorable set up strong to severe storms during the overnight hours across the region. In fact, some hi-res guidance today suggests the line may break apart as it approaches the I-65 corridor, leaving portions of East Central Indiana fairly dry. Highest confidence for storms remains across portions of Western Indiana where a few storms could be strong. There likely will be just enough surface based CAPE around 1000 j/kg in Western Indiana along with 0-3km and 0-6km shear in the 25-40 kt range to support a marginal damaging wind threat. Low level hodographs appear to be strongly curved; however with storms weakening, do not think there will be much of a tornado threat overnight unless a segment of the line shows deviant motion or a transverse wave spins up something quick. Confidence on that scenario is very low. Storms weaken as they march eastward across the state with low confidence in even a lightning threat for East Central Indiana. QPF will likely be highest for Western Indiana with upwards of a half inch along the IL/IN border and under 0.20" in East Central Indiana. Wednesday... Into Early Afternoon Wednesday... Expect low clouds in the wake of the weakening line of storms Wednesday morning with guidance hinting at lower stratus being stubborn to mix out into the early afternoon hours near the front. The actual front is expected to set up south of I-70 across Southern Indiana by midday Wednesday with convective initiation right along it. The southward trend in the location of the front is seen on all short term and hi-res guidance keeping the main storm and severe threat in South Central Indiana and points south. Clouds along the front will likely keep instability down, so not expecting much if any convection into mid-afternoon. Continued the trend of lowering PoPs for the northern 2/3 of Central Indiana through the day tomorrow. Much of Central Indiana will likely remain partly to mostly cloud through the day with temperatures in the 70s. Will have to watch observations and satellite closely tomorrow afternoon to determine where the frontal boundary sets up and if enough clearing takes place south of it to support convective activity. A SW to NE oriented upper level jet streak approaches from the west tomorrow afternoon; however low level flow considerably weakens. While there is the potential for an isolated strong storm to form with damaging winds and hail in South Central Indiana tomorrow afternoon and evening, weak low level shear and slower storm motion may lead to more of a flooding threat if storms train and backbuild off of each other. The best threat for any severe weather and flooding does appear to be south of the forecast area, but as mentioned before, will watch observations closely tomorrow afternoon to see where exactly the frontal boundary sets up. && .LONG TERM (Wednesday Night through Tuesday)... Issued at 300 PM EDT Tue May 21 2024 The frontal boundary will settle over the lower Ohio Valley for late week as a progressive quasi-zonal flow aloft sets up over the region. The presence of the front to our south and weak disturbances tracking through the zonal flow will maintain periodic chances for scattered convection into the weekend but overall model trends have shifted drier into Saturday. More substantial upper level energy will be confined well to our northwest with the bulk of the unsettled conditions remaining over western Canada into the northern Plains and upper Midwest through the end of the week. A more potent upper wave will eject out into the Plains late Saturday and approach the region Sunday with an attendant surface wave. This will be the onset of an increasingly unsettled pattern for the region with additional upper waves tracking into the region and buckling heights aloft as a ridge develops over the western states for early next week. Wednesday Night through Saturday Night The focus for any ongoing convection Wednesday evening will be across southern Indiana and more likely in the vicinity of the Ohio River and points south as the frontal boundary interacts with a modestly unstable airmass over Kentucky. The front will remain quasi- stationary through late week somewhere near or just south of the Ohio River...likely close enough to warrant a continued threat for scattered convection over southern portions of the forecast area Thursday and the first part of Friday. Drier air and subsidence associated with high pressure across the Great Lakes will limit northward extent of any rain with an increasing likelihood that many locations north of I-70 see only a few showers or storms through midday Friday. A stronger upper low pivoting through the upper Midwest Friday will aid in drawing deeper moisture back north into the region by Friday night ahead of another front. A weak wave aloft ahead of this feature may be enough to generate storms Friday afternoon with additional convection Friday night as the front swings across the region. The bulk of the deeper forcing aloft will remain displaced well to the northwest of central Indiana on Friday night however... resulting in storms likely to be in a weakening state Friday night. High pressure will then quickly return for Saturday with a lower threat for any rain and an overall pleasant day to start the holiday weekend. Temperatures will remain seasonable through Saturday with highs ranging from the mid 70s to lower 80s. Sunday through Tuesday The last few runs of the extended model suite has place an increasing focus on an upper wave rounding the western Canadian upper trough and then kicking east through the central Plains and into the mid Mississippi Valley over the weekend. In tandem with the upper wave is the development of a surface low over the High Plains Saturday evening that will track east and approach the region for Sunday. While the various models and ensemble members vary in strength and track of the surface low at this point...there is a notable signal across the model suite of the feature in the vicinity of the Ohio and mid Mississippi Valleys by Sunday afternoon with a warm front in the region as well. The threat for rain and thunderstorms is growing for Sunday into Sunday night with the aforementioned system tracking into the region and considering the potential strength of the surface low...an increasing threat for severe weather is on the table as well with ample shear and instability present over parts of the region. Remain too far out to delve into the specifics yet...but the recent model trends are not looking conducive at all for outdoor activities on Sunday with growing potential for higher impact convection in the region as well. Stay tuned. An upper level low will follow for early next week as the overall pattern aloft gradually transitions to a more amplified regime with a ridge west and a trough east. This will bring additional rounds of rain and storms through the middle of next week along with a cool down as highs fall back mainly into the 70s. && .AVIATION (06Z TAF Issuance)... Issued at 152 AM EDT Wed May 22 2024 Impacts: - South-southwesterly wind gusts to 22-26KT at KIND/KLAF thru 12z - Dissipating -SHRA through daybreak, with isolated TSHRA near KHUF - MVFR CIG possible at times within 11-16Z this morning Discussion: MVFR ceilings are possible for a few hours early this morning within the 11-16Z timeframe ahead of a weak cold front slowly crossing the region from northwest to southeast....with VFR otherwise expected into Wednesday night. Ahead of the reduced CIG threat will be a dissipating cluster of showers and perhaps isolated thunder around KHUF through 07Z, with perhaps -SHRA reaching KIND during 630-800Z. VCSH will otherwise be the rule through the TAF period, with any organized TSHRA late Wednesday expected to stay south of KHUF/KBMG. Winds will diminish through dawn over KIND/KLAF as the supporting low-level jet departs to the Great Lakes..with gusts to 22-26KT at these two terminals. Remainder of the period will find breezy SW flow sustained at 9-12KT through sundown Wednesday...and lighter winds by the end of the period veering to more northerly headings. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ UPDATE...Melo SHORT TERM...CM LONG TERM...Ryan AVIATION...AGM