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Forecast Discussion for Indianapolis, IN
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000 FXUS63 KIND 190518 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 118 AM EDT Tue Mar 19 2024 .KEY MESSAGES... - Sub-freezing temperatures through 10AM today - Wind gusts to around 35-40mph this afternoon - Elevated fire weather risk today - Lows in the low 20s Wednesday night && .SHORT TERM (Today and tonight)... Issued at 117 AM EDT Tue Mar 19 2024 Today. Gusty winds and an elevated fire weather risk is expected for today with a combination of wind gusts to 35 mph and minimum RH values around 30 percent. The near northerly upper level flow has begun to shift more northwesterly with strengthening surface and low level pressure gradients as a 994mb low over Southern Canada continues to slowly strengthen and sink southward combined with a broad area of high pressure across the Southern Gulf states. This will lead to a 45-55kt 850mb jet along and just ahead of a weak cold front with model soundings showing lapse rates around 9C/km to the top of the boundary layer which should allow for efficient mixing down of those stronger winds. The key for the day will be how deep the boundary layer mixes with models varying from around 4kt to 6kft in the more aggressively mixing models like the GFS and HRRR. The pattern favors deeper mixing and based on recent events with similar conditions, leaning more towards the HRRR solution which will bring occasional wind gusts to around 35kts and frequent gusts in excess of 30kts. One factor which will help keep winds from pushing towards 40kts is the timing of the LLJ which looks to peak around 16Z to 18Z while the highest mixing timeframe will be closer to 20Z as the LLJ begins to gradually ramp down and exit the forecast area. Will have to watch the 18Z to 20Z timeframe as being the timeframe where wind gusts could overachieve. As mentioned above, efficient mixing will also help to dry the surface air out which combined with highs today in the mid to upper 50s will lead to RH values around 30 percent. The southwesterly surface flow will be advecting in higher dewpoints during the daytime hours today which will allow for a climb from the mid teens that are ongoing to around 30 by late afternoon, but with the temperatures rising much faster than the dewpoints and some of the moisture mixing out, expect elevated fire weather danger today with the combination of very strong winds. Recent rains will help limit the overall threat but if the dewpoint rise is not quite as robust as expected, the danger would be greater and similar to conditions experienced last week with numerous small fires across central Indiana. Tonight. In the aftermath of the frontal passage, quiet weather is expected for the overnight hours tonight with westerly to northwesterly winds around 10-15kts and occasional gusts to 20kts. Skies will remain clear with any lake enhanced cloud cover expected to be limited to the far northeastern portions of the state into Ohio. These higher winds will help to limit the radiational cooling with lows in the low to mid 30s expected. && .LONG TERM (Wednesday through Monday)... Issued at 117 AM EDT Tue Mar 19 2024 Wednesday and Thursday. Quiet weather is expected for Wednesday with mostly clear skies which will help to then bring another hard freeze Wednesday night with efficient radiational cooling as winds drop to near calm to go with the mostly clear skies. The forecast continues to trend cooler with expected lows now in the low to mid 20s. The pattern then begins to shift going into Friday as the flow becomes more zonal ahead of a rain producing system Friday into the weekend. Friday and Saturday. Forecast confidence begins to lessen going into Friday with models beginning to diverge after coalescing on similar solutions in previous runs. The polar jet and associated shortwave trough continues to be the dominant feature with this system as it pushes into the Great Lakes region late Thursday night into Friday bringing precipitation to the area late Friday into Friday night as the associated surface cold front pushes southward. The new wrinkle in the forecast is the potential that a secondary low ejects to the northeast ahead of the main low pressure system associated with the subtropical jet. This feature if it plays out could bring enhanced precipitation to the southeastern counties Friday into Friday night. Confidence is this second solution is much lower, especially with it being a one-off model run but will continue to monitor trends in the coming days, With either solution, below normal temperatures are expected going into the weekend. Snow may mix in, but think that temperatures across central Indiana will remain warm enough to keep precipitation all rain but towards the far northern portions of the state. Precipitation may linger into Saturday as the flow becomes northwesterly again, but with the majority of the forcing already exited, QPF would be light. Sunday and Monday. A more impactful system then looks probable going into early next week as a seasonably strong low exits the Four Corners Region and tracks to the northeast with widespread precipitation stretching from the Gulf of Mexico into Canada. At this time heavy rain and thunderstorms looks to be the most likely threat but will continue to monitor trends for any potential for strong to severe storms as well. && .AVIATION (06Z TAF Issuance)... Issued at 117 AM EDT Tue Mar 19 2024 Impacts: -Southwesterly wind gusts to 35kts this afternoon. Discussion: VFR conditions expected through the TAF period with clear to mostly clear skies. Southwesterly winds are expected to begin gusting by mid morning with peak wind gusts to 35kts this afternoon. These stronger winds will begin to relax after 00Z with winds between 8 and 12 kts through the overnight hours going into Wednesday. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...White LONG TERM...White AVIATION...White |
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