Via @NWSIndianapolis… Another round of rain is expected Saturday evening through Sunday. A stronger system will advance from the Gulf states into the Midwest through the weekend’s second half. Rain will begin late this evening, and become heavy at times through the overnight. Widespread showers Sunday will taper off in the afternoon from SW to NE.
Expect a transition to colder conditions through next week, with high temperatures trending from around 50F on Monday to near 32F on Thursday. The following week (see maps below) is expected to continue this cold pattern, with a potential for wintry precipitation Jan 4th-7th.
NWS Technical Discussion:
.KEY MESSAGES... - Cloudy and dry today with highs in the 50s - Rain arrives tonight with periods of moderate rainfall through Sunday, total rainfall up to 2 inches - A mainly dry and progressively colder start to 2025, with wind chills as low as 10 degrees Wednesday night and Thursday night SHORT TERM (Today through Sunday)... Issued at 259 AM EST Sat Dec 28 2024 Coverage of light rain is expected to continue to decrease through the rest of the overnight hours as the low pressure system that brought the rain yesterday continues to track northward into Wisconsin and any remaining upper level forcing exits. Weak subsidence above the cloud deck today will help to keep mostly cloudy to cloudy skies in place through the day along with bringing an end to any residual light rain/drizzle. This break in the precipitation will be brief though as the next rain producing system will be tracking northward through the day today and will bring a return to widespread precipitation tonight. Temperatures today will climb into the mid to upper 60s with some spots potentially as high as 60 in the south. Tonight into Sunday. Confidence continues to increase in a moderate to briefly heavy rain event late Saturday night into Sunday. A rapidly deepening surface low is expected to track up the Mississippi River Valley into Indiana tonight into Sunday with the center of the low directly overhead central Indiana by Sunday afternoon. As the low matures, a TROWAL is expected to form along the northwestern periphery of the low which will bring enhanced precipitation with models showing a narrow axis of very strong frontogenesis. Model soundings show a saturated column with PWATs near climatological maximums for the day which further highlights the potential for periods of moderate to heavy rainfall. In addition to the rain, the tightening pressure gradients associated with the deepening low will allow for occasional wind gusts of 25-30 mph. Total QPF with this system continues to trend higher with the stronger expected cyclogenesis with the latest estimates around 1-2 inches tonight through Sunday. With this setup though, an axis of locally higher precipitation is likely with another axis to the southeast of the heavier rain likely to be underdone as a dry slot develops during the daytime hours. With the moist adiabatic temperature profile, instability will be near 0 so not expecting any thunder. These 1-2 inches of rain will lead to rises along local rivers/streams but any potential flooding looks to hold off until later in the long term period and will be discussed below. .LONG TERM (Sunday Night through Friday)... Issued at 259 AM EST Sat Dec 28 2024 Sunday Night through Tuesday... An overall troughy...yet quasi-split and at times nearly zonal upper pattern will prevail across the CONUS through the final four periods of the calendar year. An ebb and flow mixture of disturbances and fair weather will occur between the short term`s more impressive system`s departure Sunday night...a 24-hour dry period centered around Monday morning that should include partial clearing...and a 998mb Colorado Low that is expected to glide up the Ohio Valley Monday night into early Tuesday. Unseasonably mild conditions through the early week will be lead by overnight low temperatures about 15 degrees above normal courtesy of the Pacific maritime origin of the antecedent air mass, and then light southerly surface flow around the Monday timeframe. The system arriving from Colorado will be relatively small, yet locally potent...with guidance continuing to suggest rain tracking west to east across the region...dropping a rather quick, additional 0.50 inches or so of rainfall over the majority of the CWA. Latest trends are favoring a precipitation maximum along and perhaps south of the I-70 corridor, while greater rainfall across northern zones would be optimal to quell long-standing Severe Drought conditions from the Lafayette area to northern Madison County. Forecast accumulated 3-day precipitation near/above 2.00 inches through late Tuesday for central/southern counties will likely promote marginal river flood concerns on the lower Wabash and lower White Rivers. Action stage would be expected should this rainfall potential be realized, with isolated Minor Flood possible following any overperformance. Tuesday Night through Friday... New Year`s Eve celebrations Tuesday night should mark the beginning of a transition to a noticeably colder pattern that may well extend weeks into January. Ensembles are continuing to suggest the departing system will promote diminishing to isolated rain showers around the Tuesday evening timeframe...with readings falling to/below freezing by Wednesday morning for the first time in 9 days. The remainder of the workweek should be overall dry and progressively colder...as a building upper ridge over western North America slowly directs a large mass of polar surface high pressure in a southeastward direction into the central US. Seasonably cold conditions on New Year`s Day will continue to trend to below-normal levels through the late week...led by afternoon highs that may struggle to reach 30F for many locations by Friday. At times brisk W to WNW flow will diminish through overnights...with resulting overall wind chill values typically within the 10 to 25 degree range. No organized precipitation is expected, although flakes and a few flurries will be possible amid the upper cyclonic flow that should be most prevalent on Friday.
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