Via @NWSIndianapolis… Winds will increase today, with gusts to 30-40 mph after 800 AM, and a brief period of westerly gusts up to 50 mph within the midday to early evening hours. Periods of rain will continue today, especially near the Wabash Valley this morning.
231 FXUS63 KIND 291125 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 625 AM EST Sun Dec 29 2024 .KEY MESSAGES... - Wind Advisory 8AM to 8PM with wind gusts to 50 mph - Showers will continue through the morning, heaviest across the Wabash Valley - More rain expected Monday night into Tuesday, potential for up to three quarters of an inch of rainfall - Noticeably colder after mid-week with single digit wind chills possible towards the weekend - A chance for brief light snow Thursday night into Friday && .MESOSCALE UPDATE... Issued at 625 AM EST Sun Dec 29 2024 As of early this morning, the center of the low was crossing the Ohio River north of Evansville at around 999mb with the center of the low expected to move up the I-69 corridor through the morning hours deepening at a rate of around 1mb/hr. Expect to see the surface winds shift over the next hour near Indianapolis with sites just to the south now showing southerly flow. As the low continues to deepen, strong northwesterly flow will develop on the southwestern edge of the low as the LLJ continues to rapidly strengthen. Overall thoughts on the wind gust threat remains unchanged from the short term discussion below with the highest confidence across the eastern and northeastern counties later today where the lapse rates will be most favorable for mixing. Rain coverage is also becoming more scattered east of the Wabash Valley as the dry slot associated with the upper level system moves in. Rain will become more showery in nature with more scattered coverage through the remainder of the morning as cold air wraps around and begins to increase the lapse rates. Thunder potential still looks low but non-zero across the eastern counties. && .SHORT TERM (Today and tonight)... Issued at 243 AM EST Sun Dec 29 2024 Today. A rapidly deepening surface low is expected to continue to track up the Mississippi River Valley into Indiana through the rest of the overnight hours and into the day with the center of the low directly overhead central Indiana by this afternoon. As the low matures, a TROWAL is expected to form along the northwestern periphery of the low which will bring enhanced precipitation through the afternoon with models showing a narrow axis of very strong frontogenesis. Areas to the east are expected to see only periods of rain as a dry slot moves in behind the surface low. The primary threat with this system looks to be a short period of gusty to damaging gradient winds as the surface pressure gradients continue to tighten. Models continue to trend towards a much deeper low by this afternoon with a 50-60kt 850mb jet on the backend of the low. This will combine with some modest heating in the dry slow to create lapse rates steep enough to at least partially mix down these winds and create a short period (1-2 hours) where surface gusts up to 50 mph are likely along with isolated gusts that could be greater than 55 mph. The greatest uncertainty at this time to the higher end gusts will be the effectiveness of the mixing which will depend on the strength of the dry slot and its effects on the lapse rates in the lowest 2kft. At this time confidence is high enough to warrant a Wind Advisory with the nuance that the strongest winds are likely to occur over a short period of time as the surface low tracks to the northeast. Total QPF with the system is expected to be in the 1-2 inch range with the highest amounts along the I-69 corridor to the southwest of Indianapolis. These amounts may lead to isolated low-lying flooding and combined with additional rainfall later in the week could bring some river flooding which will be addressed in the long term section below. A few rumbles of thunder are possible this afternoon across eastern Indiana where the lapse rates will steepen just beyond the moist adiabatic level and bring a skinny CAPE profile of 300-500 J/kg, but chances look isolated at best. Tonight. The surface wind gusts will quickly weaken after sunset as the LLJ rapidly weakens as the low continues to track northeastward. There may be a few showers across the southwestern counties through midnight as models hint at some weak forcing on the backend of the system, but confidence in any rain falling is low at this time. Low clouds will persist through the night but expect with surface winds staying greater than 5 mph through the night that there shouldn`t be any fog formation. && .LONG TERM (Monday through Saturday)... Issued at 243 AM EST Sun Dec 29 2024 Monday and Tuesday... Yet another rainmaking system will cross the Midwest within the early week, albeit with rainfall expectations about one-third of that of the short term`s more potent system. This should keep soils near-swollen...and likely continue Action to near-Minor Flood stage on the White River at Elliston (Greene County) and points downriver. Dry conditions will prevail for at least Monday and probably most of Monday evening under weak zonal ridging between systems. Clouds are expected to finally break Monday afternoon for most counties, with decks hopefully even scattering out for a couple hours northeast of Interstate 74. The weaker Colorado low will advance quickly eastward...and despite weakening slightly following its lowest pressure in Missouri...will probably drop greatest rainfall in a broad 0.50-0.70 inch swath over much of our local region, as the circulation begins to occlude and slow before trucking across Ohio late Tuesday. Cannot rule out a few wet snow flakes mixing in as the event tapers off Tuesday afternoon north/east of the Indianapolis Metro...but with air temperatures 5-10 degrees above freezing and even warmer ground temperatures, high certainty in no impacts. At least moderate confidence measurable precipitation ends within the CWA by 700P Tuesday evening. A greater forecast challenge as the New Year hour approaches may be sky cover, with hopefully at least some clearing across western zones per forecast soundings depicting no inversion aloft. Expect noticeably cooler, yet continued above normal temperatures Monday courtesy of the subtle maritime air mass with highs around 50F. Minimums Monday night in the low to mid 40s will be the rule amid damp conditions...with readings only exhibiting a subtle rebound Tuesday as winds gusting to 15-25 mph back through northerly directions. Wednesday through Saturday... The remainder of the week will be mainly dry with progressively lower temperatures. Broad and quasi-stationary upper low pressure over eastern Canada will dumbbell and retrograde back to near Hudson Bay while dropping 10-15 dm. This will allow an elongated mass of polar high pressure to slowly plunge down the Plains and towards the Midwest during the late week. A weak wave riding along the front of the ridge`s gradient will bring chances for brief light snow within the Tuesday night-early Friday timeframe, with any potential for accumulating snow probably held to a 4-6 hour window for most individual locations. Sub-freezing conditions are then expected for the late week, albeit only 5-10 degrees below seasonable normals. That said, conditions may be blustery at times around the Friday timeframe as the ridge axis finally approaches Indiana, settling into the Middle Mississippi Valley. Forecast minimum wind chills should trend from around 15 degrees Tuesday night and Wednesday night...to single digits Friday night. The normal max/min at Indianapolis this week is 37/23. Outlook Further Into January... Confidence is increasing in a longer duration of below to well below normal temperatures into mid-January with ensembles indicating a pronounced yet stagnant upper ridge over western North America that will encourage a flow of arctic air into the eastern two-thirds of the CONUS. Potential storminess over the eastern US during the week following the Long Term would serve to enhance negative height anomalies over much of the country...especially the southeastern US where the most anomalous temperatures may occur. Across the Midwest, at least several days of temperatures well below normal and the potential for multiple, at least light, snow events is a reasonable expectation at this time. && .AVIATION (12Z TAF Issuance)... Issued at 625 AM EST Sun Dec 29 2024 Impacts: - IFR cigs through 18Z with brief LIFR, MVFR afterwards - MVFR vsbys expected with periods of moderate to heavy rain through 00Z, brief IFR conditions at HUF/LAF - 30-40kt winds this afternoon as direction shifts from northeast to west Discussion: Rain coverage will become more scattered at IND and BMG this morning through the afternoon with steadier rain at HUF and LAF while cigs gradually rise from LIFR/IFR to MVFR. Vsbys are expected to generally remain MVFR with brief IFR conditions towards HUF/LAF in heavier showers. Winds will be variable through the day, generally northeasterly through daybreak with a brief southerly direction at IND/BMG before shifting to the west/northwest late this morning into the afternoon. Wind gusts to 40kts are expected during the period of westerly to northwesterly flow but the strongest winds should be limited to a 2-3 hour period. && .IND WATCHES/WARNINGS/ADVISORIES... Wind Advisory until 8 PM EST this evening for INZ021-028>031- 035>049-051>057-060>065-067>072. && $$ MESOSCALE...White SHORT TERM...White LONG TERM...AGM AVIATION...White
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