HEADLINES
– Up to three-quarters of an inch of rain today…
– Colder temperatures will usher in the New Year…
– Dusting of snow Thursday Night…
– More significant snow possible Sunday into Monday
– Bitter arctic cold through at least next week…
NWS Indianapolis technical discussion:
231 The last rainmaker of this late December`s damp to at times rainy period will slice across central Indiana today. Widespread light to moderate rain during pre-dawn hours will lead to numerous showers over the majority of the region through at least morning and midday hours as the center of circulation tracks from Rockville to Muncie. Rain intensity and coverage may diminish at times across southern counties where some semblance of a mid-level dry conveyor attempts to advance into an otherwise rather symmetrical system. The solid majority of this system`s rainfall will have fallen by early afternoon...with expectations continuing for moderate rainfall over roughly the region`s northern half and lesser amounts south of I-70. Precipitation will slowly taper off from west to east through afternoon and evening hours, although at least a few wet snowflakes should mix in over north-central and northeast counties later today as the colder column on the backside of the system swings in from the northwest...and surface temperatures nudge down into the mid-30s. No impacts are expected given warm ground temperatures, although a thin coating of slush cannot be ruled out on grassy or elevated surfaces, especially after dark northeast of a Kokomo to New Castle line. This locally potent system will allow some gustier winds to mix down to the surface on its heels later today, with northwest winds sustained up to 20 MPH, and an area of gusts up to 30 MPH crossing the region from northwest counties this afternoon...across the Indianapolis Metro through the early evening rush hour...and down southeastern portions of the I-74 corridor through the evening. Tonight will find a slow transition to fair weather with upstream high pressure rather weak and centered back over the High Plains. Patchy drizzle/flurries may linger past midnight over mainly eastern zones, with moderate confidence no measurable precipitation lasts after the 32F isothermal`s late-night passage. Temperatures through the short term will range from highs in the 40s this morning...to widespread mid to upper 30s around midnight tonight...with lows by early Wednesday in the upper 20s for most locations. Overview: Those who love winter will be happy over the next several weeks as the much colder and potentially snowier pattern is well underway to setting up and persisting for at least two and likely three weeks. Much of this period will see temperatures remain well below freezing with sub zero temperatures and apparent temperatures as well at times. Outside of heavy snowfall potential late this weekend and early1 next week...most probable chances for snow within arctic airmass to likely come from fast moving clipper systems that will also reinforce the bitter cold. Wednesday and Thursday... These periods look mainly dry but seasonably cold as cold air advection continues in wake of short wave. Moisture profiles dry significantly by Wednesday but could see some flurries or very light snow showers, especially in the east. Will keep forecast dry this run though with flurries most likely outcome. High pressure will slide across the Ozarks and into the TN valley through this period, keeping northwest flow over central Indiana. Fast moving clipper will approach late Thursday afternoon. Best chance for accumulating snow should hold off until Thursday evening but timing will be close. These clippers often arrive a bit faster than models indicate riding the nose of upper level jet. Thursday Night... Aforementioned clipper in the form of a short wave and compact vorticity lobe ahead of a diving 300mb jet max will quickly race east Thursday evening and into the overnight. Gulf remains cut off and moisture is very limited. Area of weak frontogenesis and lift may be enough to squeeze out some light qpf, which many models are indicating. Low levels will initially be dry so concern about how much snow will go into saturating low levels before starting to reach ground and accumulate. Blends and WPC giving just under a tenth of an inch liquid which seems on the generous side. With cold air in place and little in way of Warm air advection, snow ratios closer to 14:1 to 16:1 being forecast which kicks out anywhere from a few tenths of an inch to just under 2 inches in the east. Friday through Monday... Elongated area of high pressure to slide across the region for a another quiet but even colder period into Sunday before potentially impactful winter storm moves through the Ohio valley. 00z model runs have done little to give any confidence or insight into what may happen with this system. Global NH water vapor shows fast moving jet over the western Pacific which will be the impetus for our developing storm system. 00z model fluctuations and run to run inconsistency likely arising from inability to properly sample this fast moving jetstream and embedded energy, especially closer to the weekend as jet streak comes onshore and dives into the southern plains and panhandle region. Obviously not making any changes to blended ensemble solutions as status quo with median solutions is best option for now. This leads to current forecast of mainly snow for the entire area. However, GFS trended weaker and EC much faster and further south. Really no confidence in either solution and agree with WPC extended discussion on more preference toward previous 12z runs. Think this will be a more dynamic and intensifying system given the current Pacific kinematics and potential thermodynamics a more amplified system would bring with strong baroclinic zone and gulf/Pacific moisture plumes. An evolution more similar to 30/12z runs is preferred, which would potentially bring the warmer nose and freezing pcpn back into play for parts of Indiana. We cannot say it enough, but please do not focus on any of the model snowfall accumulation maps being tossed around on social media. Way too many uncertainties not to mention about a 12-15 inch high bias in these extended model snowfall maps. Plan and be prepared and pay attention to reliable sources over the coming days. Days 8 through 14... Very cold this period with temperatures easily running 10 to 15 degrees below normal. Lows most likely to begin dipping into single digits around morning of the 8th. If snow pack exists following winter storm system, temps could be more like 15 to 25 degrees or more below normals. This still looks to be an extended period of well below normal temperatures and potentially a couple weeks of below freezing temperatures. Plan now for extended cold and pay attention to forecasts for possible cold weather alerts.
INDY SEVEN DAY FORECAST
Today: Periods of rain in the morning and midday. Scattered showers in the afternoon. Gusts to 30 mph. High 49, falling in the afternoon.
New Years Eve: Rain and snow showers. No snow accumulation. Wind gusts to 30 mph. Low 29.
New Years Day: Mostly to partly cloudy, with chills in the 20s.Flurries possible. High 32.
Wednesday Night: Partly cloudy. Low 25.
Thursday: Partly to mostly cloudy. High 35.
Thursday Night: Snow showers, with a dusting possible. Low 21.
Friday: Partly to mostly sunny. High 25.
Friday Night: Mostly clear. Low 16.
Saturday: Mostly sunny. High 28.
Saturday Night: Partly cloudy. Low 19.
Sunday: Snow likely by afternoon. Accumulating snow possible. High 28.
Sunday Night: Snow likely. Accumulating snow possible. Low 21.
Monday: Snow likely. Accumulating snow possible. High 25.

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