I would not trust any weather predictions for this week. Anything and everything are on the table this week. Here is the very verbose discussion from the National Weather Service:
.SHORT TERM /Tuesday through Thursday/... Issued at 324 PM EST Mon Dec 28 2020 Forecast challenges increase throughout the forecast period as the first part of a broad two part storm system impact the Ohio Valley and Great Lakes beginning Tuesday night and continuing beyond the short term into New Years Day. Model guidance has come into better alignment versus the last couple days and this may be at least partially due to the key features being better sampled...namely the primary upper level energy now onshore in California. This upper level trough will kick out east into the southern Rockies through midweek and Texas by Thursday before becoming a major factor locally with the second part of the system for Thursday night into Friday. More will be discussed with this feature and its impacts here in the long term discussion below. Ahead of the western trough is an amplifying upper wave that will drop out of the Canadian prairies late Tuesday into Wednesday before shearing out across the Great Lakes Wednesday night as it remains blocked by a strong ridge off the southeast coast. This feature in tandem with a strengthening surface low tracking northeast from the central Plains into the Great Lakes Wednesday will serve as the basis for the first part of the storm system and its impacts over central Indiana which will maximize Wednesday into Thursday. First though...after a dry day but with a steady increase in mid and high clouds Tuesday...a warm front extending from the surface low will shift quickly across the northern half of Indiana late Tuesday afternoon and evening. A thin axis of isentropic lift noted at 290K and above will clip the northwest part of the forecast area and may provide just enough lift to generate very light precip for a brief period. The presence though of drier air through the boundary layer may limit any precip to sprinkles or flurries. The axis of moisture aloft and isentropic lift will shift north of the forecast area quickly Tuesday evening with dry weather returning. Focus then turns to the west and northwest as an axis of steady rainfall approaches ahead of a cold front that will advance east from the Mississippi Valley Wednesday morning into the forecast area by late day. A combination of strong isentropic lift...broad diffluence aloft and a 60kt+ low level jet will transport deep moisture into the region with widespread rain developing Wednesday morning and continuing for much of the day as the front works into the region. The front will continue to progress southeast slowly Wednesday night with precipitation continuing along it. As colder air advects into the region from the north behind the front...there remains some concern at areas of light mixing of precip types on the northern flank of the rain...potentially with very light ice and/or snowfall accums. With that being said...the presence of such wet ground in wake of the earlier rain may mitigate much concern with any issues from a wintry mix and any amounts are expected to remain light through Thursday morning. The front will shift south of the Ohio River on Thursday leaving much of central Indiana within the backwash of the first system. Model soundings and RH progs continue to keep plenty of moisture over the region...and even as lower clouds depart through the course of the day...they are likely to be replaced by thicker clouds aloft as the second part of the system begins to organize to our southwest. The result will be a relatively cloudy and chilly New Years Eve for most with at least some potential for scattered light precip focused over the southern half of the forecast area. Heavier precipitation largely in the form of rain will then overspread the region from the south late on New Years Eve as the second part of the storm approaches. More on this in the long term discussion. Temps...low level thermals support undercutting guidance on Tuesday with highs mainly in the mid and upper 30s. The warmest day of the week will be Wednesday as gusty southerly flow pushes temperatures into the upper 40s and lower 50s. Highs will fall back into the 30s on Thursday north of the front. Expect lows mainly from the upper 20s to the mid 30s through the period. && .LONG TERM /Thursday Night through Monday/... Issued at 324 PM EST Mon Dec 28 2020 The second part of this week`s complex system will be fueled by a stacked and cut-off low pressure system`s advancement from the southern Plains at the start of the period...northward up the Mississippi Valley, and then across the Great Lakes to southeastern Canada by the end of the weekend. The system`s progressive nature will be promoted by another, upstream H500 trough which will meanwhile plunge into northern Mexico. While the track of the downstream system that will effect central Indiana will be dependent on how these two circulations dumbbell around each other Friday...ensembles are showing moderate/high confidence that the system will begin it`s northerly approach west of the Mississippi River. While northern stream energy is very much absent from potentially phasing with the stacked low, there will be some weak antecedent chill in the lower levels courtesy the high pressure that will have crossed into the Mid-West earlier Thursday. While the high pressure should not be strong enough to promote any long-duration/significant snow...the easterly flow it will likely provide Thursday night as chances of precipitation increase to likely POPs...may promote at least a period of wet snow/wintry mix for much of the CWA before the storm`s approach veers winds to a gusty southerly flow, ensuring an only-rain event Friday morning. Noteworthy are GFS peak PWAT values in the 1.0-1.3" range into early Friday which are into record-high territory for early January. A reflection of a bit of a tropical feed being pulled up the east side of the system and into the Mid-West, it introduces the potential for over performance of rainfall rates and storm totals. So did not hesitate to keep likely rain late Thursday night/Friday AM for the time being. An additional 1.0-1.5" of total rainfall from this part 2 is possible for the entire region. Southerly gusts in the 20-30 mph range will likely accompany the period of heavier precipitation as the storm system passes the region. Following the system`s departure to our northeast, no organized precipitation is expected for the weekend. Partly cloudy skies and seasonable chill should prevail, with a lack of any strong northern- stream amplification promoting only light/moderate breezes. For the period, high temperatures will be in the mid 40s to low 50s New Year`s Day...the mid 30s to low 40s for the weekend...and the 40s on Monday. Overnight lows are expected to be in the upper 20`s to mid 30`s both Thursday and Friday nights...and 20`s Saturday night.
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