Snow will arrive Sunday, be heaviest Sunday night, and diminish Monday morning. Still looks like a shoveler!
First, some Friday morning headlines:
– Clipper last night brought light snow, and even colder temps.
– Below normal temperatures expected for the foreseeable future.
Bitterly cold conditions likely by mid week next week.
– WINTER STORM WATCH for a significant winter storm expected to
impact the region Sunday – Monday, growing confidence on exact location,
details of precipitation types and totals, particularly across
southern Indiana.
National Weather Service technical discussion:
Tonight through Saturday night... Surface high pressure centered across the region will provide quiet weather conditions. The pressure gradient relaxing due to surface high building in should also lead to lighter winds as the short term period progresses. Expect little cloud cover Friday night into Saturday thanks to large scale subsidence. This combined with a colder airmass settling supports temperatures falling well into the teens tonight. A gentle NW breeze on top of the cold temperatures could result in single digit sub-zero wind chills for northern counties. Expect the colder airmass to persist through Saturday keeping temperatures below normal. By late Saturday, all eyes are on the significant winter storm which will begin to approach the area. Moisture streaming northward ahead of the system supports increasing clouds with some potential for wintry precipitation to begin at the very end of the period towards daybreak Sunday. Much of the wintry precipitation from this system will move in during the long term period and more details on potential impacts can be found in the forecast discussion below. .LONG TERM (Saturday through Thursday)... Issued at 306 AM EST Fri Jan 3 2025 OVERVIEW - The primary concerns for the long term forecast are twofold. 1) WINTER STORM WATCH for a winter storm expected Sunday into Monday, with potential for significant to major impacts, in the form of heavy snow, sleet/ice accumulations, and gusty winds/blowing and drifting. 2) Bitterly cold conditions arriving in the wake of this storm, likely persisting well into the week 2 period before improvement. WINTER STORM SUNDAY INTO MONDAY - Latest 03/00z runs are for the most part in good agreement; however in winter storms like this where there are sharp gradients in both precip type and accumulations, any track deviation of as small as 15- 20 miles can cause significant impact differences for specific locations. Of course, the rain to mix to snow line runs right through Central and South Central Indiana, so pin pointing exactly which counties will see what kind of precipitation and how much is very difficult as the slightest changes in the potential storm track will shift everything north or south. The guidance suite continues to display decent agreement on the synoptic situation for the coming winter storm Sunday into Monday. Latest GFS guidance has trended stronger and a tad north with the system while the ECMWF has trended weaker and further south. Model inconsistencies and slight flip flopping will likely continue for the next few model runs until the energy associated with this system pushes onshore of the west coast of the US and can become fully sampled. Mesoscale details still remain relatively uncertain, particularly across the southern half of the area, and especially given run-to-run trends which have brought the warm nose aloft further north, placing precipitation type concerns much more in play south of the I-70 corridor. No changes in antecedent conditions leading up to the main event. Widespread mid and upper level saturation will likely arrive by late Saturday night into early Sunday morning across central Indiana, but a substantial low level dry layer will take several hours to erode via evaporative processes as snow is generated aloft and falls into a 5-10KFT deep dry layer. METEOROLOGICAL SET UP Deepening upper trough ejects out of the Rockies and eastward into the Ohio Valley Sunday into Monday. Indiana will be located within the left entrance region of a departing jet streak with the right exit region of the jet streak from the approaching system nudging into Indiana... leading to enhanced lift over Central Indiana. Southerly flow through the column ahead of the trough will pump in ample moisture northward from the open Gulf into the Ohio Valley. 700-850mb mid level jet reaches 70 kts around 00z Monday as it extends from the Gulf Coast to the Ohio River with the mid level low tracking right across South Central Indiana. Guidance is in agreement with the surface low tracking ENE through the state of Kentucky, but there is still quite a bit of spread with some models showing a track through Southern KY while others show a track along the Ohio River. This will be something to watch very closely as a track difference of only 20 miles can mean the deference between all snow in the Indy metro or mixed precipitation mixing in resulting in significantly worse impacts. Nonetheless, this will likely be a very impactful winter storm for much of Central and South Central Indiana no matter the track; however a further north track would certainly be worst case scenario locally. Another area of discrepancy is the speed at which the system exits, with the GFS holding the surface and mid level low back across the Ohio Valley while the ECMWF has a more progressive and weaker solution. If the low sticks around Monday as the GFS and its ensemble members show, heavy snow from the deformation band could lead to much higher snowfall amounts across Central Indiana. A weaker, more progressive scenario would result in dry air filtering in quicker with precipitation ending faster and lower snow amounts... yet still impactful nonetheless. This will be something to watch over the next 24 hours as the system becomes sampled and that data is ingested into the models. Snow onset is likely by or a bit before daybreak Sunday in the far southwest, with snow progressively overspreading the area - arriving in the Indy metro area by mid morning and the Muncie area by early to mid afternoon. Mesoscale banding concerns are high, which could produce periods of very heavy snow with rates of 1-2+ inches per hour and/or high sleet/freezing rain rates across the south in the period when type concerns are heightened (primarily Sunday afternoon and evening). That said, dynamic cooling may help to counteract the advective component bringing the warm nose northward, which could lead to a sharp gradient between all snow and a mixed precipitation event. Based on current data and trends, Indianapolis northward should remain all snow, with mixing concerns south of the I-70 corridor, and especially across the far southern forecast area. Concerns are growing along a line from Knox County to Jennings County where freezing rain could potentially become the dominant precipitation type for several hours Sunday night. Depending on the depth of the warm nose, these row of counties could potentially see up to a quarter inch of ice accumulation. Precip will likely start as snow Sunday, then mix with or change over to sleet and freezing rain Sunday evening, then change back over to snow Monday as cold air filters in. While South Central Indiana may not get the highest snowfall amounts, this area certainly has the potential to have the most impactful conditions due to sleet and freezing rain. Also added sleet to the forecast as far north as I-70, but not including Indianapolis. Thinking areas along a line from Vigo Co to Johnson Co to Rush Co will be the northern extent of sleet mixing in, but that could easily shift north or south a row of counties. This is the area where any deviation in the track of the system will significantly alter the forecast. Any deviation northward will push the freezing rain chances northward and any deviation south keeps the worst impacts from mixed precip toward the Ohio River. For areas along and north of I-70, Snow will likely continue at least into late Sunday night and Monday morning, though it will begin to taper off as the system departs to the east, dry advection aloft begins, and forcing quickly weakens, but light accumulations may continue into Monday. Watching how long the deformation band sticks around on the backside of the system as this area could produce additional heavy accumulations on Monday, especially for Eastern portions of the state. Given the strong forcing, plentiful moisture, and long duration of the event due to the orientation and motion of the primary precipitation band with the system, probabilities are high for warning criteria snows of 5 inches or greater. Latest guidance shows high probabilities for greater than 6 inches of snow all along the I- 70 corridor with the potential for isolated areas to pick up as much as a foot. While there are still a lot of finer, mesoscale details to figure out, it is looking increasingly likely that there will be a swath of 6-8+ inches across portions of Central Indiana. Areas that see any mixing of sleet or freezing rain will see much less snowfall accumulations overall, however impacts could still be just as bad, if not worse. A Winter Storm Watch remain posted for all of Central Indiana from Sunday morning through Monday evening, no changes have been made to the timing of the watch with this forecast issuance. Winds will also be a concern, particularly Sunday night into Monday, with blowing and drifting likely becoming at least a moderate concern in that time frame, with frequent gusts in the 30-35 MPH range and locally higher gusts. BITTER COLD - Guidance strongly suggests the arrival and fairly lengthy persistence of a potent Arctic airmass in the wake of the winter storm. Well below normal temperatures are expected from Tuesday - Wednesday and into the week 2 period, with strong potential for multiple nights of subzero low temperatures and wind chills well below zero. This is, in fact, a fairly classic setup for subzero temperatures in the area, as an antecedent snowpack is nearly a requirement to get below zero, from a climatological standpoint. Sub- zero minimum temperatures with zero snow depth has only occurred 6 times in the period of record that includes daily snow observation (1884-present). Kept both highs and lows below guidance for the rest of the week, nudging temperatures toward the NBM10-25th percentile given the fact that there will be a healthy snowpack. MISCELLANEOUS - Toward the middle of next week and beyond, guidance not only strongly suggests the aforementioned persistence of a potent Arctic airmass, but also the passage of one or more upper level shortwave troughs within the much larger longwave trough/upper low over the eastern Canadian provinces and the northeastern CONUS. While moisture is very often difficult to come by for these waves, cyclonic flow in Arctic airmasses is notorious for producing persistent flurries or light snow showers, and depending upon the orientation of the flow, may allow somewhat more substantial lake enhanced activity to make it down into portions of central Indiana at times. While these more minor snows are far less predictable, particularly several days or more in advance, we are likely to see at least a few periods of light snow across some portions of central Indiana at times toward the end of the forecast period and beyond, despite the official forecast remaining dry for now. SUMMARY - Confidence is extremely high in impactful winter weather across central Indiana Sunday into Monday, and growing... though there still are forecast challenges and finer details to be worked through. Residents of central Indiana should prepare for significant winter weather impacts Sunday into Monday and monitor forecast updates in the coming days as details become clearer.
INDY SEVEN DAY FORECAST
Today: Becoming partly sunny. High 27.
Tonight: Partly cloudy to mostly clear. Low 13.
Saturday: Mostly sunny. High 25.
Saturday Night: Partly cloudy. Low 18.
Sunday: Snow arrives by late morning or early afternoon. High 25.
Sunday Night: Snow, heavy at times. Snow may mix with sleet or freezing rain southeast of Indy. Low 21.
Monday: Lighter snow, mainly in the morning. Final totals: 5-10 inches. High 26.
Monday Night: Partly cloudy. Low 13.
Tuesday: Partly sunny. High 23.
Tuesday Night: Partly cloudy. Low 8.
Wednesday: Partly sunny. High 17.
Wednesday Night: Mostly clear. Low 2.
Thursday: Mostly sunny. High 18






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