Via @NWSIndianapolis… Heat miser agrees to let go of the mild weather at end of December, with cold miser taking charge in January. Several rain chances will accompany the warm air between Christmas and New Years Day. Colder air is expected to invade in January and likely continue thru mid month.
Technical discussion from the National Weather Service:
Mid-Morning through Afternoon...Heights will continue to rise mid- morning and continue to help erode the lingering stratus shield. With anti-cyclonic flow overhead inhibiting the potential for strong ascending parcels, expect mixing to be minimal through midday and likely produce a light wind if any wind from the west/northwest. Temps should slowly warm into the lower to perhaps middle 30s in the far south. Tonight...The upper level pattern influence for the Ohio Valley will continue to see the shortwave weakening and translate eastward reaching the western periphery of the region by tonight. A broader negatively tilted trough will be slowly digging south across the Great Lakes and Northeast. This should result in more influence to the Ohio Valley and Central Indiana by Sunday morning. .LONG TERM (Sunday through Friday)... Issued at 217 AM EST Sat Dec 21 2024 Sunday through Friday... The extended period will feature a dynamic weather pattern for the Ohio Valley. Initial period of benign weather will give way to increased chances for precipitation and fluctuating temperatures as a series of weather systems traverse the region. The overall feature will be a progressive mid-latitude cyclonic activity, that will have a series of shortwave troughs embedded within a broader and potentially amplified upper level trough over the eastern CONUS. Sunday...500mb analysis leans towards a progressive pattern. The aforementioned shortwave trough from Sat will pivot east, allowing the boundary layer anti-cyclonic feature to equally lift northeast and allowing the flow to turn southerly to southwesterly by midday Sun. This will result in perhaps some upper level clouds, but the bigger story will be on rising temperatures. Guidance is starting to suggest the aggressive thermal ridge could be flirting with the Ohio Valley by Sun afternoon and usher in temps back to the upper 30s and could even see a few locations south of interstate 74 reaching the low 40s by late Sun afternoon. The main player will be clouds shielding any of the sun and limiting the rate of surface parcels realizing the potential. Monday... Relatively zonal flow pattern will still be present across much of the CONUS, with a quasi-weak ridge axis over the Ohio Valley. This will translate to the weak height gradients and generally quiet conditions at the surface despite a weak mid-lvl shortwave trying to flirt with the Western Great Lakes and perhaps some mid-lvl clouds from ascending parcels coming into Central Indiana late Mon. There is some agreement that light precip could accompany the boundary midday Mon. But confidence has backed of slightly due to the height at which the moisture is present and could result in less of a footprint for precip. Tuesday...Progressive pattern starts to take hold, with a more evident shortwave trough ejecting out of the northern Plains into the Great Lakes late Tue. This will translate into height falls across the downstream areas of the Ohio Valley and increasing mid- lvl moisture from ascending parcels and warm air advection. Wednesday...Slightly more amplified trough axis over the eastern CONUS. The phasing will result in stronger dynamic forcing with robust positive vorticity advection over the Ohio Valley. This will allow strong upward momentum, and increased chances for larger precip footprint mid-week. Thursday...Amplified trough axis will drift eastward, with a secondary shortwave trough potentially rotating through the base of the trough. This will likely lead to additional unsettled weather into the later periods of the week into weekend. Weeks 2 Through 4 Period: While the period will begin mild...the long wave pattern is expected to shift toward the new year as a building western ridge allows a deep trough to develop across the central and eastern CONUS by early January with several potential short waves crossing the region through mid month. The period from Christmas to the beginning of the new year looks very mild but also likely to be wet with an above normal precipitation signal lined up through the Ohio valley. With warm temperatures this precipitation should be mostly in the form of rain with even a possibility of thunder at times. As pattern begins to shift near New Years, timing of colder air infiltration with pcpn signals will need to be watched for possibility of snow as this transition develops. Once cold air becomes established...there is uncertainty with regards to pcpn signals. Below normal precipitation is favored in the GFS and EC weekly anomalies, and favored by CPC, but CFS looks rather active with several short waves and potential storm systems crossing the central CONUS. This could bring rain or snow depending on storm tracks and timing which cannot be resolved by any means at these projection times. Overall temperatures during this period should be near or below normal.





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