Via @NWSIndianapolis… Enjoy the sun today as clouds and rain chances move in for most of the upcoming week, including Christmas day. It will trend warmer through the week, with temperatures well above normal by mid to late week.
National Weather Service Forecast Discussion
.KEY MESSAGES... - Warming trend begins today, continues through the upcoming week - Numerous chances for rain for next week, including Christmas Day, but precipitation amounts look minimal - Temps possibly flirting with upper 50s to around 60 by Fri and Sat .SHORT TERM (Today and tonight)... Issued at 223 AM EST Sun Dec 22 2024 Relatively tranquil weather pattern remains over the Ohio Valley today, as high pressure remains the key feature albeit centered just east of the region. This will result in stable atmospheric conditions across Central Indiana today. Weak pressure gradient oriented from the southeast turning southerly should keep winds under 10kts for much of the day. Minimal moisture throughout the boundary layer will also translate into minimal clouds today but there is a narrow ribbon of moisture around 15KFT AGL that could result in a few cirrus based clouds traversing the area this afternoon. With parcels seeing minimal moisture presence at the surface, expect a slow and steady warming trend this morning across Central Indiana with temperatures approaching seasonal conditions or possibly a touch above seasonal south of Indy Metro. The longwave pattern overhead is still depicting a weak ridge axis at 500mb displaced across the Eastern CONUS that is aiding in the weak height gradients over the Ohio Valley and also resulting in the weak upper level flow. Tonight...Anti-cyclonic ridge will continue to drift east, which will allow the boundary layer isallobaric gradient to return. Orientation of the gradient will be southwest to northeast along the western periphery of Central Indiana, fortunately this will occur during the nocturnal period and the lack of a well mixed near surface environment should keep things decoupled for the most part and winds will likely just be in the 5-10kt range. There is some indication that ascending parcels could strengthen in the mid-lvls after midnight enough to further thicken the cloud shield that will be cirrus based. But confidence in this scenario remains minimal at the moment. The longwave pattern is still progressive in the zonal orientation, but there will be a developing mid-lvl trough axis across the Northern Plains that will begin to slide south, this will become the next feature to monitor for Monday. .LONG TERM (Monday through Saturday)... Issued at 223 AM EST Sun Dec 22 2024 Monday...Upper level flow will feature a 500mb trough steadily sliding east/southeast into Great Lakes region. This will cause a slight modification to geopotential heights across Central Indiana, with an associated boundary layer pressure gradient oriented from the southwest to northeast along the lee-side of a developing surface vorticity feature in Wisconsin. This will cause parcels to ascend through a moistening column across Indiana midday. With presence of some minimal forcing through the mid-lvls that will be seeing an increase in moisture, it is favorable that as precip develops it will likely be small hydrometeors at onset Mon afternoon. With a thickening cloud footprint, this should prevent temps from warming too much from the low/mid 40s despite the modest thermal ridge that is advecting warmer air into Central Indiana. A boundary does appear to become quasi-zonal oriented over Indiana late Mon eve, which could prolong the drizzle or light rain. The one concern for Mon ngt could end up being a decoupled boundary layer that is saturated and might lead to a period of some patchy fog with more drizzle. Christmas Eve - Tuesday...500mb weak ridging will sneak into the Ohio Valley which will be coupled with a weak area of warm air advection beneath at 850-700 mb layer as a thermal gradient across Central Indiana will begin to lift northward. Overall Tue should still produce a stratus layer across the region in advance of the next mid-lvl trough axis that will be developing across the southern Plains. It is possible diffluent air and some weak height rises in the near surface environment will translate into a mostly dry Tue, but expect an increase potential for precip in the western portions of the forecast area by late Tue. Christmas - Wednesday...Mid-lvl trough axis continues to demonstrate some modest strengthening, which may result in a slight negative tilt to the surface shortwave that will be lifting into Southern MO. Strong V-wind component will be in place ushering in additional moisture ahead of the evolving shortwave. This will couple with ascending parcels and expand the precip footprint across much of Central Indiana by mid-morning Christmas Day. Expect at onset droplets will likely be smaller, but with added forcing and a strengthening mid-lvl shortwave as the day progresses the precip shield will likely become more steady rain in portions of Central Indiana. Continued unseasonably warm surface will keep temps in the 40s possibly near 50 in the far southern portions of Central Indiana. Thursday...Amplified shortwave trough quickly pivots east of the region, with a weak area of divergence aloft in the wake from a potent jet streak. This should allow for a period of stronger upward vertical motion but should be short-lived as the progressive pattern continues and modest height rises return to the mid-lvls across the Great Lakes and Ohio Valley. Stronger mid-lvl vort max progged for the lee-side of the rockies, with a surface feature taking shape. Strong meridional flow returns but with a delayed moisture return, this time with a stronger thermal ribbon advecting north into Central Indiana. Expect a nice surge ahead of the next system, with temps likely nearing the low/mid 50s. If there is enough breaks in clouds in the morning hours, might even see temps push higher. Friday through Saturday...Similar pattern to close out the active weak, with the continued southerly flow of moist and warm/mild air. The difference for Fri and Sat could be that temps will be flirting with the upper 50s to lower 60s. 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
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