I know that seems hard to believe but it's true. Here's the short version: There's a 20% chance of snow on Thursday and a 90% chance of rain Saturday night. That's all the excitement for this week. Here's the long version:
Short Term...(Today through Thursday) Issued at 259 AM EST Wed Jan 5 2022 Quick Summary: --Windy conditions will continue into the afternoon with gusts to around 45 mph. --Below zero wind chills Wednesday night. --We`re confident in less snow Thursday and have trended probabilities and amounts downward. Meteorological Analysis: The first shortwave trough and attendant surface low is moving across the Great Lakes now, with a trailing cold front approaching our area. Strong cold advection will start in central Indiana around sunrise and continue through the day. Peak surface pressure gradient driving the stronger winds will occur through at least early afternoon, with a more substantial drop-off in wind speeds by around sunrise as gradient continues to relax and modest mixing subsides. We will extend the Wind Advisory through the afternoon, although some sites may fall below traditional criteria before the ending time. Also, we will see stronger gusts south of the Advisory that may fall just short of criteria but mixing/momentum transfer supports gusty winds there. We trended temperatures toward raw guidance to eliminate any influence of bias correction from calibrated/blended guidance. Upstream trajectories are over snowpack so this will be a drastic change. These much colder temperatures paired with residual westerly surface winds yield wind chill values below zero generally north of I-70 and in the single digits to the south tonight. We have trended precip/snowfall probabilities and amounts downward based on trends in the guidance. We felt comfortable with this given the fairly tight clustering of ensemble guidance from both ECMWF/EPS and GEFS. Although some very low amounts remain on the northern periphery, conceptually the cutoff of measurable precipitation in these scenarios is often much sharper than what a blended/ensemble approach with influence from a few outliers will show. So this boosted our confidence to remove precipitation from I-70/Indianapolis altogether. At this point, a slight northward shift could involve our southernmost counties, including Brownstown, Seymour, and North Vernon with meaningful snow amounts, but the greatest snow impacts are expected further south in Kentucky. A little deeper explanation--since we are seeing better agreement among ensemble and deterministic guidance it`s easier to look at deterministic model details to better understand the physical processes at play. Strong PV forcing in deterministic guidance is focused across southern Indiana into Kentucky, and this is where thermal tightening/frontogenesis and deeper saturation and omega within the dendritic growth zone resides. This region will see a better chance of saturating dry low levels from recent cP intrusion as well. && .Long Term...(Thursday night through Tuesday) Issued at 259 AM EST Wed Jan 5 2022 Thursday Night Through Friday Night. Dry weather is expected for Thursday night as the shortwave that is expected to bring snow to southern Indiana on Thursday continues to move further to the east. In its wake, temperatures will plummet as strong CAA aloft and at the surface bring the coolest air of the season thus far with lows in the single digits across central Indiana. This combined with the northwesterly winds of 10-15 mph will create periods where wind chills drop below zero and perhaps as low as -10 at times. The cold temperatures will continue through the day with highs in the upper teens to near 20 with wind chills maxing out in the single digits. This northwesterly CAA will brief with southerly flow returning late Friday into Friday night. Saturday through Tuesday. The pattern is then expected to shift going into Saturday as the southerly flow strengthens and a LLJ moves over the area. By late in the overnight hours, precipitation chances return as a broad upper level trough pushes through southern Canada with a surface front extending southwards towards Texas. Ahead of the front, southerly Gulf air will push into central Indiana with PWAT values of around an inch Saturday night. While surface temperatures may lag ahead of the precipitation, model soundings show plenty of warm air aloft which will keep rain the predominant precipitation type through the first part of the event. Towards the back end, CAA will quickly move into the area both at the surface and aloft which may allow for a brief transition to snow as the rain exits the area. Will continue to monitor this in the upcoming days as the p-type will be heavily dependent on the timing of the frontal passage and the strength of the WAA ahead of the front. Going into early next week, northwesterly flow aloft and near the surface will keep temperatures near to slightly below normal with generally dry weather as the atmosphere remains dry through the column.
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