It's currently 12 degrees outside and sunny with a light wind of 8mph. The big news is what might happen on Sunday, December 7th. Everything is on the table; rain, freezing, sleet, snow or a mixture of all. Even the National Weather Service seem unsure. The NWS is looking at it like this:
SHORT TERM /Tonight through Monday/... Issued at 352 AM EST Fri Jan 5 2018 Forecast challenges focus on temperatures initially..then shift to a complex system as moisture advects into the region ahead of an approaching cold front for late weekend set to bring potentially several precip types. The aforementioned high pressure will build south through the Great Lakes and the Ohio Valley for the first half of the weekend before shifting into the Carolinas by Sunday. The presence of the high over the area through Saturday night will essentially continue the dry and bitterly cold pattern that has dominated 2018 so far. Deep subsidence over the region will maintain mostly clear skies across the area into Saturday night. Model consensus present in finally lifting out by Sunday the amplified upper trough which has parked across the eastern part of the country for the better part of the last two weeks. Quasi-zonal flow will replace the trough with a piece of energy poised to rapidly track east from the Pacific coast Saturday night into the lower Mississippi Valley by Monday morning. At the same time... northern stream energy will drop out of the Canadian prairies serving to reestablish some level of a mid level trough by late Monday. How exactly these two features interact with a cold front approaching at the surface remains in question and leads to a challenging precip type forecast for central Indiana. The primary issue is how strong the warm advection is ahead of the front...especially for Sunday night and Monday. Initially on Sunday afternoon...precipitation will largely fall as snow with perhaps a light accumulation in spots. The global models /GGEM and ECMWF/ are both more muted with warm advection into the area while the NAM and especially GFS appear more aggressive with boundary layer warmth Sunday night into Monday. Considering the duration and intensity of the bitterly cold airmass experienced over the last 10-14 days...have some doubts as to how extensive warming aloft will be and am more comfortable at this point leaning more towards the colder global solutions. That being said...even the global guidance advects above freezing air into the boundary layer Sunday night and Monday that poses problems for precip type with soundings suggestive of a transition from snow to a snow/liquid mix or all liquid. Another and frankly more important factor to take into account is the near surface layer and ground temperatures. Current road temps have been as low as the single digits and teens and with more substantial surface warming not arriving until late Sunday at the earliest...really have a difficult time seeing ground temperatures warm substantially enough to enable rain as the primary precip type for any length of time. Am actually concerned that any period with all liquid precipitation will likely support an enhanced freezing rain potential with subfreezing ground temperatures...even if surface temps can get into the mid 30s for a few hours. With this in mind...am comfortable in introducing a potential for freezing rain into the forecast Sunday night and Monday along with other precip types. There are still many details to work out for Sunday and Monday but at this point...feel the ceiling for a snow/freezing rain mix is much higher than a snow/rain or all rain threat. Stay tuned as additional detail is employed into the forecast over the next 24 to 48 hours. Temps...continued with persistence and largely undercut temps within the cold airmass through Saturday night. Tonight will be the coldest night as the entire area goes subzero. Highs will mainly be in the teens Saturday...then jump into the upper 20s and lower 30s Sunday and 30s on Monday. Nudged temperatures down Sunday through Monday with concerns that models are overdoing warmth in general. &&
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