804 FXUS63 KOAX 171134 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 534 AM CST Tue Jan 17 2023 ...Updated Aviation Forecast Discussion... .DISCUSSION... Issued at 404 AM CST Tue Jan 17 2023 Key Messages: - Significant snowfall (6 to 11 inches) is forecast for areas north of the Platte River. Lesser snowfall amounts and light icing are forecast for southeast Nebraska and southwest Iowa. - A Winter Storm Watch is in effect for portions of the area from 6 AM Wednesday until 6 AM Thursday. - 1" per hour rates Wednesday afternoon and evening will result in near-whiteout conditions in northeast Nebraska. Today and Tonight: A messy pattern is on display this morning in mid-level water vapor imagery with the leftovers from yesterday's rain entering the Great Lakes region and a deepening trough making landfall onto the West Coast. At the surface, the pressure gradient is beginning to loosen and the breezy northwesterly wind gusts are moving off to the northeast leaving much more manageable speeds in place. For today, we'll enjoy dry conditions with clouds hanging around initially this morning, clearing out somewhat this afternoon before building back in this evening. Temperatures are expected to remain warm with highs topping out in the 30s and lower 40s. Wednesday and Thursday: The main concern of the forecast period continues to be the winter system beginning Wednesday morning, with impactful snow looking certain for a good chunk of the area with a sharp cutoff on the southeastern edge of it to lower amounts. The trough currently over the CA/AZ region is expected to undergo deepening as it crosses into the lee of the Rockies early Wednesday with precipitation spreading northeast and reaching the Beatrice area by 6 AM. Snow, freezing rain/ice pellets, and rain will then gradually build northeast over the rest of the morning before snowfall takes over Wednesday afternoon for most of eastern Nebraska and southwest Iowa. By the afternoon and early evening hours Wednesday, strong PVA, low-level warm air advection, and other lifting mechanisms will maximize snowfall values across northeast Nebraska. The 00z HREF indicates 50 to 70% chances of seeing snowfall rates over 1" per hour, resulting in near whiteout conditions and making travel very hazardous. Snow is expected to continue into early Tuesday before exiting the area by 6 AM. Left behind by this system will be a swath of heavy snow of greater than 6" with areas along a line from Columbus to Onawa seeing totals reaching above 8". Initially pessimistic snow-to-liquid ratios have been increased in response to the consistent signals in cross sections and soundings for strong lift in the DGZ. While the snow rations seem to be on the increase, we are still expecting a wet, heavy snow that will be difficult to blow around with out 20-30 mph winds that are expected. Speaking to some of the uncertainties of this system, the guidance continues to shift as far as the main axis of snow is concerned. While the operational GFS has remained rather consistent with a more southerly solution to the snow axis, the ECMWF has shifted south once again putting the Omaha/Lincoln metros (as well as I-80) back in play for heavier snowfall. We'll have to take both of those solutions with a grain of salt though, as both ensemble means' snow axes settled north of both of their respective control runs. If the southerly trend continues into the 12z runs (which will include land-based upper-air observations and hopefully more agreement later this morning), expect to see an increase to the snowfall expectations for Omaha above the current 3- 7 inches of snow. In addition to the model changes, we could see sleet/freezing rain eat into the snowfall totals on the southeastern periphery of the snow axis, resulting in a sharp cutoff between high snow totals and meager amounts, as is evident by zero-degree isothermal layers depicted in forecast soundings for portions of southeast Nebraska. The remainder of Thursday is expected to be colder thanks to the return flow on the exiting system, but not bitterly cold as we've seen earlier this winter. Expect highs to top out in the upper 20s and lower 30s. Friday through Sunday: Friday into the weekend is looking to be on the quiet side weather- wise as shortwaves dodge and duck to the north and south of the area and should leave us dry. Temperatures are expected to remain in the upper 20s and low 30s, with signals in the model guidance that we could see precipitation activity return to the area early next work week. && .AVIATION...(For the 12Z TAFS through 12Z Wednesday morning) Issued at 528 AM CST Tue Jan 17 2023 MVFR to IFR conditions are in place across the area along with westerly to northwesterly winds that should remain manageable at less than 15 kts. A brief cutout in the clouds currently keeps KOMA at VFR conditions, but this should quickly fill back in restoring MVFR conditions by sunrise. A period of VFR conditions is expected after 18z for KOMA and KLNK that should last until the very early hours of Wednesday where MVFR conditions return. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...Winter Storm Watch from Wednesday morning through late Wednesday night for NEZ011-012-015>018-030>034-042>045-050>053- 065>067-078. Winter Weather Advisory from 6 AM Wednesday to 6 AM CST Thursday for NEZ068-088>093. IA...Winter Storm Watch from Wednesday morning through late Wednesday night for IAZ043-055-056-069-079. Winter Weather Advisory from 6 AM Wednesday to 6 AM CST Thursday for IAZ080-090-091. && $$ DISCUSSION...Petersen AVIATION...Petersen