Western Winter Storm

The much talked about Arctic front is advancing South and West with an Omega Pacific Coast blocking regime and a cold upper trough diving S into the Sacramento and San Joaquin Valleys with its near 1060mb High pressure cell over Montana/Wyoming and the very cold upper trough out West continues to drop toward Southern California before closing off and forming a cold core upper Low near Las Vegas Tuesday morning. Very chilly temperatures across the West are expected and snow is likely in Las Vegas, just N of Phoenix into Tucson, very far S in New Mexico, and West Texas as the Arctic front spills E over the Eastern Mountain gaps of the New Mexico into the Rio Grande River High Plains. The Arctic high will settled into Western Kansas and modify to around 1045mb which gives us an idea of just how dense this Arctic air mass is. The front will clear the Texas Coast Tuesday afternoon/ evening with increasing cold air advection Tuesday night into New Year’s Eve. A wintry mix is possible across Oklahoma into Missouri and Arkansas.

The challenging part of the forecast for much of Texas begins in earnest New Year’s Eve afternoon as up glide and over running moisture from the Eastern Pacific begins to saturate the upper/mid levels. The worrisome forecasting challenge is what the short term meso guidance indicates Wednesday afternoon. Light precipitation breaks out along the Rio Grande as the closed upper low begins to slowly move E over Arizona. The GFS and ECMWF are a bit drier with the surface boundary versus the aggressive NAM/WRF/SREF meso guidance that suggest a couple of 100th of an inch of light drizzle or light rain breaks out across S Central Texas spreading ENE New Year’s Eve night. Those shorter range models also suggest that surface temperatures are just below freezing along and N of the I-35 Corridor from just N of San Antonio and Austin and just W of the Dallas/Ft Worth area. The 2 meter temperature profiles for SE Texas as near 34 to 36 degrees along and N of I-10. These temperature profiles at the surface may…big emphasis on may…might be too warm 72 plus hours out via the computer guidance. The NAM and SREF are suggesting an upper air disturbance arrives ahead of the main closed core upper low generating just enough lift to saturate the surface boundary during our New Year’s Eve festivities as we ring in the New Year. This continues into New Year’s Day. The next fly in the ointment is a Coastal wave developing Thursday night and just how close to the Coast a warm front actually makes it. The current thinking is the Coastal wave and warm from may remain just offshore, but warming temperatures are depicted by the guidance as the Arctic high weakens and retreats E. It is noteworthy that the computer models often are too quick to erode the cold air at the surface once it becomes entrenched, so we will need to monitor the trends the next couple of days. The most worrisome period in New Year’s Eve and early New Year’s Day at the moment. With so many forecasting challenges to a busy Holiday period, it is prudent to keep tabs on the weather closely later today and tomorrow into Wednesday before venturing out for a night of New Year’s Eve activities. The Wintry mix is expected to expand NE across the Southern Plains into Southern Missouri and Arkansas as we near the end of the week.

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