Thursday, January 1, 2015

// // Leave a Comment

Bluebird Days and Cold Nights

Through mid next week expect:
  • Ample blue sky,
  • Rebounding daytime temps with light winds,
  • Very cold mornings, strong inversions in the valleys,
  • Enjoy the high elevations being mindful of the evolving thaw/freeze snowpack conditions

Arctic air remains in the wake of the recent storm system and the strong cold front of this past Tuesday. The origin of the current airmass stems from the north pole. Figure 1 highlights the southwesterly journey taken by the air via the tropopause pressure field (left panel) and the 200 mb meridional (north-south) wind field (right panel). Note the black-line arrow along the pressure gradient trail (north to south) from the pole into the Sierra and points southward (left panel). Along the same trajectory, the corresponding north-to-south wind maxima is illustrated by the cool colors (blue-purple, right panel).

Figure 1. Tropopause pressure (left) and the 200 mb meridional (north-south) wind field (right) illustrating the origin and trajectory of the current Arctic airmass. Courtesy of the NOAA-ESRL Global Reanalysis plotting page. 
Since its arrival on Tuesday, the airmass has finally begun to modify as an upper-level ridge continues to build overtop (Figure 2). This evolving pattern will dominate our weather for the next several days (into the middle of next week) yielding nice bluebird skies and daytime temperatures rebounding gradually over the period. Evenings will be very cold with intense morning inversions, particularly in the lower valleys where light-moderate snowpack exists. With such a pattern, higher elevations should be pleasant from mid-late morning through the day and be an escape from the morning inversion air that will deteriorate a little bit more each day.

The new topcoat of snow should be light and powdery for the next day or so, before some decent melting begins to take shape. By the weekend, daytime melting and nighttime refreezing will be in full force with the snowpack consistency changing along with it, so plan your outdoor excursions accordingly.

Figure 2. NAM model 250 mb forecast (heights/winds) for Saturday late morning. Note the strong upper-level ridge continuing to build into/across the western US. Courtesy of the NCAR Real-time weather data page.


Post a Comment