Wednesday, November 5, 2014
Cooler Weather on the Way with Chances for Snow?
Overnight: Rain showers will overspread the area from the southwest with the approaching cyclone from the west within an area of moderate upward vertical motion in association with warm air advection at 850 mb. 850 mb temperatures hovering between 2 and 4 degrees C will drop to below 0 by 12Z changing an light rain or drizzle to flurries with little or no accumulation excepted.
Thursday thru Friday Night: As the surface cyclone mentioned above passes to the east, it will deepen slightly producing a strong pressure gradient between it and the surface anticyclone building into the central plains. Strong cold air advection will cause highs Thursday to be cooler then today. Only low 40s excepted with 925mb temps only around -2 C. Dryer air an subsistence behind the shortwave will clear things out Thursday night into Friday. Clouds will increase Friday afternoon with southerly winds and warm air advection ahead of the next shortwave diving in from the northwest. NAM and GFS are in very good agreement in bringing a cold front though the area after midnight Friday night. There is positive vorticity advection with neutral temperature advection seen on both NAM and, to a lesser extent, the GFS, at 06Z Saturday, so chance of rain will be in the forecast late Friday night.
Saturday and beyond: Negative vorticity advection occurs Saturday as low levels dry out on breezy northwest winds and cold air advection producing downward vertical motion and an end to any precipitation. 850 mb temps drop to -8C on the NAM and -6 on the GFS. A blend will be perferred for highs on Saturday. Sunday looks to be sunny but cool with slightly warmer temperatures at 925mb climb to around 2C so will lean highs around 40. Monday is interesting because the GFS and the ECMWF diverge with the evolution of a winter event. 18Z run of the GFS has a baroclinic zone setting up just south of the area and a weak low pressure moves northeast along this boundary and produces an area of light snow with the 5400 m thickness line right overhead. The 12Z ECMWF run however, shows a well organized surface cyclone moving in from the central plains. ECMWF is a little warmer than the previous day's run so low confidence in this system. Will lean toward ECMWF because of the run to run consistently. After that, strong cold air advection ensues after departing surface cyclone or baroclinic zone depending on model. Coldest air of the season to be seen after Monday system as 850mb temps drop to -14 to -16 on GFS and -12 on ECMWF. Highs on Veterans day may struggle to reach 30 with some wind to put even more of a chill in the air. Stay tuned.