Daily Archives: December 17, 2018

NYC Weather Update – Dec 17, 2018

NYC, Weather Update

This week starts off with a couple windy days, with Tuesday seeing a blast of Arctic air. Temperatures moderate Wednesday then start warming up on Thursday to above normal levels as a high pressure center slides off to our southeast and return flow from the southwest brings warmer air up our way. This will set the stage for a bout of possibly heavy rain to end the week.

Rest of today – partly to mostly cloudy skies. High temperatures in the mid-40s. Clouds are forecast to increase during the day as a potent 500 mb shortwave brings ample vorticity and divergence aloft. This will help induce some instability in the lower atmosphere and lead to more clouds. The other story will be blustery winds in the 15-20 mph range due to the development of a well-mixed boundary layer, allowing for effective downward momentum transfer of faster winds above to the surface.

GFS 500 mb forecast valid for 5PM today. The oranges and dark purples indicate an area of very strong positive vorticity associated with a 500 mb shortwave pushing through the area.
It may be difficult to make out, but the bottom layer of the atmosphere, starting from about 850 mb down to the surface, shows evidence of becoming well mixed by this afternoon. This is indicated by the angle of the environmental temperature profile (red) paralleling or being even more acute than the light grey lines that slope to the left at about a 45 degree angle. These are the lines of dry adiabatic lapse rates.

Tuesday – an Arctic front passes through the area early during the day. There isn’t sufficient moisture in the atmosphere to bring about any precipitation. The tangible impact of this frontal passage will instead be below normal temperatures in the mid-30s despite a sunny day as a high pressure builds. This building high pressure should maintain stiff winds as the pressure gradient stays pretty steep.

Wednesday – sunny conditions with temperatures right around normal 40°F.

Thursday – clouds increase as the high pressure responsible for sunny weather mid-week starts moving off to the southeast. As this happens, clockwise return flow on the western side of the exiting high pressure will bring some warmer air our way. High temperatures are expected to be warmer than average, in the upper-40s.