[notice]Blog Notice: I am experiencing technical issues as my computer is not working, and is likely to be fixed within the next few days. In the meantime, blog updates will continue to be posted as usual, along with an updated 8-day forecast when possible, but the 8-day forecast graphics along with planned additions to the storm archive pages which were scheduled for this weekend cannot be completed until this issue is resolved.[/notice]
Mild temperatures returned again into the region with the aid of strong warm air advection over the last 24 hours, with high temperatures today rising generally into the mid 50s to low 60s. As with the previous warmth surge, however, this warmth will remain only short lasting as yet another cold air mass returns, with highs in the 30s on Sunday and Monday as snow associated with a coastal low remains to the south of the area. These temperature swings will continue through next week as highs rebound into the 50s on Thursday along with some rain, followed by another transient cool down.
Tonight – Monday: Cooling Down, Snow Stays South
Posted above from left to right are the latest available surface analysis and radar composite from WPC, and the GFS 3-hour forecast 500 millibar heights and vorticity from NCEP MAG; both are valid at 15z (11am). An area of low pressure can be seen west of Maine, with the cyclonic flow around the low having resulted in strong warm air advection yesterday as strong south-SW winds helped to remove the frigid air mass which was previously in place on Thursday and early Friday morning. With partly to mostly cloudy skies today and a downsloping westerly wind at 10-15 mph, temperatures have warmed up into the mid 50s to low 60s for most of the area, bringing another taste of spring in a month which has so far resembled January more than a typical March. A piece of the polar vortex associated with yet another cold air mass can be seen over the eastern Hudson Bay in the 500mb map posted above, extending into southern Ontario. The southern end of the polar vortex is expected to interact with the shortwave over New York state later tonight into tomorrow, aiding in a deepening low pressure near southeast Canada while pulling the cold air mass into the northeast US, setting up for a return to more winter-like conditions on Sunday with mostly sunny skies, highs in the low-mid 30s inland and mid-upper 30s elsewhere, and a breezy northwesterly wind at 10-20 mph.
12z GFS hour 42, at 6z Monday (2am), depicting a relatively disorganized and elongated vort lobe stretching from the Ohio Valleyto Texas,with a strung out surface low pressure producing light-moderate snow south of the area (image credit: PSU e-Wall).
The next feature to pay attention to is the broad area of surface low pressure near the central US, along with two mid level shortwaves, one near Wyoming and the other near southeast New Mexico, as well as a vort lobe extending into western Canada. A complex interaction is expected between these features, which some of the model guidance struggled to handle properly; as recently as yesterday late afternoon and evening, some of the model guidance continued to depict a major snowstorm with significant snowfall extending into the NYC area and southern New England. This scenario still does not appear likely to verify, as besides the models struggling to gain a proper handle on the setup, the southward displacement of the polar vortex placing a very cold air mass over the northeastern US and a strong high pressure building into the region from Canada, as well as an elongated vort lobe stretching into the southern US which is unable to quickly turn negative and aid in significant amplification, will aid to suppress the system south of the area, with an axis of light-moderate snow accumulations centered over Virginia into Maryland and the Delmarva Peninsula. I am currently unable to complete an analysis behind this trend due to the previously noted technical issues, although I plan to expand more on this trend once this issue is resolved. Some light snow may extend into central New Jersey or possibly NYC/LI in the northern end scenario; the exact northward extent remains somewhat uncertain, but at this time continuity is maintained with the forecast from the last few days and the Sunday night-Monday period is still forecast to remain dry with a slight chance of snow showers included in the 8-day outlook for NYC and Long Island. High temperatures on Monday will peak in the upper 20s to low 30s across the area, once again much colder than average.