Mar 15, 2014: Cold Start, Warmer Ending To Week

[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]

Forecast Highlights:

f42Mild 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).

f42The 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.


Tuesday – Beyond: Warming Up, Then Cooling Down Again

The theme of temperature swings will continue through the remainder of the week as a relatively strong trough enters the northwest US and becoming negatively tilted in the Midwest, aiding in significantly rising heights ahead of it over the northeastern US, allowing for warm air advection aloft. Near the surface, however, the positioning of the surface high pressure will result in southeasterly onshore winds, preventing a significant warm up on Tuesday and Wednesday and setting up for a temperature gradient, allowing western parts of the area to warm up into the 40s while Long Island/coastal CT remain in the 30s to low 40s. As the surface low pressure tracks into Canada, the surface cold front is expected to move through overnight on Wednesday, likely preventing a significant drop in temperatures overnight. Even though an upper level trough will enter on Thursday behind the cold front, the combination of more sunshine and a breezy downsloping westerly wind at 10-20 mph will allow temperatures to warm up behind the cold front, reaching the low-mid 50s inland and mid-upper 50s elsewhere for highs. These temperatures depend on the timing of the cold front, with a slower frontal passage allowing for warmer temperatures.

Slightly cooler temperatures will return for Friday with lighter winds and highs in the 40s, while another low pressure likely tracks to the north on Saturday, producing some rain and allowing for another brief spike in temperatures into the 50s. After Saturday, the main question is whether winter is finally over; while probability for snow is decreasing, the cold temperatures may not be over yet, with hints at another potential period of below average temperatures towards next weekend or the following week, although confidence in the outlook decreases by this time range with regards to the specific details. The next potential for widespread precipitation appears to be towards the middle of next week, towards the March 25-27 time frame.

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