Mar 18, 2014: Warmth Briefly Returns This Week

[notice]Blog Notice: Due to continued computer issues, I may not be able to post daily updates beginning on Wednesday, and the 8-day forecast page will not be updated in the meantime. Once the issue is resolved, full daily updates will resume as usual.[/notice]

Forecast Highlights:

temp54Another round of cold temperatures over the last few days is gradually exiting the region, allowing for a warmer air mass to return with temperatures returning back to near and even slightly above average for the remainder of the week. Scattered showers are anticipated on Wednesday night and again on Saturday, with highs likely approaching 60 degrees on Thursday. Despite meteorological winter having ended on March 1st and astronomical winter ending in a few days, however, this year’s winter pattern is still not over, with strong indications of yet another cold surge across the region by next week.

 

 


Today – Saturday: Warmth Temporarily Returns

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Posted above from left to right are the latest available surface analysis and radar composite from WPC, and the GFS initialized 500 millibar heights and vorticity from NCEP MAG; both are valid at 12z (8am). The elongated positively tilted trough which was previously situated over the south central US has since consolidated into a shortwave trough which continues to progress ENE and offshore; associated with this shortwave trough is a developing low pressure east of Florida with heavy rain, which will track NE as well and will stay well offshore. Meanwhile, a high pressure remains centered over New England extending into Quebec, and will provide the area today with mostly sunny skies and highs in the upper 30s to low 40s.

 

12z run of the high-res 4k-NAM at hour 54, on 18z Thursday (2pm). Taking model biases into consideration, this run may be too cold by a few degrees (image credit: PSU e-Wall).

temp54Attention turns next to the upper level trough near Colorado and the surface low reflection near Kansas. This trough will become more south-north oriented as it continues NE through the Midwest and into Canada, allowing for rising heights to its east and continued mid to upper level W-SW winds over the northeastern US advecting a slightly warmer air mass into the region. Meanwhile, as the surface low pressure tracks NE into Canada, its associated cold front will shift east towards the region, resulting in increased cloud cover on Wednesday with highs in the low to mid 40s for most of the area. The frontal boundary will move through overnight with scattered showers, ending mainly by 12-2am. Rainfall amounts are anticipated to remain below 1/4 inch, although the possibility is there for a wave of low pressure to develop near the area as suggested by the NAM and CMC, which would allow for a brief period of moderate to locally heavy rain in the evening with up to or locally over 1/2 inch of rain. Even though a transient upper level trough will transverse the region on Thursday with a cooler air mass returning, westerly winds and more sunshine are expected to result in warmer temperatures behind the frontal passage. This setup is often an indication of model guidance underestimating high temperatures, as has occurred twice over the last week; the latest model guidance generally depicts highs in the low 50s, and at this time I am siding warmer than the operational models with highs peaking in the mid to upper 50s. A slight cool down is anticipated on Friday as the trough shifts eastward.

The progressive upper level flow continues through the remainder of the week as another shortwave trough enters the NW US on Wednesday night, quickly progressing eastward and reaching New England by Saturday. This will aid in the development of a fast moving low pressure over the northern US tracking eastward into the region, but with the model guidance diverging with regards to the strength and track of the low pressure. Any precipitation that affects the area will be in the form of rain, but the aforementioned difference will help to determine how warm temperatures get on Saturday, with a weaker and flatter low pressure keeping highs likely in the low to mid 50s range and a stronger and more amplified low pressure allowing high temperatures to spike well into the 50s or possibly near 60 degrees. Looking at the ensemble members of the GFS, consisting of 20 runs of the GFS with slightly different initialized conditions, there is no strong consensus, although most members depict a low pressure north of the operational run. There is no high probability regarding the exact scenario, and at this time I am siding towards high temperatures peaking in the mid 50s along with scattered showers, which is subject to some changes.

 

Sunday – Beyond: Winter Is Still Not Over

By this time of the year, average high temperatures are supposed to be in the 50s with lows in the 30s as the jet stream gradually retreats north, with snowstorms decreasing in likelihood over the region. This winter has featured frequent periods of cold and snow beginning in late November only interrupted a few times, including a 10-day stretch of warmth in mid January and a few days towards the end of February, and March has been no exception, with only 5 out of 17 days seeing a high of 50 degrees or greater in Central Park, along with 5 days of daily temperature anomalies of -10 degrees or more. The first 17 days of March have averaged out to 4.9 degrees below average, making this the coldest March since 1984 which had a total average monthly temperature of 36.7 degrees. Remarkably, despite the anomalous cold, the area has yet to observe a widespread measurable snow event this month with one major snowstorm to the north and two moderate snowstorms to the south. The next few days will somewhat moderate the temperature anomaly, but winter is not over just yet as indications strongly point to another cold air mass in time for next week.

As an upper level low shifts into the northeast Pacific Ocean, an upper level ridge is anticipated to detach from the main flow, settling as a block-like feature over Alaska, which along with a temporary spike in ridging over the western US is anticipated to lead to another southward surge of cold temperatures through Canada and into the eastern half of the US beginning on Sunday. The model guidance is likely exaggerating the southward extent of the cold, which is a typical bias in the medium to long range, although temperatures are nonetheless expected to return back to below average with highs likely to reach the 30s to low 40s range. With the cold air mass in place, the possibility of a late season snow event cannot be ruled out; the latest model runs depict a potential storm sytem around the March 25-27 time frame, although at this range it is too early to speculate on any such potential in depth.

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