Wednesday, April 6, 2016

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Why Is Spring Still On Backorder?


9:15 AM EDT 4/6 - Wondering what is going on with this April chill? For those of us who thought the season would take a sharp turn to Summer, a resurgent period of cold has obviously put those plans on backorder. Long range indications show that traditional warmth expected this time of year looks to remain delayed through at least the middle of April and possibly longer.

This "third-year-in-a-row" delay of Springtime warmth (as similar cold episodes occurred in 2014 and 2015), warranted an investigation of where northern climate indicators stand, as summarized below. See below the text for live-linked images of the cited data.
  • ARCTIC SEA ICE EXTENT: Currently reported near 10 year averages, according to the National Ice Center. We hypothesize this level of sea ice and the higher reflectivity of nearby snow cover is having a dampening effect on surface air temperatures, and thus may be retaining a colder influence on passing High pressure systems. 
  • CANADIAN & NORTH AMERICAN SNOW COVER: This measure of geographical snow extend, as reported in this graphic from the Rutgers University Snow Lab, indicates current snow cover levels as of March 30, 2016 are running slightly higher than 30-year seasonal averages. 
  • GREAT LAKES ICE COVER: An important regional influence on eastern U.S. snowcover is water temperature and ice cover on the Great Lakes. A comparison of present ice cover in 2016 to the previous two years shows interesting differences. The April 2016 lake ice coverage is a minimal 1.1% reported by NOAA, whereas this same time period in 2015 and 2014 showed levels of 37% and 54% respectively.  
ANALYSIS: Less lake ice in 2016, due to a warmer El Nino winter, in concert with cooler Canadian air masses crossing into the U.S. has permits Low pressure systems recently to harness the Lakes as a moisture source for Eastern snowfall. The resulting northeastern U.S. snowcover has in turn created a regional chilling effect on area temperatures, as each passing High pressure system has helped to reinforce the regional cold.  See below the latest snowcover imagery from the NOAA Snow & Ice Data Center and scroll further for live-linked imagery and our conclusion at the end.


ARCTIC SEA ICE EXTENT


NORTH AMERICAN END OF WINTER SNOW COVER
Note: Line of best fit denoted by Rutgers Global Snow Lab 



U.S. & CANADIAN SNOW COVER


GREAT LAKES ICE COVER EXTENT


CONCLUSION: These indicators point to the possibility that until Arctic Sea Ice and corresponding Canadian snow cover shows an appreciable decrease, a continual period of cold and occasional post-Winter snow squalls that may last through end of the monthBelow is the 6-10 day temperature probability outlook from the Climate Prediction Center, indicating in the blue shaded areas a higher probability of below normal temperatures through April 15. 


Monday, March 21, 2016

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Real Spring ...right to Summer or not?

6:00 AM EDT 3/23 - Turning the corner into the next weather pattern, our Long Range Team is evaluating indicators for how this first period of Spring is going to unfold. The investigation centers on these three scenarios for the 30 day period ahead to late April for the Mid-Atlantic. Simply put, does the region face either:
A) A typical Spring pattern of alternating periods warm/cold, dry and rainy? 
B) Prolonged periods of below normal temperatures from a resurgent northern Jet Stream? 
C) Rapid arrival of summer-like conditions with widespread above normal temperatures?    
To best assess these questions, supporting evidence is needed from current status of large scale indicators. This provides a"pulse of the pattern" in order to examine how these indicators may influence local and regional weather in the weeks ahead. The three indicators chosen are 1) Status of EL Nino's decline from the peak; 2) U.S. & Canadian snow cover; 3) Atlantic & Gulf sea surface temperatures. 

Our findings are being posted in each section as the analysis becomes available for review. 

FIRST, THE BIG PICTURE : STATUS OF EL NINO




SECOND: SNOW COVER & ARCTIC TEMPS


A brief comparison of snow cover for this time period between the current El Nino event and the last one of record in 2009-10. Although this particular date in 2016 versus 2010 is just one day in a year-long data set, the intent is to demonstrate the significant differences in snow cover from the most recent moderate El Nino event to the current strong event.



THIRD : SEA SURFACE TEMPERATURE ANOMALIES




Friday, March 18, 2016

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Spring Begins With A Winter Finale


  • LIGHT-TO-MODERATE SNOW EVENT SATURDAY NIGHT INTO SUNDAY.
  • COMPUTER MODELS BACKED OFF EARLIER IDEAS OF A HEAVY SNOWFALL. PERHAPS 1-2" WILL ACTUALLY SHOW UP ON THE GROUND, AND PRIMARILY ON GRASSY & UNPAVED SURFACES.
  • PAVED SURFACES SHOULD REMAIN MOSTLY WET WITH SOME SNOWCOVER ON SUNDAY MORNING. 
  • REFREEZING OF RESIDUAL MOISTURE POSSIBLE SUNDAY NIGHT.
BELOW: 
Updated current snowfall projection of what may fall (but not actually be on the ground) by 8 AM Sunday from the U.S. GFS model. Snow will exit the region Sunday night.



10:00 AM EDT 3/19 -  The map above depicted a recent computer model surface projection for 8 PM Saturday 3/19. The expected arrangement which has been shown for several days now is a moderate High pressure system in southeast Canada favorably positioned offset a coastal Low. This would lead to an overnight timing of precipitation that may produce accumulation on grassy, unpaved surfaces and some untreated surfaces. Key considerations:
  • Temperatures: Recent warm conditions will permitted residual heat to be retained in paved surfaces. Even though air temperatures are projected to go below freezing at times Sunday night, some ground areas should stay above freezing. Areas that are shaded, at elevations above 500 feet, or less traveled cannot be ruled out for accumulation on paved surfaces.
  • Precip Amounts: The European model backed off earlier ideas of a 10-14" snowfall along the I-95 corridor, and is now in line with the NOAA GFS model showing 3-5".
  • Sun Angle: This time of year, any model projection for high accumulation has to be taken as suspect. Angle of the sun by midday is the equivalent to mid-October. Although snow is likely to be "falling" quite heavily on Sunday, you may actually see the sun shining through the clouds -- and not much beyond an inch at any one time laying on the ground. 
PRECIP AT 2 AM SUNDAY 



 TEMPERATURES AT 2 AM SUNDAY

THE MONDAY AM COMMUTE? 



Some refreezing is possible due to temperatures dropping into the mid 20s early Monday AM as snow exits the region. However, it is probable that many roads may be just wet and any pre-treatment by salting crews should negate accumulation problems on roadways.
TEMPERATURES AT 8 AM MONDAY