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12:20 PM | **Long-lasting and significant storm threat continues for next week**

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Weather forecasting and analysis, space and historic events, climate information

12:20 PM | **Long-lasting and significant storm threat continues for next week**

Paul Dorian

 12Z GFS surface forecast map for Wednesday morning, March 21 (snow in blue; ice in red, purple; rain in green); map courtesy NOAA/EMC, tropicaltidbits.com

12Z GFS surface forecast map for Wednesday morning, March 21 (snow in blue; ice in red, purple; rain in green); map courtesy NOAA/EMC, tropicaltidbits.com

Overview
A great blizzard took place in the Mid-Atlantic region from March 18-21, 1958 with a focus on Pennsylvania where extreme snowfall amounts took place and there was a snowstorm from April 6-7 in 1982 which delayed the opening of the baseball season by several days…the point is, there can be significant snow events at the end of the winter season and even into the early part of spring.  A significant storm threat continues for next week in the Mid-Atlantic region and it could be a long-lasting event with the potential for important rain, ice and/or snow amounts in DC-to-Philly corridor.  The cold and stormy weather pattern that we are experiencing looks like it will continue right into early April this year.

General Discussion
Back in the 1950’s, 1960’s and 1970’s, March was quite often colder-than-normal in the Mid-Atlantic region and this year is certainly heading in that direction.  In that era, there were several years featuring multiple nor’easters in a short period of time - similar to what we are experiencing this year.  For example, three nor’easters took place in a short period of time in January 1966, and again during February/March 1969, and again in January 1978.  We have had three nor’easters this month and a fourth is possible next week and some long-range models even suggest a fifth could occur near the end of the month.

 12Z GFS snowfall depth forecast map by Saturday evening from weekend system (does not include next week's storm threat); map courtesy NOAA/EMC, tropicaltidbits.com

12Z GFS snowfall depth forecast map by Saturday evening from weekend system (does not include next week's storm threat); map courtesy NOAA/EMC, tropicaltidbits.com

Short-term (and the possible end of the DC snow jinx)
As a new push of cold air surged into the region this morning, there were scattered snow showers and even heavier bursts of snow in parts of the Mid-Atlantic including the DC metro region where there has been a lack of snow this winter (to say the least).  Could this be a sign that the snow jinx is coming to an end in DC? Well, perhaps it is, and there will not only be a chance for snow next week (see below), but there is a chance for small accumulations on Saturday.

 12Z NAM 500 mb forecast map for Saturday morning...convergence in the upper-atmosphere will tend to weaken the early weekend system

12Z NAM 500 mb forecast map for Saturday morning...convergence in the upper-atmosphere will tend to weaken the early weekend system

On today’s weather maps, there is a strong low pressure system in the middle of the country with a lot of precipitation and it is headed right towards the DC metro region.  However, there will be substantial weakening in this system later tonight and early Saturday as it heads east and encounters “confluence” in the upper atmosphere (convergence aloft, divergence at the surface).  The 12Z GFS snowfall map shows accumulating snow by tomorrow night extending all the way across the country – including in the DC metro region.  Bottom line, there can be a few hours with snow on Saturday in the DC metro region possibly mixed with sleet and/or rain at times and then focus will turn to an even bigger threat for next week.

Next week’s significant and long-lasting storm threat
There are signs that high-latitude blocking will re-establish itself to our north after a break for a few days and this will allow for colder air to return to the Northeast US early next week.  This cold air will be anchored by strong, cold surface high pressure building from southeastern Canada into the Northeast US – a likely key player in next week’s event.  The establishment of cold air in low-levels of the atmosphere increases the odds for frozen precipitation (including ice) next week in the DC-to-Philly corridor - all despite the fact that spring officially gets underway on Tuesday.  

 12Z GFS surface forecast map for Tuesday afternoon, March 20 (snow in blue; ice in red, purple; rain in green); map courtesy NOAA/EMC, tropicaltidbits.com

12Z GFS surface forecast map for Tuesday afternoon, March 20 (snow in blue; ice in red, purple; rain in green); map courtesy NOAA/EMC, tropicaltidbits.com

At the same time high pressure builds to our north, low pressure will be trekking towards the Ohio Valley and, unlike the Saturday system, this storm will not weaken as it moves to the east. Significant snow will take place early next week with this low pressure system from the central Plains into the Ohio Valley.  Ultimately, energy from this Ohio Valley system is likely to transfer to the Mid-Atlantic coastline and low pressure should form off of Virginia by the middle of next week.  This system will become a slow-mover as deep upper-level low builds and spins over the Mid-Atlantic region and precipitation could come in waves for the DC-to-Philly corridor beginning as early as late Monday night and ending as late as early Thursday.  

 Snowfall estimates from the 12Z GFS for next week's event....take these with a grain of salt this far out.  On the left, the snowfall accumulation amounts are estimated using a more conservative method compared to the map on the right which utilizes a 10:1 snow:liquid ratio (probably too high); map courtesy NOAA/EMC, tropicaltidbits.com

Snowfall estimates from the 12Z GFS for next week's event....take these with a grain of salt this far out.  On the left, the snowfall accumulation amounts are estimated using a more conservative method compared to the map on the right which utilizes a 10:1 snow:liquid ratio (probably too high); map courtesy NOAA/EMC, tropicaltidbits.com

Stay tuned...many details have to be ironed out and still several days away, but the threat is there for significant rain, ice and/or snow for at least parts of the Mid-Atlantic region in this potential long-lasting event.  As with the March 18-21, 1958 snowstorm, elevation is likely to play a big role in any snowfall accumulations with possible big differences between higher and lower elevation locations in the Mid-Atlantic region.  

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com 

Extended morning video discussion: