BOSTON (CBS) – The Blizzard of ’78, the Blizzard of March 2013, the April Fools’ Day Storm of 1997 – all some of the biggest and most destructive nor’easters in our recorded history.

These are not storms that we draw comparisons to very often. However, these blockbuster storms may just be the best analogs (past examples to help predict current storms) to use for this upcoming nor’easter.

Got your attention?

Good!

This storm has the potential to be an historic, crippling event for southern New England. With major coastal flooding, destructive winds, torrents of rain followed by a plastering of heavy, wet snow, the damage will be widespread and significant and the power outages likely numerous and lengthy.

Our most recent “big storm” was back on January 4th. Record flooding in Boston along with blizzard conditions made that one extremely tough to deal with. The saving grace with that event was its speed – it was a very quick mover, essentially only effecting one high tide cycle.

This incoming nor’easter will not have a quick exit, instead it will be blocked by a large area of high pressure up over Greenland. The “Greenland Block” is something that comes and goes during a winter season, but some of our biggest and most destructive storms have occurred when a strong block is in place. The situation for this storm will be just that, the block will be at its strongest thus far this season, giving the nor’easter no immediate exit, only slowly drifting away this weekend.

Combine a very slow moving storm with the highest astronomical tides of the month and you have the recipe for major coastal destruction. The problem in these situations is the ocean water never fully recedes during the low tide cycle. Coastal areas remain flooded for high tide after high tide, and essentially you have days of impassible coastal roads and communities cut off.

While the coast will undoubtedly bear the brunt of this storm, inland areas are at risk for a different set of problems.

Torrential downpours early in the storm will create widespread street and urban flooding. Smaller rivers (and perhaps even some larger ones) may spill over their banks on Friday and days to follow. Then the rain changes to a heavy, wet snow Friday afternoon.

Still the biggest wildcard with this event, the snowfall amounts are very tough to forecast.

Any significant accumulation (due to the heavy and wet nature of the snow) could cause significant issues and power outages given the strength of the wind gusts. Best chance of at last 6 inches are in the Berkshires and Worcester Hills, but we cannot rule out 6 inches or more all the way east to Boston.

TIMELINE

Midnight – 6 a.m. Friday

The rain arrives from south to north, starts as snow in western Mass. (Berkshires).

Winds start increasing out of the east-northeast, gusting 25-to-35 mph along the coast.

6 a.m.- Noon Friday

Rain ramps up and becomes heavy at times, especially in eastern Mass. Northeast wind gusts reach 40-60 mph over southern Plymouth County and Cape Cod/Islands.

Inland gusts range from 25-40 mph. Some street flooding and ponding of roadways begins.

Noon – 6 p.m. Friday

Rain coming down in buckets in central and eastern Mass. Serious street, urban, poor drainage flooding, upwards of 3 or 4 inches of water in spots.

Colder air starts to drain down from the north, changing rain to a heavy wet snow by mid-to-late afternoon in southern New Hampshire and parts of northern Mass.

While initially it may be tough to stick, by the evening commute I would expect some snow covered roads, especially in Worcester County.
Wind gusts all along the Mass. coast will frequently top 50 mph and could reach as high as 70-80 mph (peaking) during this time frame.

6 p.m. – Midnight Friday

Rain changes to wet snow in all of southern New England during this time frame.

Again, the amount of snow remains the biggest question to be answered with this storm. There is a chance of several inches of accumulation in eastern Mass. and perhaps as much as 6-to-12 inches in parts of Worcester County.

Wind gusts will only slightly weaken during this timeframe, still gusting 40-60 mph along the coastline and 20-40 mph inland.

Saturday Morning

The precipitation will taper off to just some areas of rain and snow showers by Saturday morning and any snow accumulation will be just about done. The winds will continue to howl out of the north-northeast, 30-50 mph at the coast and 20-30 mph inland.

The Rest of Saturday

Just a few leftover pockets of rain and snow.  The winds will only slowly diminish during the day. In fact we will likely see gusts up to 40 mph on the coastline and 30 mph inland right through Sunday morning.

HOW MUCH SNOW?

This is a very tough call.  The highest amounts should be located in the Berkshires and Worcester Hills, as much as 6-to-12 inches.

From there, amounts taper down quickly as you head east, 3-to-6 inches around 495 and 1-to-3 inches close to the coast.

However, there still remains a possibility that higher snow amounts could be realized in all of eastern Mass., including Boston. Six inches or more is not out of the question.

COASTAL FLOODING

This is a very dangerous and potentially life-threatening event along our coastline, particularly at ocean exposed shorelines from Salisbury to Plymouth.

Unfortunately, this storm is coinciding with astronomically high tides.

In fact, the highest tide levels of the month will occur smack dab in the middle of this storm on Friday and Saturday. Combine that with a persistent and prolonged east – northeast wind over several high tide cycles and you have the recipe for some serious coastal issues.

Widespread moderate to major coastal flooding is likely, starting with Friday morning’s high tide (around 11 a.m.) and continuing through Friday night’s high tide (around midnight) and again Saturday (around midday).

We could see a storm surge as high as 2.5 – 3.5 feet, creating tide levels similar to that on January 4th.

The seas will be rough for several days during and following the storm (it is a slow mover) and 25-to-35 foot seas are likely just offshore through at least Sunday.

Significant beach erosion is another major concern given the strength and duration of this event. Many protective dunes and sea walls will be challenged and it remains likely that some coastal communities will be completely flooded and cutoff with inundation depths of 3 feet or higher.

There is the potential for vulnerable homes along the immediate shoreline to be severely damaged.

PLEASE heed all evacuation recommendations and orders!

This storm should not be underestimated.

It has the potential to be one of our biggest and most destructive storms in recent memory.

Please heed all warnings and stay tuned to updated forecasts throughout the event on WBZ-TV and CBSBoston.com.