1/23/12 Cold Air Damming!

Yes, you read that right, and no it is not cursing the cold air!  What it is, is that a cold area of high pressure is forcing shallow layer colder air to move south. Cold air is more dense and will sink to the surface. However due to the stretch of mountains along the eastern states, the Appalachians, this cold air can get stuck as warmer air try's to move in. Below I have shown several examples.

This mornings surface weather map, and satellite. Showing a potent storm in the Great Lakes that brought severe weather to the south last night. If you notice the warm front though, it is caught up on the western side of the mountains and the cold high pressure is allowing colder air to drain down the eastern side (noted by the arrows)  Also of note. Severe weather usually can occur in situations such as this in the region between the cold front and the warm front, known as the warm sector.

 This can further be illustrated on this mornings temperature map.

Although I do not like the color scheme, the purples are colder air, and note how it flows down the east coast, where a bubble of warmer air moved northward into KY and TN and OH.

 Events like this can cause colder air at the surface and allow the warmer air aloft which should be rain, to fall to the surface a freezing rain.  

This will likely be the case here in New England today, as the cold air at the surface will be hard to displace and the warm air will try to work in. So any rain that may fall in the morning, may be freezing rain, which can also be influenced by the snow cover from 2 days ago.

Warmer air will try to work into New England  today, and will reach the south coast with temperatures near 50, mid 40's in along the north coast, but in the valley areas where the cold air is more dense and will be hard to scour out temperatures will remain cool in the 30s to near 40.

Later today, the cold air will be mostly pushed out as the warm front approaches precipitation will be light in nature. However the strong cold front does approach, a line of heavy rain will move into MA by, 7 PM and reach the Boston area after 8 PM. A rumble of thunder is not out of the question with this line.

A clap of thunder is possible tonight and rain should end by 7 AM Tuesday morning and be clear and sunny by Noon .

A description of COLD AIR DAMMING on Appalachian Mountains

1/20/12 Another Snow Fall..

Last nights snowfall was brief, but dropped around 2" in the Boston area.

Another storm tracking out of the Tennesee valley will move south of New England. Cold high pressure to the north will allow for most of the precipitation to fall as snow across much of New England, except for the lower Cape, Nantucket and MV where a mix may occur. 

The snow will arrive in Western MA around 5 AM and in the Boston area between 7 and 8 AM and continue until around nightfall with the heaviest snows happening between noon and 3 PM. 

In general expect around 2-5" in the Boston area. If the storm moves even just a few miles to the north of its path, more snow could fall.

Winds will be light in this event.

Areas south of the Mass Pike and into CT will see a longer period of snow and therefore a great amount to fall is possible.

Snowfall map for Saturday afternoon snows.

Mild, rainy weather returns on Monday.

1/19/12 Overnight Snows

A clipper cold front will push through New England during the overnight hours tonight bringing ahead of it some snow showers.  A more intense line of snow will push through the Boston area around 1 AM

6 PM weather map showing the cold front near Buffalo, NY. Ahead of it, light snow is falling around PA and NY. A heavier line of snow that is seen in the brighter blue colors will move through around 2 AM

Clouds across the northeast are in Orange as a clipper moves across Quebec with some trailing moisture.

 Overnight Forecast:

Light snow showers will begin around 10 PM a light dusting to less than an inch is possible.

By 1 AM the stronger line of snow will push through the Boston area bringing with it a heavy "downpour" of snow at a rate of 1-2" per hour, however, it will push through quickly and most areas will only see around 2" of accumulation.

The heaviest snows will stay south of Boston from Boston to New Bedford. A light mix may occur on the outer Cape.

Overnight low of 26.

Future forecast image for 1 AM January 20.  Showing the heaviest band of snow in the Blue. Rates could be 1-2" per hour and be quite heavy, but it will quickly move through with only a few flurries by 5 AM

Another snow event is poised to take aim at New England on Saturday with near winter storm conditions and a some significant accumulations possible.

1/18/12 The Coldest Day of the Year - On Average!

All you winter weather fans or haters here in Boston, today may be good news or bad news.. Today is officially the COLDEST day of the year on average! 

Tomorrow the average high temperature increases by 1 degree!  

A weak clipper system will push through overnight Thursday bringing a chance of light snow across Massachusetts.

1/17/12 Why did we get more snow last night?

Late last night, if you were awake after 10 PM, you noticed that it started to snow, and at a pretty good rate.

The overall forecast was for a warm front to push through the region, and bring a light mix of rain, snow and sleet and quickly change over to rain as temperatures rose to the lower 30s. No significant accumulations.

Well, by 11PM and midnight, I fielded 2 comments about the amount and intensity of the the snowfall. So I thought I would give a reason why this happened.

Temperature and Dew Point graph from 4PM 1/16 to 2:15AM 1/17. Recorded at  KMALYNN7

A . The arctic air mass was still in place at 5PM. Temperatures rose to a seasonal high, but as the sun set the temperature dropped to around 28F. The dew point was very dry at only 5F!

B.  As the warm front approached, the temperature slowly began to rise, but notice the dew point or the moisture in the atmosphere, it began to rise rapidly. The arctic air mass was being pushed out.

 At roughly 9:15 the temperature rose above freezing. But the dew point was still below freezing at 21F.


C. Precipitation begins to fall at around 10 PM with a temperature around 34F and dew point of 24, and relative humidity of 66%. (Meaning that the air still has to 34% more moisture to hold).

However, with the air still VERY dry the temperature fell to meet the dew point to become saturated. This is called evaporational cooling!   To best explain this think of swimming in the summer. Take 2 days. One hot and humid and one mild and comfy.  You notice that when you get out of the water on the hot and humid day it does not feel that bad and it takes along time to dry off.  However, when you get out of the water on a dry day with a breeze, you feel so much colder as you begin to dry off. The water can easily evaporate into the air and make you feel cooler. This is evaporational cooling, and it works the same in the atmosphere.


D. The temperature cooled, due to evaporational cooling to be closer to the dew point, at which point the air temperature fell below freezing to allow for a greater amount of snow to fall.




Forecast:

Today - Expect today to be mild as warm air moves in from the south and ahead of a low pressure system over the Great Lakes. Rainfall will be light and it will be mild overnight with temperatures not dropping below freezing.

This evenings weather map showing a storm over the Great Lakes with warm air over southern New England.

Wednesday - The cold front pushes through tomorrow morning and our highs only reach the upper 30s and it will become windy!

The next chance for snow showers comes Thursday afternoon as a weak clipper moves through.

1/16/12 Still no snow...and why

By now,  you may be wondering, where is the snow? Or why hasn't it snowed, or better yet, why is is so warm? The answers are complicated, of course but the main reasoning is the way that the upper atmosphere is working and has been working since the fall. 

The jet stream, which helps control the flow of weather in the middle latitudes has primarily been in a zonal flow, pretty much along the US/Canada border. 

This winters overall weather pattern. The Northern Jet Stream is locking in all the cold air to the north in Canada and not allowing it to dig into the US. The Southern Jet Stream, which usually contains a lot of moisture from the Pacific Ocean is staying south and bringing more storms to Texas and the deep south. It is also not merging with the northern Jet stream to create any snow storms for the north east!

 
The flow of air that we eventually receive here in New England is air that has been warmed by the Pacific ocean and any true arctic air has a difficult time coming down and mixing in with it. When it does, it is usually short lived, since the upper flow of air wants to keep everything locked up.

In a typical (normal) winter pattern, the northern Jet Stream will rise into Canada, tap into the cold arctic air, then dive into the Great Lakes and the Northeast to create a cold winter. As for snow storms, the southern Jet stream will also be tapped into by the northern Jet and when they meet, usually storm will form with great moisture and when mixed with moisture and cold air, a snow storm is the end result.

 

 So for this week, there are no major storms on the horizon. 

A few weak systems will work their way in on Tuesday and Thursday, but likely be in the form of rain, with a little snow mixed in.

The map below shows the cold air locked in Canada with warmer air mainly over the US.

This weather map for this coming Friday, shows how the coldest air in purples, reds are located in Canada and along the US border, where blue and green are typically mild for January.

1/12/12 Nor'Easter Hits New England

A strong NorEaster is bearing down on New England this morning, however it is not  of the classic type where any extreme event will occur.  

Highlights:   

• Snow inland (heaviest in NH and Maine)
• Heavy Rain along the coast
• Strong E- NE Winds gusting to 40-55 mph
• Coastal Flooding

Morning Satellite image showing the low pressure just south of Long Island.  Winds rotate counter clockwise around LOW pressure and will  bring an east wind to coastal NE.

 Snow will be heaviest in New Hampshire and Maine during the day today, however warmer air will work in with this storm and most southern areas will see a change over to rain.

Areas in blue will likely see a slushy mix to 2" Green 3-6"  Oranges 6-8" Dark Orange up to 10"

As the low strengthens and track into southern New England, strong east winds will pick up over the Cape and NorthShore where winds could gust up to 55 mph.

A coastal flood advisory is in effect until 3 PM today. Strong east winds will help bring tides and waves higher than normal and could flood tidal flooding prone areas.  Also a wind advisory is in effect.

A Major Arctic air mass is filling in behind this storm and will bring in cold temperatures and gusty NW winds for the weekend.

The cold air is seen on this image in the blues and purples. This air will be over New England starting late on Friday.