The visible satellite image at left shows the tops of thunderstorms mushrooming along the trough extending southward from the low pressure system over Quebec described in the previous post below. These storms flipped a truck on the Champlain Bridge in the middle of rush hour in Montreal, leading to a 7 truck pile up. Amazingly, no one was killed. Winds also knocked out power at LSC and at my home in Frelighsburg, QC.

A long line of thunderstorms like this is called a squall line and accounts for most of the severe thunderstorms in our area.

The animated visible satellite image shows how quickly these thunderstorms grow in the hour between 18Z and 19Z. It seems that these storms form as the trough hits the Lake Champlain Valley. This rapid formation is why thunderstorms are so difficult to predict. The trough and cold front which triggered the storms could be seen days before, but if these storms erupted an hour later the Champlain Valley and Montreal would have been missed entirely!

High resolution visible satellite satellite imagery for Vermont can be accessed at the LSC Meteorology Department website.

Air mass advection and fronts

The image at left from 21 Z (5 PM EDT) Tuesday 10 June 2008 will show how air mass advection and fronts around midlatitude cyclones can change the weather in New England.

A low pressure center can be seen in Quebec to the northwest of Vermont. Wind barbs indicate a counterclockwise and inward circulation around the low that is usually seen around a cyclone. A cold front extends soutwestward and a stationary front extends southeastward from the system center.

Three airmasses can be identified in the map. Over Vermont and most of New England, a marine tropical air mass predominates. It's this air mass that brought us near-record high temperatures between the weekend and Tuesday. It is bordered by the cold front to the west and a stationary front to the east, forming a wedge south of the low pressure center. Temperatures are in the 80's and 90's F and dewpoints are in the high 60's. Southerly winds in this air mass advect warm moist air northward in this region all the way from the Gulf of Mexico.

West and northwest of Vermont lies a continental polar air mass, with both temperatures and dewpoints in the 50's and 70's, the cooler temperatures residing to the north. It's this air mass that has moved in today, giving us cooler and drier conditions outside. Winds all have a westerly, with those over Canada having a more northerly component. They advect this airmass eastward. You probably noticed that it cooled off considerably yesterday evening as the front moved through with the storms yesterday.

Finally, over Maine and the Atlantic Ocean, a marine polar air mass had been destroying the hopes of anyone looking for a summer day at the beach. Temperatures and dewpoints along the coast of Maine and the adjacent ocean are all in the 40's and 50's, indicating the strong influence of cool Atlantic waters. It's these air masses that typically lead to ocean fog. Easterly and south easterly winds advect this cooler air onshore. These winds are enhanced by the afternoon seabreeze circulation.

The final feature to notice on the map is the dashed brown line, representing a trough. You can see this also in the isobar looping southward from the center of the low. This was associated with the line of thunderstorms that swept across northern Vermont and southern Quebec yesterday evening and knocked out our power.

You can access a 24 hr loop of New England fronts and weather station data at the NWS-HPC surface analysis website.

Climate data for yesterday

Clicking the image at left will give you an idea of the high temperatures reached yesterday. It was in the 90's pretty much everywhere in Vermont, with the hot spots being near the south end of the Connecticut Valley and in the southern Champlain Valley region. Mountain stations were cooler, but the 79 F maximum temperature on Mount Mansfield tied a record set for this date in 1974.

The second image shows the total precipitation that fell yesterday afternoon and evening. The effect of the Green Mountains is strong here. The largest precipitation amounts were in excess of one inch in the area of Mount Mansfield (3.67'' at Underhill, 2.52'' at Jeffersonville) and Jay (1.80'' at Jay Peak, 1.33'' at East Berkshire). In the Northeast Kingdom and Connecticut Valley, less that 1'' fell.

Precipitation is a difficult quantity to get a feeling for. Most areas of the northeastern U.S. get on average about 3 inches of rain in a month. So 3'' is about what you would normally expect to get in month. If that amount falls in a day, you're getting a lot of rain!

Both of these examples illustrate climate data that record weather extremes and totals for a given day. Local climate maps can be retrieved at the NWS-Burlington Office website.

Hot Sunday

Data from the LSC weather station around noon Sunday reads:

Time: 12:35 EST
Temp: 84.3 °F
Dew Point:67.2 °F
RH: 55.8 %

Summer is not a time of year that starts at the June 21 summer solstice and ends September 21 at the fall equinox. Summer in New England happens when southerly winds advect in a marine Tropical (mT) air mass from the Gulf of Mexico.

Clicking on the the mesoscale analysis of temperature at left (see NWS website for updated map) shows the effect of elevation on these temperatures. Temperatures on top of Jay Peak and Mount Mansfield are 79 F, whereas low elevation stations in the southern Connecticut and Champlain valleys are already in the 90's.

Everyone knows that 84 degrees F is hot in the noon day sun. What about a dewpoint of 67 F? What does that feel like? Well, you might note that it makes working outside a sticky experience. The humidity index chart shows that this humidity (corresponding to 57% relative humidity) makes 85 F feel more like 90 F and 90 F feel more like 100 F.

My personal weather gauge, Spooky the Cat, has climbed down from her current warm spot on the sofa and is sprawled out on the floor wondering when this will all end; she wants to go back to flushing out the small burrowing mammals attacking my cabbage patch. I think this means that it's uncomfortable for all species. More on why this is happening on Mondays blog.

Warm, humid air mass in Vermont

Data from the LSC weather station around noon Sunday reads:

Time: 12:35 EST
Temp: 84.3 °F
Dew Point:67.2 °F
RH: 55.8 %

Summer is not a time of year that starts at the June 21 summer solstice ends September 21 at the fall equinox. Summer in New England happens when southerly winds advect in a marine Tropical air mass is advected in from the Gulf of Mexico. Those of us inVermont is a warm, humid (mT) air mass.

Clicking on the the mesoscale analysis of temperature at left (see NWS website for updated map) shows the effect of elevation on these temperatures. Temperatures on top of Jay Peak and mount Mansfield are 79 F, whereas low elevation stations in the southern Connecticut and Champlain valleys are already in the 90's.

Everyone knows that 84 degrees F is hot in the noon day sun. What about a dewpoint of 67 F? What does that feel like? Well, you might note that it makes working outside a sticky experience. The humidity index chart shows that at this humidity (57% relative humidity), it makes 85 F feel more like 80 F and 90 F feel more like 100 F, My personal weather gauge, Spooky the Cat, has climbed down from her current warm spot on the sofa and is sprawled out on the floor wondering when this will all end and go back to flushing out the small burrowing mammals attacking my cabbage patch. I think that means that it's uncomfortable for all species.






Temperatures at 15Z (11 AM EDT) are already in the low 80's and dewpoints in the and high 60's in Vermont.

The situation is serious.

reads: The map at left shows three large distinct air masses clashing over the northeastern U.S.
between a warm front to the east and a cold front to the west.




By

RH:	55.8 %

80 F is obviously hot.