FALL WEATHER – WEATHER 101 with AL KAPRIELIAN
By: Al Kaprielian – Nov. 2016
Fall is here and now in full swing. A lot of leaves have now fallen due to recent heavy rains and gusty winds. With the sun now lower in the sky, we will see the air continue to get colder with shorter days and longer nights. Sunsets will become much earlier as Daylight Savings time ended at 2 AM Sunday November 6.
October temperatures ran a few degrees below normal while precipitation was somewhat above normal. We are still in a drought but the recent episodes of heavy rain in October have helped somewhat. We are now in the last month of hurricane season as it will end on November 30. We can still see some mild/warm weather in November, however with the time of year it does not last very long. We will see some warmer weather during the first five days of the month.
The reason for this warmer weather is the southeast US upper level high pressure system which will build northward up the east coast. This will push the jet stream to our north putting us on the south side or warmer side. Temperatures will reach the 60‘s and possibly low 70’s on one of two days.
This warm weather will not last long as a long wave through (upper level disturbance) will bring a cold front through before we get into the first weekend in November. This will trend to much cooler temperatures. We can also see coastal storms during the month of November. Some can produce snow even before Thanksgiving. This is not a prediction for this year. However, we have had snowstorms before Thanksgiving in the past. With the ocean temperatures still fairly mild and the land areas much colder, this can lead to storm development in November.
If a storm develops, the question then becomes where does it track and how intense will it become. Also the speed how fast the storm moves effects how much precipitation we get. Usually our coastal storms develop off the east coast or can even form over the Gulf coastal states.
If a coastal storm forms off the east coast to our south.,then the question becomes the track. If the storm tracks near or south of Cape Cod this will put us on the cold side of the storm and would result in more snow versus rain. If the storm tracks to our west then we would be on the east side of the low pressure which is the warmer side.
With a westward track our winds would be more east/southeast and this would bring warmer air in from the ocean. A lot of times during the winter there will be a low pressure system over the Ohio Valley/ Great Lakes.
The energy from this low pressure is transferred to a secondary low pressure off the east coast. This secondary development is caused by the temperature differences between the warmer ocean and colder land. If this secondary low becomes stronger than the primary low to the west we can see a larger impact storm. When a low pressure system forms in the Gulf of Mexico this storm can be one to have a large impact on our weather. These storms get a lot of energy (warmth from the Gulf of Mexico ocean waters). The question becomes where does this storm track.
When a low pressure system forms in the Gulf of Mexico we look to see if the northern and southern jet streams will PHASE (joining together). If they phase. this storm will track close to Cape Cod & the Islands to possibly give us a major storm. If the jet streams do not phase, then this storm will track too far to the south to give us a major storm.
In this case the storm will most likely track close enough to give the Mid-Atlantic region, the Washington DC area a major snowstorm with a miss for us. So you can see that whether the two jet streams phase or not determines how far north a coastal storm will track. How much phasing will occur this winter? This is a difficult question which myself and other meteorologists cannot answer at this time. Time will tell. One big factor we look at during the winter is the high pressure system in Greenland, known as the Greenland high. How much of a factor will this high have this winter?
This is also a difficult question to answer at this time. The effects of the Greenland high is to keep the jet stream to our south and this can cause cold weather to become locked into our region causing more snow versus rain for winter storms. Time will tell how much of a factor this Greenland high will have on our weather this winter. First it has to form and this is also difficult to tell when it will occur at this time. Stay tuned next month as we look at the weather that occurs this month and we will also have an outlook on what the winter weather may bring.
Al Kaprielian is a meteorologist who worked for 30 years on NH TV news including WNDS, WBIN. email him at email@example.com