First Alert Weather In-Depth: Beyond the 10 Day

ROCHESTER, N.Y. (WHEC) — Here is an update for “Beyond the 10 Day” on this Wednesday December 15th. Currently across the United States, we have an active jet stream pattern. Unfortunately, it is not situated for any Winter weather across the Northeast at this moment. Currently, there is a large dip across the Western US and a large ridge in the East. This setup is contributing to the severe and dangerous weather expected later today for the Central US with severe thunderstorms and fire weather. Across our region here in the Northeast, we are dealing with above average temperatures and expected record warmth for Thursday. However as we alluded to on Sunday, there is a pattern change on the way as we go into Christmas week.

With the alluded to pattern change, the chance for winter weather has popped up for Saturday. Last update, we did mention this Saturday looked like a rain event rather than a snow event but there have been some changes which have allowed the chance for light snow accumulations to increase. There is uncertainty still as the two global models are disagreeing in our region particularly. The GFS is showing warmer air being pushed into the region locally, while the Euro is a bit cooler. The differences are due to strength of low pressure and quickness of high pressure. The GFS is a bit stronger with low pressure and slower with the forward progression of high pressure to the west. A stronger area of low pressure allows for more warm air to be pushed northward as it enters Western NY and the Finger Lakes. Also, this weakens and slows the progression of high pressure to the west. This area of high pressure is important as it will be the supply of cold air across the region. At this point, the GFS is showing light snow to start before a transition over to sleet and rain. Also, the GFS is warmer with surface temperatures in the mid-30s with near freezing in the higher elevations. With that said, the real question will be if any snow sticks. The Euro on the other hand is cooler with this system and weaker with low pressure. The Euro has a stronger and faster area of high pressure to the west allowing for the cold air to be readily available. Also, a weaker area of low pressure allows for the cold air to move in and forces low pressure a bit more south than the GFS. What makes me lean towards the GFS in this situation are the ensembles. The euro seems to be a bit uncertain with itself as more ensembles have low pressure to the north when compared to the average location, while the GFS has a solidified area as to where it expects low pressure to generally be near. With all this said, I do expect light snow to be the onset before warmer weather erodes the cold and transitions us to a mixture of rain, snow, and sleet. We will watch out for a brief period of freezing rain in the higher elevations as surface temperatures may stay near freezing longer. Although we have stretched for Winter weather so far this season, there are much more favorable patterns ahead over the next two weeks.

Last update, we mentioned that after this Saturday our next chance for Winter weather could be this Tuesday (12/21). Unfortunately, major changes have occurred in the overall pattern for this timeframe which has extremely lessened the chances of that. The split flow we mentioned on Sunday is still there, but the overall jet stream is not favorable for something up the East Coast. Models are showing split flow across the center part of the nation, and then the polar jet and sub-tropical jet interacting with each other well off the East Coast. Models were hinting at a storm earlier this week, but they have since switched over to a swing and a miss with the interaction of two pieces of energy. This has occurred because a weak ridge will likely stick its nose over the Great Lakes and break up the potential interaction between the two pieces of energy. Now although we will miss out on this system for Tuesday, blocking near Alaska and over Greenland will build by this time and set up the pattern for future possibilities.

Our next opportunity will come near Christmas. The blocking will be present and the and the jet stream will turn active across the Eastern US, but there is one lingering piece in the pattern that will make it difficult. This is the troughing over the Western US. With this troughing present through the next week, or more, there will be a lack of potential dig in the jet stream over the Eastern US. You want a ridge over the Western US as this will force the jet stream to dig across the Western US, but this piece is non-existent for at least the next week. This means the jet stream will be taking a southeasterly direction across northwest US and through the Eastern US. This will open the door for more Alberta Clipper’s to swing through, but anything significant is hindered even with the blocking in place.

Models are trying to signal a position change for this trough over the Western US, but it does not come until after Christmas. Models are signaling a ridge over the Central US to move over the Western US at this time and push the troughing over the Pacific. This setup, if it occurs, will create the better chance for colder air to move in locally and a better chance for digging across the Eastern. Being near two weeks though, once again we will stress the high uncertainty out that far but the odds for Winter weather locally will increase over the next two weeks. Our next update will come this Sunday December 19th.

Temperatures: Mild to end the work week before turning near average and then slightly below average towards Christmas.

Precipitation: Generally below average the next two weeks.

Storm Chances:

December 18th: Low pressure runs along the Appalachians and towards the NY/PA border. Wintry mix solution likely with snow to a mixture of rain and sleet. Temperatures at surface will be borderline for snow to stick.

December 24th-25th: Lack of ridging out west will likely keep the pieces of energy separated until it is too late. More or less an Alberta Clipper possible with light snow showers.

December 29th-30th: Ridging out West may build by this time, creating a dig over the Eastern US. Pattern looks more favorable for a bit more snow. Cold air available.