Archive for mesoscale dynamics
00Z Models Preliminary Thoughts
Posted by: | Comments11:05 PM
The 00Z guidance confirmed my suspicion that the 12Z guidance was not handling the development of the 700 MB upper low correctly.
At this time,this storm is clearly going to have a major impact on the entire northern Mid Atlantic. While I likely will have to adjust some features on the snowfall map to the left, the overall idea that is presented here to the left. I do think that the best areas for potentially one to two feet of snow will range from Philadelphia through central and northeastern New Jersey, through New York City, and into southern Connecticut.
Portions of northeastern Pennsylvania will likely remain closer to 10 to 12 inches rather than two feet based on the development of the 700 MB low on the guidance.
I will have more information tomorrow morning along with an updated snowfall map to illustrate the areas of best mesoscale dynamics and other factors.
-- Weather When Posted --
- Temperature: 28°F;
- Humidity: 50%;
- Heat Index: 28°F;
- Wind Chill: 18°F;
- Pressure: 30.05 in.;
Final Snow Map For Event
Posted by: | Comments8:56 AM
Here is my final call for the storm as I see it based on observations of water vapor images, boundary layer observations, and radar presentation. I think many of you are going to be pretty happy with what you’ll see!
SNOW MAP:
Area One: This area will be on the fringe of the precipitation shield with only light snow showers expected. Accumulations of a dusting to 2 inches can be expected.
Area Two: The latest water vapor images suggest the warm conveyor belt (supplier of moisture) is going to be rather strong, which means moisture will build back further west than earlier expected. As such, I’ve increased snowfall totals here to 2 to 4 inches. Some isolated locations may exceed 4 inches due to the up slope wind component enhance some of the precipitation.
Area Three: These locations will be just outside the best mid level dynamics, but will still get a period of moderate to heavy snow this evening. Snowfall amounts of 3 to 6 inches can be expected in this area.
Area Four: This is where we starting getting into some interesting mesoscale dynamics! Based on the latest model guidance and the actual evolution of the boundary layer and coastal front structure this morning, this area has the potential to be impacted by the negative aspects of banding precipitation. That is why I went with a range of 6 to 10 inches of snow with locally higher amounts. The heaviest precipitation and strongest dynamics will still be east of Area Four, which means there is a potential for some localize breaks in the precipitation. I still expect most locations to exceed 8 inches, however.
Area Five: At least for this forecast area, this location is ground zero for a major snow storm! I expect a general 10 to 14 inches to fall in this location with locally higher amounts. There are several issues I want to touch upon here. First, all of the best lifting at the upper levels, mid levels, and boundary levels are all present in this location. There may be some initial precipitation concerns at the start of the heaviest precipitation as the 950 MB level to the surface will still be cooling to freezing at the start of the storm. However, most precipitation type issues will be resolved by the time the heaviest precipitation will fall, between 1 AM and 10 AM Monday. There may be some lingering precipitation issue on eastern Long Island as well due to the position of the 850 MB low as well, however the strong mesoscale lifting should counter act the warming of the 950 and 900 MB levels. Convective snowfall will be a major determination on snowfall amounts. There is a significant possibility that some locations will be impacted by snowfall amounts well above forecasted totals due to the intense banding that will be possible in this storm. It is wise to keep this in mind, as the reduction in visibility will produce near blizzard conditions, which will cause significant issues for the commute on Monday morning. If you can, stay home!
-- Weather When Posted --
- Temperature: 28°F;
- Humidity: 92%;
- Heat Index: 28°F;
- Wind Chill: 19°F;
- Pressure: 30.07 in.;
Another Quick Lesson On Mesoscale Dynamics
Posted by: | Comments8:05 PM
Don’t worry, I won’t be using any math. Wow, that brings back memories.
Okay, I want to comment on the radar and the precipitation to this point. So far, everything is on track with the forecast and the trend of precipitation.
Light snow and snow showers are entering the forecast area and will continue to intensify and expand throughout the forecast area. Light to moderate snow is now building over central and western Pennsylvania with much heavier precipitation over Ohio and West Virginia. The breaks in the precipitation over Virginia and eastern West Virginia are a direct result of the very strong lifting to the west. The same is likely going to happen over the forecast area. While some locations receive heavy precipitation early Wednesday morning, other locations will have a significant break in the precipitation.
-- Weather When Posted --
- Temperature: 28°F;
- Humidity: 39%;
- Heat Index: 28°F;
- Wind Chill: 28°F;
- Pressure: 30.41 in.;
Answering Some Questions
Posted by: | Comments12:56 PM
Sorry about the break, had to take care of some family stuff.
So, I got all your emails and IMs about where is the snow. Well, first let me say that at this point, the forecast is still on track however I am going to make a few tweaks here in this post. The moderate to heavy precipitation is on the way and the rate of this precipitation is impressive over central and western Pennsylvania. So what’s going to happen going foward?
Well, I’ve been keeping a steady eye on the progression of the 0 degree line at 850 MB via the Penn State E-wall site. What we are not seeing is a huge blast of warm air, but a slow progression at 850 MB. That being said, the position of the warm air and the rate of movement is going to have an impact on the forecast for the Philadelphia locations. So here are the changes.
New York City Metro, Northeast PA, and point north: No change in the forecast. I think the idea of snowfall in the range of 4 to 8 inches is certainly on the way, but I would lean more towards the 4 inches, thus no change in the forecast at this time. Light to moderate snow will fall through the afternoon and evening hours with a mixing of sleet and freezing rain towards mid night.
Philadelphia metro area: I’m lowering accumulations here to 2 to 5 inches. The reason why is not the warm air movement, but the position of the best dynamics as they move through the forecast area. As I said in the forecast about 2 days ago, there will be locations that will benefit and locations that will get hurt via the position of the best mid level and mesoscale dynamics. Sorry Philly, that’s you. I do expect snow to come to your locations, but not as heavy as the New York City metro and points north.
Southern New Jersey: Nothing, zip, nada. The low level boundary layer is being overwhelmed by the Atlantic, which means a mix of rain and snow with little in the way of accumulation.
Just a note, I know some are sending e-mails or asking about specific locations even after a forecast map or discussion is issued. I’m not responding to those posts or emails because if I do that for one person, I have to do that for everyone. That’s not fair to those looking for updates on this site, and really it’s just not possible to answer 100 IMBY emails (litterally 100 since Thursday). So I hope you understand when you don’t get a response.
I will however answer or respond to meteorology questions, like for example why is the precipitation weakening, or what do you mean by divergence. That’s reasonable. Thanks in advance!
-- Weather When Posted --
- Temperature: 28°F;
- Humidity: 68%;
- Heat Index: 28°F;
- Wind Chill: 21°F;
- Pressure: 30.22 in.;

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