Where the Polar vortex is position will determine how cold we get. If it is positioned to the west, the cold will be to the west and we will be under the influence of the subtropical ridge, which will pump warm, SE winds into the area. The polar vortex to the east, say Ontario, Canada, will better as this will allow the cold air to spill south into the area.
Models have been flip-flopping between There are two model camps, one wants to keep the PV to the west, therefore keeping it warmer here and more rain. This was the 00z euro run, which brought temps up into the 40s and 50s for out area. The most recent trend has been to shift south, allowing the cold air to rush in. The GFS was on the forefront of this trend, advertising an extreme cold air damming event. It progged temps to fall below freezing as the precip arrived, continuing to drop through the 20s on Monday and bottom out in the teens on Monday night, as the precip is pulling away. This would create a buffet of rain, freezing rain, sleet, and snow. P-type and the amounts of each precip varied between runs.
This is a Skew T chart...
It represents the vertical column of the atmosphere at any given point. This Skew T is for Silver Spring on Monday, March 3, at 7:00AM.
Now how to read them:
The bottom of the chart the ground level, the top is about 16000 meters up, or 10 miles.
The red line is in temperature so in this case, the surface temperature will be between 0 and -10 c
The dark green line that is roughly parallel to the red line is the dewpoint. It is not always following the red line, and when it does, it means that the air is saturated. If it curves sharply to the left, it means that there is dry air at that level.
The 850 temp is commonly used to mark the rain snow line. If the air is below freezing between the ground and the 850 line, you can assume that there will be snow. If there is a warm layer in between, there could be freezing rain or sleet. If the surface is above freezing, it will likely be rain.
To the right are some weird symbols. Those are wind barbs, denoting wind speed and directions at different altitudes.
This Skew T shows surface temps are well below freezing, in the mid 20s, but the 850 temps are still slightly above freezing. This would indicate a warm nose aloft from southerly flow, resulting in melting of snowflakes. Judging by the depth of the cold layer, it will be sleeting at this time. Notice that within the red circle, the bottom most 2 wind barbs are pointing to the bottom left. That indicates NE winds, this would reinforce the cold wedge and that is why we are below freezing at the surface. This is classic cold air damming. the only thing unusual is that it is during March. Notice the other wind barbs are pointing in the opposite direction, resulting in warm air overrunning the cold an producing precipitation.
Previously, the Euro had been the polar opposite of the GFS, keeping the PV in western Canada, and therefore, skimping on the cold air and letting the surface low ride to our north, keeping us in the warm sector for most of the run. Since the Euro has the best reputation, this also cast doubt on the GFS solution. The Euro also caught on in its last run, bringing the low center much farther south than before, and giving us a good hit of snow and sleet with very little liquid precip. The operational run was also backed by the ensemble runs. These are lower resolution runs of the same model algorithm using slightly different data to account for any data errors. If the ensembles come out to be similar to the operational, it indicates that the solution is sound, there are no data errors that cause calculation errors to add up, significantly affecting the solution. It essentially verifies the solution. There are no graphics because they require payment for their data. all info is from other people with subscriptions, not from any personal observations.
The Canadian model gives a warm start to the storm before bringing it colder and giving us a good thump of snow on the back end. The Canadian has been flipping between cold and warm-ish solutions and never showed any all rain solutions.
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| Hour 106 Monday, 3AM |
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| Hour 120, Monday, 7:00PM |
Pitfalls:
1. Model limitations. Garbage in garbage out is the saying. The disturbances that will form this storm is still over the pacific and Canada. This means they have not been sampled enough. the models are taking wild guesses at what the storms are like. If they guess wrong, then the outcome will be really wrong. A simple example: 2^32=4,294,967,296 2.001^4,364,222,021.24. That's a 10 million difference when you only change the number by .001. Imagine these computers doing billions of calculations a second for hours to run these models. A small error really does add up. It should take the storms another day or two to reach the US, where there are more data collection points so it will take another 2 days until we get a firm handle on what might happen.
2. The PV position at the time of the storm is still unresolved. although the Euro was colder in its last run, it still has the PV farther west. The time in which it gets here will be critical, too late and we will just get rain with a little bit of snow. Stay in western Canada and we get warm rain. We need it to get here earlier.
3. The models still disagree on the magnitude and how the event will unfold. The GFS is calling for a strong first part, and then a weak second part. The Euro wants to keep it all weak. The Canadian wants to bring in the second part stronger and colder with a weak and warm first part. All these scenarios are still in play
4. Timeframe: we are still 3 days out. still plenty of time to shift favorably or non favorably. The 00z and 12z Euro runs were worlds apart. It only took 12 hrs to go from a non-even to a possibly major event. It could take the same time to go back too. we are also out of range of many of the short range, hi-res models. those would help a lot in pinning down the freezing line.
The bottom line is there is the potential of a major winter storm on Monday and Tuesday of next week. the precip types and amounts we get are not resolved yet and it will be a decent time before they are.
Thanks for reading!
-Alex
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