heavy_wx

Seeing some of the largest aggregates of the event right now in State College. A sign of both improved snow growth and temperatures approaching freezing aloft.

This will certainly be a very dynamic event. The image above shows a pretty good setup for heavy precipitation in central PA with the area between the right entrance region of the northern jet streak and the exit region of the southern jet streak (add in some curvature on the latter and that increases the favorable lift for our area). You can see below that this circulation is also tied to mid-/low-level frontogensis; this region of enhanced lift moves northward Thursday afternoon and will be associated with the heaviest precipitation. A forecast profile from this time shows the maximum lift (i.e., negative omega) around 600 mb at UNV. It happens to also coincide with the dendritic growth zone so that, coupled with the near-freezing temperatures between 850-750 mb should lead to very large, wet aggregates around this time. The duration of snow vs IP or ZR is of course predicated on how resilient the cold air will be at low levels. There is noticeable 500-mb confluence over northern New England currently, helping to promote anticyclogenesis and associated cold ageostrophic flow into our region. However, the surface high moves eastward and weakens late Thursday into Friday, allowing for temperatures to warm above freezing the in the 800-700 mb region. Things do cool off again for potentially another round of moderate snow as the energy from the secondary low moves east through the region Friday morning (probably more favorable for areas in eastern PA). It's definitely a cold airmass for this time of year, but I have been burned before up here with mixing occurring earlier than expected. Will be a fun one to watch!

Congrats, enjoy the "real" storms out there!

I use it quite frequently, especially for the dual-pol observations. For reflectivity, I use the super-res, because its basically the same resolution as the "raw" level-2 data; the other ones are processed further and are lower resolution. The composite reflectivity is the max return in height observed by the radar at given location (though areas closer to the radar only have limited coverage in height, so precipitation aloft may not be detected). I usually go with the lowest-level tilts because those will be most representative of what's happening at the ground. Of course if you are interested in looking at precipitation at higher levels above you, go for the higher tilts! WDT is a company that provides the radar data over the internet. I think it can be faster if lots of people are looking at the data at the same time (e.g., during chase season or other high impact weather events). Let me know if you have any other questions about radar. I happen to study radar meteorology here at Penn State.

Things have definitely greened up noticeably in the past couple days here. Interesting tracking the backdoor front; KIPT dropped about 8F in the last hour with northerly winds while it's still in the low 80s here.

Haha, we have become so cynical up here. Anyway, definitely more chances for snow in the next two weeks, and more waiting for those of us seeking warm weather...

Yeah, not a bad analogy.

Yeah, I was kind of planning on doing that beforehand anyway just because I had a long drive back. I probably would have stayed around a bit longer otherwise.

I left maybe 10 minutes after totality. Traffic was fine on I-40 east until I got to the exit ramp. All of the local roads from Tennessee into Kentucky towards I-75 were bad, and it ended up being a 5-hour drive to I-75 that takes under 3 hours without traffic. After a few miles on I-75 traffic was fine and opened up a lot once I got to I-64 east in Kentucky. That part of the trip was definitely helped by the lower populations of West Virginia, western MD, and central PA.

I ended up witnessing the total eclipse at Edgar Evins state park 60 miles east of Nashville. The build-up to totality was amazing; it got noticeably colder and the cumulus died as if an outflow boundary had swept through the area. The light got noticeably dimmer, and it kind of looked like those scenes in old movies where they film shots in the day and darken them to make it seem like night. Totality itself was of course awesome; light from the corona seemed to extend away from the sun in a wishbone shape, with one wispy strand of light to the left and two strands to the right. We were also able to see Venus, and I think Mercury during totality. My favorite picture of the event (the only one I took during totality):

Leaving for TN soon. Good luck everyone!

Got to my hotel in Richmond, KY. Very light traffic from PA through MD, WV, and KY. I'll probably head south for central TN around 5 am, and hopefully there won't be much traffic at that time.

Watertown is about 3 hours from Scranton. But maybe it's a bit early to plan lol.

The best bet might be the cumulus shadows near the Ontario and Erie lake shores. Of course in April, there could also be widespread overcast throughout the Great Lakes.

Same, I've never been to Kentucky or Tennessee. I'm thinking I'll probably leave my hotel in KY around 4-5 am just to be safe with regards to traffic. I have plenty of work to keep me busy while I wait anyway...

Some supersaturation wrt ice around 200 mb but otherwise southeastern TN is looking pretty good as of now.

I think one of the MODIS passes should cross the path of totality.

I think it's probably best to be at your intended viewing location at least a couple hours before the eclipse. I would definitely avoid big metro areas like St. Louis or Nashville if possible. Major interstates near the path of totality will probably be OK a few hours before the eclipse. Interstates that connect directly to large cities like I-55 and I-70 in Illinois, I-65 in IN/KY, and I-75 in KY may be pretty busy early in the day if people are driving south for the day. I'm considering going to Sparta, TN because it isn't near any north-south interstates and it's also not really that close to I-40, so traffic shouldn't be bad a few hours before the eclipse.

It's only like an extra second longer in southern IL vs. central MO so I'm not sure that will really cause people to seek out that area especially; weather and convenience are probably the dominant factors in where people end up going. Getting to the center of the totality path is also important if you want a longer eclipse. I booked a hotel in Richmond, KY for Sunday night with plans to drive into central TN or western KY depending on the weather.

Yeah, I think folks who have been looking at model data and observations for a while know from experience where to expect the heaviest precipitation in relation to a 500 mb PV max. I like looking at where banding sets up in relation to mesoscale jet streak circulations because it gives some physical insight into why enhanced precipitation may occur over a certain region. Hopefully we have at least one nice example this winter! I have a friend with a B.S. in meteorology who teaches a meteorology lab at a state university part time, so that could be one option.

Technically, we correlate synoptic scale lift to differential positive vorticity advection (actually differential cyclonic vorticity advection, to include our friends in the Southern Hemisphere), meaning that PVA increasing with height, not simply PVA, is correlated to lift. However, in the case of cyclogenesis, most of the time PVA is stronger at 500 mb than below so PVA at 500 mb is generally a decent proxy for positive differential PVA. Of course, a lot of the precipitation associated with cyclogenesis is due to mesoscale processes such as frontogenesis, where semi-geostrophic theory is more appropriate than quasi-geostrophic theory. Check out this presentation for more information about frontogenesis and how it produces lift. http://www.weather.gov/media/lmk/soo/frontogenesis_lmk2.pdf

Way late, but just to add, there are actually Level 1 WSR-88D radar data. These data are the raw voltage time series at each range gate and are used by the signal processor to calculate the Level 2 "base" moments of reflectivity, mean Doppler velocity, spectrum width, correlation coefficient, differential reflectivity, and differential phase. Level 1 data are not archived because they require more storage space than Level 2 data and very few users find the time series data useful. Time series data can be used to estimate the full velocity power spectrum, which can give us more information about the types of particles within each radar sampling volume. The Level 2 data are considered "raw" data because little quality control or smoothing is done to the base moments. For example, if you compare differential reflectivity from a Level 2 source to that from a Level 3 source, you can see that the Level 2 data is much noisier. The noise would be further reduced if the radar sent out more pulses, but that would increase the dwell time and lead to less frequent sweep updates. Level 3 data are thus further processed Level 2 data where the base moments are smoothed to reduce the noise, specific differential phase is calculated from differential phase, and other products such as radar-estimated precipitation are derived. One drawback with the Level 3 data is that only the lowest 4 elevation scans are processed in this way, so information from the higher elevation angles is only available in the Level 2 data.

That map clearly shows how it was a much colder than average February for parts of the upper Midwest. It was also an anomalously warm February in the southwest US. The raw temperature departures don't tell the whole story; there is significantly more variability during the winter in the Midwest vs. the southwest US. Using the example of Needles vs. Lansing, one standard deviation of mean February temperatures is 4.9F in Lansing and 2.9F in Needles. This past February had a greater number of standard deviations from the mean temperature at Needles than Lansing so the warmth there was more unusual than the cold in Lansing.