Welcome to American Weather


  • Content count

  • Joined

  • Last visited

About heavy_wx

Profile Information

  • Four Letter Airport Code For Weather Obs (Such as KDCA)
  • Gender
  • Location:
    State College, PA

Recent Profile Visitors

1,054 profile views
  1. The 00z Euro was too warm for snow over most of PA, aside from maybe NE for several hours at the onset of precipitation. There is a high strengthening over Quebec that allows for some ageostrophic flow of cold air into our region. However, the air mass is fairly mild ahead of the coastal storm so this cold ageostrophic flow may not be enough to produce snowy atmospheric profiles, even with evaporative cooling. Also, the relatively mild air mass results in a weaker temperature gradient with respect to the Atlantic ocean temperatures, leading to lower available potential energy for cyclone growth. So the dynamics of this system are not going to be on the same level as a classic, rapidly-deepening cyclone.
  2. Some glazed sidewalks and roads that are untreated here currently; looks like we got a few tenths of an inch of snow today.
  3. At equilibrium, the net flux of photons leaving the Earth system is the same as the net flux of photons entering the Earth system; I think we would agree on this point. If the CO2 concentration increases by a fixed amount, the net flux of photons entering the Earth system is constant but the net flow of photons leaving the Earth system decreases initially as CO2 absorbs LW radiation transmitted by the Earth. Because of the absorption by CO2, the air warms; this warming will continue until the increased emission by the warming CO2 causes the net flux of photons leaving the Earth system to be equal to the net flux of photons entering the Earth system; this point is of course a new equilibrium where the air temperature is warmer than the initial equilibrium before the increase in CO2 concentration. The above description is of course a simplification of the true response of the Earth system to an increase in the CO2 concentration, where we are essentially considering a single atmospheric layer with a homogenous temperature and CO2 distribution. We have not violated conservation of energy in this simplified model if we consider that the flux of photons entering the Earth system is always the same as the flux of photons leaving space and the flux of photons leaving the Earth system is always the same as the flux of photons entering space. As the solar radiance is constant for the Earth, we need consider only the flux of photons leaving the Earth system and entering space to show that space will necessarily cool to compensate for the warming of the Earth system in this model. As I described earlier, the flux of photons leaving the Earth system decreases initially as the CO2 absorbs photons; this absorption leads the flux of photons leaving the Earth system and entering space to be initially less than the flux of photons entering the Earth system and leaving space, resulting in a net cooling of space and a net warming of the Earth system. This difference between the flux of photons entering and leaving the Earth system continually decreases as the atmosphere warms and emission increases, until reaching a new equilibrium where space is cooler, the Earth system is warmer, and the flux of photons leaving and entering the Earth system is the same. Now what you alluded to is the phenomenon of stratospheric cooling resulting from increased CO2 concentration. This cooling has the net effect of decreasing the radiative forcing of increased CO2 concentration at TOA due to the cooling of the stratosphere. However, modeling studies (e.g., Hansen et al. 1997) suggest that this cooling does not balance out the warming of the troposphere and still allows CO2 to have a substantial forcing for warming surface temperatures. Also, the link you provided illustrates the mechanism for stratospheric cooling nicely but does not indicate that the cooling balances out the warming occurring in the troposphere. One final thought: fully understanding the net radiative forcing that occurs given an increase in CO2 concentration (not even accounting for other climate system effects) requires us to consider the temperature, air density, and CO2 profiles throughout the atmosphere and is therefore difficult to assess without a radiative transfer model. If you have come across a modeling study showing stratospheric cooling offsetting tropospheric warming as a response to increased CO2 concentration, I would very much like to read it and hopefully increase my understanding of this process.
  4. Energy is conserved only for a closed system; the Earth and its atmosphere are not a closed system because the sun transmits radiation to the Earth and its atmosphere and the Earth and its atmosphere transmit radiation to space. When the concentration of CO2 molecules increases in the atmosphere, more infrared radiation is absorbed by the atmosphere. This increased absorption occurs because CO2 molecules may become torqued by electromagnetic radiation at these wavelengths given the permanent dipole moment of CO2. The increased rotational energy of the CO2 molecules results in air molecules with higher kinetic energy (due to collisions) and thus warmer temperatures. These increased temperatures will also lead to an increase in infrared emission; however, this emission depends on the temperature and is therefore not, in general, the same as the absorption by these molecules. If the CO2 concentration increased by a certain amount and then stayed constant, the temperature of the atmosphere would increase to a new equilibrium. This is of course ignoring the feedbacks of the climate system. The bottom line is that with increased greenhouse gas concentrations, the total energy of the Earth system (the atmosphere, land, and ocean) increases. Energy is conserved in this scenario because the energy that would have been radiated to space without the greenhouse gases is instead stored in the Earth system. Once the new equilibrium is reached, the energy stored in the Earth system is constant.
  5. Nice break from the cold weather today with highs in the 50s.
  6. Moderate snow with maybe a half inch on the ground so far.
  7. Are you referring to Tuesday? Looks like snow to sleet/freezing rain with the warm air advection-driven precipitation. Beyond that, we get quite mild for Thursday and Friday as a surface wave tracks over the eastern Great Lakes. The baroclinic zone associated with that system slowly works its way into our region, allowing for potentially more frozen precipitation as another wave develops along that boundary. Thanks to a shift in the position of the east-Asian jet, much of the CONUS gets flooded with Pacific air in the long range, which should lead to generally milder conditions over the eastern US.
  8. I think you're alluding to quasi-geostrophic theory in your question. This theory is only applicable for large-scale troughs and ridges, and the vertical motion induced by QG mechanisms is generally much weaker than vertical motion induced by mesoscale forcing such as upslope flow or convection. Therefore, significant upslope will usually be more important than QG effects for vertical motion. As an example, lake-effect snow usually occurs in CAA regimes where synoptic-scale sinking motion is favored. However, lake-induced instability and upslope flow (i.e, like over the Tug Hill plateau) produce vertical motions at least an order of magnitude greater and thus outweigh the sinking motion induced by the large scale flow.
  9. Temperatures and dew points in the mid-40s F here, along with this morning's rain, have eaten into the snowpack. What is left will likely become a sheet of ice after the cold frontal passage.
  10. There are some noticeable radial spikes in ZDR in that band. These features could be depolarization streaks that are caused by oriented ice crystals in an electric field. It matches pretty well with observations of lightning in the area. Sent from my SM-G900V using Tapatalk
  11. Guidance suggests we will have some modest forcing in the lifting branch of a jet streak Friday night/Saturday morning. Bufkit profiles from the 4K NAM and GFS show a brief period of snow here before the mid-levels become subsaturated as the forcing weakens. We get into a region of good isentropic lift late Saturday morning; however, the warm layer near 850 mb will change precipitation over to sleet and eventually to freezing rain and rain later Saturday. I'm not sure if we end up with a net gain of snow here; the GFS brings surface temperatures into the mid 40s F by late Saturday with rain. We'll have to watch the initial light snow early Saturday and how quickly we change over as the forcing increases later in the day.
  12. Measured about 3" of new snow on the ground. Looks beautiful outside with the wet snow sticking to everything.
  13. Decent size aggregates falling here...looks to be a combination of stellar/plate-like crystals growing aloft and the onset of melting that's leading to the enhanced sticking efficiencies and larger aggregates.
  14. More junky flakes over the past few hours as temperatures warm aloft.
  15. Yup. There is a few km-deep ice supersaturated layer where temperatures are within the range of plate-like crystal growth. Dendrite and stellar crystals tend to stick together pretty efficiently; I saw some aggregates of just a few dendrites stuck together earlier.