IPEX field Log for the Final IOP, DOW 2

Jeff Trapp, Ph. D.- NOAA/NSSL   02/24/00
Research Meteorologist,
NOAA/National Severe Storms Laboratory and
Cooperative Institute for Mesoscale Meteorological Studies
Boulder, CO

11:00 am
    The front's position to the south of DOW2 has changed very little in the last couple of hours. (By definition, the cold front is analyzed on a weather map at points where the air temperature starts to drop off; i.e., the "leading edge" of the cold air. A drop in pressure and humidity, and also a wind shift also may accompany a cold front.) This slow movement-and a period of radar-system stability-has finally allowed me to examine the data more carefully. I've been scanning the radar in an RHI (range-height indicator) mode, which essentially provides vertical slices, in this case, through the front.

   From DOW2's viewing perspective, the front-indicated on radar as a layer of northerly winds, below a layer of more southerly winds-is only 500 meters deep. I expected a much deeper front. So did the Dave Schultz and others on the P3, who, because of flight restrictions, couldn't fly low enough penetrate the front. In fact, these restrictions kept the P3 above the snow-producing clouds: the tops of the radar echoes, showing approximately the cloud tops, were only 2.5 to 3 kilometers above the ground. Considering the very deep thunderstorm clouds, whose tops can extend 12 to 15 kilometers above the ground, it amazed us that such shallow clouds could be dumping so much snow in the valley and in the mountains!

   The P3 is scheduled to land at noon. We'll shut down the radars at that time, in order to conserve resources and also rest for the next and final day of the project.

    Once again, I had no problem with the return trip to Salt Lake City, despite some brief, white-knuckled periods of heavy snow and low visibility. It felt odd to then return to the hotel in continued moderate-to-heavy snow, thinking that maybe we should have instead stayed in Ogden and collected data through the afternoon and early evening-even though we'd already collected 10 hours worth of data, contributing to one of the most successful IPEX IOPs! Limited resources and crew fatigue during late stages of field programs necessitate tough decisions about operations.

   The next day's event never materialized as advertised by the computer models, leaving us with lots of retrospective "what ifs" and "we should haves." And, it served as a reminder that the difficulty with which the computer models have at accurately predicting precipitation in the Intermountain West is precisely what motivated IPEX!

Non-Flash Journal Index IPEX Log for DOW #2    1    2