The water vapor imagery that forecasters are accustomed to viewing in AWIPS is the GOES Imager water vapor band at 6.5 microns as shown in the upper right panel. Keep in mind that there are notes at the bottom of each frame in the loop. \u00a0To summarize what we see, an initial shortwave moves across northern Colorado between 0600 – 0900 UTC 5 Dec. followed by another shortwave thereafter with a fairly distinct signal in all water vapor bands, all within a strong westerly jet. \u00a0The dominant signal after 1800 UTC 5 Dec. is an elongated region of warmer brightness temperatures associated with the westerly jet slowly drifting southward, most readily observed in the mid- (6.5 micron imager and 6.95 micron sounder) and upper-level (6.2 micron sounder) bands. \u00a0One thing to note is that amidst the general warming signal we see an area of cooler brightness temperatures lingering over the central mountains of Colorado; what do you think this feature is? \u00a0As will be shown in other imagery later, what we are seeing are the tops of a lower cloud layer that persists.<\/p>\n
Next, we bring up a loop of multiple products, including the CIRA Layered Precipitable Water (LPW) product, along with GOES IR, visible as well as mosaic radar at night:<\/p>\n
http:\/\/rammb.cira.colostate.edu\/templates\/loop_directory.asp?data_folder=training\/visit\/loops\/5dec16_lpw<\/a><\/p>\n Forecasters are likely familiar with a satellite derived Total Precipitable Water (TPW) product, such as the NESDIS blended TPW product on AWIPS. \u00a0The LPW product is derived from microwave instruments onboard multiple polar-orbiting satellites. \u00a0The unique aspect of the LPW product is that the moisture is shown for 4 separate layers as indicated on the looping imagery. \u00a0Keep in mind, the resolution of the instruments is considerably less than GOES and varies between instruments which is why the products appears more “blocky” at some times compared to others. \u00a0Also, the satellite passes occur at irregular times, therefore post-processing displays what data is available at 3 hour intervals. \u00a0The product time shows the latest available satellite pass, however keep in mind the most recent pass at a point may be several hours old due to irregular satellite pass intervals. \u00a0For example, look at central Nevada between 0918 and 1218 UTC 5 December, the same data is displayed since a new pass does not occur until after 1218 UTC, which shows up in the 1517 UTC image. \u00a0This product is still experimental, however it is available from CIRA in real-time<\/a>, as well as in AWIPS as a satellite proving ground product (contact us at Edward.J.Szoke@noaa.gov<\/a>). \u00a0Additionally, CIRA is currently developing an advected version of the LPW product that will display at higher resolution and appear less blocky.<\/p>\n One of the main points to emphasize in this particular case is that we do not see a sharp north-south gradient over central\/western Colorado in the 700-500 mb layer of the LPW (this is the most applicable layer for moisture flowing over the elevations of the Colorado mountains). \u00a0Let’s focus on the 0018 UTC 6 Dec. LPW imagery when we had a higher resolution pass over Colorado. \u00a0We may have concluded from the GOES water vapor imagery shown earlier that the region of warmer brightness temperatures was associated with “drying” through a deep layer upstream of the mountains (i.e., western Colorado). \u00a0The LPW product clearly shows that there is moisture present in the 700-500 mb layer at 0018 UTC across western Colorado that would still be available to later move over the mountains in the westerly flow. \u00a0We don’t see this moisture in the various water vapor bands since the weighting function profile is not low enough (even at 7.35 microns). \u00a0If moisture is your primary forecast issue, the LPW product can clarify moisture at different levels in a more definitive way than implying it from GOES water vapor imagery alone. \u00a0In this case, the moisture that remained produced a period of snow that lasted past 0600 UTC 6 Dec. in the mountains which was not predicted, perhaps owing to what looked like a drying signal in the water vapor imagery. \u00a0This shallow moisture was also way underdone by even the high resolution models which predicted almost no snowfall and as seen in some of the radar mosaic images, was not resolved by radar either (due to overshooting beam). \u00a0Here, the lower level moisture was sufficient to produce moderate snowfall because of the steep lapse rates that were present behind the initial shortwave, as seen in the Grand Junction sounding:<\/p>\n
![\"GJT_201612060000\"](\"https:\/\/rammb2.cira.colostate.edu\/proving-ground-blog\/wp-content\/uploads\/sites\/6\/2016\/12\/GJT_201612060000-1024x704.png\")
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