All,
Resurrecting this string of emails in the hopes of narrowing the list of potential sources of the discontinuities in QPE. The state of Colorado once again saw some pretty drastic differences across RFC boundaries on 2/15. For the images in this email I will focus on the Colorado RFC and Missouri RFC boundary along the Park Range in northern Colorado. It's the western border of Jackson County, eastern border of Routt County, bordered on the north by Wyoming. On Feb 15th a nice snow event hit northern Colorado. First, the AHPS 24 hr QPE for the 15th:
Next, the AHPS QPE for the 16th. Note that most of the QPE fell from 00Z on the 15th through 00Z on the 16th, but AHPS doesn't allow 24hr amounts from 00Z to 00Z, so you'll have to mentally add the 2 images.
The Park Range is the N-S oriented high QPE that starts at the Wyoming border in the top center of both images. Notice that pretty good QPE extends east of the max. For west upslope events, the max in snowfall occurs along the terrain gradient on the west side up to the ridge tops, but a lot of QPE "blows over" to the east, sometimes all the way to the valley floor in central Jackson County. Granted, it's FAR less in places like Walden but on the east slopes of the Park Range, high QPE can still occur. In fact, a CoCoRAHS observer on the east side of Jackson County (well east of the traditional max along the ridge top) had 0.60 liquid from 12Z 2-15 to 12Z 2-16. All that said, these AHPS graphics seem to capture the real QPE patterns and amounts well for northern Colorado. Keep this in mind when you look at the URMA graphics next.
First, what we get in GFE. We have 6 hour grids for URMA QPE. This is a loop of the last 6 days of QPE. You'll notice that at 06Z on 2-15 there is high QPE Park Range for the Colorado RFC side of the mountains but nothing on the Missouri RFC side. This pattern of higher QPE in Colorado RFC vs. very little for Missouri RFC continues until 18Z on the 15th. The east slopes of Jackson into the north park area of Jackson county never see any QPE for this event in URMA, despite a good amount shown in AHPS. Again we feel AHPS is accurate while the URMA QPE for this event is not.
Finally, from the Veritas website the 24 QPE ending at 06Z 2-16 is shown below.
I chose 06-06Z because that was the bulk of the precip event in Jackson County. 00Z to 00Z would have shown pretty much the same thing here. What it shows again matches what we have for URMA in GFE. It is in stark contrast to AHPS QPE. It's clear this URMA image is not taking advantage of CoCoRAHS and the 0.60 amount 5-10 miles east of the max QPE. Further east, across the Medicine Bow Mountains (eastern Jackson County/Western Larimer County west of Ft Collins) where AHPS has 0.3-0.6 total across the 2 days, URMA has 0.05 to 0.1. I am not saying which is more correct in the Medicine Bows because there are very few obs there, and no CoCoRAHS obs at all.
The question remains: Is URMA using the best available QPE from the Missouri Basin RFC? Seems as though the AHPS page QPE has higher quality data for our mountain sites across northern Colorado. On the Colorado RFC side of our area the URMA amounts look more realistic and in line with observations.
Thanks,
Paul
