Summary: January 15, 2019
Since the beginning of January, most of the Intermountain West region has been dominated by an active weather pattern and slightly cooler than average temperatures. The eastern part of the region (east of the Continental Divide) shows a shift to a warmer than average pattern. For the past two weeks, most of the high elevation mountain ranges have received over half an inch to two inches of moisture. While this is good news, a reminder that this is typical for this time of year. We are now in the heart of winter when consistent precipitation (specifically snowfall) is key to keep the snowpack building up toward the peak. It's easy to fall behind with one or two mild weeks in there.
Snowpack throughout the IMW is mostly between 75% to 100% of average. The lower values in the Four Corners region have actually shown quite a bit of improvement since the beginning of December. Unfortunately, since the beginning of December, snowpack conditions have deteriorated in western Wyoming.
The large scale snowpack and temperature patterns are starting to show signs of the developing El Niño. With an El Niño, we typically expect to see warmer than average temperatures and less snow in the northern portion of the IMW, and a wetter signal in the southern portion of the IMW.
The 7-day outlook gives us some good news. With the entrance of an atmospheric river from the Pacific and into California, we're expecting to see plenty of moisture pumping into the region later this week. The outlook calls for high elevation areas to receive over an inch and the majority of the Upper Colorado River Basin to receive more than a quarter inch. Forecasted snowfall amounts could be as high as 15 inches over the high mountains of central Utah and large areas of western Colorado. Longer term, we're expecting a mixed bag in terms of temperature and precipitation - but that could be good news too as it might suggest more troughs passing through and bringing more active weather with it.
Wyoming: Some expansion of D0 (black outlines) and D1 (maroon outlines) is recommended. Western WY SPIs are below -1 on all timescales from 30-days to 6-months. Snowpack percentiles in the Wyoming and Wind River ranges range from the single digits to the low 20s. Basin snowpack in the region is around 75-80% of average, and the Upper Green is showing about a 1.5 inch deficit in SWE. There's still time to make up these deficits, but this region needs to be closely watched as we approach spring.
UCRB: With the exception of areas described in Wyoming, status quo is recommended for the remainder of the UCRB. While widespread precipitation did accumulate over the past week, January is a time when getting half an inch of moisture in a week is just keeping up with average. Snowpack percentiles are improving, which is good for this season, but still struggling to make up for large deficits from last winter. If the current 7-day QPF pans out, we could be looking at improvements next week. Stay tuned.
Eastern Colorado: We recommend a 1-category improvement in the Arkansas valley. The area to improve (green outline) received half an inch of precipitation over the last week, which is more than the entire monthly average for January. This storm, along with a decent start to the water year, has pushed the SPIs to mostly positive values on all timescales. Reports are that winter wheat was successfully planted, and we haven't had any reports of negative impacts this water year yet. We're limiting the improvements to not go further west over the Sangre de Cristos and into the San Luis Valley until we see how the next week pans out with lots of moisture in the forecast.
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