JACKSON, Wyo. – The calendar has flipped to May, but warm air is nowhere to be found as a cold and active pattern has taken hold. Near record cold on Wednesday will give way to a brief warm-up by Saturday, then a significant storm is possible Sunday-Monday with the potential for heavy mountain snow.
April Recap
While we always see ups and downs at this time of year, April ended up being a very average month overall. Temperatures ended up right around normal for the month with an average high in the low 50s and an average low in the mid 20s.
The warmest temperature of the month in the town of Jackson was 67ºF, which we hit twice on April 13 and April 24, and the coldest temperature of the month was 14ºF on April 18.
The town of Jackson received 1.20 inches of precipitation and the Moran/Jackson Lake weather station received 1.62 inches of precipitation, which are both slightly below average.
In terms of snowfall, it was around average in the valley with a total of 4 inches in the town of Jackson. In the mountains, the Rendezvous Bowl Plot at 9,580 feet received 39 inches of snowfall, which is below the April average of 61 inches.
In terms of mountain snowpack, we started the month of April right around average, but the melt rate was greater than average in mid April due to a period of warmer temperatures and little mountain snowfall. As of May 1, snowpack in the Upper Snake River Basin is 90% of average.
However, the rate of melting has recently slowed due to colder temperatures and new snowfall, and melting will be limited during the first week of May with below-average temperatures and additional snowfall expected.
In terms of water supply, we are in good shape heading into the spring and summer as precipitation has been above average during the past two water years (defined as the annual period starting October 1).
Currently, reservoir water storage is 113% of average in Jackson Lake and 144% of average in Palisades Lake.
Current and Upcoming Weather Pattern
If you’re just returning from a spring desert or beach trip, or if you’re just ready for summer and warmer weather, then the first week of May is going to hurt. On the plus side, moisture at this time of year is always beneficial (so long as we aren’t dealing with flooding, which we’re not) before we head into the summer months.
Multiple low pressure troughs will be tracking across the Pacific Northwest and the Northern Rockies, bringing in cold air (below average temps for early May) and moisture to our region.
The first day of May has been unseasonably chilly with periods of snow showers. We started the day with 1-5 inches of new snow in the Tetons above 9,000 feet as of 5 a.m. and preliminary reports indicate another 2-4 inches has fallen since then (as of Wednesday afternoon).
In the town of Jackson, snow showers have briefly dusted grassy surfaces from time to time. The high temperature so far on Wednesday has only reached 38ºF and this occurred early in the afternoon with temperatures hovering in the low to mid 30s since 2 p.m.
If the temperature fails to exceed 38ºF for the rest of the day, this would end up setting a new record low maximum temperature for the date. Even in Jackson, sub-40 degree high temperatures are rare in the month of May.
On Thursday and Friday, a weaker low pressure system will move through the area, which will result in alternating periods of sun and clouds with scattered snow showers. Temperatures will remain well below average for early May with highs in the 40s. For perspective, the average high in early May is around 60 in Jackson.
We will see a one-day reprieve on Saturday with highs warming up into the low 60s under mostly sunny to partly cloudy skies. If you’re looking to get outside and play, this will be the best day in the near future.
On Sunday and Monday, a more potent low pressure system is expected to move into our region, resulting in more widespread precipitation along with a drop in temperatures.
Snow levels are projected to start out in the 9,000-9,500 foot range on Sunday, before steadily falling on Sunday night and into Monday morning as colder air arrives.
The potential exists for significant snowfall accumulations in the mountains (mainly above 8,000 feet) on Sunday night and Monday, while the valley can also expect some snowflakes with wet accumulations possible first thing on Monday morning, especially north of town.
Powder conditions (relatively speaking in terms of snow density considering it’s May) are not out of the question for backcountry skiing in the Tetons on Monday.
An unsettled pattern looks to continue into the middle of next week with additional snow and rain showers along with well-below-average temperatures.
Here is a liquid-equivalent precipitation projection for the next 7 days:
Here is a snowfall projection for the next 7 days:
Looking further out, we may see a gradual warming trend toward the end of next week and into the weekend of May 11-12 with a trend toward decreasing precipitation amounts and frequency. However, this could always change as weather models tend to be less reliable beyond about a week during transition seasons such as spring.
Alan Smith, Meteorologist
