The State of the Atmosphere: Sunday, May 29, 2016

May 2016 will quietly come to an end Tuesday, with meteorological summer getting set to begin on June 1st. Overall, the month went generally as one might expect May to go in Colorado. For Denver, it started chilly with even some snow to end April and begin May but we quickly transitioned to more of a warm-season pattern with afternoon thunderstorms becoming more and more frequent as the month progressed.

Statewide snowpack saw several good boosts in April and again in May, which put Colorado at 124% of normal as of May 24. You can see in the chart below, while numbers are above normal for the date, snowpack is now dropping sharply now as we head into the summer months.

If you thought the month was colder than normal, you wouldn't be wrong. May featured below normal temperatures for much of the country, with some of the greatest anomalies being focused over eastern Colorado. According to records at Denver International Airport, through May 28th, Denver is running 2.8 degrees below normal for the month.

PRISM temperatures compared to normal, May 2016

As for precipitation, we not surprisingly saw more of a mixed bag. Much of the state, however, saw above normal precipitation, the exception being across southeast Colorado. For Denver, the city recorded 2.32" of liquid through this morning, which is 0.44" above normal. We'll have a chance at seeing those numbers go up a bit before the end of the month, with at least a chance for storms in the forecast each of the next several days.

PRISM May precipitation anomalies

The week ahead
As May comes to a close and we head into meteorological summer, our days continue to lengthen and chances for snow (though not unheard of in June!) become an afterthought for the next several months.

Related: What's Denver's weather like in June?

Our focus instead becomes keeping an eye on often daily thunderstorm chances and potential for severe weather across eastern Colorado. While we've already seen several tornadoes across the state this season, peak severe season is June for eastern Colorado.

View a larger version of this map on U.S. Tornadoes here.

For the next several days, it looks like Monday will feature the greatest threat for severe storms across the plains of Colorado.

In terms of the severe weather threat, deep-layer shear over Colorado will likely be the limiting factor, with the main shortwave remaining well to our north over Eastern Montana and the Dakotas.

12Z NAM 500 mb Geopotential Height/Wind Speed for 00Z Tuesday|COD Weather

Though not overly impressive, moisture shouldn't be a limiting factor for severe thunderstorms across the Eastern Plains as dewpoints will likely remain in the 45-50°F range, which is sufficient when initiating thunderstorms over the High Plains.

12Z NAM 850 mb Dewpoints for 00Z Tuesday| COD Weather

With the lack of deep-layer speed shear and low-level veering (clockwise turning of the wind with height), the greatest threat will be large hail and damaging straight-line winds. Here is a forecast sounding for Wray, CO:

12Z NAM Forecast Sounding for Wray, CO at 00Z Tuesday|COD Weather

Note the "Inverted-V" profile, implying a dry microburst threat. The steep mid-level lapse rates indicates that large hail is also a threat.

As you can see in the image below, right now it looks like the greatest threat for severe storms will be east of Denver, but we do expect thunderstorm activity across the I-25 urban corridor as well on Memorial Day.

SPC severe weather outlook

For Tuesday we'll see what may be the coolest temperatures of the week across the metro areas, with the chance for showers and drizzle from Monday night through Tuesday.

Beyond Tuesday we start to dry things out a bit more and warm up as well. Models are in decent agreement that a pretty strong ridge will build into the Great Basin by the end of the week and next weekend, which would likely translate to some of our warmest temperatures of the year so far.

ECMWF shows big ridge to the west by next weekend | Weather5280 Models

GFS showing warm temps across the west next weekend, including much of Colorado

As for precipitation, we'll see some decent totals where convection occurs over the next several days, with large-scale models focusing some of the greatest QPF along the Palmer Ridge and southern I-25 corridor. Coverage will be a bit spotty, but certainly nice to see the chance for more rain before we dry things out to end the week:

Brendan Heberton

Brendan is founder of Weather5280. He is co-founder of FreshyMap, and develops software for geospatial data analysis and visualization.

Denver, Colorado
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