If you enjoyed yesterday’s somewhat cooler weather, you’ll be in a treat for this week. A break from the summer heat has arrived with temperatures expected to be near or below average, especially on this Monday. We also cover the increased rain chances for the next several days. Read on for more details.
A break from summer
Today will have that “autumn” like feel to it. Highs are expected to be in the 70’s across the Metro area. This is all thanks to a cold front that pushed through yesterday. Below shows the 700 mb temperature pattern this afternoon, as well as for Wednesday. Today’s picture shows temperatures at 700 mb of about 8 to 10°C, much cooler than where we were last week. The front is positioned basically along the Front Range, with easterly upslope flow in place.
GFS/NAM 700 mb temperature today (top) and Wednesday (bottom)
Below average temperatures, with exception of Tuesday
Another cold front dips through on Wednesday (see above), with yet another push of cooler air from Wyoming. While there will be some swings in temperature, most of the week should remain near or slightly below average. This is depicted below from the GFS ensemble temperature outlook for the week and upcoming weekend. Areas in blue are below average, which is present today and the latter part of the week. Our coolest day will be Monday, while the warmest days look to be Tuesday and Wednesday with highs then likely in the mid to upper 80’s. We should end the week in the lower to middle 80’s.
GEFS model ensemble forecast of maximum daily temperatures for the week
As for today, the upslope flow at the surface will combine with the already moist flow from the monsoon. Below’s 500 mb map shows the ridge has shifted to the south into central New Mexico. That has allowed for a return flow of monsoonal moisture from Arizona. Storms will develop over the High Country this afternoon and move onto the Plains for rain showers during the late afternoon and evening. The coverage of the rain, though, will depend on the amount of sunshine during the morning. If the low clouds stick around through the day, expect a more scattered-nature to the storm activity. We are a little concerned about localized heavy rainfall in some storm cells given the high precipitable water over the area, as well as chances for one or two storms to produce 1″ hail and strong wind gusts in and around Denver. We’re putting today’s rain chance at around 50%.
GFS 500 mb absolute vorticity for today (top) and Thursday (below)
Jet stream moves south to end the week
Much of this week’s weather can be summed up in the above two images. Today, the mid-level flow will be out of the west and southwest. But the pattern shifts come mid to late week (above), where the flow turns from the northwest thanks to a trough in the Great Lakes and another in the Pacific Northwest. The ridge will also shift more to the west over Arizona at this time. This pattern change will spell out the threat of isolated to scattered storms each day, as storms develop over the higher terrain and traverse eastward onto the Plains. This northwest flow will also keep temperatures on the cooler side, as mentioned earlier.
Another view of this pattern for the latter-week is evident in the upper-level jet flow at 250 mb (see below). Notice how the jet stream starts out the week across Montana, while by Thursday, the jet has trekked southward and is oriented northwest to southeast.
GFS 250 mb jet stream today (top) and Thursday (bottom)
Precipitation chances exist each day
As for precipitation, today and Wednesday appear to be our prime chances. These two days will feature upslope conditions from a cold front to bring in the low-level lift, as well as monsoonal moisture and instability. On Tuesday, the ridge shifts a little more south to keep storms more across southern Colorado – yet isolated storms cannot be ruled out for our region. Thursday and Friday should see the chance of scattered storms each day thanks to the northwest flow aloft combined with the weak easterly flow at the surface and moisture lingering. Overall, the GFS is predicting the heaviest rainfall residing over eastern and southern Colorado this week (see below), which we do tend to agree with. Still, chances for rain in our neck of the woods will be about as high as we have seen since the remnants of Hurricane Bud moved through more than than six weeks ago.
GFS total accumulated precipitation through Friday
On Thursday and Friday the storms could possibly become severe, primarily across northeastern Colorado. Below shows the convective available potential energy (CAPE) and wind shear between the surface (green arrows) and 500 mb (red arrows). Upslope conditions will be present at the surface, with northwest winds aloft. In addition, CAPE may exceed 2000 J/kg in eastern Colorado. This combined with the jet stream overhead may support the threat of supercells later in the week. It’s too far out to tell for sure, but something we will keep an eye on.
GFS instability and shear on Friday evening across Colorado
Forecast Specifics:
Monday: Mostly cloudy with showers and thunderstorms developing in the afternoon and evening. Some storms could produce heavy rainfall, 1″ hail, and strong outflow winds. Highs in the mid to upper 70’s across the Plains and mid 60’s in the Foothills.
Tuesday: Mostly sunny in the morning then partly cloudy with isolated thunderstorms in the afternoon and evening, primarily south of Denver. High temperatures in the upper 80’s to 90 for the Plains with upper 70’s in the Foothills.
Wednesday: Increasing clouds and cooler once again. Scattered thunderstorms, some of which could produce heavy rainfall, are expected in the late afternoon and evening. High temperatures in the low to middle 80’s across the Plains with low 70’s in the Foothills.
Thursday and Friday: Mostly sunny skies transitioning to increasing clouds and isolated to scattered thunderstorms in the afternoon and evening. Some storms could be severe. Highs for the Plains in the low to middle 80’s, with low to middle 70’s in the Foothills.
Weekend Outlook: The ridge of high pressure will move more south and west into Arizona as the week goes on, allowing the jet stream to dominate. That will keep the area in a northwest flow pattern, leading to near normal or slightly below average high temperatures, along with the chance of afternoon and early evening thunderstorms over the High Country and Plains.
High Country: Scattered storms will be possible statewide today with the monsoonal flow from west to east across the state. On Tuesday, the focus for storms will be across west and southern parts of the state. The wet pattern returns Wednesday through Friday, with isolated to scattered storms each day in the afternoon/early evening in the northwest flow. Check out SummitCAST for twice daily updated forecasts for more than 120 Colorado hiking destinations!
DISCLAIMER: This weekly outlook forecast was created Monday morning and covers the entire upcoming week. Accuracy will decrease as the week progresses as this post is NOT updated. To receive daily updated forecasts, subscribe to BoulderCAST Premium.
.
Share our forecast!
You must be logged in to post a comment.