The severe weather threat today has changed just a bit. Longmont is now under a Marginal Risk (1 on a scale of 1-5) with large hail being the most likely threat (Figure 1 update). *Just* on the east side of I-25, there is a Slight Risk with a 2% chance of tornado formation within 25 miles of a given spot (Figure 2 update). There is a 5% chance of large hail falling within 25 miles of most of Longmont (Figure 3 update). This jumps to a 15% (including a 10% chance of hail larger than 2 inches in diameter) just on the other side of I-25. Storms should initiate around 1-2pm in the foothills and spread across I-25 in the early to mid-afternoon (earlier than recent storm events).
End 9am update.
Pretty simple today, with a trough to our west (the ridge is passing), we’ll have more lift over Colorado today – BUT- the convergence zone (or dry line) is expected to set up from Ft. Collins then down to the south southeast out on the Plains to our east (about 30 miles or so away to the east). Figure 1 draws this as a yellow line. Even if thunderstorms start in the foothills, they won’t really take off and get severe until they hit the deeper moisture to the east of that line.
Figure 2 shows the resultant marginal (1 on a scale of 1-5) and enhanced (2 on a scale of 1-5) risk of severe weather (hail and strong winds) just to our east and beyond. IF things change, and the convergence line sets up further west, I’ll update this post in the morning.
The longer range forecast:
The fair chances of rain showers today are shown on the left edge of the bottom graph. That is followed by a dry Saturday and Sunday AM. Sunday afternoon into Monday, we’ll have another cool trough effect the state (cool down in the blue circle – Figure 3) and multiple chances of storms/showers. Will severe weather come back again? We’ll look at this more tomorrow!