We've been preaching about this pattern for weeks now. From a lackluster winter to an active April and May, so far it has performed. If our recent "Sunday roller coaster" hasn't been enough (84 degrees yesterday, highs in the 30s with snow the week prior, and 85 degrees the Sunday before that) maybe this week's severe weather and heavy rain threat, and increase in mountain snow melt will get your attention.
Tuesday's convective outlook
After another day with highs in the 80s today, a cold front passes through northeast Colorado Monday night. This will cool temperatures by about 10 degrees for Tuesday, but the severe storm risk will remain relatively low for the greater metro area Tuesday afternoon, with best chances for storms to turn severe over northeast Colorado. Expect a few storms Tuesday, but they will not be as widespread as we expect they'll become later in the week.
Increased severe threat Wednesday
Better ingredients come together Wednesday to support more widespread and stronger storms. CAPE, shear, instability and moisture all appear to be present. This means conditions will be favorable for storms that do develop to become severe, with damaging wind and hail the main threat, but certainly a chance for a tornado as well.
The Storm Prediction Center's probabilistic outlook for Wednesday shows all of northeast Colorado under 15% chance for severe weather to occur within 25 miles of a given point.
This is supported by nearly all the parameters we look at in forecasting severe weather. NAM CAPE values (convective potential energy) are forecast to be between 500 - 2000 across eastern Colorado Wednesday afternoon -- meaning in essence there is a lot of instability, and support for storms to turn severe.
There will also be moisture. Dew points are forecast to be greater than 50 degrees F across much of northeast Colorado Wednesday afternoon, and all models indicate some storms could produce heavy rainfall. Remember, as is typical with severe weather season, not everyone sees these heavy storms, so we won't be pinpointing exact rainfall.
Storms will continue into Wednesday night across the Plains, but diminish as the night progresses. It looks like we'll do it all over again Thursday, with another round of storms likely. There is less confidence in severe potential Thursday, but but certainly won't rule it out. The greatest risk here appears to be along the I-70 corridor through central Colorado Thursday.
As for rainfall totals. . . Expect rainfall amounts to be hit and miss depending on where heaviest cells develop over the coming days as mentioned above. Generally speaking, totals will range from a trace to two inches through Thursday. The 18z NAM has heaviest precipitation occurring well east of the metro area through Wednesday, but tries to pull the zone of precipitation a bit further west for Thursday/Friday. The GFS/EURO are a bit further west with some of this precipitation, a solution I prefer at this point. Storms through Friday will likely keep much of southeastern Colorado drier, with most of the activity along and north of I-70.
Afternoon storms possible through the weekend
Afternoon storms stick with us through the period, some producing heavy rains. Models differ on how fast the