For the Front Range and High Plains of Colorado and southeastern Wyoming, significant rainfall is likely later today through Wednesday for much of the area, with some localized areas of heavy rainfall. Minor flooding is likely in places, and the possibility exists for localized areas of damaging flooding or slope failures.
Numerous slow-moving showers and thunderstorms should develop Tuesday afternoon and evening. Some localized areas may receive 1-3 inches in just a few hours. Then, widespread somewhat steady rain is likely to effect many locations during the night and into Wednesday, with another 1-2 inches over a large area. By Thursday morning many parts of the region will likely have storm totals of over an inch, and some locations will probably have totals in the 3-5 inch range.
Comparison with September 2013:
The moisture content of the atmosphere today is likely to reach about 150% of average for about 12-24 hours, compared to over 200% of average for 60 hours in the storm last Sept 10-12th. So the magnitude today is not quite the historic proportions that we saw last September. But it appears likely that the rain later today through tomorrow may be heavy enough to cause some problems.
The general pattern today, last September, and in other big rain events share some basic similarities. 1) A weak atmospheric disturbance is enhancing mid-level “monsoon” moisture from the tropical Pacific, 2) humid easterly flow in the low levels will bring in Great Plains moisture, and 3) the upslope flow combined with instability will help to turn that moisture into clouds and precipitation.