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<\/a><\/p>\nAfter a busy stretch of monsoonal rainfall through early August, Colorado went through a dry and warm period over the past 7 days or so. Lucky locations mainly over central and eastern Colorado picked up a few tenths of an inch of rainfall over this time, while very hot temperatures (up to 6F above normal over the Plains) and smoky conditions were the main headlines.<\/p>\n
Fortunately, we are still in mid-August, and while average Precipitable Water<\/span> (PW<\/span>) has begun its initial seasonal decline from monsoon<\/span> season, climatology suggests that there is still plenty of chances for rainfall before the drier fall season begins. As shown in the water vapor image, below, this does indeed appear to be the case for the first ~5 days of this Outlook. Moisture, both of monsoonal origin as well as from the Great Plains, has begun to infiltrate into Colorado, and will continue to do so over the next few days. Although the dynamical support for rainfall remains rather subtle, the ample moisture will be enough to support a 4-day period with an Elevated flood threat (Event #1). Scattered<\/span> to regionally widespread<\/span> showers and thunderstorms are expected over the course of this time, initially over central and eastern Colorado on Friday, then shifting towards the southwest and southern higher terrain by Saturday through Monday.<\/p>\n As shown in the forecasted PW<\/span> plumes, below, moisture will increase even further by the middle of next week, this time statewide. The driving force behind this will be a large-scale trough<\/span>, currently entering the Gulf of Alaska, that is forecasted to strengthen and move into the Pacific Northwest by late Monday and further east-southeast by Wednesday. Deep southerly flow is expected to develop in advance of the trough<\/span> passage, which will support a strong moisture surge for Colorado. PW<\/span> forecasts suggest values as high as 1.2 inches in Denver, which is noteworthy for this time of year. The good news is that widespread<\/span> rainfall is looking more and more likely for a large part of Colorado with this trough<\/span>, Event #2.<\/p>\n From the perspective of the flood threat, there are two major wildcards with this feature. First, as seen in the water vapor image, the eastern subtropical Pacific currently has an extreme moisture gradient, with dry air to the east of Hawaii but significant moisture closer to Mexico. If the dry air is pushed far enough east, there will be a strong atmospheric river-type tropical connection for Event #2. This could support moderate to heavy rainfall for longer durations than our typical 1 hour period, say 6-12 hour. The second wildcard is that it is unclear if there will be enough instability to support anything beyond moderate rainfall intensity. This will depend on the exact timing of the trough<\/span> passage. For example, an early morning passage would constrain instability and lead to widespread<\/span> moderate rainfall but not much of a flood threat. At this time, as a blend of these possibilities, we are posting an Elevated threat for Event #2. Much more certainty will exist by Monday’s updated Outlook.<\/p>\n After the passage of Event #2, a significant cooldown is expected across the entire state, with temperatures at least a few degrees below normal and limited precipitation chances.<\/p>\n Each of the two identified precipitation events are described in more detail below.<\/p>\n On Friday, scattered<\/span> showers and thunderstorms, capable of moderate to heavy rainfall, are expected both over the higher terrain mainly along and east of the Continental Divide<\/span>, as well as the adjoining foothills and plains to the east. Up to one inch per hour of rainfall intensity is expected over the higher terrain. Isolated<\/span> heavy rainfall will also remain a possibility further east, especially along the KS border, where intensity up to 2 inches per hour will be possible. However, the coverage over the Plains is uncertain, but currently appears to remain on the isolated<\/span> side.<\/p>\n By Saturday, and through Monday, most of the activity will shift over the central, southern and southwest higher terrain where scattered<\/span> to possibly numerous<\/span> showers and thunderstorms will be likely each afternoon and evening. Isolated<\/span> rainfall intensity over 1 inch per hour looks like a good bet at this time, which supports and Elevated flood threat. However, with only modest instability available, it does not appear that the threat will be constrained to be only isolated<\/span> in nature.<\/p>\n<\/a><\/p>\n<\/a><\/p>\nEvent #1: Friday – Monday (August 13 – August 16)<\/strong><\/h3>\n
Elevated Flood Threat<\/span> Mainly For Both Higher Terrain And Plains<\/strong><\/h4>\n