Wet week starts after the Fourth of July
Saturday, July 4, 2015
Similar to the last few days, there will be a chance of afternoon storms today, though with increasing atmospheric moisture there is a greater chance of wetting rains. As discussed in last week’s forecast, a strong cold front for the summer season is forecast to cross the area around sunset Sunday. Coincidentally, a weak wave from the southwest is forecast to cross over our area around that time or even as early as noon. The end result is showers should increase through the day as temperatures drop, especially later in the day, with some storms producing periods of heavy rain. Showers should continue overnight and into Monday morning.
The cold front will keep temperatures quite cool on Monday with continued showers. Again, some of these showers could produce locally heavy rainfall, though the cool air will moderate the strength of these storms.
Moisture will remain over our area for the following workweek, allowing for the possibility of storms each day though Friday that may produce continued locally heavy rainfall. Storms on Tuesday may be enhanced by another much weaker cold front moving though the area that day.
The forecast pattern is monsoonal-like, though the northward moisture transport in this case is not solely caused by the usual mechanism of upper level flow rotating around the eastern side of a strong western ridge. Instead, waves of energy moving over our area, including the cold fronts on Sunday and Tuesday, appear to be the primary driver of our wetter pattern.
Dry air is currently forecast to return to the area for next weekend as a storm from northern California drags dry air over our area as it passes to our north. This looks to end our wet week as a dry ridge is then forecast to build over the west, bringing a return to hot and dry weather.
Standard summertime weather on tap
Sunday, June 28, 2015
A large and stable ridge of high pressure over the Great Basin responsible for the record warmth in the northwest will stay just west of our area through most of the next week. Some moisture moving around the periphery of the ridge will continue the threat of afternoon storms through Tuesday as temperatures stay seasonably warm to hot.
By Tuesday night or early Wednesday, models forecast some cool air from the Canadian plains flattening the Great Basin ridge and allowing for the possibility of nocturnal activity late Tuesday and then afternoon storms Wednesday. Another weak wave passes Thursday and is forecast to be followed by some drier air for the rest of the workweek and into the first part of the Fourth of July weekend, reducing the threat of afternoon storms for then.
By Saturday, models have a much stronger Pacific northwest storm crossing the coast and threatening our weather later in the long Fourth of July weekend as it incorporates another surge of cool Canadian plains air. At this time, it looks noticeably cooler and more showery certainly by Monday, and perhaps as early as Sunday, with unsettled weather extending into the first half of that week.
Warm to hot weather continues until mid-next week
Thursday, June 25, 2015
After a small threat of afternoon storms today that will likely produce mostly windy conditions due to the very dry lower atmosphere, temperatures soar to above normal by the weekend. A building ridge just west of us over the Great Basin will keep us hot and dry for at least the first half of the weekend. Some moisture is forecast to be drawn northward along the western periphery of the ridge and eventually move over our region, leaving a small chance of storms starting Sunday afternoon and extending through Tuesday.
By Wednesday, models forecast some cool air from the Canadian plains flattening the Great Basin ridge and allowing for the possibility of stronger storms from Wednesday afternoon and extending through the Fourth of July weekend. The American GFS has the cool air approaching our area around Wednesday while the European ECMWF minimizes this surge mid-week and delays the brunt of the cool air until later in the workweek or early in the weekend.
Longer-term, the continued surges of cool air will keep the ridge from rebuilding over our area, keeping seasonable temperatures in the forecast beyond the Fourth of July weekend.
Quintessential Colorado summer weather on tap for the next week
Thursday, June 18, 2015
For the first time in about 6 weeks, the forecast is easy! Beautiful dry and seasonably warm to hot sunny days and cool nights should grace our area for the next week as this weekend’s forecast shortwave will end up passing well north of our area with no sensible effect on our weather.
By the end of the next workweek, models show the possibility of our summer monsoon season starting as moisture is drawn northwards over Colorado from Old Mexico. The possibility of afternoon storms will likely increase heading into next weekend as this moisture settles over our state.
Gradual drying along with afternoon storms for the next week
Friday, June 12, 2015
Though it looks like our past few days of very wet weather will change today, we will still be susceptible to the typical summer afternoon thunderstorms through the next week. Storms may be limited today by the cool air left behind by the departing storm yesterday, but I would expect Saturday to have a good chance of afternoon storms.
Some dry air does sneak in here Sunday for a a downturn in the afternoon storm chances, but a wave traveling north of us along the Canadian border will allow some cool air to infiltrate the region on Monday and destabilize the atmosphere. This, along with additional ill-defined waves for Tuesday and Wednesday will delay the strong drying advertised in the last forecast and lead to a good chance of afternoon storms for each of those days.
The dry air is now timed to arrive around Thursday and last into at least part of the following weekend, limiting or even eliminating the chance of the summer afternoon thunderstorm. There is model disagreement near the middle of that weekend as forecasts are at odds with the degree of interaction between a Pacific wave entering the northwest coast and cool air over the Canadian plains, leading to an uncertain forecast for then.
