Summer returns tomorrow for the following week, except on Sunday when another fall front moves through
Thursday, August 28, 2014
This incredibly wet and persistent monsoon is forecast to at least be interrupted starting this afternoon after the Steamboat Springs area received well over an inch of rain in the last two days. Currently, light rain persists as rain wraps around the backside of the departing low, and skies should clear with occasional showers by this afternoon.
Seasonal weather should return for Friday and Saturday, though there is enough remaining moisture from this last monsoonal surge to keep the threat of afternoon thunderstorms present each day.
By Saturday night or early Sunday, another strong front is forecast to clip Colorado and bring cooler temperatures and showers for much of the day Sunday, with snow showers likely at the highest elevations of the northern Colorado Rockies. Behind this front, much drier air first from the northwest early in the week and then from the southwest by midweek will invade our area, interrupting the dominant monsoonal pattern and bringing us beautiful late summer weather for the duration of the workweek.
Models forecast some sort of storm approaching the west coast by the end of the workweek, so the forecast for next weekend is uncertain. Some models hint at a reestablishment of the monsoon pattern as southwest flow ahead of the storm transports moisture from the south over our area again.
First fall cold fronts move through the area Saturday and again next week
Thursday, August 21, 2014
Currently, mid and high level clouds from tropical storm Lowell off the Baja cost have overspread the area, keeping temperatures cool in the wake of a storm system that moved through the area late Tuesday and Wednesday. Cool temperatures should minimize the threat of showers today before a complex area of low pressure currently located off the northwest coast affects our area later Friday and through Saturday.
As this low pressure system moves west, another area of low pressure left behind from the Tuesday night storm in southern California will be forced to move northeastward and will travel over our state by late in the day Friday. There is some model uncertainty with regards to the exact track of this system and that will affect whether the rain comes earlier or later Friday, but periods of heavy rain appear likely sometime Friday afternoon through early Saturday morning.
Following closely on the heels of this system, the main fall-like storm from the northwest will first produce showers later Saturday and then produce rapidly falling temperatures and likely heavy rain again as the main front moves through late in the afternoon or evening. Rain is forecast to persist for a significant portion of the night before clearing early Sunday morning, and there may even be a dusting of snow at the highest elevations of the Colorado Rockies.
Sunday should be unseasonably cool in the wake of our first fall front, with lots of sun early and perhaps a stray shower late. At this point, further model disagreement about the evolution of a trailing wave makes the forecast very uncertain. The European ECMWF hangs this wave back before finally moving it over our area mid to late week, while the American GFS keeps this wave progressive, moving it over our area around Tuesday.
In either case, another rainy and cool day looks to occur sometime during the next workweek. After this storm passes, the forecast points towards dry weather and seasonably warm temperatures as westerly flow cuts off the very persistent and long-lasting monsoon, which has been producing steady rains since the beginning of July.
Very wet Wednesday and Thursday before weekend drying
Tuesday, August 12, 2014
As discussed in last Thursday’s forecast, the monsoon pattern has been reinvigorated by southerly flow around the west side of the strong western ridge and will produce very wet conditions for our area later Wednesday through Thursday. Before that, another beautiful summer day is on tap for today with some more clouds than yesterday, especially in the afternoon, but with any precipitation staying likely staying south of us until tomorrow.
A subtropical wave currently over the Arizona - Mexico border is forecast to move first northward and then northeastward as it approaches our area tomorrow. This wave will be accompanied by very moist air and rain showers will likely begin ahead of this wave around noon or early afternoon tomorrow. Showers will increase and transition to periods of very heavy rain by later in the afternoon as this first wave moves over our area sometime Wednesday evening.
Coincidentally, a large area of low pressure currently over the northwest coast will move eastward, and it appears some of this energy will be absorbed by a second subtropical wave from the south, keeping the likelihood of continued heavy rain over our area for Thursday.
Conditions improve considerably by Friday as the subtropical wave moves to our east, but plenty of moisture left behind will fuel afternoon storms on Friday. By Saturday, the northwest low, still well north of us, moves eastward, bringing a much drier westerly flow over our area. There will be a chance of storms Saturday and Sunday afternoons as there will still be lingering moisture, but the westerly flow is forecast to end the monsoonal pattern for a while, bringing classic beautiful late summer weather to our area for the following workweek.
Less moisture this weekend before a weaker monsoon is re-established for next week
Thursday, August 7, 2014
Lingering moisture from the monsoonal surge this past week will keep the threat of storms for this afternoon, though the wet pattern will be reduced for much of the weekend as some dry air from the desert southwest moves over the area.
However, subtle waves in the mean flow will keep some threat of showers over the area, especially in the afternoons. Additionally, a weak wave moving along the Canadian border will increase the forcing Saturday afternoon and suppress the drier air southward for some possibly stronger storms then.
A piece of this wave will be left behind along the central west coast by late in the weekend, re-establishing the moist monsoonal pattern as southerly flow ahead of the wave drags up more moisture. This lingering wave is forecast to move over us sometime around Wednesday and Thursday, increasing the chance of more wetting rains.
This wave then phases with another wave well to our north as it moves east of us last in the workweek, carving out a longwave trough in the Great Plains and leaving us with a rapidly building ridge to our west. This scenario should lead to dry conditions heading into the following weekend, with seasonably cool temperatures as we will be in close proximity to the much cooler airmass to our east.
Temperatures warm for the weekend before another surge of monsoonal moisture for next week
Thursday, July 31, 2014
The moisture and cool air discussed in the Monday morning forecast verified nicely, and there is a slight chance of afternoon storms today as the main push of monsoonal moisture retreats south. However, the remnants of former hurricane Herman off the coast of Baja will keep some moisture over our area tomorrow, allowing for a greater chance of the typical afternoon storm then.
Most of the weekend is forecast to be considerably drier and warmer, however, the monsoonal pattern is re-energized late Sunday and through much of next week. This occurs as an easterly wave present in the east to west tropical flow over Mexico is entrained into the clockwise flow around the western ridge, moving moisture and upward forcing over our area, similar to what occurred this past Tuesday and Wednesday. Interestingly, this wave is forecast by some models to split into two pieces, with the first piece moving over our area on Monday leading to the threat of more heavy rain.
The second piece is forecast to merge with a separate wave moving into the Pacific northwest and move over our area midweek, again increasing the likelihood of heavy rain that may last until the end of the workweek. Finally, a different and further south Pacific wave is forecast by some models to cross the central west coast sometime around next weekend, with drying and warming expected as the flow veers from the south to the southwest ahead of the wave and drags some warm and dry air over our area.