Wet and cold weekend followed by improving conditions next week
Friday, May 8, 2015
A large and impressively cold storm currently located near Las Vegas will first move eastward across the southern Great Basin and then northeastward over Colorado through the weekend, continuing the current streak of wet weather. Furthermore, this very cold storm will likely bring snowflakes to the valley floor as early as Saturday night and accumulating snows down to 8000 feet or so, though most of the precipitation will have ended by the time the coldest air arrives for the second half of the weekend.
Showers should decrease and possibly end later this afternoon as the current blob of energy ejected from the storm exits the area, but may pick up again this evening as pieces of energy are periodically ejected from the parent storm. By Saturday morning, the forecast position of the storm along the Colorado and New Mexico border may force a dry slot over our area during part of the day tomorrow, which, as the name implies, may bring precipitation-free and perhaps even sunny weather to our area for a time tomorrow.
Don’t be fooled by the break, though, as unseasonably cold air is is drawn southward over our area later in the day as the storm intensifies in eastern Colorado during Saturday afternoon. Moderate to sometime heavy precipitation will be noted around the frontal passage, with showers behind the front expected through the rest of the weekend and into Monday morning in the cold and unstable northwest flow behind the departing storm.
Temperatures will be slow to respond Monday, but by Tuesday we should be returning to more seasonable temperatures as another storm moving over the Baja peninsula approaches our area. Similar to the storm last Tuesday night, but considerably weaker, I expect rain showers to increase in much warmer air at all elevations by late in the day Tuesday and lasting through the day Wednesday.
We will have another break in steady precipitation on Thursday and Friday, though we may be susceptible to typical summer afternoon storms as very warm temperatures invade the area. There is considerable model uncertainty after this though, as the Amercian GFS keeps another major storm just west of our area through the weekend, while the European ECMWF, in the latest forecast from this afternoon, moves this storm over our area during the weekend.
Summer-like weather continues until midweek
Friday, May 1, 2015
The weather for this weekend and early next week looks to be fairly similar to what we are now experiencing, with warm temperatures and the threat of afternoon storms. There is a grazing wave along the U.S. - Canadian border that will drop temperatures a bit on Sunday and may lead to a greater chance of wetting rains, especially in the afternoon.
However, it looks like our weather will be turning wet during next week as a storm crosses the Baja peninsula on Monday. There may be a greater chance of afternoon storms by Monday afternoon over our area as ill-defined pieces of energy eject from this storm.
Current forecast have this storm moving northeastward, though the track looks to swing first south of us by Tuesday and then east of us by Wednesday, favoring the Front Range of Colorado. Additionally, a much stronger storm enters the Pacific Northwest coast on Tuesday, and at the very least will keep our weather unsettled through the week.
There is a lot of model uncertainty as to the evolution of this second storm, with the American GFS model bringing pieces of this storm over our area by the end of the workweek, while the European ECMWF is a bit slower moving the storm eastward. In either case, models are favoring a wet solution for at least part of next weekend.
Wet weather this weekend followed by almost summer-like weather for midweek
Friday, April 24, 2015
A wave currently traveling through northern New Mexico has brought moister air into our region, increasing the threat of afternoon storms today. Another far more significant storm is currently located along the West Coast around the US - Canadian border and will be be Colorado’s major weather-maker for the weekend and early next week.
This storm is forecast to elongate and split as it approaches the Great Basin on Saturday, eventually becoming a closed low later in the weekend and traveling slowly along the Arizona - Utah and New Mexico - Colorado borders. Temperatures will remain mild ahead of the storm even as cool air begins to filter into the region during the day Saturday. Showers should increase and eventually turn more persistent by later in the day and lasting overnight. Snow levels will initially be quite high, around 10,000 feet, before dropping overnight to around 8000 feet.
This storm does have some similarities with last week’s meteorologically impressive storm, though it is far weaker and faster moving. But unfavorable mountain-top easterly flow is again predicted again by later Sunday for our northern Colorado region, and that may end or limit precipitation for a while around then.
A trailing wave crosses through the area late Monday into Tuesday keeping unsettled conditions in place and increasing the chance of precipitation again, but the wind barely turns northwesterly and likely limits precipitation amounts. The cool air associated with this wave will keep temperatures seasonably cool through Tuesday, but sharp warming will lead to almost summer-like weather by Wednesday, with even the typical afternoon thunderstorms forecast for Thursday and Friday.
The storm I initially thought would impact us around May Day is now forecast to weaken and stay mostly to our north, yielding a pleasant weekend, but another warm Pacific storm approaches the West Coast around then and may bring more beneficial moisture to our region around the following midweek.
Impressive spring storm continues with snows through tonight
Saturday, April 18, 2015
This very impressive spring storm continues with at least 2 more waves of snow for our area later this afternoon and overnight. The snows I thought may occur yesterday and Thursday night were overwhelmed by the strong winds downsloping from the east off the Park Range. In fact, you could see evidence of breaking atmospheric waves in the turbulent cloud structures overhead Thursday and Friday as the TROWAL was overhead. However, the upward motion from the TROWAL only briefly and intermittently appeared as the strong downward motion from the easterly winds dominated atmospheric motions.
But as the storm intensified and finally moved east of the Divide, another TROWAL moved over our area this morning. 2” of snow on my deck this morning and moderate to heavy snowfall rates on the hill in northerly flow resulted as this second feature gathered moisture from the Gulf of Mexico.
Models indicate another surge of moisture and upward motion later this afternoon that will produce another round of moderate to heavy snows. The kicker wave responsible for the eastward motion of this storm is currently in northern Montana, and will send more cool air through our area around midnight. This additional forcing will be far more moderate but will again produce snows for a time late tonight and decrease the snow densities, resulting in light fluffy snow on top of a dense base for Sunday. While the Steamboat Ski Area is notoriously guilty of closing just before we are impacted by these spring snowstorms, those willing to hike for turns will benefit.
The very active second half of April forecasted earlier this week looks to occur as the cold Canadian air to our north expands westward and southward and interacts with Pacific energy entering the West Coast. The persistent snow from this storm system will be replaced with showers tomorrow afternoon and Monday as moist and cool northwest flow remains over our area.
By Tuesday, another Pacific storm crosses the southern West Coast and will force the upper level winds to back to the southwest. But the current storm, even though by then forecast to over the Great Lakes region, will continue to affect us as waves of energy rotating around the storm continue to drag cool Canadian air over our area.
Showers midweek should turn to more persistent precipitation as the relatively warm Pacific air interacts with the cool Canadian air. The Pacific trough looks to cross our area around the end of the week when precipitation should be at its heaviest for this event.
But following closely on the heels of this southern system, another Pacific wave is forecast to cross the northern West Coast by the American GFS, again increasing precipitation for next weekend and lasting into the next workweek. The European ECMWF has a brief ridge crossing over our area before bringing a different wave across our area later in the weekend, so there is uncertainty for then. But in either case, drier weather will return only briefly as more Pacific energy crashes into the West Coast around May Day.
Evolving numerical guidance now includes the possibility of heavy snow Thursday into Friday
Wednesday, April 15, 2015
As discussed in yesterday’s forecast blog, model guidance has since evolved and we now have the possibility of heavy snows tomorrow afternoon extending into Friday. The American GFS has finally joined the other models in forecasting a consolidated circulation center that is currently spinning to our west. Furthermore, all models are now forecasting a more northward track of the cutoff low across Colorado which greatly increases our chance for significant snow.
The cutoff low is forecast to move southward along the Colorado - Utah border before being nudged eastward by the kicker wave mentioned yesterday approaching the West Coast. Even though the flow aloft will turn easterly for our area, this normally dry scenario can sometimes produce impressive snowfall when a TROWAL (TROugh of Warm air ALoft) develops. A TROWAL develops when warm and moist air is lifted ahead of the storm and rotates counter-clockwise around the parent low. The lifting of this elevated unstable layer over the cooler air near at lower elevations can create impressive precipitation rates, and it appears we may benefit from that process.
I do not have a lot of confidence in this solution since a small change to the track of the storm will change the location of this TROWAL. But the possibility exists for moderate to heavy snows from tomorrow afternoon through Friday afternoon. We may still get the 2-6” originally forecast for the hill, or we may get as much as 10-20”. Furthermore, the valley will also see significant snowfall if the wetter solution verifies.
Lastly, for those headed west for mountain biking, the slower and farther north solution offered by this morning’s model guidance would have the Grand Junction and possibly Moab areas wet through Friday, with cool conditions lasting at least through the weekend.
