Weather turning unsettled mid-week ahead of next storm
Monday, November 18, 2013
A weak wave traverses our state on late Tuesday into Wednesday leading to some showers producing only a few inches on the hill and light rain in the valleys.
A strong wave entering the west coast on Wednesday splits, with the southern portion forming a cutoff low moving southward along the coast while the northern portion moves along the US border with Canada.
By Thursday, cold air from the northern wave will be over our area as energy begins to eject to the northeast from the cutoff low now forecast to be just off the coast of southern California. The interaction of this ejecting energy and the cold air from the north could create significant snows lasting into Friday.
Current forecasts have a nice but chilly weekend for northern Colorado as the cutoff low moves across the desert southwest. These cutoffs are notoriously difficult to forecast as their movement depends upon upstream energy that is difficult to measure in the data sparse Pacific. If the cutoff low moves further north than forecast, the nice weekend forecast may be in jeopardy.
There is a lot of cold air lurking to our north after next weekend, and some models want to build a ridge over the Gulf of Alaska which will shunt this cold air over our region. Timing is uncertain, but confidence is growing that an active wet and cold storm track will grace our area around the end of the month.
More snow starting mid-week
Sunday, November 17, 2013
Showers may continue for most of the day on the hill while the valleys should clear this afternoon.
Temperature will warm significantly on Monday and stay warm for at least Tuesday. A weak wave traverses our state on late Tuesday into Wednesday leading to some showers producing only a few inches on the hill and light rain in the valleys, although model runs are trending a bit stronger with this disturbance.
It appears model differences have been resolved for the storm later in the week as the American GFS model has trended strongly towards the European ECMWF model. A strong wave entering the west coast on Wednesday splits, with the southern portion forming a cutoff low moving southward along the coast while the northern portion moves along the US border with Canada. By Thursday, some of this cold air from the northern wave will be over our area as energy begins to eject from the cutoff low now forecast to be just off the coast of southern California.
Some models forecast significant precipitation form this interaction for Thursday and most of Friday, before skies clear by the weekend. There is uncertainty with regards to how much energy is split between the northern and southern streams, so the forecast is subject to change.
More snow tonight before warming and drying early next week
Saturday, November 16, 2013
Snow continues this afternoon between the two waves before the main cold front arrives around sunset, Sharply colder temperatures and a burst of heavy snow is likely with snow continuing through the night as cold and moist northwest flow traverses the region. Likely an additional 6-12” or more by Sunday morning on the hill, with showers tapering off during the morning and ending by the afternoon as the cold air mass stabilizes.
Temperature will warm significantly on Monday and stay warm for at least Tuesday. A very weak wave traverses the northern part of our state on Wednesday leading to clouds and possibly some showers in seasonably warm air.
A stronger group of wave moves across the area around beginning Thursday afternoon and continuing through the day Friday. The European model has in the past few model runs split the jet stream which would weaken the storms in our area as most of the energy is forecast south of us, while the American model still brings these waves across in a coherent manner. Stay tuned as model differences are resolved in later forecasts.
Two waves to produce significant precipitation by Sunday afternoon
Friday, November 15, 2013
Rain in the valleys and snow on the hill should begin by this afternoon as temperatures start to gradually cool. Probably 2-4” around mid-mountain by Saturday morning.
There may be a smal break earlier Saturday before the main event begins to affect our area by later in the day. Sharply colder air and a burst of heavy snow should cross the area around sunset, with snow continuing through the night as cold northwest flow engulfs the region. Likely an additional 6-12” by Sunday morning on the hill, with showers tapering off during the morning and ending by the afternoon as the cold air mass stabilizes.
Temperature will warm significantly on Monday and stay warm through mid-week. A very weak wave traverses the northern part of our state on Wednesday leading to clouds and possibly some showers in seasonably warm air.
A stronger group of wave moves across the area around beginning Thursday afternoon and continuing through the day Friday. This may produce significant precipitation as winds are forecast to turn to the northwest while cooling, though earlier model runs had this wave more split, so the forecast will evolve.
Significant precipitation still on track for the weekend
Wednesday, November 13, 2013
A weak wave moving over our area tonight will produce some slight cooling and possibly light precipitation by the morning. A second wave now looks to impact our area by later Friday followed by a much stronger and colder third wave Saturday night.
While all models predict some precipitation by Saturday morning, subtle differences between them create uncertainty for our area. Specifically, 1-3” is expected on the hill by Saturday morning unless the winds turn northwest behind the first wave, in which case I would expect 3-6”.
A front stalls over our area between these two waves leading to cool and showery precipitation early in the day Saturday. As the trough to our west begins to move eastward, the stalled front will begin moving south around sunset, increasing precipitation and decreasing temperatures during late afternoon and continuing through the night.
I would expect this thrid wave to bring significant precipitation by Sunday morning. The trough is expected to bring favorable mountain-top northwest flow to our area by early Sunday, enhancing snowfall rates, especially near sunrise. The storm will grow colder as it evolves from Saturday night through Sunday afternoon, so snow densities will be decreasing, increasing the snow quality. I would guess a very tentative 6-12” or more by Sunday afternoon on the hill.
Monday morning will be dry but seasonably cold, with rapidly warming conditions by Tuesday and Wednesday.
Another dry and weak storm is currently forecast later around midweek, and possibly some interesting weather by next weekend as cold air is predicted to be lurking just to our north.
