Colorado Snow Pack in Good Shape to Begin Snow Season

The weather pattern has been active in the mountains during portions of October into the first week of November resulting in snow pack being above normal for this time of year in every drainage.  While this is good news for ski resorts to start the season we still have a long ways to go building up the snow pack through the winter for runoff this spring.  Above is the current snow pack map for the state of Colorado and can also be found on the web at: 

https://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/co_swepctnormal_update.pdf     

Much Needed Snow For the Colorado High Country

Ski season is quickly approaching the Colorado high country as snow starts to ramp up!  The Colorado high country is currently in an active weather pattern as snow has fallen this weekend with more expected through the week as Pacific moisture brings more beneficial snowfall for the central and northern Colorado mountains.  A Winter Weather Advisory is in effect for most of the central and northern mountains until 11:00 AM Monday morning.  An upper level jet will move over northwestern Colorado and move southeast throughout the day which will bring strong westerly winds leading to blowing snow and white out conditions, especially on mountain passes.  Another 6-12” of snow is expected through Monday morning, with isolated higher amounts favoring west facing slopes.  Although tough driving conditions will persist into next week, it is good to see the Colorado high country get some much needed moisture and hopefully enough snow for ski resorts to open early!

 

Weekend Snow Totals provided by CoCoRaHS 11/2/2018 & 11/3/2018:

Walden: 4.5”

Fairplay: 5.0”

Vail: 3.5”

Granby: 2.9”

Buena Vista: 3.3”

Frisco: 3.0”

Breckenridge: 3.0”

Steamboat Springs: 2.6”

Powderhorn: 2.0”

Silverthorne: 2.0”

Crested Butte: 2.0”

 

A Scary Halloween Forecast for the Front Range of Colorado

Halloween can be notorious for bad weather here in Colorado along the I-25 corridor from Fort Collins to Pueblo.  The past few years the weather has been fairly nice but residents that have lived here awhile know all to well about how cold and snowy it can be on Halloween.  This year is shaping up to be active as the month ends with a storm system moving into Colorado on Tuesday the 30th.  This storm system will likely start out as rain for many areas outside the mountains and foothills but colder air will arrive overnight Tuesday with rain changing over to snow.  Snow is then likely into the day on Wednesday (Halloween) slowly ending form N to S as the day progresses.  As the storm clears temperatures will drop making for a frighteningly cold trick or treat forecast with snow on the ground and ice developing Wednesday evening.  Make sure you are prepared to deal with cold temperatures and slippery surfaces as you take the kiddos out trick-or-treating Wednesday evening.     

Category 5 Hurricane Willa

Hurricane Willa is located off the western coast of Mexico (~Latitude: 19.4 North, Longitude: 107.2 West). 

cone graphic

Hurricane Willa rapidly developed from a tropical storm Saturday October 20th into a category 5 hurricane Monday October 22nd with sustained winds of 160 mph.  This rapid development indicates that Hurricane Willa will have a major impact on the western coast of Mexico as it makes landfall early morning Tuesday October 23rd.  Along with strong winds, heavy rain will produce potentially life-threatening flooding and rock/mud slides along the coastal areas Tuesday into Wednesday.  As Hurricane Willa moves onto land Wednesday it will decrease quickly in intensity, but with an abundant amount of moisture, heavy rain and the threat for flash flooding will impact southern Texas Wednesday night into Thursday.  As the remnants of Hurricane Willa travel eastward, heavy rain will be expected in the northern Gulf region through the week bringing a chance for flash flooding throughout the region.  More information can be found on Hurricane Willa at the National Hurricane Center.

 

Broncos Game Day Forecast

Mid and upper level moisture is on the increase today from the SW resulting in partly to mostly cloudy skies through early afternoon then mostly cloudy to cloudy through sunset.  An area of showers over central and southwest Colorado currently will move northeastward and introduce a chance for isolated to widely scattered rain showers and possibly a weak thunderstorm later this afternoon and evening.  Best chances for rain showers/thunderstorms will be between 4-7pm although a slight chance will linger through about 9pm.  Typical rainfall amounts will be in the TR-0.10” range but if a thunderstorm is observed up to 0.25” cannot be ruled out.  Winds are a little tricky to forecast today as they may become variable in or near shower activity but overall winds expected to be from the E to SE most of this afternoon and early evening, generally under 10mph.  Higher wind gusts may be observed near storms.  Temperatures today are being held down due to the cloud cover but will spend quite a bit of time in the 60s through 6pm then mainly in the 50s through the game.  GO BRONCOS!!!   

Hurricane Florence to Make Landfall in the Carolina’s

Hurricane Florence will make landfall late tonight or early Friday morning in the Carolina’s.  Currently Florence is a Category 2 Hurricane with sustained winds of 110mph.  Storm surge and damaging winds will heavily impact coastal areas.  As Florence moves inland it will rapidly weaken but copious amounts of rain will impact the SE US initially and then as the storm takes a turn to the NE it will impact the mid Atlantic states and well as the NE US.  More about Hurricane Florence can be found on the web at the National Hurricane Center.

El Nino in Store for USA This Winter?

According to the Climate Prediction Center there is a “60% chance of El Nino in the Northern Hemisphere fall 2018 (Sept-Nov), increasing to 70% during winter 2018-2019”.  The image above shows a typical winter El Nino pattern.  The Winter El Nino pattern map and more can be found on the web at:  https://www.climate.gov/ 

Storm system bringing late August snow to Northern Rockies along with improving air quality

A hot and dry summer across a large portion of Western North America has resulted in widespread fire activity from California to Idaho to British Columbia.  Many of these fires have been very large, and over the past month smoke has been persistent across much of the West.  However, the seasons are beginning to change as we near the end of August, and there are some clear signs that fall is right around the corner.

In general, the Western U.S has already been experiencing cooler temperatures over the past 1-2 weeks compared to a hot first half of August west of the Continental Divide.  Today, a more substantial change is occurring as a deep trough of low pressure is pushing into the Northern Rockies, resulting in unseasonably cool temperatures along with much needed moisture.  The image below shows the height anomalies at the upper levels of the atmosphere, which depict this fall-like system well over Montana and Wyoming (source: weathermodels.com).

 

 

Even though the calendar says late August, this system has a wintery side as well, and snow is falling at the higher elevations of the Northern Rockies, including Grand Teton, Yellowstone, and Glacier National Parks.  The webcam image below shows fresh snow near the top of Jackson Hole Ski Area in Wyoming.

 

 

The moisture, cold temperatures, and snow with this system should help out with the wildfire the smoke situation.  While this system won’t totally extinguish wildfires in the Northern Rockies, it will certainly help to reduce fire behavior, and most areas should see significant improvement with regards to smoke and air quality this week as a result.  The exceptions will be in areas such as California and Nevada, which are missing out on the moisture.

Farther south, Colorado is on the dry side of the trough and jet stream today, and as a result hot, dry, and windy conditions are present across the Front Range instead.  The fire danger is elevated here today as a result, but fortunately a cold front will arrive tonight with much cooler temperatures on Tuesday.  Some parts of Colorado could see some light showers on Tuesday, but in general the state will be missing out on significant moisture with this system.  Upslope flow pooling east of the Continental Divide could bring some more smoke to the Front Range on Tuesday, but then improvements are expected for the remainder of the week.

Severe Weather & Northwest Flow

Warm and dry conditions returned to the Front Range Tuesday,  following an active period of severe weather last week and weekend. Several tornadoes touched down over eastern Colorado, along with numerous reports of large hail and heavy rainfall. 

Photo courtesy of 9News

This photo shows a UPS truck damaged by a tornado near Byers last Friday. The driver of the truck was reportedly taken to an area hospital, but luckily did not sustain major injuries. 

Severe weather can strike Colorado’s Front Range any time during the spring, summer, and fall periods. According to NOAA’s Storm Prediction Center (SPC), Denver’s severe weather season spans May 3rd-September 5th. Severe weather occurrences typically peak during the second-half of May through the first-half of June. 

Although thunderstorms are a relatively-small, short-lived, and local phenomenon, large-scale weather patterns certainly contribute to a higher likelihood of severe storm occurrence. Last week/weekend’s storms were largely the result of high pressure positioned W of Colorado, and an upper-level disturbance arriving under northwest flow.

The synoptic pattern depicted above can be a classic setup for severe weather outbreaks over the northern and central plains. So, what is it about northwest flow that stirs the atmosphere so convincingly? 

Instability

Instability is at the core of any discussion concerning thunderstorms, severe weather, or even cloud formation. Very simply, stability is the resistance of an air parcel to rise vertically into the atmosphere. Under favorable conditions, vertically-rising air expands, cools, and condenses into clouds, thunderstorms, and eventually precipitation. However, stability can vary significantly in the atmosphere. 

We know that warm air rises.

During the warm season, the air at the surface is typically warmer than the air above it. This is why we see more surface-based convection and thunderstorms this time of year. Warmer temperatures also yield higher moisture levels, which further contributes to storm development. The vertical profile of the atmosphere (temperature and moisture) dictates instability on any given day. Sometimes, there is resistance to rising air which can suppress storm formation. A good example of this would be a layer of warm air aloft, or a temperature inversion at the surface or mid-levels. 

Similarly, unusually-cold air above the surface can increase instability, leading to faster ascent, expansion, and condensation. 

Colder air aloft typically accompanies atmospheric disturbances – like centers of low pressure, troughs, and shortwave troughs. These upper-air disturbances are an effort to equalize differential heating from the equator to the poles. Some disturbances are stronger and colder than others. Disturbances arriving from the north or northwest typically feature colder air aloft, which can contribute to higher instability at the surface. 

Image result for unstable atmosphere

Figure courtesy of North Carolina Climate Office, NCSU

In the case of last weekend, an upper-level trough dropped out of the Northern Rockies into Colorado, which helped destabilize the vertical profile of the atmosphere. Furthermore, colder, sub-freezing air closer to the surface also helped contribute to hail growth in the thunderstorms that did form. 

Wind Shear

The second ingredient accompanying northwest flow is enhanced vertical wind shear. Vertical wind shear is either defined by a turning in wind direction with height (directional shear), or a change in wind speed with height (speed shear). Both are important considerations for severe thunderstorm development.

Directional wind shear can be common with upper-level disturbances, especially with moist SE surface winds in place. With the arrival of the disturbance from the northwest, the result is a clockwise-turning of wind direction with height – known as “veering.” In contrast, counterclockwise-turning of wind with height is known as “backing.”

Figure courtesy of Learn Weather

Directional shear helps thunderstorm cells develop a rotating updraft, which is the first stage in formation of a mesocyclone and eventual funnel cloud or tornado. Severe thunderstorms can develop in the absence of directional shear, but true tornadoes are not possible without this detail. 

Speed shear is of equal importance for severe thunderstorm formation. Increasing wind speed with height can produce a tilted updraft. This detail effectively keeps different parts of the thunderstorm separate  – e.g. the updraft vs. the downdraft. This allows for stronger, longer-lived, inflow-dominant thunderstorms that can mature to supercell status. 

Image result for directional wind shear

Image courtesy of the National Weather Service 

Inflow-dominant thunderstorms with strong, tilted updrafts will produce the largest hail. These storms also have the best chance of persisting for long periods of time and impacting large areas. 

In the case of last week, vertical speed shear was strong over Colorado due to a passing upper-level wind maximum (jet streak). The result was long-lived, severe thunderstorms over a wide swath of the northern and central plains. 

Enhanced instability and wind shear can push garden-variety storm cells into severe, supercellular status. The result can be impressive, destructive, and downright scary weather phenomenon.

Severe weather can result from a variety of large-scale weather patterns, and we didn’t discuss other required factors for strong thunderstorm formation – e.g. lifting/trigger mechanisms and moisture. However, northwest flow can simultaneously put several favorable-ingredients on the table, quickly increasing the threat for high-impact severe weather along the Front Range.  

Monsoon pattern brings heavy rain, flash flooding to Arizona and Utah

In our last blog post, we discussed the start of the monsoon season across the Southwest U.S.  Over the past week, this pattern has brought a significant increase in moisture to the canyon regions of Arizona and Utah, and as a result significant rainfall to many areas.  Much of the drought-stricken region has experienced above-average rainfall over the past 7 days, as evidenced in the map below.  Farther north into the Wasatch of Utah, and farther east into Colorado, rainfall has been less impressive.

 

 

While moisture in general is welcome news to the Southwest right now, as is often the case with monsoon season rainfall, too much rain in a short amount of time also causes problems.  Flash flooding has become a common occurrence with thunderstorms in recent days, and on Thursday July 12, a major flash flood occurred at a popular backcountry destination – Havasupai Falls in Grand Canyon National Park.  Backpackers who had hiked down to the popular falls noticed the turquoise waters began to turn muddy, and shortly thereafter, water levels quickly rose.  The many hikers in the vicinity were forced to quickly scramble up the hillsides to escape the rising torrent.  A total of 200 people ended up being rescued by helicopter from this area, but fortunately no injuries or fatalities occurred.

In Utah, a recent burn scar from the Black Mountain Fire that occurred earlier this summer received heavy rainfall and significant runoff and flooding late this past week.  Burn scars are highly susceptible to flash flooding and mudslides since the recently burnt soil can’t absorb much water.  Portions of Zion National Park and surrounding areas also received heavy rainfall and flooding that forced road and trail closures and home evacuations.  The heavy rains extended farther west into Nevada as well, with portions of the Las Vegas metro area receiving heavy rain and flash flooding.