Cold Front: February 22, 2017

A cold front swept through Utah yesterday evening. You can see it move north to south at the locations plotted below.

• Blue = Salt Lake Airport
• Green = Point of the Mountain
• Red = Orem
• Orange = Spanish Fork

Nearly a 30 degree drop in temperature is quite impressive for a cold front. It rain most the evening and turned to snow overnight mostly impacting Utah County

A look at the wind speed and direction:

More figures here: http://home.chpc.utah.edu/~u0553130/Brian_Blaylock/cgi-bin/ts_multistations.cgi?stn1=KSLC&stn2=FPS&stn3=UTORM&stn4=UKBKB&start=2017-02-21+08%3A38&end=2017-02-22+15%3A38&units=F

FROPA (That's short for Frontal Passage)

Watching another frontal passage this afternoon...

I'm expecting at least a 14 degree temperature drop at my house in Spanish Fork in the next 90 minutes.

Cold Front

On days like today the atmospheric sciences department cancels classes and graduate students abandon work. Students lined up against the window of the 8th floor conference room in the William Browning Building today as a massive cold front, the strongest one in years, approached. The cold front hit the University of Utah at 11:35. Temperatures dropped 20 degrees in fifteen minutes.

Notice the crane turned to the north. This is before the frontal passage with winds still strong from the south.

The crane turned south after the frontal passage.

Strong Winds

Strong winds in northern Utah this morning preceding a winter storm. Shown below is wind speed and wind gusts in mph.

Looks like the cold front and precipitation is on it's way...

Right now the Cold Front is at Dugway. Look at the drastic temperature contrast! On the east side of the front temperatures are at 10 C, warm enough to get away with a jacket. On the west side of the front in the cold air, temperatures are at 2 C, near freezing!

From the HRRR, looks like the front is expected to reach the Salt Lake Valley between 12:00 and 1:00.

Did you feel that cold front??

There was quite the cold front this evening pass us in Provo. Did you feel it? It didn't notice it get any colder, but it was windy. Playing volleyball, everyone got sand in their eyes. Just after 19:00 (7:00 PM) you can see the temperature decrease about 8 degrees and the wind suddenly shifted from a calm southeast wind to a 19 mph wind!

Weather Update

Here I am stuck on the Frontrunner after an incident causing an hour or longer delay. I'm late for class, so I'll just look at the weather and take a closer look at this cold front moving in. 

Currently, it is 61 degrees and sunny at the airport. The southerly winds have also contributed to the warm morning.
Looks like it's going to be a nice day, but don't be fooled.

An approaching cold front is expected to reach Utah this afternoon. I would expect some big changes in the weather around 3:00 PM. In the radar image below you can see the front over Nevada this morning.

Looking at the NWS point forecast for this afternoon and evening. Our high temperature of the day will be at 11:00 AM. Then, in the afternoon when we usually keep warming due to solar heating, the temperature drops steadily to evening. Looks like temperatures behind the cold front are about 25 degrees colder than it is right now. Brrrrr! Oh, and it will be pretty windy, too.

Since yesterday, the precipitation ensembles is forecasting slightly more rain and snow. The ensemble mean suggests 0.5 inches of water. There is one outlier model that thinks we'll only get a sprinkling, but I would say that case is pretty unlikely today. Many of the individual members are predicting a bit more, about 0.7 inches of water. Safer to expect a half inch of water.

It doesn't look Provo will get this much water. 

Since the cold front will bring much colder this rain will turn into snow as we approach the evening hours. By morning we could wake up to an inch or two. The thirsty mountains will sure love this spring storm.

UPDATE: April 14, 2015 2:00 PM
The cold front is at our doorstep. Look at the shift in winds between Dugway and the Salt Lake Valley. Numbers on the map are wind gusts in miles per hour. I-80 has been closed due to tipped over semi trucks.

Below is a time lapse showing the blowing dust in the valley. It looks kind of nasty out there.


Where is the dust coming from? It's from the west desert. I'm still waiting for the TERRA satellite to pass over Utah to get another look at the dust, but by the next orbit we might be socked in with clouds.

From the University of Utah, it's pretty difficult to see anything in the distance. Plus, here is a "storm selfie" of me and some of my classmates:

In the TRAX air quality measurements show unhealthy levels of PM 2.5.

The front is about to reach the University of Utah. If you thought it was dusty two hours ago (12:45 PM), look outside now (2:45 PM)!

William Browning Building 12:45 PM

William Browning Building 2:45 PM

And now we can look at the cold front passage at the airport. Yay!

The best way to classify a cold front is by cold air. In the last half hour, temperatures at the airport have dropped 20 degrees.

 Also, note that winds at the airport have shifted from the south to the west, northwest. It's incredible that winds are gusting at 65 miles per hour!

An an updated view of PM 2.5 in the valley: at the Neil Armstrong Academy concentrations are almost at 250!!! Downtown is also extremely polluted. This air is not good to breathe. 

Compare the camera image at 3:17 PM with the one at the top of this post from this morning...

Update 4:16 PM
Now with the front passage and some rain, the dust has cleared out quite a bit. Visibility has improved at the Neil Armstrong Academy.

Summer Storms and Rainbows

Summer thunderstorms are always the highlight of this time of year. We have had a lot of moisture this last week. Even though the season is turning into fall the sun is still strong enough to kick-start some afternoon thunderstorms. Yesterday's storm was exciting. I was sitting inside when all of a sudden the winds picked up around 7:00 PM (19:00). This was a gust front associated with a thunderstorm that had just passed through Payson. (Maybe someday I'll write about gust fronts). The winds settled down a little bit and we had a brief downpour of rain--about a quarter of an inch. There was some lightning and thunder, too. While this was a fun to watch, it got rather chilly very quick. You can see in the charts below that the temperature following the gust front decreased quickly--about 20 degrees in 20 minutes.

Here is a link to my weather station during this time: Link. (For current conditions click "current conditions" on the right side panel.)

Today's storm was a little calmer. There was even a beautiful rainbow in the backyard. Looking a little closer, I saw two rainbows!

(c) BKB

(b) BKB

The brightest rainbow is the "primary bow." Rainbows are caused by light being refracted and reflected in raindrops. Sunlight looks white, but it actually consists of all the wavelengths of light. When that light travels through a water droplet, the different wavelengths of light are separated. When thousands of water droplets refract the light, we see a rainbow. The inside of the primary bow is always violet. As you move outward the colors go as followed: indigo, blue, green, yellow, orange, and red on the outside.

(c) BKB

The second bow is called, (you guessed it) the "secondary bow." The colors in the secondary bow are reversed, with red on the inside and violet on the outside. This is because this bow is caused by a double reflection inside the drop. You may have notice that the colors are more faint. This is because not all the light is reflected off the water droplet. For each reflection, some light passes through and never reaches your eye. The double reflection for the secondary bow thus looses more light than a single reflection.