Severe Weather Possible

The same storm system dropping temperatures 30 to 50 degrees in the center of the nation and bringing all the wind will potentially bring a round of severe weather too.

The greatest risk today is from the southern Mississippi River Valley north into the Great Lakes region. (Louisiana to Indiana/Ohio)

Some storms could produce tornadoes -- there is a lot of wind shear, or winds changing direction and speed with height -- across the center of the nation -- and this is a main ingredient that forecasters look for to get thunderstorms rotating.

Windy Week Ahead

It will be a windy week for much of the nation as a storm system moves across the country and drops temperatures up to 50 degrees.

The weekend featured quite the mini-warmup and preview to spring. Here in Denver we topped out in the 60s on Sunday.

The frozen upper midwest saw highs climb into the 40s, such as in North Dakota and Minnesota.

By Tuesday, some of those locations will see highs stay below zero!

So what does this huge contrast in temperature mean? A sharp pressure gradient, or large difference of air pressure over a relatively short distance -- and that translates into WIND!

It will be a very windy week for most locations east of the Rockies. I was rocked out of bed this morning here in the southeast metro Denver area by winds so strong the doggie door was almost 90 degrees to the wall, and the big area rug under my kitchen table was folded over.

I checked the closest automated weather observations to where I live and gusts were around 45 mph at the time.

I suspect that initial burst of wind was closer to 60 mph when I jumped out of bed -- honestly, I was afraid the bay window was going to shatter -- and there loose dirt that was hammered against it was incredible.


Winds may not be that bad where you live this week, but let's just say it may not be the smoothest week for flying or driving high profile vehicles -- white knuckled driving or flying as I like to call it.

Misc. Weather Info

Let me attempt to answer a few comments from my post on Wednesday.

Someone was asking about the various temperature scales (C and F). Click this link to learn more.

There is a very detailed history of how these scales were defined.

The other comment was about the math from the 1938 Winter Storm in upper Michigan -- and how the new snow that fell didn't match up with the difference between the pre-storm and post-storm snowpack.

I agree a few look suspect -- but one thing did stand out in my mind as I read it. The snow was described as very heavy and wet -- so there was likely a lot of settling and compacting.

We had a snow like that here in Denver a few years ago. I recorded 42 inches of snow at my place but it barely piled up to 2 feet during the storm because it was so loaded with water. The snow was almost like a wet cement.

In fact -- as crazy as this sounds -- the weight of the snow was squeezing the water out of the snow below it. When you stood back and looked at the snow, the bottom half of the snowpack had an aqua blue tint to it.

That was the storm that dropped almost 5 inches of water on the Front Range and filled up some lakes that were nearly dry after the drought of the early 2000s.

SO -- if that is how that snow was in 1938, then I can see how the snow never really "piled up" like one would think.

When Does The Low Temperature Usually Occur?

Hello -- it is Chris -- back from sunny and very warm south Florida. A cold front did go through on Sunday and man was it windy down there. I have never seen such constant wind. Sustained 20-30 for 2 days.

I can only imagine what a full blown tropical storm or hurricane must be like. Even with just 20-30 mph winds there was some costal flooding and beach erosion, as well as downed trees and debris.

The pool cushions on the chairs around the pool at the resort were all over, one was on the bottom of the pool!

While I was away, a few people left comments talking about the coldest part of the day -- and how they have observed it is often just after sunrise.

Assuming it is just a normal day with normal weather, no cold fronts, extremely windy situations, etc. then the maximum cooling typically takes place at or after sunrise.

Even though the sun may have risen over the horizon, it takes a while for the sun's rays to overcome the radiational cooling that took place all night -- so despite the sunrise, the temperature continues to fall.

Once the sun's rays are strong enough, and overcomes the escape of heat from the Earth back out into space, the temperature reverses and begins to rise.

Winter Hits The Southeast

Some folks are waking up to snow and/or ice this morning in Georgia, the Carolinas, east Tennessee and the Virginias.

Hey -- it doesn't matter what form the precipitation comes in across these parts of the country -- they need every last drop.

Unfortunately it will mean tough travel for many who aren't used to winter driving. My best advice is stay home unless you really have to go out.

I saw one headline where a family was killed in Georgia after skidding off icy roads and into a lake.

That work on your desk will be there tomorrow or the next day so stay home and enjoy your family if at all possible.

Some major airport hubs are located in Atlanta and Charlotte, so flights on Delta and USAirways may be tough today nationwide due to the ice and snow.

Speaking of flying, I am off to south Florida for a work meeting. I will not be on a computer until I get back to Denver early next week -- that means no blogging I am afraid.

I could take my laptop, but you know -- with working two jobs 5 days a week, I am going to enjoy the non-meeting hours of this trip and lay around on the beach listening to the ocean.

By the way, I often hear from several of our CoCoRaHS observers who read the blog. I know some days my entries are rushed and dry, and then there are times I get inspired and produce a mini-meteorology lesson.

By all means if you have a question about CoCoRaHS, weather, etc. let me know. It really is great to hear from you... and your thoughts and questions inspire my blogging.

Speaking of that, here is a thought. My co-worker in the San Francisco Bay area called me today and said where she was located it was windy as all get out. And just a few dozen miles down the road where her husband was located it was completely calm and sunny.

She wondered why.

Tough question -- I first told her that wind is produced by a difference in air pressure -- and that if they both had a barometer handy, I am sure there would be different readings from the two locations.

I then asked about the terrain -- is one location closer to mountains, the ocean, in a canyon, etc.

Weather is so cool -- it can be like night and day just a few miles apart, esp. in the western part of the country.

Back east it is a little more uniform because there isn't quite the diversity in landforms and elevation as in the west.

Where I live in the southeast Denver metro, on nights when it has been warm and dry, we get incredible wind gusts between about 9pm and midnight -- this happens almost every night in the warm season.

These winds are called drainage winds -- and they blow off the Palmer Divide toward the lower terrain in Denver.

In the daytime the sun keeps the atmosphere mixed -- but at night, the radiational cooling of the surface takes over -- and as the air becomes heavy and dense, it flows downhill.

These winds are cool and dry.

Arctic Express -- All Aboard

Rather you want to or not, many reading this blog will be taking a ride on the Arctic Express this week.

In Meteorology, there are so many descriptive sayings for various weather patterns. One is the Arctic Express -- often used when the jet stream flows straight from northwest Canada and Alaska right into the heart of the lower 48 states.

This upper level wind pattern typically brings bitterly cold air to the states. The pattern is most common during winter.

Another "express" we sometimes see is the Pineapple Express. This is when a long fetch of moisture stretches from Hawaii right into the west coast of the United States.

Since the moisture has origins in Hawaii, it is nicknamed the Pineapple Express.

Winter Blast Ahead

Just a few blogs ago I talked about watching Alaska for cold air building up -- well it is on the move and much of the eastern U.S. will see some of the coldest air of the season this week.

In parts of the Upper Midwest, it will be bitterly cold, with highs and lows staying below zero for a few days.

Even the south is expecting a cool down. Rain and snow is in the forecast for the lower Mississippi River Valley by Thursday.

I am hoping it doesn't make it all the way to south Florida because I leave on Friday for a company meeting in Boca Raton!

Interesting Sunspot Info

I just ran across this article about a new solar cycle that could impact communications at times over the next 11 years. It was interesting to read.

For those who didn't realize this, forecasts like this come from Space Weather Prediction Center, located in Boulder, Colorado.

I have visited it a number of times -- a REALLY cool place to go.

Record January Tornadoes

What a month it has been for tornadoes in our country. It's not rare to see severe storms this month, or even tornadoes, in portions of the south. What is rare is to see the outbreak we saw that extended up and down the Mississippi River Valley, from Illinois and Wisconsin south into Arkansas and Mississippi.

There have been at least 3 tornadoes classified EF3 over the past week, one in Missouri, one in Illinois and one in Wisconsin.

Missouri and Mississippi have been the hardest hit in terms of the number of twisters.

Let's hope this was just a freak event and not a sign of the spring season that lies ahead.

Keeping An Eye on Alaska

This is the time of year when forecasters must keep an eye on Alaska.

A large dome of cold arctic air has been building up there for several days now. Highs from Fairbanks to Barrow, and across the Yukon Territories, have been running around 25 below with overnight lows 40 below zero.

Heading into next week these locations will be warming up a bit, with highs closer to 5 below and lows around 20 below.

So where is that arctic air moving?

Some long range models show the upper air patterns opening up so that very cold air spills right down the spine of the Rocky Mountains and into the eastern United States.

Now if this happens, it will definitely modify as it moves south -- but nevertheless -- a big cool down may be in store for the eastern half of the nation next week.

Stay tuned to your local forecasters!

Wild January Weather Brings Deadly Tornadoes

The wild weather continues -- with an outbreak of tornadoes from southeast Wisconsin to northwest Arkansas on Monday.

It was only the second time a tornado has even been documented in the state of Illinois during the month of January.

Hardest hit was the state of Missouri where several injuries and a few fatalities were reported in the southwest part of the state near Springfield. (Webster and Greene Counties)

In the western Great Lakes states, fog is the big story. All this warm air moving over fairly deep snowpack is making for widespread dense fog from Duluth to Des Moines and Milwaukee to Madison.

Our friends in the northeast are almost ready to head to the beach -- literally! Highs are well into the 60s across southern New England. This time of the year they should be in the 30s to near 40 degrees at best.

As I blog the Storms Prediction Center has just issued a tornado watch for most of Arkansas as another round of severe weather gets underway. There are some warnings out just to the northwest of Little Rock where my family resides so I am going to get them called and make sure they are keeping an eye to the sky.

Unfortunately the weather bug that bit me didn't bite them -- except for my grandma. She and I spent hours each day watching the weather channel when I was a kid.

Now that she is retired sometimes she sleeps in -- so I want to just make sure they are abreast of the situation today given what we saw happen on Monday.

January 2008 Full of Extremes

CoCoRaHS observer Ken Watters sent me this picture from his station near Gardnerville, Nevada.

He is one of the stations that saw over 4 inches of precipitation from the monster western storm this past weekend. He told me in the entire calendar year of 2007 his town barely saw over 3 inches of moisture.

The western storm will go down into the record books for many reasons. A widespread 2 to 4 inches of rain fell in the San Francisco and Los Angeles regions. That is nearly the normal precipitation expected during the entire month of January from one storm.

Incredible hurricane force winds also were reported. A gust of 70 mph was recorded on the Golden Gate Bridge.

In the Sierra Mountains, winds topped 100 mph on the highest peaks, and snow totals ranged from 90 to 135 inches in several locations.

On the flip side, the eastern US is feeling more like April! Over 3 dozens record highs were set from the Gulf Coast to the Great Lakes on Sunday.

And on Monday morning, a very rare event was taking place in Wisconsin and Michigan -- thunderstorms! It is VERY rare to get thunderstorms this time of year in those states.

On Sunday, a massive and deadly car accident took place on the Interstate just outside of Madison, Wisconsin due to fog.

Today, anticipate some severe weather in my home state of Arkansas, as well as in the rest of the lower Mississippi River Valley.

What A Snow Forecast!!

What would you do if you saw the following...

Friday -- Rain and snow. Snow accumulation up to 32 inches. Strong winds. Gusts up to 130 mph over the crest.

Friday Night -- Rain and snow. Snow accumulation up to 40 inches. Strong winds. Gusts up to 115 mph over the crest.

Saturday -- Rain and snow. Snow accumulation up to 18 inches. Very windy.

Well this really exists -- at least it did when I posted this blog. The location? Yosemite National Park in California.

The coastal storm is moving in and the state of California is about to be hammered with high winds, heavy rain at lower elevations and heavy snow in the mountains.

I thought this was pretty neat and wanted to share it. I hope people there take the forecast seriously -- that isn't any kind of weather to be out and about in the parks and high country hiking or skiing.

This large storm will move slowly eastward, bringing unsettled weather to the middle of the country early next week.

Even our western mountains here in Colorado are already under winter storm watches.

Historic Snow For The Sierra Mountain Range

A HUGE storm system will slam the west coast over the next few days, bringing very heavy rain to lower elevations and paralyzing snow to the mountains of California.

I was checking out one model and it gave over 5 inches of rain to the San Francisco Bay area this weekend with up to 5 feet of snow in the mountains around Lake Tahoe.

That will combine with a 150 knot jet stream overhead, and that means wind gusts up to 100 mph in the mountains and up to 50 mph along the coast.

This storm system will impact the entire state of California, but northern Cali. will see some of the heaviest precipitation.

You can definitely expect to see this storm making weather headlines as we head into the weekend.

Not All Maps Active This Week

Oregon and Nevada will be two of the most active CoCoRaHS states the rest of this week and over the upcoming weekend as they prepare for several days of valley rain and mountain snow.

Keep in mind that this is their rainy season so nothing too unusual.

If you are traveling west, anticipate potential weather delays at times, especially into Seattle, Portland and San Francisco due to low clouds, fog and rain.

Meanwhile, people from northeast Colorado to Wisconsin can anticipate a warming trend over the new few days. This morning many spots started the day below zero in these states.

It was a real chiller all the way down into Dixie this morning with several of our Alabama observers making note of how cold it was in their comments. Some teens reported near Albertville, Alabama!

The station near Mims, Florida reported the first freeze since March 6, 2007 this morning along with cartop frost.

Temps fell into the upper 30s and lower 40s as far south as Tampa, Orlando and Palm Beach County.

U.S. Snow Cover

Well Happy New Year -- it is 2008. The first of a new year can be an exciting time. It is a fresh start for any and all situations. I wish you the best of the best this year.

On to the weather...

Click this link and it will bring up the National Operational Hydrologic Remote Sensing Center (NOHRSC).

Scroll down just a little bit and you will see several thumbnails. Look at the middle one on the top row called Snow Depth. Click it to view larger in a new window.

Just look at how much of the country is covered in snow!! The deepest snow outside of the mountains of the west is across northern New England and around Lake Superior.

Despite all the numerical weather forecast models out there, a forecaster must take information like this into account when making a temperature forecast.

For instance -- the ETA/NAM model has Denver with a high of 53 degrees on Wednesday, Jan 2.

We are projected to have a south/southwest wind so I can definitely believe warmer air will be advecting into the state -- but with that large of a snowfield on the ground across the region, I doubt we will hit the 50s.

A large portions of the sun's energy will be used by the snowpack to melt versus warming the air that much.

Now if we didn't have snow on the ground -- then yes, we could hit the lower 50s.

As you can see, there is a lot of things to consider for something as simple as making a temperature forecast.

On the flip side, it works the opposite for overnight lows. One model may be predicting 4 degrees for a low -- but if a location had clear skies, no wind and a large, deep snowpack -- the actual overnight low could easily drop 5 to 10 degrees lower than the model predicts.

A beauty of technology is we can see from space just how much snow is out there, the amount of real estate it covers -- and therefore, take it into account as we forecast high and low temperatures.

If a forecaster is really on his game and knows local variability, then even better. A good example is a town here in Colorado called Greeley, just a county away to the northeast of Denver. In some respects, it could be considered a distant suburb.

Last week we had some very cold air move into the state. Cold air is heavy and dense -- and the weather station in Greeley happens to sit in the South Platte River Valley.

As with most winter mornings in the Front Range, we woke up to an atmospheric inversion -- that is where the temperature actually warms with height as you go up from the surface.

So the inversion trapped that cold air down in the river valley -- and let them cool much more than nearby locations just up from the river.

So on a weather map -- it looked like a mistake that Denver and locations in northeast Colorado were in the single digits above zero for overnight lows and Greeley was 18 degrees below zero. By that afternoon, most locations were in the upper teens and lower 20s and Greeley had only struggled to 3 above zero.

It is that small detail of forecasting and knowing your area that makes a meteorologist shine.