Wunderground Meteorologist Shaun Tanner

Second Round Of Wet Weather Set For West Coast

By: shauntanner, 6:42 AM GMT on November 29, 2012

The first storm in a parade of storms made its way through Northern California Wednesday. As expected, the storm brought areas of heavy rain and widespread moderate rain mainly north of the San Francisco Bay Area. Here are some Wednesday rainfall amounts for the hills north of San Francisco. These areas are normally the wettest for storms like what was experienced on Wednesday.

SONOMA COUNTY AIRPORT............. 1.27
SANTA ROSA........................ 1.14
VNOC1 VENADO 1260`................ 2.00
HWKC1 HAWKEYE RAWS 2024`.......... 1.54

NAPA COUNTY AIRPORT............... 0.70
MSHC1 MOUNT ST HELENA 4140`....... 1.73
NAPC1 ATLAS PEAK 1680`............ 0.64

In addition, here are Wednesday rainfall amounts for counties farther to the north such as Mendocino, Del Norte, and Humboldt.

ELK VALLEY (1705 FT)(COOP) 0.20 IN

1 SW HONEYDEW (370 FT)(COOP) 2.80 IN
WILLOW CRK 1 NW (464 FT)(COOP) 1.78 IN
4 SE MIRANDA (266 FT)(COOP) 1.00 IN

FORT BRAGG 5 N (123 FT)(COOP) 1.38 IN
LEGGETT (703 FT)(COOP) 1.24 IN

Now, I know what you are thinking. When you look at those rainfall numbers, they don't seem all that impressive. There is a lesson that can be learned from looking at these rainfall amounts. When a parade of storms like what the West Coast is experiencing sets up, the first of these storms often ends up being weaker than what the models had predicted. Arguably, this case could be made for the storm that moved through Northern California Wednesday. But, this shouldn't be the lesson for the rest of the parade. Often, this first storm primes the atmosphere with moisture that the subsequent storms could utilize bring very heavy rain to the state. This appears to be the case for the next two storms.

Second Storm Poised To Strike

A second storm out in the Pacific Ocean is set to move gradually closer to the coast Thursday, but California will largely experience a brief break from the wet conditions for much of Thursday. The second storm will be stronger than the first, washing onto the north coast of California in the afternoon and evening.

The severe weather map paints a story of what to expect in California.

Winter Weather Warnings are posted for the western slopes of the Sierra Nevadas as as much as 30 inches of snow is expected to fall to Friday afternoon for elevations higher than 6,000 feet. This is a fairly high elevation for snow level for the Sierras for a storm during this time of year.

Also, Flood Watches are posted for some rivers in Northern California. One of these rivers is the Navarro River, which currently has a stage of 2.9 feet. Here is what is impressive. The flood stage for the Navarro River at Navarro is 23.0 feet. That means that it is currently 20 FEET below flood stage, yet the NWS has determined that it is prudent to issue a Flood Watch for the river. Further, flood stage may be reached by Friday morning and the river could hit 26 feet by midday Friday. So between Thursday morning and Friday afternoon, the river is expected to rise as much as 23 feet. That is a tremendous amount of water.

This is the HPC precipitation forecast for the second storm. You can see a bulls eye of rain along the western slopes of the Sierras. The third storm over weekend is expected to be even stronger.

Winter Weather Flood


Storm Door Opens In Western U.S.

By: shauntanner, 6:46 AM GMT on November 28, 2012

I have been watching models for the past week or so in disbelief as both the GFS and ECMWF have both been consistently predicting a very wet period for the West Coast. Perhaps this disbelief is the reason I am writing this blog so close to the beginning of the wet period.

It has been quite some time since the West Coast has seen rain like what is expected for the next several days, so let's break down what is to be expected.

The first storm will slam into the coast Wednesday, lasting into Thursday. This storm will likely be the weakest in the series, which is a testament to how intense these storms will be. This is because nearly 2 inches of rain is possible in the wettest areas in Northern California, as noted in the precipitation forecast for Wednesday through Thursday morning.

The good people at the NWS have also posted various watches and warnings mostly in California in anticipation of this precipitation. Wind Advisories are posted for parts of the Northern California as southeast winds will gust to 40 mph. Winter Weather Advisories are also posted for the western slopes of the Sierra Nevadas, but snow levels will be a relatively high 6,000 feet. In fact, this will be a theme for this wet period as these storms will be rather warm in nature. So while the rain is certainly a blessing for dry areas of California that are in the brink a more serious drought (see below), it would have been great is some more of this precipitation would fall as snow. Not only would this help the water supply, it would also help the skiing industry in the Sierra Nevadas that has suffered greatly over the past 12 months.

The next storm to slam into the coast will arrive Thursday and last through much of Friday. This storm will be considerably wetter, as the first storm will do a great job in priming the atmosphere. The wettest areas (see below) could see over 7 inches of rain. This will be on top of the rain that has already arrived on Wednesday.

This is just the first two storms. Needless to say, the West Coast will be rather wet and wild through the first week of December. There are some interesting notes I want to bring to your attention.

First, if you look at the 5 day precipitation forecast from Wednesday through Sunday, you will see that there is a bulls eye of rain expected for Northern California. The storm track has consistently pointed directly at the California coast north of the San Francisco Bay Area. It is safe to say that if nearly 11 inches of rain fall on this area over the next 5 days, there will be some flooding issues for the mountainous areas of Northern California. The good news is that the streams in the area are fairly low at this time of year.

Second, one of the reasons I have been in disbelief at the amount of rain expected from this parade of storms is that a significant amount of subtropical moisture is needed. For these types of storms, the subtropical moisture can usually be seen on satellite as a thick line of clouds that extends from near Hawaii and is pointed directly at the West Coast. When this type of pattern sets up, California can receive days upon days of heavy rain. This is often called the "Pineapple Express", or more scientifically, the "Atmospheric River". If you are interested in watching this atmospheric river set up, watch the satellite on WunderMap.

Third, while the heavy rain from these storms is expected through the weekend, I still question slightly the actual location of the heavy rain. Certainly, the heaviest rain is likely in the hills of Northern California, but any southward movement of this deep moisture could bring the bulls eye closer to the San Francisco Bay Area. However, a more northward track would bring significantly less rainfall to San Francisco. This is only worth a mention at this point.

Winter Weather Flood


What Is An Average Thanksgiving?

By: shauntanner, 5:33 AM GMT on November 22, 2012

When you think of an "average Thanksgiving", images of a typical America Holiday may spring to mind. Moist turkey, gross cranberry sauce (sorry, not my favorite), and yelling relatives. Mmmmm, the yelling relatives.

However, being a meteorologist, when I think of the average Thanksgiving, temperatures spring to mind. Using Weather Underground's extensive historical archive, I have managed to bring back the temperature record for each Thanksgiving from 1950 to present. I have managed to give two numbers for each Thanksgiving...average national high temperature and average national low temperature. Granted, these numbers are not scientific for a number of reasons (the observation density has increased over the years, how valuable is an average national temp, etc...), but they are still fun to look at...especially after a hefty Thanksgiving dinner.

The dark blue line is the average national high temperature for each Thanksgiving, while the pink line is the average national low temperature.

There are a couple notes that jumped out at me when I looked at this graph for the first time. First, there was a definite period of cool Thanksgivings from about 1976-1990. These cooler Thanksgivings were bookended by periods of warm Thanksgivings.

By this measure, the warmest Thanksgiving since 1950 was November 26, 1998. This year had a national average high of 61 degrees. The warmest temperature on that day occurred in Santee, CA when the Southern Californian city hit 87 degrees. Just to round it out, the coldest maximum temperature on that day was on top of Mt. Washington, NH at 24 degrees.

What was the "coldest" Thanksgiving over the past 60+ years? Well, there is actually a tie. 1993 and 2002 tied with an average low of 25 degrees. If you dig even deeper into these two Thanksgivings, an interesting pattern emerges. In 1993, over 70 cities reported a low temperature below 0 degrees. The coldest of these temperatures was recored in Laramie, WY when the city hit -25 degrees. Initially, I expected the 2002 dataset to mirror this cold outbreak with a smililar number of cities below 0 degrees. However, only two weather stations reported sub-zero temperatures (Mt. Washington at -11 degrees, Saranac Lake, NY at -9 degrees).

Now, normally it would take a huge task to compare the temperatures regionally between these two years. But, Weather Underground has just made that difficult task extremely easy. GO ON THIS JOURNEY WITH ME. Weather Underground has recently released its newest version of WunderMap. The newest WunderMap allows you to, very easily, go back in time. So, you can go back to Thursday, November 28, 2002 and click forward hour-by-hour to see how the temperatures change. IT IS AWESOME! All you have to do is click on the link above and then click on "Adjust Time" near the bottom-middle of WunderMap. Then click the "Hour" buttons.

What you will see is that there was a hefty amount of cold air in the Northeast that prevented many areas of New England from warming past 20 degrees. Further, afternoon temperatures in the 30s and 40s were observed well into the Southeast. This means that the eastern half of the country struggled to reach 40 degrees in the warmest spots. But, remember, we were investigating the coldest temperatures. If you go back a few hours to see what the morning temperatures were, you will see nearly the entire country in the 10s, 20s, and 30s.

Thanksgiving 2002 minimum temperatures.

Now, compare that with Thanksgiving 1993 and you will see where all the subzero temperatures were recorded that year. Temperatures below 0 degrees were recorded from the hills of Oregon through the Rockies.

Thanksgiving 1993 minimum temperatures.

The only reason 2002 tied 1993 was because temperatures in the Southeast 1993 were quite warm, offsetting the cold temperatures in the West. One can imagine the classic setup of a very deep low pressure trough over the West and a strong high pressure ridge in the East, bringing warm air into the Southeast.

Anyway, I could literally do this all day, but I will leave the WunderMap investigation to you.

What to expect this Thanksgiving

Well, one look at the above forecast would lead someone to believe that this Thanksgiving should be one of the warmer ones. Unseasonably warm temperatures are expected well north into the Great Lakes. The warmest temperatures are anticipated in Texas where some cities will be in the 80s.

I want to bring one more thing to your attention. Chicago's forecast high this Thanksgiving is in the mid-60s with a chance of rain. But, just one day later, Chicago is expected to struggle to reach 40 degrees. Over 20 degrees of cooling in 24 hours! This is only one example as much of the Upper Midwest will experience this cool down as a strong low pressure trough blasts through the region. Welcome to late Autumn.

Anyway, enjoy the food everybody!


Updated: 5:54 AM GMT on November 22, 2012


Before And After Webcams From Brutus

By: shauntanner, 6:01 PM GMT on November 12, 2012

I admit it, I have a new obsession. Several times a day, I search WunderMap for interesting webcams that tell a weather story. Images from these webcams are graciously given to us by the fantastic Weather Underground community and provide a very valuable resource to determine what the weather is like during major storms. You see, weather stations themselves don't tell the entire story. When a weather station reports that it is 25 degrees outside with heavy snow, one must imagine what the conditions are like on the ground. But, if you have a webcam nearby, one does not need to imagine!

A major Winter storm blew through the western half of the United States beginning Thursday and lasting into the weekend. This storm carried with it some majorly cold air that pushed temperatures to well below freezing in parts of the Intermountain West. Cut Bank, MT reached -17 degrees on Sunday! Any volunteers to move to Cut Bank? Without wasting more of your time, I present to you some images taken last Wednesday before the storm hit compared to the same webcam today. Enjoy!

Glacier National Park

Last Wednesday


Seeley Lake, MT

Last Wednesday


Homewood, CA

Last Wednesday


I-80 in Sierra Nevadas

Last Wednesday


Salt Lake City, UT

Last Wednesday


Varney Bridge, MT

Last Wednesday


Winter Weather Brutus

Updated: 5:58 PM GMT on November 16, 2012


Election 2012 Forecast

By: shauntanner, 6:49 AM GMT on November 06, 2012

After what seems like an endless election cycle, Election Day 2012 is finally upon the United States. It seems like weather plays at least a minor part of every national election, so let's take a look at what the weather will be like nationwide on Tuesday (and yes, while the biggest weather factor for this election could actually be Hurricane Sandy, I am more concentrated on the forecast for Tuesday itself).


The Northeast is expected to be quite chilly with temperatures for New England in the 30s and 40s. You will have to move southward into Virginia and the southern Ohio Valley in order to see temperatures in the 50s.

Dry conditions are expected for the Ohio Valley and Northeast, so expect minimal weather-related issues. By the way, this is not to say the dry conditions will continue into Wednesday as a strong nor'easter will move up the eastern seaboard.


With regard to weather, the Southeast could possibly be the most active area in the country this Election Day. A developing storm will swing through Alabama and Georgia before moving out into the Atlantic Ocean in the afternoon and evening. While the rapid intensification of this storm will not happen until it is over open water, it will contain enough moisture as it moves through the Southeast to produce moderate to occasionally heavy rain in Tennessee, Alabama, and Georgia. The intensity of the rain could produce some polling problems as people hit the streets to get to polling places.

Afternoon temperatures should be relatively pleasant as most areas should expect temperatures in the 50s-70s. Some higher elevations of the Appalachians should expect afternoon temperatures in the 40s.


Nothing too much of note is expected in the Plains as the region will be in the transition area between a developing low pressure trough in the east and a high pressure ridge in the West. A few morning showers are possible for coastal Texas, including the Houston area, but dry conditions will govern weather conditions from Nebraska through Texas.

Temperatures are expected to be pleasant, with the warmest areas in southern Texas possibly reaching into the 80s.

Upper Midwest

I am going to through in the Dakotas into this region as well.

A storm from central Canada will move steadily from the Dakotas into Wisconsin. Because of its origin in Canada, it will carry a fairly good amount of cold air with it. This cold air is expected to produce cool rain and even some snow mostly in Minnesota.

This area of the country will also be quite cool, with areas from North Dakota through northern Wisconsin and the Upper Peninsula of Michigan only rising into the 30s by the afternoon. Meanwhile, 40s are expected for the rest of Wisconsin, Michigan and parts of the Ohio Valley.


A high pressure ridge over much of the West will give way to a Pacific storm that will move into the Pacific Northwest beginning in the afternoon and lasting into the evening. This should lead to minimal problems at polling stations, with temperatures in the 50s and 60s, with the exception of higher elevations of the Cascades and Rockies, which will be cooler.

Rain and high elevation snow will begin in Washington and Oregon late Tuesday evening and into Wednesday.


The warmest area of the country will be the Southwest as a high pressure ridge will continue to provide unseasonably warm temperatures for early November. Areas of Southern California and Arizona will rise into the 90s once again, while inland areas of California should expect temperatures in the 80s. Needless to say, this should be good weather for voting.

All-in-all, this appears to be a good day for voting throughout the country. This is especially true since a strong Nor-easter is expected to affect the Northeast on Wednesday, while a major storm is anticipated to move onto the West Coast and further into the Rockies later this week and into the weekend.

In fact, in order to find weather that cound affect voter turnout, one may have to travel to Alaska. A strong storm in the Gulf of Alaska is expected to bring heavy rain to the panhandle, while a mix of rain and snow could fall as far north as Anchorage.

So get out and vote!


Updated: 6:50 AM GMT on November 06, 2012


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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Wunderground Meteorologist Shaun Tanner

About shauntanner

Shaun Tanner has been a meteorologist at Weather Underground since 2004.

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