This Week’s Forecast For Week Of February 22, 2015

20150223_SurfaceTemperatureAnomaly_NH

A nation literally divided. Eastern US is in record cold, while Western US is in record warmth. All the cold air came from Siberia and went over the Arctic. It found its way into the Eastern US. It is much colder in Boston than in Anchorage. The Western US is very warm as if summer decided to come early. Normally cold Alaska was very warm last week. They wonder where winter went. So, why did the Eastern US get so cold, while Western US got so warm. Here is a upper level anomaly map from last week.

20150223_500mb_GeopotentialHeightAnomaly_NH

There is troughing at the upper level, which is the (drum rolls please) polar vortex. It came down south from Canada. When the polar vortex goes down south, it brings cold air with it. Normally, the Arctic region has troughing over it as it keeps the cold air up north. Sometimes, the polar vortex breaks off and goes down south. That can lead to cold blasts. Meanwhile, the Western US has upper level ridging, especially over Northwest Canada and Alaska. That is the negative East Pacific Oscillation (EPO) and positive Pacific/North American teleconnection pattern (PNA). The ridging from negative EPO and positive PNA causes cold air to be shunted southward, leaving areas under the ridging warmer than normal.

So, how will this week be like weatherwise? Always, a special thanks to Levi Cowan and his Tropical Tidbits. The GFS model has a freeze by the end of the week again. It is going to get cold again despite the fact that March is looming.

20150223_GFS_2MeterAirTemperature_90Hour_1800Z

However, the Canadian has it above freezing. I think regardless, it will get cold by the end of the week.

20150223_CMC_2MeterAirTemperature_90Hour_1800Z

Now, why would it be cold? Let’s look at the upper level forecast.

20150223_500mbGeopotentialHeightAnomaly_NH_90Hour_1800Z

All of them have a upper leveling ridging over Alaska. That is a negative EPO right there is also troughing over the Eastern US, which allows cold air to come down south along with ridging over Alaska. This type of setup favors another cold week for east of the Rocky Mountains. The Western US will be wondering where winter is. We can also use the past to forecast what the weather could be like. Let’s start with the 6 to 10 days analog forecast.

20150223_6To10Day_AnalogForecast

3/3/2002-Houston sees another freeze from 3/2 to 3/5. Houston has 22°F, while Austin Bergstrom has 17°F on 3/4, coldest recorded for that date.
3/11/1963-A warm week from 3/11 to 3/13 throughout the Southeastern US. It is abnormally in Houston. Houston records a high of 88°F on 3/13, which is second warmest on that date and ties with 1980.
3/3/2003-Cold blast hits Central Texas. Ice storm hits Central Texas on 2/23-25.
3/5/1955-Large area of America east of the Rocky Mountains is in a March heat wave from 3/11 to 3/21. Houston sees a high of 86°F on 3/13, which is second warmest and ties with 1974.

Some of the analog dates for the 6 to 10 day forecast stands out. This suggests that it could either be cooler or warmer than normal. This is centered at day 8. This suggest there is an equal chance for another cold blast or warm up by next week. The end of the week is likely going to be a cold one as mentioned previously. Now, let’s look at 8 to 14 days analog forecast.

20150223_8To14Day_AnalogForecast

2/28/1989-A strong cold front comes on 3/4. Houston sees 25°F on 3/5 and 3/6 and 28°F on 3/7, shatter low temperature records for those dates. Night time sees freezes from 3/4 to 3/9. East of the Rocky Mountains sees a March cold blast.
3/8/1955-Large area of America east of the Rocky Mountains is in a March heat wave from 3/11 to 3/21. Houston sees a high of 86°F on 3/13, which is second warmest and ties with 1974.
3/12/1963-A warm week from 3/11 to 3/13 throughout the Southeastern US. It is abnormally in Houston. Houston records a high of 88°F on 3/13, which is second warmest on that date and ties with 1980.
3/4/2002-Houston sees another freeze from 3/2 to 3/5. Houston has 22°F, while Austin Bergstrom has 17°F on 3/4, coldest recorded for that date.
3/12/1976-A cold blast hits east of the Rocky Mountains following 3/12. Houston sees a low of 32°F on St. Patrick’s Day (3/17), which is second lowest recorded on that date.

Like the 6 to 10 day analog forecast, it could either be warm or cold. I think this will be a period of cooler than normal weather until mid March. Here is a temperature anomaly map for the next one month from the Climate Prediction Center.

20150219_OneMonth_TemperatureProbability

Western US is likely to be warmer than normal, while Eastern US is likely to be cooler than normal. For, equal chance for cooler or warmer than normal. Like I said, it will be cooler than normal. It is one month, so I do not out much stock into it. This week will be interesting weatherwise.

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