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There’s more where that came from! sub-continental scale below-normal temperatures will continue!
(03/21/2015 − 03/26/2015)
STRAT_K will occur within the last few days of March and first few days of April. Associated with STRAT_K are several rounds of cold air outbreak events for North America and Eurasia starting this weekend till the end of the first week of April, as we first forecasted on 02/18 (see “forecasts” for more detail) .
STRAT_L looks like to be the last stratospheric event of this winter season, which is expected to occur around April 16-22, as we first forecasted last week. STRAT_L is going to be a weak event and the associated cold air outbreaks will be modest.
Together with STRAT_J, STRAT_K and STRAT_L will make a fairly cold spring for the year of 2015.
Forecasts Made on March 26, 2015
Follow up on Forecast Made in Previous Weeks:
Within the last week of March and into the first week of April, STRAT_K will deliver another cold surge across the mid-latitudes. Originally forecasted on 2/18, STRAT_K will be a longer lasting event with a duration of about 4-7 days. As we forecasted on 02/18, STRAT_K is comparable to STRAT_E, which caused break-up of the stratospheric polar vortex around the New Year. Since the STRAT_K is going to cause a major stratospheric warming, as STRAT_E, we expect STRAT_ K to follow a similar pattern: multiple peaks and long lasting. The first peak will lead to the cold air surges over both continents in a few days from today, but the second peak of this event will lead a series of stronger cold air outbreaks. Synoptic-scale wave activities will be strong in the first week of April due to the break-up of the polar vortex that is squeezed out into mid-latitudes by the warm air transported into the polar stratosphere. Since it takes a week to disperse these synoptic scale waves, we are expecting a week-long series of cold air breaks circulating mid-latitudes, resulting in approximately 60-70 % of the area across the mid-latitudes of both Eurasia and North America to experience below-normal temperatures.
STRAT_L forecasted last week to occur around April 16-22 will be the last STRAT event. There is no change in this week’s forecast for STRAT_L. The polar stratosphere is going to be warmed up soon as the sun returns to the Arctic. The new polar vortex to be rebuilt after STRAT_K is going to be weak and short lasting. Therefore, we forecast this event as a weak STRAT event. Nevertheless, this is a relatively very late event. Therefore, we expect up to 50-60% of area over North America and Eurasian to report below-normal temperatures.
New Forecasts Made on March 26, 2015
No new events are forecasted in this week's forecast.
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