You've no doubt seen the marketing emails and commercials: Now is a great time to refinance.

Great news, right? But why now? Why is it suddenly a good time to refinance?

The obvious answer is that interest rates have dropped, in some cases, to levels not seen since 2013. Even though the Federal Reserve began raising benchmark interest rates in December, a potent mix of economic factors have actually pushed rates lower since then. Crazy, huh? The Fed raises rates, and mortgages get cheaper!

This event has opened doors for homeowners to save money by securing lower rates. The Mortgage Bankers Association this month reported its Refinance Index surged 16%. And for six consecutive weeks, mortgage interest rates dropped, according to research from Bankrate.com.

So, what's creating this environment?

1. Low oil prices. Wait, low oil prices means cheap gas, right? Yes. And cheap gas is a good thing, right? It is if you're driving the kids to school in a gas-guzzler. But long-term low oil prices can take steam out of the economy. Here in the U.S., oil production has become a major piece of our economy as new technology has made it easier for domestic oil producers to drill for oil here. But low demand for oil worldwide and an oversupply of oil has driven prices to extreme lows. That's bad news for oil producers in the U.S. and it slows down our economic growth overall, even if it is offset by all of us saving money at the gas pumps. Our recent monetary policy has made slow growth equal low interest rates.

2. Economic growth in other countries, especially China and Japan, has been disappointing. Investors around the globe are worried about China's economy. The world's second-largest economy has slowed down, and now investors are worried what a potential recession in China could mean for the rest of us. At the same time, leaders in Japan have taken a drastic step to increase economic growth there — they've adopted a negative interest rate policy. That means the country's central bank is charging banks to keep excess reserves, rather than paying interest on those deposits. It's a strategy designed to push more money out of savings and into economic growth and investments. But it also sends investors looking to other places to keep their money safe. And where do they find that?

3. U.S. Treasurys. Yes, the combination of a weak oil market and weak economies overseas has increased the demand for U.S. Treasury bonds. These bonds, issued by the U.S. government, are seen as some of the safest investments in the world. When investors make a "flight for safety," as economists say, most buy Treasury bonds. For the mortgage market, that can make interest rates cheaper. How? Treasury yields (basically the interest paid to the investors who own the bonds) decrease when demand for them goes up. And mortgage rates tend move in the same direction as the 10-year U.S. Treasury. So, as Treasury yields go down, so do mortgage rates. The 10-year Treasury yield at the beginning of the year was about 2.24%. It dropped all the way to 1.63% by mid-February and has stayed in the 1.70s since then. As a result, mortgage rates have dropped, too.

There you have it. How long will it last? Hard to say. As long as the yields on U.S. Treasurys are under 1.80%, it's a pretty good refinancing environment. In addition to China, Japan and oil prices, keep an eye on upcoming reports about the job market, retail sales and inflation. If those numbers suddenly look much stronger than expected, rates might go back up. The next round of reports come out in early March.

Until then, the best way to know if you should refinance is to talk to a mortgage professional. There are many programs available and too many options to cover in a simple article. A mortgage banker can help you understand what you're paying now and if there's a better option for your budget and long-term goals.