Red flag warnings; rare quad rainbow goes viral

April is leaving little doubt that it's our windiest month of the year.

Red flag warnings are flying once again today for southwest and south central Minnesota. The combination of low humidity and high winds means high fire danger again today. It's been a common theme this spring.

THE NATIONAL WEATHER SERVICE IN TWIN CITIES/CHANHASSEN HAS ISSUED

A RED FLAG WARNING...WHICH IS IN EFFECT FROM 1 PM THIS AFTERNOON

TO 7 PM CDT THIS EVENING.

* WIND...NORTHWEST 20 TO 25 MPH WITH GUSTS TO 30 MPH.

* HUMIDITY...20 TO 25 PERCENT.

* IMPACTS...ANY FIRES THAT DEVELOP WILL LIKELY SPREAD RAPIDLY. OUTDOOR BURNING IS NOT RECOMMENDED.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A RED FLAG WARNING MEANS THAT CRITICAL FIRE WEATHER CONDITIONS ARE EITHER OCCURRING NOW...OR WILL SHORTLY. A COMBINATION OF STRONG WINDS...LOW RELATIVE HUMIDITY...AND WARM TEMPERATURES CAN CONTRIBUTE TO EXTREME FIRE BEHAVIOR.

The gales of April continue today. Wind speeds will not be quite as high as the past two days. Highest winds favor south central Minnesota.

Winds at the surface are driven by pressure differences. That's why meteorologists place low and high pressure centers on the forecast map. High pressure and lighter winds ease in tonight through tomorrow. Oh yes, and sunshine returns to most of Minnesota.

Here's the graphical forecast breakdown. Freezing mornings the next two days, slow moderation to 60 by Sunday.

Sky show: Rare quad rainbow in New York

You don't see this everyday. In fact I have never witnessed a rare quadruple rainbow. But this is what Amanda Curtis captured in New York.

Amanda was lucky to have just the right perspective; a rainbow with a water body nearby to create the right reflection. Capital Weather Gang's Jason Samenow posts more details on the rare quadbow.

While waiting for her train this morning at the Glen Cove train station in Long Island, NY, Amanda Curtis grabbed her phone and snapped a photo of an incredibly rare atmospheric phenomenon: A quadruple rainbow.

When she posted the photo on Twitter – where it went viral, some folks were incredulous. They said the photo was photoshopped or that Curtis had shot it through glass, causing a reflection.

But, in the interview posted below, Curtis told The Weather Channel the image was authentic and taken in the open air:

The photo was convincing to Paul Neiman, who works as a research meteorologist at NOAA’s Earth System Research Observatory. He posted this very helpful explanation on his Facebook page, which he allowed me to republish:

 This is an outstanding example of a primary and secondary rainbow (relatively common) occurring together with their reflected-light counterparts (quite rare). Allow me to elaborate.

A typical primary rainbow is caused by refraction and one internal reflection of sunlight within raindrops, resulting in a rainbow that is positioned 41 arc degrees from the anti-solar point (i.e., the point directly opposite the sun – for example, if the sun is 10 degrees above the horizon at your back, the anti-solar point is 10 degrees below the horizon directly in front of you).

The refraction causes the separation of white sunlight into its component colors, with red on the outside of the rainbow and violet on the inside.

The secondary rainbow, which is centered 51 arc degrees from the anti-solar point (i.e., the larger of the two bows during a typical display), involves two internal reflections of sunlight within the raindrops rather than one, resulting in a reversal of the color sequence (red on the inside and violet on the outside).

We can usually only see the portion of these rainbows above the horizon, because there isn’t a sufficient density of raindrops between the observer and the ground to see the rainbow below the horizon (exceptions include full-circle rainbows viewed from locales such as airplanes and mountain tops).

So far, so good. For the much rarer reflected-light rainbows shown in this spectacular photo, a large glassy-smooth water surface is required behind the observer. This smooth water surface reflects the sun, such that a second solar light source is generated.

This reflected sun, which is located the same the number of arc degrees below the horizon as the real sun is above the horizon, creates a second primary and secondary rainbow on the opposite side of the sky from the sun, but with the center of these reflected-light rainbows above the horizon.

The geometry dictates that the regular and reflected-light rainbows will join at the horizon, as this photo shows.

Neiman’s explanation requires a body of water to be behind the observer. And, indeed, Oyster Bay – located about 2 miles east-northeast of the train station “likely provided the reflective surface to create the reflected-light rainbows," he said.

Amanda's photo proves you just never know what you're going to see looking up at the sky.