Weather winning streak; “Perfect” 4th of July? “Monsoon” will ultimately douse AZ fires

Weather Perfection?

One thing you learn after 30 years of forecasting weather in Minnesota is Minnesotans love all kinds of different weather.

There may be no “best” weather that all of us would agree on…but this week has to be as close to “perfect weather” as we get in Minnesota.

Especially in the reluctant Summer of 2013. Better late than never.

Our weather winning streak continues this week, and the 4th of July looks about as good as it gets. Your parade and pool party, boat/beach day or backyard barbecue should go of without a hitch tomorrow.

Image: Twin Cities NWS

The “Yarnell Hill Wildfire” tragedy in Arizona where 19 brave “hot shots” gave their lives last weekend has a bigger back story.

It’s called the “North American Monsoon” and it may be both the reason for the wildly erratic winds that trapped the hot shots, and the saving grace will ultimately put out Arizona blazes.

We can be thankful on this 4th of July that a cool, wet Minnesota spring means low fire danger for us.

The fireworks display at last year’s Music in Plymouth. (MPR Photo/Elliot deBruyn)

The Perfect 4th of July? It doesn’t get any better than this folks.

After sweating thought the hottest 4th of July on record at 101F last year, Minnesotans will be rewarded with about the best weather most could ask for on the 4th tomorrow.

This is as good as it gets.

Here’s the breakdown of the 4th from the European Model, which insists on plenty of sun…a light south breeze and temps in the low to mid 80s tomorrow afternoon.

Image: Norwegian Met Institute

Fireworks time should be ideal around 10pm tomorrow night. Look for mainly clear skies, a gentle south breeze and temps around 80F.

Weather Tip: Set up just to the north of the fireworks show if possible if you want the rockets red glare and skybursts going off right overhead.

Weekend Thunder Threat? Dry skies hold for now…but with higher humidity scattered thunder will return this weekend. Scattered T-Storm chances arrive by late Saturday, and linger into Sunday & Monday in Minnesota. It does not appear we’ll see a return to the “Monsoon like” conditions of May and early June…but an uptick in scattered rain & thunder looks likely by this weekend and into early next week. Here’s the 7-day rainfall outlook from NOAA. Note the flooding rain potential from a slow moving front in the southeast USA, and a welcome uptick in rainfall for parts of Arizona.

Image: NOAA

Arizona Fires: “North American Monsoon” will ultimately put them out During my 9 years as Chief Meteorologist for the ABC affiliate in Tucson, I was part of a group of Arizona meteorologists who worked to come up with a definition for the start of the so called “North American Monsoon.” Ultimately we arrived at using the dew point as the most reliable indicator to call the beginning of the monsoon in Tucson.

Dew point tracker for Tucson, AZ. Image: Tucson NWS

Historically, 3 consecutive days of dew points at or above 54F seemed to be the most reliable signal that the upper wind flow had made the annual shift from the westerlies of June to the tropical easterlies…and that monsoonal moisture has arrived to stay in southern Arizona.

The “4-Corners High” is a typical monsoon set up for Arizona. Tropical moisture from the easterly wind flow brings frequent “monsoonal thunderstorms” from July into September. Image: Tucson NWS

The word “monsoon” comes from the Arabic word “Mausim” meaning “season.” It describes the annual shift in upper air wind flow that brings the tropical moisture that fuels sometimes daily thunderstorms that bring life giving rains to the parched Sonoran Desert in summer.

Over half of the annual rainfall (6″+) for southern Arizona comes during the monsoon from July into September. Here’s much more on the amazing North American Monsoon from the Tucson NWS.

Yarnell Hill Fire, Arizona
On July 1, 2013, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this image of the Yarnell Hill fire burning in Arizona near the town of Yarnell. Red outlines indicate hot spots where MODIS detected unusually warm surface temperatures associated with fire. The image is centered at 112.791° West longitude and 34.225° North latitude. The destructive fire killed 19 firefighters and destroyed more than 200 homes.

“Dry Microbursts” May have fanned Yarnell Hill Fire: The downside of the early part of the Summer Monsoon in Arizona is so called “dry thunderstorms.” Until deep moisture arrives from the Gulf of Mexico and California, early monsoon storms can produce plenty of lighting capable of starting fires…and “dry microbursts” that produce gusty shifting winds in excess of 70 to 80 mph.

These dry thunderstorms may be what caused the erratic winds that fanned the flames…and trapped the 20 hot shots in an instantly perilous location as the fire suddenly raced in a different direction Sunday.

Here’s a look at a so called “dry microburst” in Tucson. You can see some rain from the storm…but also mainly dry winds sweeping areas of the valley as the “evaporationally cooled” air races toward the ground and fans out at high speed.

http://www.youtube.com/watch?v=sAQQrae9ZjI

These gust fronts produce dust storms…or haboobs as they sweep the valley.

It will take some time to research, but my strong hunch is that one of these “dry microburst” induced gust fronts is what produced the suddenly erratic wind patterns that fanned the flames and trapped the 20 hot shots and killed 19 of them last weekend in Arizona.

The good news is as the monsoon ramps up rains will become heavier and more widespread. Higher humidity and heavy downpours are what will ultimately douse the wicked Arizona fire season of 2013.

Paul Huttner