Something To Talk About

As boring as the weather has been here lately it has been pretty active in the midwest, north-central states and back east. Snow from North Dakota all the way to New York-a foot in some areas.

Yesterday was interesting because there were record highs and record lows across the US. Oddly enough, the biggest temperature disparity was in the Western US. While it reached nearly 110 for the high in Arizona, about 900 miles north in NE Utah the lowest temperature in the US was recorded when the overnight low was 7 degrees.

For our area, tonight and tomorrow bring the best chances of rain we have seen in a long time. For several days the models have been very consistent in bringing the rain and high elevation snow to break up the monotony of these dry sunny windy days. I wish it was that simple.

As good as the chances of precipitation are it is going to be spotty at best.  One of the methods used to predict rain is to look at Precipitable Water Values or PWATS. PWAT is a measurement of the total depth of liquid precipitation at the surface if it fell all at once.

There are a couple of ways to display this. First, there is the actual measurement.

Here is the PWAT at 3 pm today.

pwatsun3pm

Here it is at 6 am tomorrow morning.

pwatmon6am

What you should be thinking right now is: “Is that good or bad?”Good question.  We need to establish a baseline.  So I prefer to view PWAT as a percentage of the climatological average for this time of year.

Here is 3 pm today. This measures the PWAT anomaly (percentage of normal). Line up the colors with the chart on the bottom and you will see a range of 100%-150% of normal.

PWAT3pmanom

Now, look at 6 am tomorrow. Again line up the colors and you see a range in our area of 140% to 275% of normal.

PWAT 6amanom

And here is the animated version which shows the ranges from 3 pm today through 6 am Tuesday morning.

2NAMPWAT

The other thing to be on the lookout for with this approaching wave is surface-based CAPE. CAPE is just a measure of energy available to create thunderstorms. This region of the country pales in comparison to other areas of the country when it comes to CAPE. Over the last 12 years, any CAPE value in our area above 500 catches my eye.

Here is the CAPE forecast for 5 pm from the latest model run

cape5pm

Here is 8 pm from the latest run

cape8pm

But here was the same model 6 hours earlier. It shows 1564 at the airport and 2800 over downtown Durango!

06zcape8pm

The model run (in)consistency does not exactly leave me feeling warm and fuzzy. There is one more model run between now and 8 pm that I can look at and see which run it is closer to.

When I look at precipitation totals from the models they are not encouraging. They show most of the accumulations occurring in the higher elevations above 8,500 feet.

So what does all of this mean taken as a whole?  It tells me that most of the precipitation will evaporate below 8,000 feet before it hits the ground, despite the high PWATs. It also tells me that there is a chance of mostly dry thunderstorms. If you are new here, dry thunderstorms produce lightning, high winds, and very little rain. That is a deadly combination for fire danger. It also tells me to check back when the afternoon models come out. If the extreme CAPE values emerge again on the next model run I will do another post, if they don’t I will consider the older model run an outlier and I will post again Monday morning.

Thanks for following, happy Mothers Day to all of you Moms out there!

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