Its not about L. Ron Hubbard…..but we will try to be “clear” about what happened yesterday morning.
The short of it: when its snowing hard above you, the snow level drops. So, when yesterday’s well-predicted-by-all (models, humans, etc.) frontal band turned out to produce heavy snow above us, the snow level dropped to levels that were lower than expected (below 3500 feet elevation). Those big flakes take longer to melt, chilling the air to the freezing point as they fall and melt. So, down goes the freezing level for a short time during the heaviest precip. When the heavy precip ends, the freezing level moves up again.
We call this lowering of the snow level in heavy precip a “diabatic” effect, maybe get into the effects of enthalpy of fusion, too, because when we miss a forecast, we want use some jargon to make it sound like a very complicated process occurred, one that only Einstein could have anticipated.
Anyway, the diabatic effect yesterday involved heat transfer from the air to the melting snow; melting sucks the life out of the temperature because work is involved in melting snow . Often a little isothermal layer (temperature is steady with height) is present in the atmosphere when light, steady snow is falling in the layer where the snow melts into rain before reaching the ground due to this same effect.
BTW, there was a U of WA IMA Department of Weather softball team called the “Diabatics”. I insert this as a smile-producing distraction to get you off the thought of error.
I’m guessing the media weathercasters were all over “diabatic” effects as well yestserday.1
Got 0.26 inches, 1 inch max depth of snow here at the house, missed “middle ground” prediction of 0.23 inches by only a slight amount. However, there was 0.36 inches, 1.5 inches of snow at a Sutherland Heights gage.
It was so great to see snow just sitting there, melting away slowly on ground in the desert yesterday and on those new grasses and weeds trying to spurt skyward in our droughty winter (so far). For a wider look at the precip totals, go to the U of AZ rainlog site here and input February 8th because even though the precip fell on the morning of the 9th, by convention for the U of AZ, its assigned to the prior day, which is the 8th in this case. If you do go there, you will see that for the TUS region, those areas north of Pusch Ridge got a quarter to a third of an inch while south of Pusch Ridge, totals were far lower. Lucky us.
The most I saw in 24 h in the Pima County ALERT gages as of 5 AM morning was 0.39 inches at CDO wash, northeast of Saddlebrooke.
Might not have been so great for the free range cattle, several of which were gumping down cholla buds as I drove along Equestrian Trail Rd! Ouch! Apparently that snow cover was just enough to prevent them from eating the dry grass out there.
Here are a couple of belated snow shots for your files:
Yesterday’s clouds and precip
They were again tremendous, when combined with the Catalinas, Tortolitas, and our deep blue skies! Took too many photos again, more than 200! Hard drive filling up fast!
After the slow dissipation of the stratiform deck in the morning, lifted and thinned, as was happening in the first photo, the Stratocumulus underneath that higher layer gradually dispersed into Cumulus clusters, and with the freezing level so low, ice readily formed in them.2 Scattered showers developed by mid-day, and most, in the early going, produced graupel, tiny snowballs, soft hail or snow grains (really tiny ones).
The best CMJ’s out there no doubt rushed out before those little snowballs melted and were treated to the sight of “conical” graupel, cone-shaped little snowballs. Conical graupel, which is kind of comical-looking because it looks like a little, pointy clown hats, forms when an ice particle, say a plate-like crystal in a cloud consisting mainly of supercooled droplets, falls face down. The one side facing down the whole way, with the cloud droplets hitting on that one side, freezing as they do leading to that space shuttle entry vehicle shape. Kind of fun to see them and think of that ice crystal falling face down like a clown, and then it ends up looking like a clown’s hat! Quite funny. Hence, the nickname, “comical” graupel. Here’s one that fell on Catalina yesterday for your edification:
Some cloud shots:
I could go on and on with more photos I liked from yesterday, but must close. Haven’t looked at a single prog yet!
The weather ahead
Looks like tomorrow will be a lot like yesterday afternoon (no rain/snow band likely), cold cumuliform clouds with afternoon virga and showers here and there, graupel, soft hail occurrence is a certainty from some of those clouds, followed by a nice recovery in the temperatures for a five day or more spell before the next winter onslaught of storms in the 10-15 day range from now (20th to 25th of February) hits. Hope they do. Those storms are “moderately” supported in the NOAA spaghetti plots.
Let me titillate your rain bucket with this forecasted behemoth on Monday, February 25th:
1It is also interesting that CMP, writing that the temperature would fall “15-20 F” in an hour after the front passed and rain started, did not realize that “15-20 F” minus the temperature of say, 50 F, at the start of the rain, leads to snow falling, fer Pete’s Sake! Kind of an arithmetic oversight.
2Not sure why the Beowulf Cluster at the U of AZ did not have scattered showers in the afternoon around Catalina in that 11 PM AST run I looked at–would have to be a problem in the model microphysics or the forecast cloud depth being too shallow.