What Was Behind Mammatus In the Sky Today & This Evening?

There were Mammatus pouches in the sky today at times. These are usually only with severe t'storms, right?

Posted: Apr. 22, 2019 9:09 PM
Updated: Apr. 22, 2019 10:59 PM

A few places got to 80 degrees today.  Of the observations site in the area, Morocco, Fowler, Delphi & Frankfort have all gotten to 80 so far this year.  We have had 79 at the Purdue Airport.  We have hit 80 here at WLFI (79.6).  Highs today ran 75-80 over the area.

It was a mix of clouds & sun today with gusty south-southwest winds up to 35 mph in the viewing area.

Skies varied from partly to mostly cloudy skies off & on.  In-between, there were bouts of mostly sunny skies.

The sky as a painted pastry of interesting cloud types of altocumulus castellanus, altocumulus duplicatus, lots of castellanus floccus amidst areas of altostratus with conspicuous mammatus pouches & swirls & streaks of virga in the sky today.

Aren't mammatus usually associated with severe t'storms?  Well, not necessarily.  They can occur with multiple cloud types, but appears most-ominous, best-formed & conspicuous with severe t'storms on the underbelly of cumulonimbus.

A cross-section of the troposphere from late afternoon model sounding shows what was behind the clouds & the mammatus.

Lafayette model sounding shows lots & lots of dry air just above mid-levels & below.  It was extremely dry between 1 & 3 km.

However, above that, there was a very sharp drop temperature to cause nice, towering altocumulus castellanus to bubble up with layer of elevated CAPE (buoyancy or nice, freely-rising air parcels).  There was a band of nice moisture in this zone, but it was way, way up above 3 km.

Freezing levels were even pretty low for a 75-80 day.  In a storm situation with a warm day of ample CAPE, shear & low-level moisture (dew points in the 60s), freezing level at around 3 km would give you large, severe hail.

We went from 59 degree at 1.5 km to 32 by 3 km, which is an impressive lapse rate to really bubble up clouds.

So, these castellanus towers rooted high up, but began to produce precipitation that evaporated on the way down.................


Storm system & its cold pocket aloft with steep lapse rates was skimming by our area.  Better moisture with the cold air aloft & dynamics was northwest of our area.  We were extremely dry for thousands & thousands of feet up, despite layer of elevated CAPE (instability) & the lapse rate way up.  Thus, we could not really get storm action to go.

Severe storms with wind damage & large hail occurred in eastern Iowa & over northern Illinois.

Precipitation began to fall in big drops above 3 km.  When the precipitation falls heavily in a cold environment with low freezing level & evaporates in much warmer air, you get these mammatus pouches.

Note the elevated towers of castellanus.

Note how these castellanus towers are producing virga (precipitation evaporating or drying up on the way down).

Castellanus & duplicatus with virga & early stages of mammatus pouch formation.

Altocumulus castellanus & mackeral sky at sunset.

As virga fell & saturated the mid-levels, this patch of asperatus was formed this evening.

As the upper low passes northwest of our area overnight, a few t'showers are possible, followed by a few showers (as we saturated the mid & low levels in parts of the area).

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