First Signs of a Storm System

Smoke from western wildfires creates a hazy sky. Photo copyright 2022 by Craig Johnson, Weather Briefing, LC. Cedar Falls, Iowa.

The same photo with the haze artificially removed. Photo copyright 2022 by Craig Johnson, Weather Briefing, LC. Cedar Falls, Iowa.

This is a Larger version of the photo on the right above. The smaller cellular clouds could be Cirrocumulus rather than altocumulus. It is splitting hairs. Estimating cloud heights takes experience and even then it can be tough especially when looking at a photo like this. It is much easier to determine the difference between low and middle level clouds. The difference between cloud types is not an exact science and remember, clouds can be mixtures of different types and don’t always follow nice neat rules. The size of the cloud elements helps when estimating how far away they are. Smaller clouds are often just farther away. Photo copyright 2022 by Craig Johnson, Weather Briefing, LC. Cedar Falls, Iowa.

Yesterday we had patch cirrus that was visible through a smoke filled sky courtesy of the western U.S. wildfires. Today more clouds are returning to Iowa’s skies. While the clouds are more numerous and more interesting than yesterday, they still have very high bases due to the stability of the air and no upward forcing that would create lower clouds.

A storm system approaching from the west will be increasing the relative humidity and dew points due to increasing southerly winds during the next 48-hours. As water vapor is added to the air and temperatures warm, lower-level air will become a little less stable which will eventually lead to showers and thunderstorms. Upward motion, from the flow of air through the storm system and increasing low-level instability underneath the upper flow will generate showers and thunderstorms.

Clouds today are the vanguard of the next storm, with high altocumulus indicating some instability in the upper levels of the atmosphere. The storm will clear the upper air of any smoke from the western wildfires.

The two small photos above are the same photo. The one on the left shows the sky as it really looks. We continue to have high based haze from the western wildfires. The right photo has had the haze artificially removed by digital photo software. The larger third photo makes it easier to see the cirrus, altocumulus, and altostratus clouds. The cirrus are very high and wispy with ragged edges. It takes an eagle eye to spot them. The smooth based opaque clouds are very high altostratus and the lumpy clouds are altocumulus - also very high. This photo is looking south southeast.

Photo copyright 2022 by Craig Johnson, Weather Briefing, LC. Cedar Falls, Iowa.

This photo is looking south. The haze has been removed making the altocumulus very distinct. The entire photo is nearly all altocumulus but there are a few altostratus visible near the bottom center and bottom left.

Map plotted by Digital Atmosphere software available at www.weathergraphics.com.

The above map shows the surface fronts early this afternoon as drawn by the National Weather Service. There is an area of low pressure near the North Dakota - Minnesota border and an area of low pressure from southwestern Nebraska to southeastern Colorado. A warm front extends eastward across Lake Superior to northwestern Ohio with a cold front from northwestern Ohio to the Atlantic Ocean. A cold front extends from southeastern North Dakota to the low pressure in southwestern Nebraska and then essentially a stationary front from there into Colorado then northwest along the Front Range and the eastern slopes of the Rockies into Canada. A stationary front cuts across Florida from the Atlantic to the Gulf of Mexico. See the map below to see how the surface wind direction is related to these fronts.

Map plotted by Digital Atmosphere software available at www.weathergraphics.com.

The map above shows the surface wind flow at 2:00 PM CDT this afternoon. The southerly flow coming off the Gulf of Mexico is bringing warmer air and moisture northward in to the Great Plains and the Upper Midwest. The lines are called streamlines. Sinking air is spreading away from high pressure centered in the vicinity of Lower Michigan, Indiana, and Ohio. It is flowing to the Atlantic Coast before turning southwest to the northern Gulf of Mexico then converging into low pressure in the eastern Dakotas. There is a westerly and northwesterly flow off the Pacific Ocean in to the far western and southwestern United States.

Use our Station Model Tutorial to decode the surface weather observations on the map.

Map plotted by Digital Atmosphere software available at www.weathergraphics.com.

The streamlines on the upper air chart show clockwise flow around a warm high pressure aloft near Memphis, Tennessee. A broad southwesterly flow is moving through the western United States. As the upper high pressure moves east the southwest flow will move further east allowing upper level waves to pass across the Upper Midwest. With low level moisture and warmer air increasing through the middle of the United States and a front moving east from the Great Plains, we can expect showers and thunderstorms to spread east too. Each wave is a storm system that will produce rising motion, clouds, and showers and thunderstorms as it moves through the warm moist Midwestern air mass.