The dominant story in the continental United States on February 18 is the significant winter weather that is impacting nearly every state east of the Rocky Mountains. A glance at this morning’s National Weather Service alert map shows a continuous band of cold weather warnings from the Canadian border down to central Texas, with a fierce winter storm stretching from Kansas to the Atlantic Ocean. NWS forecasters are reporting that they are camping out in their offices in order to ensure continuity of coverage so that the public they serve can remain safe and aware of these dangerous conditions.

Overnight lows in the upper midwest were particularly cold, with temperatures below -30 F in parts of the Dakotas (the coldest minimum temperature was -45 F at Antelope Creek ND). These extremely cold temperatures are often associated with notable temperature inversions above the surface. As surface temperatures cool overnight, the strong infrared emissivity of snow enhances the radiative cooling. However, as air is a poor conductor of heat, temperatures aloft remain relatively unaffected. This is particularly clear in the 1200 UTC balloon launched from Bismarck, North Dakota. Note how the surface temperature (-36.3 C) is barely warmer than the temperature at 500 mb (-37.7 C). The sounding also notes that the lifting condensation level (LCL) of around 890 mb is substantially warmer than the surface.

When cloud temperatures are the same or warmer than surface temperatures, it can be challenging to interpret infrared satellite imagery. For example, here is the GOES-16 ABI Band 13 image from 1150 UTC as displayed using the enhanced infrared color scale.

Looking at the northern shore of Michigan’s upper peninsula and the western shore of the lower peninsula, it appears that the banded structures of lake effect snows are present in the shades of blues. Therefore it is reasonable to assume that a lake effect event is ongoing in that region of the image, but given that the temperatures of the clouds are basically the same as the underlying surface, it’s not obvious. But discerning what is happening in the Dakotas and Minnesota is far more difficult. Are there large stratiform clouds present, or are the surface temperatures so cold that they have cloud-like temperatures? This is where products like the night microphysics RGB can be very useful.

Normally, the noisy orange regions seen in the upper midwest and northern great plains indicate high, thick, very cold clouds. The speckles appear when brightness temperatures are less than -30 C due to noise in the 3.9 micron channel at extreme cold temperatures. However, there are clues in here that we’re actually looking at clear skies in those orange regions. Let’s zoom in on northern Minnesota.

Here, it is clear that the lakes, most notably Upper and Lower Red Lake in the center of the image, are differently colored than the surrounding regions. The greener tinge is a result of reduced influence of the 12.4-10.4 micron difference and enhanced influence of the 10.4-3.9 micron difference. This likely is surface ice which means this region is clear. Therefore, the orange regions in the RGB product indicate that skies are basically clear in Minnesota and North Dakota, with some cloud coverage in southern and western South Dakota showing up as darker reds. The lake effect snows are much more clearly visible as yellow in the RGB compared to the IR image where they are basically the same temperature as the surface. Since the RBG recipe uses the 3.9 micron channel as an ingredient, this product shouldn’t be used for interpretation much after 1200 UTC this time of year as the sun is about to rise and solar reflectance at 3.9 will dominate over emission.

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Overnight in the eastern Indian ocean, a tropical storm underwent significant deepening to become Severe Tropical Cyclone Zelia. The name “tropical cyclone” might make one think of a comparatively weak storm compared to a hurricane, but that is because the names of these systems vary depending on the part of the world they take place. There’s no functional different between a hurricane, typhoon, or severe tropical cyclone, just a different ocean basin where they can be found. The category rankings are the same for all tropical cyclones, and as of sunrise on 13 February, it had become a Catergory 4 storm, with winds over 209 km/h (130 mph). Forecasts from the Australian Bureau of Meteorology indicate that it will continue to strengthen to a Category 5 system before taking a sharp left hand turn and heading south. Zelia is currently lashing the coast with winds and rain as it strengthens, and because of some locations will be under this system for many hours, some rainfall forecasts are in excess of 50 cm (20 inches).

The rapid development of an eye can be seen in the following loop of Band 13 (10.4 microns, the infrared window) from the Advanced Himawari Imager (AHI) aboard Japan’s Himawari-9 geostationary satellite, . Because this eye development took place in the nighttime hours, visible-wavelength imagery cannot be used to observe this process. Longtime viewers of tropical cyclone imagery might be slightly started to see Zelia spinning in a clockwise direction, but that’s expected for a Southern Hemisphere cyclone.

This strong intensification is not unexpected given the extremely warm sea surface temperatures found just northwest of Australia. The NESDIS High Resolution Sea Surface Temperature analysis (available from SSEC’s Real Earth) shows temperatures at or above 25 C (over 77 F), which contribute substantially to the latent heat processes needed for tropical cyclone development and maintenance.

For the latest updates, be sure to check the BOM’s Tropical Cyclone website.

 ===== 14 February Update =====

2.5-minute Himawari-9 Visible (0.64 µm, left) and Infrared (10.4 µm, right) images, from 2212 UTC on 13 February to 0502 UTC on 14 February (courtesy Scott Bachmeier, CIMSS) [click to play animated GIF | MP4]

2.5-minute Target Sector JMA Himawari-9 Visible and Infrared images (above) showed that Zelia made landfall along the coast of Western Australia (near Port Hedland) not long before 0500 UTC on 14 February. Cloud-top infrared brightness temperatures in the eyewall region were in the -80 to -85ºC range (shades of violet to purple).

A Suomi-NPP VIIRS Day/Night Band image (below) provided a high resolution view of the cloud-filled eye of Zelia, shortly after the tropical cyclone made landfall.

Suomi-NPP VIIRS Day/Night Band (0.7 µm) image, valid at 0524 UTC on 14 February (courtesy Scott Bachmeier, CIMSS) [click to enlarge]

In a ~2 day animation of 2.5-minute Himawari-9 Infrared images (below), it was apparent that Zelia remained generally quasi-stationary for an extended period on 12-13 February — and as mentioned in a Joint Typhoon Warning Center discussion, this led to a wind-induced upwelling of cooler sub-surface water beneath the Category 4 intensity tropical cyclone (which likely played a role in reducing further intensification). The images include surface plots from Port Hedland (YPPD), which reported a wind gust of 65 knots at 0700 UTC. Also of note: during much of the day on 12 February, thunderstorms moving inland across the Port Hedland region exhibited cloud-top infrared brightness temperatures as cold as -90 to -95ºC (shades of yellow to gray, embedded within darker purple areas) — these thunderstorms were producing periods of heavy rain (YPPD METARs).

2.5-minute Himawari-9 Infrared (10.4 µm) images, from 1502 UTC on 12 February to 0702 UTC on 14 February (courtesy Scott Bachmeier, CIMSS) [click to play animated GIF | MP4]

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From left to right: GOES-18, GOES-17, GOES-19 and GOES-16 Dust RGB images, from 1900 UTC on 11th February to 0300 UTC on 12th February [click to play animated GIF]

10-minute Full Disk scan Dust RGB images from GOES-18 (GOES-West), GOES-17, GOES-19 (Preliminary/Non-operational) and GOES-16 (GOES-East) created using Geo2Grid (above) showed vivid signatures of blowing dust (brighter shades of magenta) that originated over parts of northern Mexico and southwestern New Mexico — and was subsequently transported northeastward across southern New Mexico and southwestern Texas on 11th February 2025.

The respective satellite locations over the Equator are: GOES-18 (137.0 W longitude), GOES-17 (104.7 W longitude), GOES-19 (89.5 W longitude) and GOES-16 (75.2 W longitude). However, GOES-17 has been temporarily brought out of storage and is drifting slowly from 12th-15th February 2025, approximately 0.3 degrees of longitude in total. All ABI imagery during this “Longitude Test” will be resampled to the nominal 105 W location. GOES-17 products will be analyzed for any potential impacts that this shift in longitude might cause. The overall goal of the Longitude Test is to determine what product impacts (if any) there might be when GOES-16 (currently operational as GOES-East) is moved to 75.5 W in March, ahead of GOES-19’s arrival (GOES-19 is then scheduled to become operational as GOES-East on 4th April). Tangentially, this also tests our ability to track a GOES-R series satellite as it moves (and still receive data).

5-minute CONUS Sector GOES-16 daytime True Color and Nighttime Microphysics RGB images from the CSPP GeoSphere site (below) highlighted the hazy tan-colored appearance of the blowing dust during the hours leading up to sunset, followed by the brighter shades of magenta dust signature at night (the Nighttime Microphysics RGB makes use of the 10.3-12.3 µm “Split Window Difference“, which is effective for dust detection).

GOES-16 daytime True Color RGB and Nighttime Microphysics RGB images, from 1901 UTC on 11th February to 0236 UTC on 12th February [click to play MP4 animation]

A GOES-16 Visible image (below) included plots of the strong winds that were creating the blowing dust — which at that time was restricting the surface visibility to 1/2 mile at El Paso, Texas (KELP).

GOES-16 Red Visible (0.64 µm) image with plots of Surface Wind barbs (white), Peak Wind gusts (cyan/yellow) and Ceiling/Visibility/Weather (green) at 2301 UTC on 11th February [click to enlarge]

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One of the first things that meteorologists learn in their Intro to Weather class is that low pressure means cloudy skies and rain while high pressure means clear skies and sun. Of course, the second thing that meteorologists learn is that weather often doesn’t behave in a textbook way. The southeastern United States today is a good example of that.

Looking just at the surface observations from the Weather Prediction Center, one would think that the Atlantic southeast is under fairly quiescent conditions. A strong high pressure system is centered over southeastern Pennsylvania, but an arm of this high extends south all the way into northeastern Georgia. A stationary front parallels the northern border of Florida. Even the low pressure system in northern Mississippi is quite weak, with a central pressure that is higher than the average mean sea level pressure. All in all, it looks to be a fairly ordinary day.

But the satellite on SSEC’s Real Earth tells a different story. Here’s a loop of true color imagery from GOES-16 this morning.

Obviously, the Atlantic southeast is dominated by clouds, which seems to stand in opposition to what the surface map indicates should be happening. Some of the cloudiness is due to overflow from the midwestern cold front. But a good deal of the cloudiness is caused by the cyclonic flow around the high pressure in the northeast. The flow is coming from over the ocean, where is becomes laden with moisture. As it moves ashore, it runs into the southern extend of the Appalachian Mountains where orographic uplift forces it aloft and clouds and rain ensue.

One of the localized phenomena that arises from this kind of flow in northeastern Georgia has been dubbed the “wedge.” In wedge events, a shallow, stable layer of cold air forms due to cold air damming against the Appalachians. A sounding from the 1500 UTC RAP analysis shows this clearly:

This time of year is historically home to the strongest cold air damming events in this region, and their effects can be significant. Low level inversions like the one seen today can contribute to hazardous wintertime precipitation like freezing rain, as snow formed in a saturated layer aloft melts as it falls through the elevated warm layer then freezes again when it contacts the surface. In April 2023, a wedge event received national attention: the Masters golf tournament was interrupted by a backdoor cold front that formed from the wedge of cold air flowing southward along local terrain. During that event, winds exceeded 30 mph, trees were felled near spectators, and play was interrupted due to these hazardous conditions.

Days like today are a reminder that it’s always a good idea to get a bird’s-eye view of the weather using the wealth of observations that satellites can provide.

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