NOAA-20 overflew the Samoan islands shortly after 1200 UTC on 22 January 2024, as shown above. The animation displays a series of 13 profiles and derived parameters to the east of American Samoa and Samoa. with locations as indicated by the circle. Most Unstable CAPE values derived from the profiles all are derived from the near-surface 986 mb — except for the profile location denoted in yellow, which has a MUCAPE level at 959 mb. That point also has the smallest value of MUCAPE: <200; Other values range from 2200 to as high as 4400. NUCAPS profiles are a useful source of thermodynamic information (independent of models) in regions where data are lacking.

GOES-18 also viewed this region, and the toggle below compares derived Total Precipitable Water and Lifted Index at 1200 UTC, the approximate time of the NOAA-20 overpass. The TPW shown below shows structures and values similar to the MIMIC TPW shown above. A careful observer will also see the convection below associated with the red NUCAPS sounding availability point above (many red points associated with the large convective complex near 17^o S, 166.5^o W are hidden in the figure above, but are viewable here). GOES Level 2 products are able to highlight relatively small-scale variability in moisture/stability (for example, the region of relatively stable air stretching southeast to northwest — tannish brown in the LI color enhancement — to east and north of the Samoan Islands. Use them in concert with NUCAPS fields (available in all sky conditions) to get a good feel of the moisture distribution in data-poor regions.

---

Important NUCAPS note: NOAA-21 NUCAPS profiles are scheduled to flow via SBN to NWS forecast offices in February. At present, they will augment (not replace) NOAA-20 profiles, allowing forecasters to see short-term trends in NUCAPS fields.

View only this post Read Less

Target Sector (2.5-minute interval) JMA Himawari-9 AHI Clean Infrared Window (10.4 µm) images (above) showed Tropical Invest 90P as it moved westward across the Coral Sea on 20 January 2024. Intermittent convective bursts within the growing cold cloud canopy contained multiple overshooting tops that exhibited infrared brightness temperatures of -100ºC or colder (internal clusters of red pixels embedded within yellow-to-black regions). In fact, the minimum infrared brightness temperature of -103.83ºC on the 17:09:44 UTC image was colder than the -103.55ºC measured by Himawari-8 with Typhoon Kammuri in 2019 (which at that time was thought to be the coldest cloud-top infrared brightness temperature on record as sensed by a geostationary satellite).

Himawari-9 Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Invest 90P was moving through an environment of high deep-layer wind shear — which was inhibiting its further intensification.

View only this post Read Less

With the total solar eclipse occurring over parts of the contiguous U.S. on April 8, 2024, there are many wondering what the cloud cover might be on that day. As anticipation builds, we decided to look at the past 28 years of GOES cloud products on April 8. This is not a forecast, but a look back at the cloud climatology. Every spot on the eclipse path has had April 8ths where it was cloudy and every spot has had April 8ths where it was clear. So while you may choose to travel to southwest Texas to see the eclipse because that gives you the best chance historically at clear skies, there is going to be some uncertainty involved for eclipse viewers all along the path as to whether or not they’ll get a clear-sky view of the event. The potentially clearest areas still have at least 30% chance of being cloudy on April 8 based on the historical record. Of course the climatology does not have days with a total solar eclipse, and we have seen in earlier events how some fair-weather cumulus cloud coverage is briefly reduced as a result of the reduced incoming solar radiation. Still, an eclipse can be a fun event if you’re on the path even when it’s partly cloudy. This is an opportunity to discuss the science related to cloud cover on the upcoming eclipse day.

For comparison, see similar images derived from MODIS data and the ERA-5 (re-analysis). In general, climatologically it is more clear in Texas and less clear in New England in early April. Of course that is not a forecast for what will actually happen in 2024.

More information

There is much more information about this event, including this CIMSS Satellite Blog post, and the NWS and NOAA Satellites.

H/T

This image was made by M. Gunshor, UW/CIMSS (who also helped write this blog post) with NOAA geostationary cloud files processed by S. Wanzong, UW/CIMSS, with input files from UW-Madison, SSEC; SSEC Data Services. Thanks also for the Eclipse Predictions by Fred Espenak, NASA’s GSFC. T. Schmit works for NOAA/NESDIS/STAR and is stationed in Madison, WI.

View only this post Read Less

Morning radar on the morning of 19 January 2024 (shown below from this source) showed a single band of snow squalls moving southward over central Lake Michigan. Then band moved inland over northwestern Indiana, resulting in a winter storm warning over northwestern Indiana (More information from NWS IWX) and hazardous travel conditions through that heavily-traveled corridor between Chicago and Detroit. GOES-16 Clean Window Infrared (Band 13, 10.3 µm) imagery, below, shows a subtle lake-effect band signature emerging as the clouds associated with a system that deposited widespread light snow over the upper Midwest exits to the east. Surface observations, especially of CMAN sites, show convergence over the lake. Note the east/northeast winds at stations LDTM4 (Ludington MI) and BSBM4 (Big Sable Point MI) over central lower Michigan and the northwest winds along Lake Michigan’s western shore. Sometimes lake effect bands are vigorous enough to produce convection. That was not the case for this band; GLM detected no flash events (in addition, LightningCast probabilities were less than 2%!)

---

Merged Snowfall rates (source; a field that combines observations from radars and from polar orbiting satellites’ microwave observations of the atmosphere), below, show that the single band started to coalesce shortly after 0700 UTC. Microwave observations over the Great Lakes did not occur at the hourly intervals shown (although some observations are present over the Pacific Northwest, where the gap-filling between radars is more important!); however, there were microwave estimates of snowfall rate at 0850 and 0920 UTC, as shown in this toggle. Light snow in Madison WI was just ending at 0900 UTC/3 AM CST; compare the 0900 mSFR field (radar-only coverage over the midwest) and the 0850 UTC/0920 UTC mSFR fields (here are all 3 in an animation): satellite-based microwave estimates of snow better capture the back edge of the light snow than the radar-only image.

---

The single band is increasingly apparent in the animations below of Day Cloud Phase Distinction and Day Cloud Type RGBs. Because the airmass is very cold, the Day Cloud Phase Distinction RGB (that has as its red component the 10.3 brightness temperature) shows low-level snow-cover as much redder than in the Day Cloud Type RGB that has as it red component the 1.38 reflectance. (There is sufficient water vapor in the atmosphere that a surface reflectance signal is absorbed). Both RGBs show the mid-lake convective band as a series of discrete convective towers forming a sinuous band as it approaches the southern Lake Michigan shoreline. Shortly the end of the animation one of the towers over north central Lake Michigan is vigorous enough that LightningCast probabilities have reached 10% (click here to see the Day Cloud Type RGB at 1601 UTC) .

A bit more zoomed in Cloud Phase Distinction RGB, as well as ABI “red” visible band 2 (still and movie). These images were made with the geo2grid software.

---

MetopC overflew the western Great Lakes shortly before 0200 UTC on 19 January 2024. Advanced Scatterometer (ASCAT) imagery from that time (source) show northeasterly winds, suggesting mid-lake convergence, along the southeast edge of the swath.

View only this post Read Less