Very cold air over the Great Lakes on 17 February helped lead to the development of one long Lake-Effect Snow (LES) band that stretched from the Upper Peninsula of Michigan east-southeastward to Lake Huron then over the Bruce Peninsula and into eastern Lake Ontario and on to the Tug Hill Plateau over upstate New York. Surface observations show surface winds converging into the line: west-southwest winds over southwestern Ontario just south of the band and west-northwest winds just to the north of the band. In the RGB, the LES band clouds are orange/yellow in color. The cold snow-covered land surface is green, as are ice-covered regions on the Great Lakes (for example: Green Bay and the North Channel of Lake Huron). Low clouds (that probably aren’t supporting significant precipitation) are cyan or periwinkle in color.

Microwave sounder data (from, for example, ATMS on Suomi-NPP, NOAA-20 and NOAA-21 or AMSU-A/-B on NOAA-19) can be used to estimate snow fall rates, and this information is available online here. (Click here for a Quick Guide) Snowfall rates for this event are shown below. The LES snow band is obvious from Lake Superior east-southeastward into upstate New York, and strongest snowfall rates are just downwind of Lake Ontario. As the cold air sweeps from Canada southeastward across Lakes Superior, Huron and Ontario, it is warmed and moistened at the lowest levels (that is, it is destabilized) by the open waters of the Great Lakes. Once the band reaches the Tug Hill plateau, it has been prepped by the lakes upstream to unleash a torrent of snow.

Merged snowfall rate, shown below, combines MRMS radar observations with satellite-based microwave estimates of snowfall rate. As you see, the radar observations show a considerably thinner snow band. Even though the microwave footprint has a larger horizontal scale than the LES snow band, the microwave signal is large enough to show where snow is falling. A user must combine the microwave estimate of snow fall rate with their knowledge of the size of the LES — based on infrared satellite imagery, or on surface observations — to use the microwave snowfall rate estimates most effectively.

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GOES-18 infrared imagery, above, shows a cyclonic circulation over the northeastern Gulf of Alaska. Shower development is suggested by the evolution of brightness temperatures changing from cyan to blue to green (showing cooling); showers then dissipate as the brightness temperatures warm. Do you think these are showers of rain or of snow? Note in particular the motion of the clouds over Prince of Wales island, the southernmost large island of the southeast Alaskan archipelago, just north of Haida Gwaii (formerly called Queen Charlotte island) that is at the southern edge of the domain. Cloud motion is parallel to the development of colder cloud tops.

Microwave sounder data are used to estimate snowfall rates (SFR), and those estimates are available at this website; additionally SFR is inserted into Alaska Region AWIPS. Because microwave sounder data are available from many different polar orbiting satellites, coverage over Alaska can be quite solid. In particular, a cluster of observations comes in from NOAA-19 and Metop satellites; then a second cluster of observations occurs thanks to NOAA-20/NOAA-21 observations.

For this event, training convective snow showers spread over Prince of Wales Island allowing regions to receive around 8 inches of snow at sea level and over 15 inches of snow at higher elevations (as predicted well by forecast models). Satellite SFR products showed the convective snow showers over the southern Gulf of Alaska before they moved over the island and produced 1”/hour snowfall rates with visibilities of less than a quarter mile. The animation above shows the estimates during the day on 30 January; the animation below focuses on times after 1900 UTC. This case demonstrates how model information can raise situational awareness for incoming adverse weather (in the near term), and satellite information can confirm its existence in the short term as well as aid forecasters in making operational decisions to notify the public. Note how the SFR persistently identifies a snowband over Prince of Wales Island, something that continues through at least 0500 UTC on 31 January!

Many thanks to Spencer Fielding, WFO Juneau, for alerting me to this event. A comparison between Microwave snowfall rates and radar observations over CONUS is here. Note in particular how the width of a snowband might be overestimated by the large microwave footprint!

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It has been an active period of impactful weather in and near Australia, and today is no exception. Severe Tropical Cyclone Alfred continues to spin northeast of Queensland. The latest update from the Australian Bureau of Meteorology indicates a central pressure of 956 mb. Over the last day, it was downgraded from a Catergory 4 to a Category 3, but sustained winds are still at 85 knots (155 km/h) and gusts are reaching 120 knots (220 km/h). Recent Band 14 (infrared window) and true color imagery from AHI aboard Himawari-9 as displayed on RealEarth confirms Alfred’s weakening, with a filled-in eye that is well over 100 km across.

The current forecasted track for Alfred is to continue along a largely southerly path, and it is  expected to pass between mainland Australia and the French island of New Caledonia with no landfall.  The most significant impacts expected to be storm surges and waves. However, outer rain bands may prove to be challenging to the Queensland coast, which has already been struggling with the aftermath of recent significant rainfall.

MetOp-C passed directly over the center of Alfred on 26 February enabling ASCAT analysis of the near-surface winds. While most meteorologists already know that the strongest hurricane winds are not directly in the center of the rotation but near the eyewall, this image helps to reinforce that idea. Due to the relatively narrow swath of ASCAT and the geometry of low earth orbits, it can be challenging to get more frequent wind updates.

Alfred was one of three named tropical cyclones that were concurrently active in the tropical western Pacific Ocean this week, alongside Seru and Rae. While these latter storms were not as intense as Alfred at its peak, the impacts were more significant due to passing much more closely to the Pacific island nations of Vanuatu and Fiji. This true color AHI loop shows the rare sight of three Category 1+ tropical storms in such close proximity. Since then, the later two storms have both weakened and moved away from the populated islands.

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High pressure and mild temperatures over the western Atlantic and adjacent Gulf waters early on 26 February 2025 (here is the 1200 UTC surface analysis) meant NOAA-20 VIIRS data could provide near-complete views of sea- (and lake-) surface temperatures. The above image was captured from the RealEarth website. The warm waters (mid-70s ^oF) of the Gulf Stream off the North Carolina coast are in very close proximity to cold (mid-40s ^oF). Direct Broadcast data processed into AWIPS-ready VIIRS tiles are available from CIMSS and an example swath is shown below.

A zoomed-in view over the Outer Banks of North Carolina, below, shows the strength of the SST gradient, from very warm to much colder in less than 40 miles.

The SSTs over the northern part of the South Atlantic bight, shown below, include filaments of colder water extending from the shelf waters out into the open ocean.

NOAA-20 True-Color imagery, below, from the VIIRS Today website, shows filaments of turbid water that suggest a link between the observed cold filaments above and cold fresher water from the Continent. (Note also the smoke plumes over the southeastern US!)

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