New England Nor’easter

January 27th, 2015

GOES-13 was placed into Rapid Scan Operations mode during the evolution of the strong Nor’easter that affected much of New England (HPC storm summary), and the 10.7 µm IR imagery, above (available for download here as an MP4 and here as an animated gif) shows the development of the system over the 2-day period of 26-27 January. Of particular note in the animation is the southeast to northwest motion of cold cloud tops over central and eastern Long Island around 0500 and 0600 UTC on 27 January. Those cold clouds tops never quite made it to western Long Island or to New Jersey, where snow totals were less. The GOES-13 visible image animation for these 2 days is shown below (available for download here as an MP4 and here as an animated gif).

GOES-13 0.65 µm Visible Imagery, 26-27 January 2015 (click to play animation)

GOES-13 0.65 µm Visible Imagery, 26-27 January 2015 (click to play animation)

ASCAT microwave data continues to show the surface circulation. The METOP-A overpass at 1513 UTC, below, shows a center about 100 miles southeast of Nantucket, where gusts past hurricane force have been occurring. A large area of winds exceeding 50 knots (in red) is present over the northern Gulf of Maine.

METOP-A ASCAT winds, 1513 UTC on 27 January 2015 along with surface METAR reports (click to enlarge)

METOP-A ASCAT winds, 1513 UTC on 27 January 2015 along with surface METAR reports (click to enlarge)

A comparison of 1-km resolution MODIS 0.64 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images from 17:49 UTC is shown below. One observation of interest is a ship report just southeast of the storm center: 50-knot winds from the south-southwest, with blowing spray reducing surface visibility to 2-3 miles.

MODIS 0.64 µm visible, 11.0 µm IR, and 6.7 µm water vapor images (with surface/ship/buoy reports and surface analysis)

MODIS 0.64 µm visible, 11.0 µm IR, and 6.7 µm water vapor images (with surface/ship/buoy reports and surface analysis)

===== 28 January Update =====

Aqua MODIS true-color image

Aqua MODIS true-color image

As the Nor’easter departed and the clouds began to clear over the northeastern US on 28 January, the Aqua MODIS true-color Red/Green/Blue (RGB) image shown above revealed the areas with significant snow on the ground. Note the thin areas of snow cover along the spine of the Appalachian Mountains, extending as far southward as Tennessee and North Carolina. Closer views of New York City and Washington DC are also available.

===== 29 January Update =====

Terra and Aqua MODIS true-color images

Terra and Aqua MODIS true-color images

The clouds had cleared from the Boston region on 29 January; a comparison of the Terra and Aqua MODIS true-color images (above) showed the changes in the offshore sediment patterns in the ~90 minutes between the overpasses of the 2 satellites. The strong winds of the storm caused upwelling of colder waters along the coast and nearshore areas, with the Suomi NPP VIIRS Sea Surface Temperature product (below) showing SST values as cold as the 30-33º F range (darker purple color enhancement).

Suomi NPP VIIRS Sea Surface Temperature product

Suomi NPP VIIRS Sea Surface Temperature product

Antecedent Conditions for a Nor’easter

January 26th, 2015
GOES-13 Sounder Skin Temperature derived product image

GOES-13 Sounder Skin Temperature derived product image

Forecasts have been consistent in the past days for a storm of historic proportions over parts of southern New England. What conditions that are present now argue for the development of a strong winter storm? The image above is the GOES Sounder Land Surface Temperature (or “Skin Temperature”) product; cold air is present over southeastern Canada, with surface temperatures near -30 C, associated with a surface high pressure system. The high pressure will act to reinforce the cold air at the surface, preventing or delaying any changeover to liquid or mixed precipitation (a MODIS Land Surface Temperature product at 1500 UTC on 26 January similarly shows cold air banked over southern Canada).

GOES_SkinT_1400_26January2015

GOES Sounder estimate of Skin Temperature, 1400 UTC 26 January 2015 (Click to enlarge)

Winds over southern New England early on the 26th continued out of the north and northwest, maintaining cold air at the surface. The ASCAT (from METOP-A) imagery above shows brisk northwesterly winds south of southern New England just before 0100 UTC, with southwesterlies east of Georgia and South Carolina just before 0300 UTC. Those southwesterlies are helping moisten the atmosphere, and heavy snows require abundant moisture. MIMIC Total Precipitation (below; click image to play animation) testifies to the moistening that is occurring off the southeast coast as this system develops; the storm appeared to tap moisture from both the Gulf of Mexico and a pre-existing atmospheric river over the Atlantic Ocean.

[Added: The 1540 UTC ASCAT winds show the surface circulation east of Hatteras and the mouth of the Chesapeake Bay! Winds south of New England have shifted to northeasterly. The location of the circulation well off the coast suggests cold air can be maintained over land.]

MIMIC total Precipitable Water (click to play animation)

MIMIC total Precipitable Water (click to play animation)

Given that moisture and cold air are present, what features argue for the development of a strong storm? The GOES-13 water vapor images (below; click image to play animation; also available as an MP4 movie file) with cloud-to-ground lightning strikes superimposed show the potent system developing off the US East Coast and blossoming over the Gulf Stream as a secondary warm conveyor belt forms (a water vapor image with lightning animation from 25-26 January is available here). Strong sinking motion behind the system is indicated by the development of warm water vapor channel brightness temperatures (yellow color enhancement), and strong rising motion ahead of the system helps to generate widespread, strong convection. Convection also occurred over the Deep South late on 25 January in response to solar heating. The system depicted in the Water Vapor imagery is obviously quite vigorous.

GOES-13 6.5 µm water vapor channel images (click to play animation)

GOES-13 6.5 µm water vapor channel images (click to play animation)]

Suomi NPP VIIRS 11.45 µm IR channel and 0.64 µm visible channel images (below) showed that there was a great deal of convective banding within the secondary warm conveyor belt.

Suomi NPP VIIRS 11.45 µm IR channel and 0.64 µm channel images, with lightning, surface fronts and METAR reports

Suomi NPP VIIRS 11.45 µm IR channel and 0.64 µm channel images, with lightning, surface fronts and METAR reports

Total Column Ozone is frequently used as a proxy of tropopause folding; tropopause folds accompany very strong storm development and the vertical circulation associated with the potential vorticity anomaly (maximum) associated with the folding draws stratospheric ozone down into the troposphere. GOES Sounder Total Column Ozone derived product images (below; click to play animation; also available as an MP4 movie file) show that the dynamic tropopause — taken to be the pressure of the PV1.5 surface, red contours — descends below the 400-450 hPa level along the southern gradient of the higher ozone values (green to red color enhancement) as the potential vorticity anomaly pivots eastward along the Gulf Coast states and then northeastward toward the intensifying storm. The presence of clouds prevented ozone retrievals over many areas, but some ozone values over 400 Dobson Units (red color enhancement) could be seen, which is characteristic of stratospheric air.

GOES Sounder Total Column Ozone derived product images (click to play animation)

GOES Sounder Total Column Ozone derived product images (click to play animation)

As the storm approached New England, a MODIS 11.0 µmIR channel image (below) revealed the presence of widespread embedded convective elements within the broad cloud shied, with some cloud-top IR brightness temperatures as cold as -65ºC (darker red color enhancement). These pockets of convection could enhance snowfall rates once they moved inland.

MODIS 11.0 µm IR channel image, with lighting strikes, METAR surface reports, and fixed buoy reports

MODIS 11.0 µm IR channel image, with lighting strikes, METAR surface reports, and fixed buoy reports

An overlay of the RTMA surface winds (below) helped to locate the position of the surface low east of the Delmarva Peninsula. That position agrees well with ASCAT winds from 0158 UTC on 27 January.

MODIS 11.0 µm IR channel image, with RTMA surface winds

MODIS 11.0 µm IR channel image, with RTMA surface winds

A comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm IR channel images at 06:39 UTC or 1:39 AM Eastern time is shown below. With illumination from the Moon in the Waxing Gibbous phase (at about 60% of Full), the DNB provided a “visible image at night” which showed the expansive offshore “comma cloud” of the storm, along with the locations of bright cloud illumination from dense lightning activity (note the bright lightning signature east of Cape Cod, which corresponded well with a cluster of positive cloud-to-ground lightning strokes). Numerous pockets of convective development were seen well off the coast of North and South Carolina, due to strong cold air advection over the warm waters of the Gulf Stream.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images (with cloud-to-ground lightning strikes)

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images (with cloud-to-ground lightning strikes)

Tropical Storm Niko (07P) in the South Pacific Ocean

January 20th, 2015
MIMIC Total Precipitable Water product, with Tropical Surface Analyses (click to play animation)

MIMIC Total Precipitable Water product, with Tropical Surface Analyses (click to play animation)

AWIPS images of the MIMIC Total Precipitable Water product (above; click image to play animation) showed a broad moist plume in the equatorial South Pacific Ocean, within which Tropical Storm Niko began to develop during the 19 January – 20 January 2015 period. By the end of the animation, Gale Force winds were being analyzed within the eastern semicircle of the developing cyclone. Metop ASCAT surface scatterometer winds at 08:01 UTC (below) showed winds as strong as 42 knots (though the direction of the stronger yellow wind barbs was suspect, likely due to rain contamination).

MIMIC TPW product, with Metop ASCAT surface scatterometer winds

MIMIC TPW product, with Metop ASCAT surface scatterometer winds

After daybreak on 20 January, McIDAS images of GOES-15 (GOES-West) 0.63 µm visible channel data (below; click image to play animation) showed the development of spiral banding wrapping into the central low-level circulation center as the system reached tropical storm intensity by 18 UTC.  In addition, a few strong convective pulses with distinct overshooting tops could be seen near the core of Niko.

GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

An animation of GOES-15 10.7 µm IR channel images from the CIMSS Tropical Cyclones site (below) included an overlay of contours of the deep layer (200 – 850 hPa) wind shear at 18 UTC — Tropical Storm Niko developed in a region characterized by low wind shear, which enabled the storm to rapidly intensify.

GOES-15 10.7 µm IR channel images, with contours of deep layer wind shear

GOES-15 10.7 µm IR channel images, with contours of deep layer wind shear

The trans-Atlantic flow of moisture and strong winds

January 14th, 2015
SSEC RealEarth™ Infrared satellite image featured on NBC Nightly News

SSEC RealEarth™ Infrared satellite image featured on NBC Nightly News

The SSEC RealEarth geostationary satellite infrared (IR) image composite shown above (which was first sent out via Twitter by Stu Ostro of The Weather Channel…thanks Stu!) was featured on the NBC Nightly News on 14 January 2015 (link) because it illustrated a vivid example of the trans-Atlantic flow of moisture from a disturbance off the US East Coast to a rapidly-deepening storm approaching the British Isles (surface analysis maps | water vapor images with surface analyses).

A sequence of hourly geostationary satellite water vapor channel image composites (below; click to play animation) showed that there was a clear trans-Atlantic connection in terms of middle to upper tropospheric moisture/clouds, and a comparison of the 20 UTC water vapor image with the corresponding MIMIC Total Precipitable Water product indicated that there was a lower to middle tropospheric moisture connection as well. This type of long and narrow fetch of TPW is often referred to as an “atmospheric river”.

Geostationary satellite water vapor image composites (click to play animation)

Geostationary satellite water vapor image composites (click to play animation)

Another interesting point brought up during the NBC Nightly News segment was the recent presence of unusually strong trans-Atlantic jet stream winds, which has allowed aircraft flying from New York City to London to set record times in terms of conventional passenger aircraft (such as the 08 January flight of British Airways 114). Note the strong dry-to-moist (darker blue to white to green color enhancement) along the northern edge of the trans-Atlantic water vapor image moisture feed: such a moisture gradient often coincides with the axis of a strong jet stream. AWIPS images of water vapor imagery with overlays of MADIS cloud-tracked and water-vapor-tracked winds (below; click image to play animation) showed many high-altitude wind vectors in the vicinity of the jet stream moisture gradient with speeds in the 150-160 knot range (with 175 knots seen on the previous day).

Water vapor images with MADIS atmospheric motion vectors (click to play animation)

Water vapor images with MADIS atmospheric motion vectors (click to play animation)