Satellite signatures of a “sting jet”

GOES-16 Lower-level (7.3 µm) images, with hourly plots of buoy and ship reports [click to play MP4 animation]

GOES-16 Lower-level (7.3 µm) images, with hourly plots of buoy and ship reports [click to play MP4 animation]

Satellite signatures of a phenomenon known as a “sting jet” have been shown previously on this blog here, here and here. GOES-16 (GOES-East) Lower-level (7.3 µm) Water Vapor images (above) revealed another classic example of the “scorpion tail” signature of a sting jet associated with the rapidly-intensifying storm off the coast of North Carolina on 04 January 2018.

The passenger cruise ship Norwegian Breakaway was en route to New York City from the Bahamas when it experienced very strong winds and rough seas early in the morning on 04 January (media story) — it appears as though the ship may have been in the general vicinity of this sting jet feature (ship data), where intense winds were descending to the surface from higher levels of the atmosphere:

A comparison of GOES-16 (GOES-East) and GOES-13 Water Vapor images (below) demonstrated how the GOES-16 improvement in spatial resolution  (2 km at satellite sub-point, vs 4 km for GOES-13) and more frequent imaging (routinely every 5 minutes over the CONUS domain, vs 15-30 minutes for GOES-13) helped to better follow the evolution of the sting jet feature. The 2 known locations of the Norwegian Breakaway around the time period of the image animation are plotted in red.

"Water

Water Vapor images from GOES-16 (6.9 µm, left) and GOES-13 (6.5 µm, right), with the 2 known locations of the Norwegian Breakaway plotted in red [click to play MP4 animation]

The sting jet signature was also apparent on GOES-16 Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (below).

GOES-16 Mid-level (6.9 µm) images, with hourly plots of buoy and ship reports [click to play MP4 animation]

GOES-16 Mid-level (6.9 µm) images, with hourly plots of buoy and ship reports [click to play MP4 animation]

GOES-16 Upper-level (6.2 µm) images, with hourly plots of buoy and ship reports [click to play MP4 animation]

GOES-16 Upper-level (6.2 µm) images, with hourly plots of buoy and ship reports [click to play MP4 animation]

In addition, the sting jet signature was evident in a Suomi NPP VIIRS Day/Night Band (0.7 µm) image at 0614 UTC or 1:14 AM Eastern time (below). Through the clouds, the faint glow of city lights in far eastern North Carolina could be seen along the left edge of the image. The cloud features shown using the “visible image at night” VIIRS Day/Night Band were brightly-illuminated by the Moon, which was in the Waning Gibbous phase at 92% of Full. A VIIRS instrument is aboard the JPSS series of satellites, such as the recently-launched NOAA-20.

Suomi NPP VIIRS Day/Night Band (0.7 µm) image [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) image [click to enlarge]

Another view of the sting jet signature was seen in a 250-meter resolution Aqua MODIS Infrared Window (11.0 µm) image at 0725 UTC (below).

Aqua MODIS Infrared Window (11.0 µm) image [click to enlarge]

Aqua MODIS Infrared Window (11.0 µm) image [click to enlarge]

Beauty is a Beast: The East Coast Storm

An extraordinarily intense, rapidly developing, and structurally beautiful storm is now moving up the east coast of the U.S., bringing strong winds and heavy snow to the Northeast.

The satellite pictures this morning are simply stunning, made even more impressive by the imagery available from the new NOAA/NWS geostationary weather satellite, GOES 16.

On the left is an image at 6 AM PST using visible light.   You can see the tight swirl of clouds that circle into the low center.  Beautiful.  Cold air is streaming off of the Carolinas and Georgia and rapidly becomes unstable and cloud filled off the coast. (Cold air is going over the warm Gulf Stream; cold air above warm air near the ocean produces a large change of temperature with height, which causes the atmosphere to convect).


The picture to the right is at the same time, but uses the infrared part of the electromagnetic spectrum.  Infrared takes the temperature of the clouds and surface, with colder temperatures generally indicating higher clouds.   Note the shield of high cirrus-type clouds extending to the northwest and north of the low center. The colors indicate the highest clouds, black is low level stuff, with grays at intermediate altitudes.

A close up of the low center will impress:



The National Weather Service surface analysis at 4 AM PST, shows a strong cyclone with an estimated central pressure of 964 hPa--very strong for the area--with an intense pressure gradient to the south and west of the low center.  This is the classic structure of a marine cyclone.


One of the impressive features of this storm is its rapid intensification during the past 24 h.   According to the NWS HRRR analysis (see below), the pressure dropped from 1011 hPa yesterday at 4 AM PST (12z yesterday) to 967 hP at the same time this morning--a decline of 44 hPa.  Huge.
A storm that deepens by 24 hPa or more in 24h is undergoing explosive cyclogenesis and often called a "bomb".    Some edgy meteorologists sometimes call the process bombogenesis....but you won't find such loose talk in this blog.

The latest runs of the NWS HRRR model takes the low northeastward up the coast (see forecasts for 8 AM and 1 PM PST below).  A huge pressure gradient will pass over eastern Long Island and SE New England:  expect gusts over 50 mph there and power outages.




And with cold air streaming off the continent, there will be plenty of snow.  The 18-h forecast of the NOAA/NWS HRRR model over an 18-h period starting 1 AM PST this morning shows over a foot from eastern LI into coastal New England.  And this doesn't include the whole event.


Finally, this storm was very well forecast, with the threat indicated over a week ago.  The NOAA/NWS 78hr GFS model forecast (sea level pressure and precipitation) valid 10 AM PST this morning was very good (see below, courtesy of Colorado State).


But you want to be really impressed?  Here is the 360 hr forecast (15 day!) for 10 PM last night.  HUGE storm predicted.    A little fast, but amazing none the less.


The forecasts are so good now, the marine traffic avoids the storm.  This plot shows the the wind gusts and circulation around the storm at 1 AM PST, with ship locations plotted.  Only one errant ship on the SE side of the low...I hope they don't get into trouble.  In the old days, ships would get into the centers of big storms and give us reports (if they didn't sink).  Few ship observations in storm centers now.


Talking of avoidance....almost no flights across coastal NY and New England!


Numerical weather prediction has come a huge way in the last few decades...and my colleagues at the National Weather Service can be proud of the highly useful products they are providing to the nation.

Explosive cyclogenesis off the East Coast of the United States

GOES-16 Clean Window (10.3 µm) Imagery, 0102-1337 UTC on 4 January 2018 (Click to animate)

A strong extratropical cyclone that deposited snow in the deep south developed explosively during the early morning hours of 4 January 2018. The GOES-16 Clean Window (10.3 µm) animation, above, from 0102 – 1337 UTC on 4 January, brackets the explosive development: from 993 hPa at 0000 UTC to 968 mb at 0900 UTC, a strengthening that easily meets the “Bomb” criteria set forth by Sanders and Gyakum (1980). The Clean Window animation shows the strong surface circulation with well-defined conveyor belts. Convection develops at the leading edge of the dry slot that is approaching southern New England at the end of the animation. The Low-Level Water Vapor (7.3 µm) animation for the same time, below, suggests very strong descent behind the storm, where brightness temperatures warmer than -10º C (orange in the enhancement used) are widespread.

GOES-16 Low-Level Water Vapor (7.3 µm) Infrared Imagery, 0102-1332 UTC on 4 January 2018 (Click to animate)

This storm can also be viewed using Red-Green-Blue composites (in addition to the single-channel animations shown above). The Airmass RGB, below, combines the Split Water Vapor Difference (6.2 µm – 7.3 µm) as Red, Split Ozone (9.6 µm – 10.3 µm) as Green, and Upper level Water Vapor (6.2 µm) as Blue. (Other storms analyzed with the Airmass RGB can be seen here, here, and here). The strong red signal in the Airmass RGB south of the storm suggests very strong sinking motion.

GOES-16 AirMass RGB Product, 0102-1332 UTC (Click to animate)

ASCAT Scatterometer winds over the system at 0205 UTC showed an elongated surface circulation with multiple observations of winds exceeding 50 knots (in red), and a large region (in yellow) of winds exceeding 35 knots.

GOES-16 ABI Clean Window (10.3 µm) and ASCAT Scatterometer winds, 0205 UTC on 4 January 2018 (Click to enlarge)

GOES-16 ABI Red Visible (0.64 µm) and ASCAT Scatterometer winds, 1520 UTC on 4 January 2018 (Click to enlarge)

The 1520 UTC ASCAT pass, above, sampled half the storm, and hurricane-force winds were indicated.

The snow that was deposited in the Deep South by this storm (also discussed here) persisted through a cold night and was visible in the GOES-16 Visible (0.64 µm) imagery, below. Highly reflective snow can be difficult in a still image to distinguish from clouds — but the Snow/Ice Channel on GOES-16 (1.61 µm) detects energy at a wavelength that is strongly absorbed by ice. Thus, snow (and ice) on the ground (or in clouds), has a different representation. (Here are toggles between the two images, with and without a map). The snow cover over coastal Georgia, South and North Carolina appears dark in the Snow/Ice channel because the snow is absorbing, not reflecting, the 1.61 µm radiation.  It is noteworthy that the 1.61 µm image is especially dark over far southeastern Georgia northeastward along the immediate coastline of South Carolina.  These are regions where freezing rain and sleet fell, versus predominantly snow to the north and west (as also noted here; The National Weather Service in Tallahassee tweeted out an ice/snow accumulation map that also agrees with the 1.61 µm image).  Ice in the cirrus clouds northeast of North Carolina is also apparent in the Snow/Ice 1.61 µm imagery.

GOES-16 Band 2 Visible (0.64 µm) Imagery, 1412 UTC on 4 January 2018 (Click to enlarge)

GOES-16 ABI Band 5 Snow/Ice (1.61 µm) Imagery, 1412 UTC on 4 January 2018 (Click to enlarge)

Suomi NPP overflew the storm shortly after midnight on 4 January; Day Night band visible imagery (courtesy Kathleen Strabala, CIMSS), below, shows a well-developed cyclone covering much of the northeast Atlantic Ocean. Snow cover is apparent over the deep south of the United States.

Suomi NPP Day Night Band Visible (0.7 µm) Imagery, 0614 UTC on 4 January 2018 (Click to enlarge)

(Added, 5 January 2018: This website shows a during-the-day CIMSS True Color Image animation of the storm on 4 January 2018. Animation courtesy Dave Stettner, CIMSS).

A Remarkable Forecast of a Beast of a Storm

Intense frontal cyclones don't come much prettier than the nor'easter rampaging up the east coast today.  Satellite imagery and radar for 1200 UTC shows the beautifully wrapped up system with the low center just a shade ESE of Virginia Beach.  Precipitation was heaviest near or just offshore (radar imagery well offshore is nonexistent). 


If we slap on the RAP 925-mb analysis (roughly 750 m above sea level and a good level for seeing the frontal structure) we see the classic structure of an intense frontal cyclone predicted by yesterday's NAM (see prior post) with the cold and occluded/warm fronts oriented at right angles, weakening of the temperature contrast associated with the cold front near the occluded/warm fronts (known as the frontal fracture), the frontal temperature contrast associated with the occluded front maximizing near and west of the low center, and the occluded front extending through the low center as a back-bent occlusion.  One can also see a near cutoff pocket of warm air near the low center (a.k.a. the warm-core seclusion) as cold air encircles the system.  The area in purple shows an intense low-level jet with winds in excess of 40 m/s (80 knots, light purple) wrapping cyclonically from the west to south of the low center, culminating in a maximum in excess of 45 m/s (90 knots, dark purple) known as the poisonous tail of the back-bent occlusion.  In this case, the wind maximum likely represents a sting jet, a local wind maximum near the tip of the comma cloud head that is produced by the descent of strong winds from aloft.  For more on this subject, see What is a Sting Jet?


The 30 hour NAM forecasts that we presented yesterday were quite remarkable and I've reproduced them below for comparison with the RAP analyses above.  The frontal structure, low center position, and low center intensity are very well captured.  The NAM forecast central pressure of 961 mb is a bit overdone compared to the RAP analysis 967 mb, but analysts at the National Weather Service Weather Prediction center put it at 960 mb, so the NAM forecast is certainly within the uncertainty. 




Such a forecast is a remarkable scientific achievement.  We shouldn't take it for granted.  Through the mid 1980s, operational numerical modeling systems frequently failed to predict intense frontal cyclone development of this type.  Scientific papers describe errors in central pressure forecasts of as large as 55 mb.  You read that right.  55 mb.  Basically, a complete and total failure to predict the cyclone development. 

Today, it's almost impossible to believe numerical forecasts could be that bad, but they were, and many on the high seas paid with their lives.   It is only through advances in understanding, observing systems, computing infrastructure, and numerical modeling techniques that we knew a storm like the one above was coming (in fact, many days in advance).  Surely there will be some issues with details of the local forecasts that require further research and model improvements, but forecasts of intense frontal cyclones have come a long long ways. 

An Unusually Sunny Midwinter

One of the minor negatives of living in the Pacific Northwest is the lack of sun during midwinter, the result of our northern latitude and considerable cloudiness.

Some folks get depressed from the darkness, developing  Seasonal Affective Disorder (SAD).   A problem that can be addressed by securing a light box, getting out during midday, or heading to a southern clime during the holiday season.

But this winter has been much better than most, with more sun than usual.

Noon Today

Let me show you the proof.    Aaron Donohoe of my department has examined the solar radiation data collected on our roof since the year 2000.   Here is his plot of cumulative solar radiation during the month of December.  The black-red line is this year.  For much of the month, this year was the sunniest since 2000, but fell into second place at the end.  No complaints.
And the first few days of January have been plenty bright, as illustrated by Space Needle PanoCam above and the solar radiation measured on the Atmospheric Sciences Dept roof (see below).


The sunny December is a huge boon to Seattle's psyche, since this month is generally the most depressing, with the shortest days and weakest sun.   By the end of January, things are starting to brighten and by the end of February, Northwest spring is upon us.

Why such sunny skies?  Because we have had persistent high pressure over the West Coast, and high pressure is the enemy of clouds.  To demonstrate this, here is the anomaly (difference from normal) of sea level pressure during December.  A big positive (high pressure) anomaly over our region.

And the high pressure also brought extensive dry periods.  Take a look at the cumulative precipitation at Sea Tac during the past 4 weeks.   We had less than normal, and nearly all the rain occurred over a few days when weather systems broke through the ridge.  Most of the month was dry, particularly the first two weeks.
The unexpected sunshine has attracted some Northwest residents out of hibernation.  Here is someone you might know....