A toggle between 250-meter resolution Terra MODIS True-color and False-color Red-Green-Blue (RGB) images from the MODIS Today site (below) provided a more detailed view of the Lake Erie ice dam and upwind drift ice at 1615 UTC. Snow and ice appear as shades of cyan in the False-color image, in contrast to supercooled water droplet clouds which are shades of white.The Terra MODIS Visible (0.65 µm) image with an overlay of RTMA surface winds (below) showed the southwesterly flow across the long axis of the lake. A toggle between 1607 UTC Terra MODIS and 1757 UTC Suomi NPP VIIRS Visible images (below) showed the motion of the lake drift ice during that time period.
On the following day (07 January), 250-meter resolution Terra MODIS true-color and false-color RGB images from the MODIS Today site (below) showed that a larger V-shaped ice floe was located just southeast of the Peninsula, with its vertex pointed toward the Hampton Roads Bridge-Tunnel (HRBT). Snow and ice also appear as shades of cyan in the MODIS false-color image.07 January also happened to be the last full day of imagery to be broadcast by the GOES-13 satellite — a comparison of 1-minute Mesoscale Sector GOES-16 (GOES-East) Visible (0.64 µm) and 15-30 minute interval GOES-13 Visible (0.63 µm) images (below) showed that the V-shaped ice floe continued to drift southwestward toward the HRBT. However, it was difficult to tell whether the ice feature made it over and past the tunnel; even with the improved GOES-16 Visible spatial resolution (0.5 km at satellite sub-point, compared to 1.0 km for GOES-13) and the 1-minute rapid image scans, the ice floe became harder to track during the afternoon hours before high clouds began to overspread the region. However, a close examination of Suomi NPP VIIRS true-color and false-color images at 1826 UTC (below) indicated that some of the ice had indeed moved westward past Fort Monroe (on the far southeastern tip of the Peninsula) and over/past the HRBT. On the topic of cold temperatures in southeastern Virginia, a new daily record low of -3 ºF was set at Richmond on the morning of 07 January, and at Norfolk new daily record low and record low maximum temperatures were set (10 ºF and 23 ºF, respectively).
— NWS Marquette (@NWSMarquette) January 6, 2018
For perspective, the daily morning minimum temperatures at Embarrass, Minnesota are also plotted on the images — on these 3 days Embarrass was the coldest official site in the US (including Alaska).
The VIIRS images were captured by the Space Science and Engineering Center direct broadcast ground station.
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.
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.
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.
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.
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.
(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).
In a toggle between Suomi NPP VIIRS true-color and false-color Red-Green-Blue (RGB) images from RealEarth (below), the deeper snow cover in Georgia appears as darker shades of cyan.
===== 04 January Update =====A toggle between Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0620 UTC (1:20 AM Eastern time) on 04 January (above; courtesy of William Straka, CIMSS) showed a nighttime view of the rapidly-intensifying storm when it had an estimated minimum central pressure of 972 hPa or 28.70″. Note the signature of snow cover — extending from southeastern Georgia across eastern portions of South Carolina and North Carolina — which is evident on the “visible image at night” Day/Night Band (made possible by ample illumination from the Moon, which was in the Waning Gibbous phase at 92% of Full). A full-resolution version of the Day/Night Band image is available here.
During the following daytime hours, 30-second interval Mesoscale Sector GOES-16 “Red” Visible (0.64 µm) images (below) showed the evolution of the low pressure center of circulation as it continued to rapidly intensify (surface analyses) off the US East Coast.
Curious about the historical context of this system impacting the East Coast? Interestingly, there was a similar system WPC found that dated back to–oddly enough–January 4, 1989. pic.twitter.com/WcNbJUp2yp
— NWS WPC (@NWSWPC) January 4, 2018
During the subsequent daylight hours, 1-minute Mesoscale Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (below) showed the Chesapeake Bay streamer cloud moving southward. Note that this cloud produced light snow as far south as Currituck, North Carolina (KOTX) from 14-15 UTC or 10-11 AM local time. It is possible that some light snow also occurred across a portion of the Eastern Shore of Virginia and the Outer Banks of North Carolina, but verification is not possible due to the scarcity of surface observation sites in those areas.
Comparisons of POES AVHRR/Terra MODIS/Suomi NPP Infrared (10.8 µm/11.0 µm/11.45 µm) and Visible (0.86 µm/0.65 µm/0.64 µm) images along with an overlay of the corresponding Real-Time Mesoscale Analysis (RTMA) surface winds (below) provided views of the mesovortex at 1522 UTC, 1714 UTC and 1852 UTC, respectively.During the preceding nighttime hours, a comparison of Suomi NPP VIIRS Infrared (11.45 µm) and Day/Night Band (0.7 µm) images at 0729 UTC along with an overlay of 07 UTC RTMA surface winds (below) showed in spite of patchy thin cirrus clouds over the region, ample illumination from the Moon (which was in the Waxing Gibbous phase, at 96% of Full) enabled a signature of the early stage of mesovortex formation to be seen on the Day/Night Band (DNB) image. Ice crystals within the thin cirrus clouds were responsible for the significant scattering city light signatures on the DNB image. As an aside, it is interesting to note that ice could be seen in the nearshore waters of Lake Michigan — both in the western part of the lake, off the coast of Wisconsin and Illinois, and in the eastern part of the lake off the coast of Lower Michigan. The lake ice appeared as darker shades of cyan in the 250-meter resolution Terra MODIS false-color (Band 7-2-1 combination) Red-Green-Blue (RGB) image from the MODIS Today site (below).
An animation of GOES-16 Snow/Ice (1.61 µm) imagery (below) showed that the high reflectance (brighter white) signature of the lower-altitude stratiform cloud deck persisted across southern Minnesota into western Wisconsin and northern Iowa during the daylight hours, along with widespread surface reports of light snow. In contrast, higher-altitude clouds composed predominantly or entirely of ice crystals exhibited a darker gray appearance (since ice crystals, as well as surface snow cover and frozen lakes/rivers, are strong absorbers of radiation at the 1.61 µm wavelength).In the corresponding GOES-16 “Clean” Infrared Window (10.3 µm) animation (below), much of the aforementioned lower-altitude stratiform cloud layer exhibited cloud-top infrared brightness temperatures in the -10 to -20 ºC range across far southern Minnesota into northern Iowa, with colder -20 to -30 ºC values seen in the more northern and eastern portion of the stratus cloud. Plots of rawinsonde data (at 12 UTC on 28 December) from Aberdeen, South Dakota and Chanhassen, Minnesota (below) showed that the temperature profiles within the low-altitude cloud layers were close to isothermal, with air temperatures generally in the -16 to -22 ºC range. So how could snow be falling from stratus clouds whose tops appeared be be composed of supercooled water droplets? A journal article titled “Vertical Motions in Arctic Mixed-Phase Stratiform Clouds” demonstrated that in-cloud glaciation can and does occur below the supercooled liquid cloud top in an arctic air mass. This example certainly shows that in an arctic air mass, mixed/supercooled cloud above snow or ice cloud is possible, particularly in temperatures between -20 ºC and -30 ºC — and cloud phase classification for operational decisions must sometimes look beyond the examination of single-band satellite imagery (or even derived products such as Cloud Phase).
Thanks to Mike Pavolonis (NOAA/NESDIS/CIMSS) and Jordan Gerth (CIMSS) for their insightful explanations regarding cloud phase — and thanks to the NWS La Crosse staff for bringing this interesting case to our attention!
With an additional 3.5″ of snow at the Erie, PA airport as of 5PM, this brings the two day (12/25-26) total up to 58″ and the storm total (From 7PM Christmas Eve thru 5PM 12/26) up to 60.0″. Heavy snow continues to fall. Here is a look at some of the records. #pawx pic.twitter.com/BN5txOpByZ
— NWS Cleveland (@NWSCLE) December 26, 2017
(27 December Update: additional lake effect snow at Erie on 27 December brought the final storm total accumulation to 65.1 inches: NWS Cleveland summary. NOHRSC plots showed a maximum snow depth of 49 inches just southwest of downtown Erie; the maximum snow depth at Erie International Airport was 28 inches on 26 December, which was still less than their all-time record snow depth of 39 inches on 21 December 1989)
A sequence of Infrared Window images captured by Terra/Aqua MODIS (11.0 µm) and Suomi NPP VIIRS (11.45 µm) is shown below. The coldest cloud-top infrared brightness temperatures associated with the dominant lake effect snow bands were in the -30 to -35 ºC range (dark blue to pale green color enhancement), similar to what was seen in the GOES-16 Infrared Window imagery.Farther to the northeast, these Lake Erie lake effect bands also produced significant snowfall in far southwestern New York, with 32 inches reported at Perrysburg (located 20 miles west of Dunkirk, station identifier KDKK). In addition, lake effect snow bands over Lake Ontario were responsible for even higher snowfall amounts:
Updated storm total snowfall for:
Perrysburg off of Lake Erie = 32.0″
8 N Redfield off of Lake Ontario = 56.9″ pic.twitter.com/3cngvFZRR7
— NWS Buffalo (@NWSBUFFALO) December 26, 2017
1-minute GOES-16 “Red” Visible (0.64 µm) images (below) showed the lake effect snow bands over Lake Ontario on 26 December.