Atmospheric Bore between the Grand Banks and New England

May 8th, 2015 |
GOES-13 0.63 µm Visible images (click to play animation)

GOES-13 0.63 µm Visible images (click to play animation)

Atmospheric Bores form in stable air and create horizontal cloud bands that propagate perpendicular to the along-band direction. The feature seen above in GOES-13 visible imagery formed in stable air south of a High Pressure system that pushed a backdoor cold front into New England (surface analyses). The southern edge of this bore was likely eroding as it became influenced by warmer less-stable air over with the Gulf Stream — the warm waters of the Gulf Stream were apparent in the toggle, below, of POES AVHRR 0.86 µm visible and 12.0 µm infrared imagery at 1055 UTC. The bore was apparently moving over the top of a shallow layer of sea fog that had formed in the colder waters north of the Gulf Stream.

POES AVHRR 0.86 µm Visible image and 12.0 µm Infrared image at 1055 UTC on 8 May 2015 (click to enlarge)

POES AVHRR 0.86 µm Visible image and 12.0 µm Infrared image at 1055 UTC on 8 May 2015 (click to enlarge)

Suomi NPP overflew the area at ~1800 UTC, affording a very high resolution view of the bore structures with the VIIRS 0.65 µm visible channel, below.

SNPP_DNB_1807UTC_08May2015

Suomi NPP VIIRS Visible (0.65 µm) imagery, 1807 UTC on 8 May 2015 (Click to enlarge)

The daytime propagation of the bore feature could also be followed on POES AVHRR 0.86 µm visible channel images, shown below.

POES AVHRR 0.86 µm visible images (click to enlarge)

POES AVHRR 0.86 µm visible images (click to enlarge)

Tropical Disturbance off the Southeast US Coast

May 7th, 2015 |
GOES-13 0.63 µm Visible images (click to play animation)

GOES-13 0.63 µm Visible images (click to play animation)

A disorganized subtropical system (Invest Area 90L) located over the southwest Atlantic to the east of Georgia and north of the Bahamas has the potential to become the first named system of the 2015 Atlantic Tropical Season (if named as a subtropical storm, this would be Ana). Visible imagery, above, shows a low-level swirl that is separated from any convection. However, during the 6 hours of the animation, the low-level swirl moves westward, moving more closely to active convection over the Gulf Stream. [Update, 2100 UTC 7 May: later images in the visible animation, above, showed strong convection developing over the surface circulation; another visible image animation with ship reports can be seen here]

Sea-surface temperatures (link) and wind shear (link) from the CIMSS Tropical Cyclones site show nominal conditions for strengthening.

MetOp-A passed over the southeast United States just after 1500 UTC on 7 May. The ASCAT scatterometer data (below) show a well-defined low-level circulation (with most winds just below tropical storm force) south and east of the deepest convection off the South Carolina/Georgia coasts.

ASCAT_07May2015

ASCAT winds from Metop-A and GOES-13 10.7 µm imagery, both near 1500 UTC on 7 May 2015; Surface observations from Fixed Buoys are also plotted (click to enlarge)

Suomi NPP overflew this system at 0700 UTC on 7 May, and imagery from the VIIRS Day/Night Band gave information that allowed a definitive estimate of the location of a low-level circulation. A comparison of the 0702 imagery, below, and the 1826 UTC imagery, following, shows changes in the organization and vertical structure of the developing system.

ASCAT_07May2015

Suomi NPP 11.45 µm infrared and 0.70 µm DayNight band visible imagery at 0702 UTC on 7 May 2015 (click to enlarge)

ASCAT_07May2015

As above, but at 1826 UTC on 7 May 2015 (click to enlarge)

Suomi NPP 1.61 µm near-infrared imagery can be used during the day to identify cirrus clouds: ice particles absorb (and do not reflect) radiation in these near-infrared wavelengths, but water droplets reflect. Thus, ice clouds appear dark. In the visible, both water and ice clouds are bright. The toggle below shows the 1.61 and the Visible imagery from Suomi-NPP.

ASCAT_07May2015

Suomi NPP 1.61 µm near-infrared and 0.65 µm visible imagery at 1826 UTC on 7 May 2015 (click to enlarge)

At 2006 UTC, the International Space Station’s RapidScat instrument provided surface scatterometer winds (below) that depicted the broad circulation of Invest AL90; the strongest winds were located farther away from the center of the feature.

GOES-13 0.63 µm visible image with an overlay of RapidScat surface scatterometer winds

GOES-13 0.63 µm visible image with an overlay of RapidScat surface scatterometer winds

08 May Update: Invest Area AL90 was upgraded to Subtropical Storm Ana by the National Hurricane Center around 02 UTC. A Terra MODIS 11.0 µm IR image at 0249 UTC is shown below, with overlays of the MSLP analysis, buoy reports, and RTMA surface winds.

Terra MODIS 11.0 µm IR channel image, with MSLP analysis, buoy reports, and RTMA surface wind analysis

Terra MODIS 11.0 µm IR channel image, with MSLP analysis, buoy reports, and RTMA surface wind analysis

A few hours later, a 0643 UTC comparison of Suomi NPP VIIRS 11.45 µm IR and 0.7 µm “visible image at night” Day/Night Band data is shown below.

Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band images

Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band images

For more information on this system, see the National Hurricane Center website.

GOES-15 Navigation Anomalies

May 4th, 2015 |
GOES-15 0.62 µm visible imagery, times as indicated on 3 May 2015 (click to enlarge)

GOES-15 0.62 µm visible imagery, times as indicated on 3 May 2015 (click to enlarge)

A GOES-15 (GOES-West) Star Tracker failed on 23 April 2015 at 2032 UTC. This leaves just one working Star Tracker; consequently image navigation has degraded. The image above shows three successive visible images centered near Crater Lake, OR, on 3 May 2015. The navigation shifts over time. An animation of 3.9 µm imagery, below, also from May 3rd (available here as an mp4), shows image navigation shifts throughout the day. A two-day animation of visible imagery centered on the Washington coast near Hoquiam (bottom, available here as an mp4) also shows the navigation anomalies that can be as much as 8 km in the infrared. Users who require precise animation in their GOES-15 imagery should be alert to this issue. NOAA/NESDIS, NASA and factory engineers are investigating possible fixes; GOES-15 status updates will appear here.

GOES-15 3.9 µm infrared imagery, 1400-2200 UTC on 3 May 2015 (Click to enlarge)

GOES-15 3.9 µm infrared imagery, 1400-2200 UTC on 3 May 2015 (click to enlarge)

GOES-15 0.62 µm infrared imagery, 1400-2200 UTC on 1 and 2 May 2015 (Click to enlarge)

GOES-15 0.62 µm infrared imagery, 1400-2200 UTC on 1 and 2 May 2015 (click to enlarge)

Thunderstorms in Arizona

May 4th, 2015 |
GOES-13 10.7 µm IR images (click to play animation)

GOES-13 10.7 µm IR images (click to play animation)

4-km resolution GOES-13 (GOES-East) 10.7 µm IR channel images (above; click image to play animation) showed the development and northward propagation of clusters of thunderstorms across Arizona on 04 May 2015. The coldest cloud-top IR brightness temperature was -49º C (darker red color enhancement). As the storms later organized into a mesoscale convective system, cloud-to-ground lightning strikes were seen to exceed 100 per 15-minute period.

A higher resolution view could be seen in a comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm IR channel images at 0940 UTC or 2:40 AM local time (below). Since the Moon was in the Waning Gibbous phase at 99% of full, this served as a good example of the “visible image at night” capability of the VIIRS Day/Night Band.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR images, with METAR surface reports and 1-hour cloud-to-ground lightning strikes

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR images, with METAR surface reports and 1-hour cloud-to-ground lightning strikes

One ingredient that aided in the thunderstorm development was rich moisture, as was noted in this excerpt from a NWS Phoenix forecast discussion:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
840 AM MST MON MAY 4 2015

HOWEVER WHAT WAS NOT SO OBVIOUS…AND A MODEL FAILURE…WAS THE AMOUNT OF BOUNDARY LAYER MOISTURE ADVECTED INTO SOUTHERN AZ FROM MEXICO LATE YESTERDAY AFTERNOON AND NIGHT. JUST LOOK AT THIS MORNINGS TUCSON BALLOON SOUNDING. IT SHOWED AN 800 MB DEWPOINT OF 9 DEG C WHICH LOOKS MONSOONISH. IN OTHER WORDS THE BOUNDARY LAYER MOISTURE THROUGH 700 MB WAS IMPRESSIVE.

This northward transport of moisture could be seen on GOES-15 sounder Total Precipitatble Water (TPW) derived product images (below; click image to play animation); TPW values even exceeded 30 mm or 1.18 inches (yellow color enhancement) as early as 02 UTC on 04 May, reaching a peak of 33.4 mm or 1.3 inches at 04 UTC. A comparison of the Tucson rawinsonde data profiles from 12 UTC on 03 May and 00/12 UTC on 04 May can be seen here — TPW values at that location increased from 13.5 mm (0.53 inch) to 22.3 mm (0.88 inch) during that 24-hour period.

GOES-15 sounder Total Precipitable Water derived product images (click to play animation)

GOES-15 sounder Total Precipitable Water derived product images (click to play animation)

Later in the day on 04 May, as thunderstorms moved northward across the Interstate 40 corridor in northeastern Arizona, swaths of rain-cooled wet ground appeared as lighter-gray areas on the Aqua MODIS 11.0 µm IR image at 2008 UTC (below). These swaths of wet soil exhibited IR brightness temperatures that were as much as 10º C cooler than the adjacent dry soil surfaces which were heating up quickly during the early afternoon hours.

Terra (1828 UTC) and Aqua (2008 UTC) MODIS 11.0 µm IR images

Terra (1828 UTC) and Aqua (2008 UTC) MODIS 11.0 µm IR images

The corresponding 2008 UTC Aqua MODIS Land Surface Temperature (LST) product (below) made it easier to discriminate between the cooler swaths of wet ground (LST values between 70 and 85º F, shades of green) and the adjacent areas of dry soil (LST values as warm as 100-116º F, darker shades of orange).

Aqua MODIS Land Surface Temperature product

Aqua MODIS Land Surface Temperature product