Occluding cyclone over the Labrador Sea

January 7th, 2009 |
GOES-12 6.5 µm water vapor images + QuikSCAT winds

GOES-12 6.5 µm water vapor images + QuikSCAT winds

AWIPS images of the GOES-12 6.5 µm water vapor channel data  with an overlay of polar-orbiting QuikSCAT winds (above) showed the a rapidly-occluding cyclone over the Labrador Sea on 07 January 2009. The classic “dry swirl” signature on the water vapor imagery is a tell-tale indicator that a mature cyclone has reached the occluded phase. Note that the GOES-12 satellite had just returned to service as the operational GOES-East satellite on the previous day.

QuikSCAT wind speeds were as high as 58 knots (red wind barbs) off the southern tip of Greenland at 09:00 UTC. A comparison of the atmospheric motion vector coverage derived from GOES-12 IR and water vapor channel data with those derived from the WindSat instrument on the polar-orbiting QuikSCAT satellite (below) demonstrate the advantage of the 12.5 km resolution data from the QuikSCAT satellite — however, the QuikSCAT winds are valid near the surface, while the GOES-12 winds are valid at higher levels within the lower, middle, and even upper the troposphere.

GOES-12 water vapor image + GOES-12 winds + QuikSCAT winds

GOES-12 water vapor image + GOES-12 winds + QuikSCAT winds

The Blended Total Precipitable Water product (below) depicted a plume of higher PW values (in the 15-25 mm range) wrapping around the eastern and northern periphery of the occluding cyclone. The polar-orbiting AMSU instrument indicated that rainfall rates were as high as 7-9 mm/hour within this plume of PW.

Blended Total Precipitable Water product

Blended Total Precipitable Water product

GOES-12 water vapor image + 24-hour forecast of surface fronts/pressure

GOES-12 water vapor image + 24-hour forecast of surface pressure

The 24-hour forecast had the position of the surface low a bit far to the southwest (above) — however,  using the “dry swirl” signature on the water vapor imagery, the well-trained analysts at HPC were able to accurately depict the location of the surface low center as it moved northwestward across the Labrador Sea (below).

GOES-12 water vapor images + HPC surface front analysis

GOES-12 water vapor images + HPC surface frontal and MSLP analysis

The effect of stratus clouds on temperatures

January 6th, 2009 |
GOES-13 fog/stratus product

GOES-13 fog/stratus product

AWIPS images of the  GOES-13 fog/stratus product (above) showed a patch of stratus cloud that developed quickly as it moved northeastward across southern Wisconsin during the pre-dawn hours on 06 January 2009. In advance of this cloud feature, air temperatures were dropping off as clear skies and light winds were promoting strong radiational cooling – in southern Wisconsin, Boscobel (station identifier KOVS) dropped to 2º F (-17º C) and Madison (station identifier KMSN) dropped to 6º F (-14º C) shortly after 08 UTC (2 AM local time). However, after the arrival of the cloud feature, surface air temperatures quickly began to rise into the middle to upper teens F as the cloud deck began to trap heat that was radiating from the surface.

Comparisons of the 4-km resolution GOES-13 fog/stratus product with the 1-km resolution MODIS fog/stratus product  during the early stages of formation of this stratus cloud deck (below) demonstrated the superior feature detection capability of the MODIS instrument. Also note that the GOES-13 fog/stratus product exhibited a “false signal” along the western coast of Lake Michigan, where colder water temperatures in the low-mid 30s F were “confusing” the product — the improved spatial and spectral resolution of the MODIS channels allowed the creation of a “cleaner” fog/stratus product.

GOES-13 and MODIS fog/stratus product

GOES-13 and MODIS fog/stratus product

GOES-13 and MODIS fog/stratus product

GOES-13 and MODIS fog/stratus product

The development and growth of the stratus cloud feature was also evident on the GOES-13 Low Cloud Base product (below), portrayed an an extensive area of clouds having bases less than 1000 feet above the surface (red color enhancement).

GOES-13 Low Cloud Base product

GOES-13 Low Cloud Base product

This cloud feature was apparently fairly deep, with the GOES-13 sounder Cloud Top Height product (below) indicating cloud tops in the 12,000 to 14,000 feet range (light green color enhancement).

GOES-13 Cloud Top Height product

GOES-13 Cloud Top Height product

Welcome back GOES-12

January 5th, 2009 |
GOES-13 and GOES-12 visible image (centered over Tampa, Florida)

GOES-13 and GOES-12 visible images (centered over Tampa, Florida)

The GOES-12 satellite (which had experienced a thruster anomaly back on 14 December 2008) was re-activated on the morning of 05 January 2009 (beginning at 15:15 UTC). A comparison of GOES-13 and GOES-12 visible images (above) centered on Tampa, Florida showed that the GOES-12 image navigation was initially a bit “shaky”, but seemed to stabilize after a couple of hours. The NOAA/NESDIS Office of Satellite Operations (OSO) and Office of Satellite Data Processing and Distribution (OSDPD) will continue to monitor the performance of GOES-12 during the Image and Navigation  Recovery (INR) period, before the decision is made to re-establish GOES-12 as the operational GOES-East satellite (possibly on the morning of 06 January 2009?).

For the latest information, see the NOAA Satellite Services Division Special Bulletins.

— 06 JANUARY UPDATE —

As of 15:15 UTC on 06 January 2008, GOES-12 has resumed duty as the operational GOES-East satellite.

GOES-12 visible image

GOES-12 visible image

Upper Midwest ice storm

January 4th, 2009 |
MODIS visible, snow/ice, and IR window channel images

MODIS visible, snow/ice, and IR window channel images

A freezing drizzle / light freezing rain event occurred across parts of the Upper Midwest on 03 January04 January 2009 — an ice accrual of 0.1 to 0.2 inch was reported at some locations in northern Iowa, southern Minnesota, and southern Wisconsin. Post-event AWIPS images of the 1-km resolution MODIS visible channel, the 2.1 µm  “snow/ice” channel, and the 11.0 µm “IR window” channel (above) demonstrated the utility of using the snow/ice channel imagery to depict the areal coverage of significant ice accrual. Snow (and especially ice) are strong absorbers at the near-IR 2.1 µm wavelength, so those show up as much darker features on the MODIS snow/ice image (in contrast to supercooled water droplet clouds, which show up as much brighter features).

A mixture of low and high clouds covered  the southern, southeastern, and eastern portions of satellite images shown above — but most of the MODIS image scene on 04 January was cloud-free snow cover. Even though there was generally more snow cover in place across the northern half of the image area (from eastern South Dakota to northern Minnesota), the ice-glazed snow pack farther to the south across norther Iowa and southern Minnesota appeared even darker on the snow/ice image.

The National Weather Service forecast office at Milwaukee/Sullivan, Wisconsin posted an excellent  discussion of the classic thermal profile for ice for this particular event.

— 05 JANUARY UPDATE —

On the following day (05 January), conditions were relatively cloud-free over most of the region, allowing a view of the ice accrual farther to the east across southern Wisconsin (below). The western half of the darker “ice accrual signal” over western Iowa seemed to be diminishing, due to full sunshine and brisk southwesterly winds helping to erode the thickness of the surface ice glaze somewhat. MODIS Land Surface Temperatures were in the upper 20s to around 30 F (darker green colors) across the ice-covered areas of northern Iowa at 17:30 UTC (11:30 am local time).

MODIS visible, 2.1 µm snow/ice, and Land Surface Temperature images

MODIS visible, 2.1 µm snow/ice, and Land Surface Temperature images