A suspicious area of “haziness” began to appear over the Pacific Northwest region (specifically, Washington state and adjacent parts of northern Oregon and southern British Columbia) on the late afternoon and early evening GOES-12 visible images (above) on 06 July 2008. A MODIS true color image from the SSEC MODIS Today site (below) also shows the haziness over the Pacific Northwest and the adjacent offshore waters, as well as thick smoke farther to the south due to active fires that continued to burn in parts of California.

My first thought was: “Wow, all that smoke from the California fires has moved that far north again today (like it did on the first 3 days of July)?” — but that didn’t seem like a meteorologically plausible scenario for this particular day. Then I recalled seeing MODIS true color imagery of thick smoke from fires burning in far eastern Russia that was moving across the Sea of Okhotsk and the Kamchatka Peninsula on 30 June and 02 July; could this haziness seen on the GOES-12 visible imagery possibly be smoke from those Russian fires? Backward airmass trajectories using the NOAA ARL HYSPLIT model (below) seem to support that idea — air parcels arriving over Washington state at 2000, 3000, and 4000 meters above ground level came from the region where the thick smoke was seen on MODIS true color imagery several days earlier.

It is also interesting to examine the corresponding GOES-11 visible imagery (below) from the same time period as the GOES-12 imagery shown above. Why is the haziness over the Pacific Northwest region not as apparent? The answer to that question is: forward scattering. The forward scattering of light by the relatively small smoke particles increases as the angle between the sun, the smoke particles, and the GOES-12 (GOES-East) satellite approaches 180 degrees — this forward-scattered light makes the smoke appear “brighter” during late afternoon and early evening. The GOES-11 (GOES-West) satellite is positioned much farther to the west (at 135º W longitude, compared to 35º W longitude for GOES-12), so there is no forward scattering geometry to enhance the appearance of the airborne smoke over the Pacific Northwest region.

However, note that the hazy signature of the airborne smoke is evident on GOES-11 visible imagery from the next morning, when the sun was illuminating the smoke from the east (thereby creating a favorable forward scattering geometry with respect to the GOES-West satellite).

View only this post Read Less

GOES-11 visible images (Animated GIF)

Given the rather large satellite viewing angle (or “zenith angle”) of geostationary satellites positioned over the Equator, one would think that the imagery would not be of much value over places such as far northern Alaska. However, a forecast discussion issued by Fairbanks, Alaska mentioned the utility of GOES visible imagery for monitoring fog and stratus along western parts of the Arctic coast of Alaska:

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
347 AM AKDT SAT JUL 5 2008

.DISCUSSION…

OVER THE ARCTIC…GOES VIS LOOP SHOWING AN EXTENSIVE AREA OF STRATUS OVER AREAS FROM BARROW NORTH THROUGH SOUTHWEST…INCLUDING MOST OF ZONE 201. THIS STRATUS IS MISSED BY THE LOW LEVEL RH PROGS ON BOTH THE GFS AND NAM MODELS. THIS AREA IS LIKELY TO REMAIN FOGGY THROUGH TONIGHT WITH ONSHORE FLOW CONTINUING…ALTHOUGH VISIBILITY MAY COME UP SOME DURING THE AFTERNOON AND EARLY EVENING. DENSE FOG HEADLINES WILL BE POSTED FOR ZONES 201 AND 202. THE EASTERN ARCTIC COAST IS LIKELY TO REMAIN FOG-FREE.

GOES-11 visible imagery at 30-minute intervals on 05 July 2008 (above) does indeed do a fairly good job of showing the movement of the bank of fog and stratus that had moved inland over locations such as Barrow (PABA), Wainwright (PAWI), and Point Lay (PLIZ) during the day. A surface meteorogram for Wainwright, Alaska (below) shows that the surface visibility remained at or below 1 mile during much of that particular day, and temperatures dropped below freezing as onshore winds persisted.

Wainwright AK surface meteorogram

Other features of interest to note on the GOES-11 visible imagery shown above:

1. a long smoke plume from a wildfire, which originates just southeast of Fort Yukon (PFYU) and blows southwestward across central Alaska
2. the high amount of sea ice that remained in the Arctic Ocean north of Alaska
3. the snow-covered mountains of the Alaska Range in the southern part of the state — between Minchumina (PAMH) and Talkeetna (PATK) — which includes the summit of Mount McKinley (Denali) at 20,320 feet (6,194 m)
4. northern Alaska experiences 24 hours of continuous daylight during this part of the summer

View only this post Read Less

As noted in the previous Blog entry, Tropical Storm Bertha became the Atlantic Basin’s second tropical storm on 03 July 2008. Apparently, Bertha set a new record for the furthest east named storm formation in the tropics (classified as south of 23.5N) prior to 1 August since 1950. It became classified as a tropical storm at 24.7W which easily beat the old record set by Anna in 1969 (36.0 W).
Meteosat-9 IR images with overlays of QuikSCAT and ASCAT satellite winds (above) from the CIMSS Tropical Cyclones site on following day (04 July 2008) showed some bursts of convection around the tropical cyclone, and verified the presence of tropical storm force winds. The CIMSS wind shear product (below) indicated that Bertha existed in an environment of low wind shear, which was favorable for continued intensification.

Meanwhile, on the previous day (03 July 2008), the afternoon MODIS visible image and Land Surface Temperature product (below) showed mostly cloud-free conditions and very hot surface temperatures across much of the Desert Southwest region of the United States. Death Valley in California reached a high temperature of 122º F, the hottest day so far this summer season (121º F had been reached at that location a few times in June 2008); other high temperatures in the region that day included 118º F at Bullhead City, Arizona and 115º F at Laughlin, Nevada. While the MODIS LST values were generally about 20-30º F higher than the actual air temperatures that were measured in instrument shelters about 5 feet off the ground — the highest LST values seen on this day were near 150º F (darker red colors) in parts of California, Nevada, and Arizona — the LST product is still useful for depicting where the hottest areas might be (since the coverage of stations that report air temperature over any given region might be somewhat sparse).

View only this post Read Less

Jesse Ferrell highlighted an undular bore emerging off the coast of Africa this morning, as seen in the annotated 1200 UTC Meteosat-9 image above (or click here). Bores occur when impulses move underneath stable layers, exciting a series of closely-spaced lines of clouds, as shown here, for example. Bores are associated with stable air, and you can note the lack of cumuliform clouds in the vicinity of this bore as it emerges off the coast of Africa just to the north of developing Tropical Depression #2 (update: Tropical Storm Bertha). A meteorogram showing data from station GQNN (Nouakchott, Mauritania, at 18 N, 16 W) — located halfway between the mouth of the Senegal River to the south and Cape Timiris to the north, or just to the south of the east-west band of cirriform clouds that straddles the coast — shows the characteristic pressure perturbation and wind shift at 0800 UTC as the bore passed.

A loop of visible imagery shows the two bore structures moving over the waters of the Atlantic Ocean. The genesis of these bores appears to be in dying convection over eastern Africa. Note also the presence of von Karman vortex streets that occur in the marine clouds downwind of the Canary Islands, which Islands are at the extreme northern boundary of the image.

An interesting aspect of this case is that the bore is along the southern edge of a Saharan Air Layer (SAL) that has emerged from northern Africa and is moving east southeastward into the central Atlantic ahead of the developing Bertha. The dry air associated with this layer of air can be a significant deterrent to tropical cyclone intensification. Thus, if the storm moves to the northwest, or moves close enough to the SAL to entrain dry air, do not expect rapid strengthening. The dry air associated with the SAL is also apparent in the MIMIC TPW loop available here.

For the latest information on tropical storm Bertha, refer to the CIMSS tropical weather page or to the National Hurricane Center.

View only this post Read Less