January 12th, 2010

2010 Annular Solar Eclipse PFS Bulletin No. 4

Published at 23:15. Filed under Precision Forecast Service; no comment so far.

FOREWORD

This is 2010 Annular Solar Eclipse PFS Bulletin No. 4, issued in both English and Chinese. No major changes were made on the forecast philosophy since last bulletin. The forecast diagrams mentioned below may be found at http://7timer.y234.cn/V3/product.php?language=en&product_id=2, https://www.fnmoc.navy.mil and http://www.ecmwf.int. Numeric forecast for various locations may be found at http://7timer.y234.cn/V3/product.php?language=en&product_id=1. RSS feed of this service is available at http://7timer.y234.cn/V3/wordpress/?feed=rss2&cat=46.

ANALYSIS

NCEP GFS JAN12/06Z's forecast shows a significant westerly trough around 103E 28N, the associated wet area reaches 116E over the annularity path. Over the east, the 1030hPa contour reaches 30N, but the near-surface wind forecast suggests the winter monsoon has weaken at that time.

ECMWF JAN12/00Z's forecast shows the same westerly trough over western China, but is about 3-5 degrees west of GFS's forecast. Meanwhile, ECMWF gives a slightly stronger winter monsoon persisting over East China.

FNMOC NOGAPS JAN12/06Z's forecast gives a westward westerly trough located between the ECMWF's prediction and GFS's prediction, centred at 100E, 28N. NOGAPS also expect a strong but weakening winter monsoon persisted over east, with 1030hPa contour reaches as south as 25N. NOGAPS also notes low visibility (<10km) may be applied at Sichuan Basin and at the annularity path over Yangtze Valley. FNMOC EFS JAN12/06Z's forecast suggests minimum chance for significant rainfall along the annularity path.

For analyses of the models above, we can depict: a westerly trough lies at somewhere over the northern Indo-China Peninsula, and a winter monsoon is weakening over mainland China; however there is still considerable divergence over the location of the westerly trough between the models.

FORECAST

Since the divergence between the models is still quite significant, the uncertainty of this forecast remains moderate. The situation varies over the models. If GFS gets it right (on an eastward trough and a weak winter monsoon), then we can expect a fair weather over the west of Yunnan, but generally poor sky around Sichuan Basin and some parts of Central and South China. However, statistically ECMWF has a better performance, and what is more, NOGAPS also suggests a slow moving trough, so in this forecast the author consider the situation of a slow moving trough and a slow weaken monsoon. It should point out that many weather websites employ GFS, which is somehow against the philosophy of this forecast, as their numeric model, so there can be significant difference between this forecast and the weather information from the internet.

Local forecasts are listed below.

• In Myanmar: mainly clear with a few clouds, with some haze in valley. More clouds to the northeast.
• In Yunnan, China: mainly cloudy along the annularity path; however, if the westerly trough moves faster than expected (or close to GFS's forecast), then there will be a good chance for a less cloudy or even sunny weather.
• Around Chongqing, China: foggy.
• Around Shiyan and Nanyang, China: sunny weather possible with fair visibility for solar observation at low elevation.
• In Shandong, China: sunny or less cloudy weather possible, but the visibility may be low for solar observation at low elevation.

NEXT UPDATE

Brief final update around January 14 0400 UTC.