The cold has arrived...early Thu. temps. will drop into the mid 20s across inland Ga....upper 20s near & west of I-95...low to mid 30s at the beaches. It's not the coldest air of the season but darn close. Especially surprising is that this will only be the 2nd freeze this month. Still...this will not be record cold nor "pipe-busting" cold. It'll be another cold night early Fri. with lows in the upper 20s to low 30s with widespread inland frost thanks to lighter winds. What wind there will be Thu. night will come off the Atlantic which will keep the beaches & intracoastal a little milder.
The silver lining -- we're set up for a very pleasant weekend.
Another high end "event" -- storm, in other words, is in the cards for early next week -- Mon. night into Tue. & could bring another round of heavy rain & storms to the area.
Tuesday's rainfall averaged a third to three-quarters of an inch with a few higher amounts. Reports from the Jax N.W.S. Community Collaborative Rain, Hail & Snow Network (CoCoRaHS):
GAINESVILLE 8.1 SW * : 0.45
GAINESVILLE 3.8 W * : 0.51
MACCLENNY 2.5 S * : 0.33
GREEN COVE SPRINGS 6.2 N * : 0.25
ORANGE PARK 4.8 SSW * : 0.89
KEYSTONE HEIGHTS 6.9 ENE * : 0.87
KEYSTONE HEIGHTS 7.6 ENE * : 1.21
ORANGE PARK 4.7 SW * : 0.90
KEYSTONE HEIGHTS 3.5 ENE * : 0.86
ORANGE PARK 3.0 WNW * : 0.96
ORANGE PARK 0.7 NNE * : 0.78
ACKSONVILLE 6.2 ENE * : 0.69
JACKSONVILLE 5.9 SW * : 0.32
JACKSONVILLE 8.4 SSE * : 0.74
NEPTUNE BEACH 0.5 NNW * : 0.60
JACKSONVILLE 8.1 SSE * : 0.73
JACKSONVILLE 8.8 E * : 0.56
JACKSONVILLE BEACH 4.5 W * : 0.60
BUNNELL 7.7 SW * : 0.40
TRENTON 8.0 ENE * : 0.17
JASPER 5.5 S * : 0.91
BELLEVIEW 6.0 SSE * : 0.48
LADY LAKE 4.8 WNW * : 0.24
MICANOPY 3.6 SSW * : 0.85
FERNANDINA BEACH 5.4 SW * : 0.65
HILLIARD 5.4 NW * : 1.00
SATSUMA 0.2 WSW * : 0.36
PALM VALLEY 8.1 SSW * : 0.47
ST. AUGUSTINE SOUTH 2.1 S* : 0.45
LIVE OAK 9.1 NW * : 1.26
LAKE BUTLER 0.8 ENE * : 0.30
We've done pretty well in the rainfall department this month -- 2.31" above avg. for Feb.
No so wet -- parts of Africa...this from "Earth Gauge":
Lake Chad sits on the borders of Chad, Niger, Nigeria, and Cameroon. It also sits on another border, the Sahel, a grassland which divides the Sahara Desert to the north and the more humid savannah to the south. The Lake’s watershed covers almost one million square miles, with most of the Lake’s inflow coming from the south. Because it is a shallow lake, with average depths of between 16 and 26 feet, Lake Chad’s surface area fluctuates readily with changes in climate. The Lake has oscillated in size over the millennia. During the late Pleistocene and early to mid-Holocene (14,500 – 5,500 years ago), the lake covered an area as large as 154,000 square miles and had a maximum depth of 568 feet; during the Ice Age, it was even larger. For comparison, the Caspian Sea, which is the largest enclosed body of water on the planet today, is 143,000 square miles. Paleontologists refer to ancient Lake Chad as Lake Megachad.
Then, about 5,500 years ago, North Africa experienced a rapid transition from a relatively humid land with lakes, marshes, extensive vegetation cover, and numerous human settlements, to the much drier and barren state that we see today. This transition has been referred to as a “regime shift.” When this happened, Lake Chad began to shrink in size and by 2,500 years ago, it’s area had fallen to about 8,800 square miles. Since then, it has experienced periodic oscillations. Because it sits under a powerful northeasterly low-level jet stream, the area that used to be submerged under Lake Megachad is now the Planet’s single largest source of atmospheric dust.
In 1963, after the wet decade of the 1950’s, Lake Chad covered about 9,500 square. Back then, fisherman would take about 230,000 tons of fish out of the lake each day. Fish larger than the fishermen themselves were common catches. Then, in the late 1960’s, the Region entered a period of drought from which it has yet to recover. This has also been called a regime shift. Rainfall in the Sahel over the last three decades of the 20th Century was 25-40 percent lower than it was between 1931 and 1960. Today, the Lake covers between 115 and 200 square miles and fishermen are only catching about 50,000 tons a day. Areas that were submerged as recently as a few years ago are now being farmed, with many of the farmers being former fishermen.
This most recent regime shift illustrates the impact that global climatic changes can have on a specific region, as well as how those regional impacts can stimulate feedback cycles that reinforce the original impact. A shift in the distribution and an overall increase in sea-surface temperatures (SST’s) since the late 1960’s appear to be the initial triggers for the last three decades of dry conditions in the Sahel Region. Specifically, the SST shift has altered the monsoon pattern that brings seasonal rainfall. Several other factors, however, have contributed to the duration and severity of these dry conditions:
· The initial drought resulted in changes in vegetation cover. This vegetation shift changed the Region’s albedo (or how reflective the surface is), and the proportions of rainfall that become surface runoff, groundwater, and water vapor. These changes worked to reinforce the dry conditions. The changes in plant cover that result from changes in rainfall work to lower the frequency of wet and dry cycles; in other words, wet conditions favor plants that work to promote wet conditions and dry conditions favor plants that promote dry conditions. Thus, regions tend to stay in either a wet or a dry state regardless of year to year differences in rainfall, and only when there is an external forcing strong enough is there a shift from one state to another.
· A boom in the Region’s population has resulted in land cover changes, primarily due to grazing activities. This has helped to quicken the pace at which the Region’s vegetation changed from a composition favoring wet conditions to one favoring dry conditions. Most of these land cover changes, however, did not happen until after the drought conditions were established.
· The Region’s population boom, and the accompanying boom in agricultural activities, have resulted in increases in the withdrawal of water that would otherwise be flowing into the Lake. Indeed, human water use accounts for an estimated 50 percent of the decline in Lake Chad’s water supply. Similar to the land cover changes due to grazing, however, most of the hydrologic changes did not happen until the drought conditions were established; the drought conditions stimulated much of the need for irrigation.
· While the SST induced drought, the grazing induced vegetation changes, and the water diversion projects all worked to reduce the water levels in Lake Chad, it is important to note that in large lakes, lake generated precipitation due to evaporation forms a significant portion of a lake’s water budget. A decrease in water levels, for whatever reason, is likely to change the Regional climate in a way that promotes further loss of lake water.
As the lake water retreats, the exposed rich and moist soil (which is moist due to a high water table) is ideal for plant growth, and the land becomes covered by green grasses and crops (which appear as red in the satellite photos). Note how as the lake shrinks the dune features, which are hundreds of thousands of years old, become exposed. Also note the changes between the 1987 and 2000 photographs: the dune features are enhanced, the amount of wetland vegetation in the water increases, the amount of wetland vegetation on the outside edges decreases, and there is more irrigated land along the Chari River in the southeastern section of the photographs.
Sources:
Wang GL and Eltahir EAB (2000) Role of vegetation dynamics in enhancing the low-frequency variability of the Sahel rainfall. Water Resources Research 36, 1013-1021.
Coe, MT and JA Foley (2001). Human and natural impacts on the water resources of the Lake Chad basin. Journal of Geophysical Research 106, 3349–3356.
Foley, J.A., M.T. Coe, M. Scheffer, and G. Wang (2003). Regime Shifts in the Sahara and Sahel interactions between ecological and climatic systems in Northern Africa. Ecosystems 6, 524-539.
Wang GL, Eltahir EAB, Foley JA, Pollard D, Levis S (2004). Decadal variability of rainfall in the Sahel: results from the coupled GENESIS-IBIS atmosphere-biosphere model. Climate Dynamics 22, 625-637.
“Africa’s Lake Chad Shrinks by 20 Times Due to Irrigation Demands, Climate Change.” Science Daily, 1 March 2001. Accessed Online 22 February 2008
Drake N and Bristow C (2006). Shorelines in the Sahara: geomorphological evidence for an enhanced monsoon from palaeolake Megachad. The Holocene 16, 901-911.
Li, K.Y., M.T. Coe, and N. Ramankutty (2005). Investigation of hydrological variability in West Africa using land surface models. Journal of Climate 18, 3173-3188.
Odada EO, Oyebande, L, and Oguntola, JA (2006). Lake Chad: Experience and Lessons Learned Brief. Lake Basin Management Initiative. Accessed Online 22 February 2008
University of Pennsylvania: African Studies Center (2006). Excerpted from Africa’s Lakes: An Atlas of Environmental Change. Accessed Online 22 February 2008
United States Geological Survey and NASA: Landsat Project. Lake Chad, Africa. Accessed Online 22 February 2008
