ࡱ> 574Y 9!bjbjWW -6==9]""""" .4" vvvvvQQQ:Q ] i $X L b QQQQQ vvvQvv""QvbR"þ""g"SEASONAL OUTLOOK SEA ICE CONDITIONS FOR: BAFFIN BAY, DAVIS STRAIT, LABRADOR SEA AND THE SOUTHWEST GREENLAND WATERS SUMMER 1999 NATIONAL ICE CENTER / NAVAL ICE CENTER Historically Baffin Bay melt does not begin until June, although the first signs of the North Open Water are observed in May. During the beginning of the melt, the western boundary of the pack ice begins to recede eastward, meeting the north open water. A broad flaw lead forms along the Greenland coast and gradually moves northward to Melville Bay. The pack ice begins receding, leaving an ice bridge across Baffin Bay (from NW Greenland to Central Baffin Island). This ice bridge will break sometime between the last weeks of July and the third week of August. The remaining ice will be composed of rotten floes that are rapidly falling apart, which by mid-September will disappear completely. The main objective of the Eastern Seasonal Outlook is to forecast the thinning of the ice bridge to help plan escorted shipping operations, and to forecast the breaking of this ice bridge to help plan for unescorted operations. Overall, conditions throughout the route across the Labrador Sea, Davis Strait and Baffin Bay are expected to be slightly ahead of schedule for the beginning of the upcoming shipping season. Table 1 provides the forecast opening dates for the transit to Thule, Greenland. Table 1 Forecast and Normal Opening Dates Thule, Greenland PORT FORECAST NORMAL FORECAST NORMAL ESCORTED ESCORTED UNESCORTED UNESCORTED OPENING OPENING OPENING OPENING DATE DATE DATE DATE Thule July 15 July 20 July 31 August 5 Escorted: Concentrations of ice encountered on the transit to Thule will be 7/10s or less and any fast ice will be in a weakened state. Unescorted: Concentrations of ice encountered on the transit to Thule will be 1/10 or less. Page 1 Freezing Degree Day (FDD) Accumulations and Ice Thickness (Table 2) are shown for the 1998-1999 winter season and historical Maximum, Minimum, and Mean data for selected locations in the Baffin Bay / Davis Strait / Labrador Sea area. (See Figure 1 for port locations). Ice thickness values are thinner than the mean climatological thickness in all cases for early May 1999. The Freezing Degree-day values for all stations are also below normal for the start of May 1999. Both give an indication of a slightly early then normal navigation season. Table 2 Current and Climatological Freezing Degree Days / Theoretical Thickness (Freezing Degree Days - Degrees C) (Theoretical Thickness - Centimeters) LOCATION MAXIMUM MINIMUM MEAN 09 MAY 99 FDD / THK FDD / THK FDD / THK FDD / THK Thule 5093 / 178 3721 / 142 4496 / 168 4369 / 164 Upernavik 3654 / 149 2207 / 75 3043 / 134 2536 / 120 Sondrestrom 4010 / 146 1915 / 26 2927 / 108 2737 / 125** Cape Dyer 4607 / 171 3204 / 137 3927 / 155 3534 / 145 Frobisher Bay 4660 / 171 3182 / 122 3866 / 155 3476 / 144 Angmagssalik 1793 / 94 949 / 41 1260 / 81 959 / 54* Resolution Is. 3766 / 152 2066 / 105 2927 / 132 0 / 0* * Values reset before 09 May 99. ** Value is suspect. Page 2 Table 3 lists the distance in nautical miles from select ports to the nearest ice edge for the climatological mean and the present distance. As can be seen from Table 3, the position of the ice edge is less than the mean at Thule and Upernavik, at the mean at Cape Dyer, and greater than the mean distance at the southern stations. Table 3 Distance From Selected ports to the ice edge in nautical miles. PORT MEAN(May 1) PRESENT (May 3, 1999) Thule 540 490 Upernavik 210 190 Cape Dyer 130 130 Frobisher Bay 240 290 Angmagssalik 60 70 Resolution Is. 80 140 Figure 2 indicates the climatological maximum, mean and minimum positions of the ice edge for May 15th. Figure 3 depicts the actual ice conditions present on the May 17, 1999. The ice extent in the northern Labrador Sea lies between a climatological mean and a maximum. The southern Labrador Sea and Baffin Bay from Disko Island to 60N/60W is near a climatological mean. The openings of the North Open Water and the polynyas in the vicinity of Disko Island were near the mean and indicate that the northern section of Baffin Bay is also at a climatological mean. Two charts of note are the Foxe Basin and Hudson Bay, both regions are running at the minimum. Some areas of the Foxe Basin and Hudson Bay may be at record melt out conditions. Page 3 Several factors were considered during the preparation of the outlook. Their description and weight in the outlook are discussed in the following paragraph. Values plotted on standard ice thickness curves for Thule, Upernavik and Angmagssalik showed values below the mean climatological curves for the entire winter season. Temperatures from the late winter 1999 and early spring 1999 showed warm temperatures south of Davis Strait with normal or cool values in Baffin Bay. When values for freezing degree-days accumulation and ice thicknesses are compared with past years as shown in Table 2 all stations were below the climatological mean. As noted in Table 3 the distances to the ice edge are below the mean in the North and above the mean in the South. The greater distance to the edge in the southern Baffin Bay and Davis Straits would normally lead the forecaster to believe a heavier winter ice season was experienced. After further investigation, the heavier ice conditions were determined to be a result of the extreme melt out in the Foxe Basin. The early break out of the Foxe Basin created a greater volume of ice in the Labrador Sea and southern Davis Straits than would be anticipated in a milder ice year. Next, we compared the ice edge and concentration conditions from the Gulf of St. Lawrence to North Open Water, and we determined 1986 as the best fit for an analog year. When we looked at the Escorted and Unescorted transit times in 1986, they were between slightly late and normal. This caused some concern since the analog year transit time didnt match what our other indicators were telling us. This temporarily lowered our confidence in the dates chosen for the seasonal forecast. We next consulted the Canadian Ice Service (CIS) which produces a similar product for their summer shipping season. In examining the Canadians temperature and thickness data, we saw a similar trend to our earlier findings in that the thicknesses and FDD accumulations were less than the mean. Forecasters from CIS were in agreement with our initial forecast for a slightly earlier than normal transit season. Therefore we decided to throw out 1986 as the analog year. Whereas 1986 matched our current ice conditions, the trend for a much colder summer, which was the case in 1986, is not the likely scenario for the summer of 1999. Figures 4 and 5 show mean climatological and expected ice conditions for July 15, 1999. Due to the combination of factors listed above, the opening of the ice route for the transit to Thule, Greenland is forecasted to be approximately one week earlier than normal. 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