Dec 28 (Reuters) - U.S. natural gas futures edged lower on Tuesday on forecasts for milder weather and less heating demand over the next two weeks than previously expected. On their second-to-last trading day as the front-month, gas futures fell 0.5 cent, or 0.1%, to settle at $4.055 per million British thermal units (mmBtu). On Monday, the contact rose nearly 9% to $4.060, registering its highest close since Dec. 3. "Natural gas prices continue to flip flop on concerns about weather. When the forecast turns a little colder, the market rallies and when we turn a little bit warmer like today, the market goes back down," said Phil Flynn, senior analyst at Price Futures Group in Chicago. "Also, we have to look to the futures expiration for the January natural gas contract which could provide some real volatility in the market. The weather is holding us back, but our expectation is that as soon as winter hits, we think the market is going to be well supported." Data provider Refinitiv estimated 419 heating degree days (HDDs) over the next two weeks in the Lower 48 U.S. states, slightly lower from the 420 HDDs estimated on Monday. The normal is 438 HDDs for this time of year. HDDs, used to estimate demand to heat homes and businesses, measure the number of degrees a day"s average temperature is below 65 Fahrenheit (18 Celsius). Refinitiv projected average U.S. gas demand, including exports, would jump from 108.8 billion cubic feet per day (bcfd) this week to 123.9 bcfd next week as the weather turns seasonally colder. Those forecasts were lower than Refinitiv"s outlook on Monday. In recent months, global gas prices hit record highs as utilities around the world scrambled for LNG cargoes to replenish low stockpiles in Europe and meet insatiable demand in Asia, where energy shortfalls have caused power blackouts in China. The amount of gas flowing to U.S. LNG export plants has averaged 11.9 bcfd so far in December, now that the sixth train at Cheniere Energy Inc"s (LNG.A) Sabine Pass plant in Louisiana is producing LNG. That compares with 11.4 bcfd in November and a monthly record of 11.5 bcfd in April. Output in the U.S. Lower 48 has averaged 97.0 billion cubic feet per day (bcfd) so far in December, which would top the monthly record of 96.5 bcfd in November. Week ended Dec 24(Forecast) Week ended Dec 17 (Actual) Year ago Dec 24 Five-year average Dec 24 U.S. weekly natgas storage change (bcf): -116 -55 -120 -121 U.S. total natgas in storage (bcf): 3,246 3,362 3,476 3,207 U.S. total storage versus 5-year average +1.2% +1% Global Gas Benchmark Futures ($ per mmBtu) Current Day Prior Day This Month Last Year Prior Year Average 2020 Five Year Average (2016-2020) Henry Hub 4.05 4.06 2.58 2.13 2.66 Title Transfer Facility (TTF) -- -- 5.82 3.24 5.19 Japan Korea Marker (JKM) -- 40.98 9.46 4.22 6.49 Refinitiv Heating (HDD), Cooling (CDD) and Total (TDD) Degree Days Two-Week Total Forecast Current Day Prior Day Prior Year 10-Year Norm 30-Year Norm U.S. GFS HDDs 419 420 390 385 438 U.S. GFS CDDs 10 11 2 4 3 U.S. GFS TDDs 429 431 392 389 441 Refinitiv U.S. Weekly GFS Supply and Demand Forecasts Prior Week Current Week Next Week This Week Last Year Five-Year Average For Month U.S. Supply (bcfd) U.S. Lower 48 Dry Production 97.3 98.2 98.3 84.7 U.S. Imports from Canada 8.4 7.5 8.4 8.9 U.S. LNG Imports 0.0 0.0 0.0 0.3 Total U.S. Supply 105.7 105.7 106.7 93.9 U.S. Demand (bcfd) U.S. Exports to Canada 3.5 3.3 3.4 3.0 U.S. Exports to Mexico 5.6 4.9 5.5 4.6 U.S. LNG Exports 12.7 12.6 12.5 5.0 U.S. Commercial 15.6 13.3 16.8 15.0 U.S. Residential 25.8 21.4 28.5 25.4 U.S. Power Plant 29.5 23.0 24.9 25.8 U.S. Industrial 24.6 23.0 24.8 24.6 U.S. Plant Fuel 4.8 4.8 4.9 4.8 U.S. Pipe Distribution 2.7 2.3 2.7 2.4 U.S. Vehicle Fuel 0.1 0.1 0.1 0.1 Total U.S. Consumption 103.2 88.0 102.7 98.1 Total U.S. Demand 124.9 108.8 123.9 110.7 U.S. weekly power generation percent by fuel - EIA Week ended Dec 31 Week ended Dec 24 Week ended Dec 17 Week ended Dec 10 Week ended Dec 3 Wind 13 12 15 13 11 Solar 2 2 2 2 2 Hydro 7 7 7 7 6 Other 2 2 2 2 2 Petroleum 1 1 1 1 1 Natural Gas 34 36 34 36 37 Coal 19 19 18 19 19 Nuclear 22 22 22 21 22 SNL U.S. Natural Gas Next-Day Prices ($ per mmBtu) Hub Current Day Prior Day Henry Hub 3.45 3.56 Transco Z6 New York 2.86 2.60 PG&E Citygate 7.20 6.77 Dominion South 2.66 2.45 Chicago Citygate 3.36 3.29 Algonquin Citygate 4.58 6.00 SoCal Citygate 8.70 7.35 Waha Hub 2.95 2.70 AECO 4.73 4.23 SNL U.S. Power Next-Day Prices ($ per megawatt-hour) Hub Current Day New England 66.75 74.00 PJM West 21.75 19.00 Ercot North 28.75 22.50 Mid C 100.47 134.00 Palo Verde 76.75 83.00 SP-15 80.00