BLUE HILL METEOROLOGICAL OBSERVATORY MILTON, MASSACHUSETTS 02186 ELEVATION 635 FEET, 10 MILES SSW OF BOSTON, MA DAILY DISCUSSION AND CLIMATE SUMMARY SUNDAY, DECEMBER 13, 2009 ALL TIMES ARE IN EASTERN STANDARD TIME FIRST ICE COVER ON NEARBY PONDS THIS MORNING TEMPERATURES MODERATE OVERNIGHT AS WINDS BACK FROM THE PREVAILING WEST-SOUTHWEST AND WESTERLY DIRECTION OF THE PAST SEVERAL DAYS TO SOUTH After a couple of the coldest days of this season to date temperatures began moderating overnight as west winds backed to southwest and south. The cold weather has brought the first ice of the season observed on our nearby ponds to the southeast of the Observatory early this morning. Ponkapoag Pond is covered with a skim of thin ice and we'll consider it frozen for the first time this season. The deeper of the two, Houghton's Pond, has a good amount of skim ice too but may not be quite completely covered, close though. The low temperature for the night here at the summit occurred just before 1 a.m. at 23F or just one degree colder than the normal. Low readings dropped to 14F at both Norwood and Taunton Airport. The past two days averaging 8 and 9 degrees colder than normal have decreased what was a significant positive temperature departure for December down to just one degree above the long-term average through Saturday. Today's observations: 7 A.M. Weather: Clear, few altocumulus and variety lenticular to the distant south and south thru southwest and few cirrus southwest and north thru east Temperature: 28F, Dew point: 14F, Wind: S at 14 kts, Sea-level pressure: 30.42 inches Hg, falling Visibility: 25 miles, distant haze, inversion present 6-hour minimum temp: 23F Average snow depth: 1 inch BHO SA 1155 CLR 25 302/28/14/1814/042/ FEW AC/ACSL DSNT S-SW FEW CI SW AND FEW CI DSNT N-E DSNT HZ LAYER ALG HRZNS ALQDS INVSN PRSNT/ 8/041 4/001 56008 10028 20023 10 A.M. Weather: Scattered altocumulus and cirrus, layers S-WNW invading the sky with clear sky overhead thru east Temperature: 36F, Dew point: 21F, Wind: SSE at 10 Kts, Wind: Direction gradually backing past hour Sea-level pressure: 30.35 inches Hg, falling Visibility: 30 miles, thin smoke layer NW-N, hazy all quadrants, inversion present BHO SA 1455 75 SCT 130 SCT 250 SCT 300 SCT 30 278/36/21/1610/035/ AC/CI LYRS S-WNW INCRSNG CLR SKY OVHD-E THN K NW-N HAZY ALQDS INVSN PRSNT WND GRDLY BACKING PST HR/ 8/055 58024 WEATHER SUMMARY FOR SATURDAY, DECEMBER 12 TEMPERATURE (DEGREES F) MAX.....30 NORMAL.....39 MIN.....18 NORMAL.....25 MEAN....24 NORMAL.....32 DEPARTURE FROM 30-YEAR AVERAGE.............-8 TOTAL DEPARTURE FOR THE MONTH.............+17 [+1.2 DEGREES/DAY] HEATING DEGREE DAYS TOTAL HEATING UNITS FOR YESTERDAY............41 DEPARTURE........+8 TOTAL HEATING UNITS FOR THE MONTH...........355 DEPARTURE.......-15 TOTAL HEATING UNITS FOR THE SEASON.........1515 DEPARTURE......-144 TOTAL HEATING UNITS LAST SEASON TO DATE....1592 DIFFERENCE......-77 PEAK GUST AND AVERAGE WIND SPEED (MPH) PEAK WIND GUST FOR YESTERDAY.............36 W AT 11:58 A.M. AEROVANE..............33 W AT 11:58 A.M. ASOS..................35 W AT 11:59 A.M. DAVIS.................36 W AT 12:29 P.M. THE FASTEST MILE FOR YESTERDAY...........23 W AT 2:02 P.M. * MAXIMUM 2-MINUTE ASOS AVERAGE............24 W AT 12:00 P.M. (NOON) MAXIMUM 2-MINUTE DAVIS AVERAGE...........25 W AT 1:25 P.M. AVERAGE WIND SPEED AND DIRECTION.......15.2 W ASOS................14.0 DAVIS...............13.5 WSW [250 DEG] * last of several occurrences... PRECIPITATION (INCHES) THROUGH THIS MORNING (EST) TOTAL PRECIPITATION 24 HRS ENDING 7 A.M....0.00 DEPARTURE....-0.14 ASOS..............0.00 TOTAL PRECIPITATION FOR THE MONTH..........3.20 DEPARTURE....+1.41 ASOS..............3.25 TOTAL PRECIPITATION FOR THE YEAR..........52.77 DEPARTURE....+4.32 ASOS.............54.01 SNOWFALL (INCHES) THROUGH THIS MORNING (EST) TOTAL SNOWFALL 24 HRS ENDING 7 A.M..........0.0 DEPARTURE.....-0.3 TOTAL SNOWFALL FOR THE MONTH...............11.0 DEPARTURE.....+7.8 TOTAL SNOWFALL FOR THE SEASON..............14.0 DEPARTURE.....+8.2 PRELIMINARY CLIMATE SUMMARY FOR DECEMBER 2009 CALENDAR DAY DATA DATA REPORTED: DATE: MAX/MIN/MEAN/DEP/PRECIP/SNOW/SUN(MIN.)/SUN(%)/ PEAK GUST/AERO GUST AERO: Aerovane wind recording system gust when significant TSTM: Thunderstorm day (thunder heard some time during day) ....: Data not yet available, records not finalized 12/1 41/28/35/-1/0/0/497/89 29 NW 12/2 51/33/42/+6/0.08/0/345/62 30 SSE 12/3 67/47/57/+22/1.01/0/428/77 69 SSE AERO 73 MPH SSE 12/4 52/40/46/+11/0/0/488/88 26 W 12/5 42/30/36/+1/0.79/4.7/000/00 36 N 12/6 33/25/29/-5/0.09/0.6/.../.. 36 NW 12/7 36/25/31/-3/0/0/.../.. 22 WSW 12/8 39/25/32/-3/0/0/.../.. 27 WNW 12/9 45/29/37/+4/1.23/5.7/000/00 52 ENE AERO 46 MPH ENE 12/10 40/26/33/0/0/0/.../.. 46 WSW AERO 39 MPH W 12/11 26/20/23/-9/0/0/.../.. 46 WSW AERO 41 MPH WSW 12/12 30/18/24/-8/0/0/.../.. 36 W AERO 33 MPH W 12/13 our morning low temp: 23F; the normal low is now 24F NEW DAILY RECORD FOR DECEMBER 2009 12/3 NEW RECORD HIGH MAXIMUM TEMPERATURE of 67F; surpasses previous record of 61F in 1932, 1950. DAILY EXTREMES Temperature and precipitation records back to 1885, and wind records back to 1940 (e = estimated): RECORDS FOR DECEMBER 13 HIGH 60 IN 1984 LOW 0 IN 1893 PRECIP 1.45 INS. IN 1983 SNOWFALL 9.2 INS. IN 2007 PEAK GUST 81e WNW IN 1976 RECORDS FOR DECEMBER 14 HIGH 62 IN 1901 LOW -6 IN 1893 PRECIP 1.94 INS. IN 2002 SNOWFALL 8.0 INS. IN 1907 PEAK GUST 78e ENE IN 1941 TODAY'S REPORT PREPARED BY: Robert Skilling