BLUE HILL METEOROLOGICAL OBSERVATORY MILTON, MASSACHUSETTS ELEVATION 635 FEET, 10 MILES SSW OF BOSTON, MA DAILY DISCUSSION AND CLIMATE SUMMARY WEDNESDAY, SEPTEMBER 18, 2013 ALL TIMES ARE IN EASTERN STANDARD TIME VERY CLEAR, SUNNY, MUCH MILDER TODAY, UNLIMITED VISIBILITY CLEAR SKY, CALM WINDS ALLOW STRONG RADIATIONAL COOLING EARLY MORNING LOW TEMPS. FALL INTO THE 30'S URBAN CENTERS AND HILLTOPS MUCH LESS COLD THIS MORNING Under a clear sky and unlimited visibility up to 85 to 90 miles (Mt. Washington reports 130 miles) our temperature is rising 10 degrees warmer than yesterday to the lower 70's early this afternoon. Humidity is very low in the dry air with dew points around 40F and the relative humidity dropping to 30 to 35%. Temperatures dropped off rapidly overnight last night and many locations had lows this morning down in the 30's. In many cases these were the coldest of the season to date. The Hingham Cooperative station had a low of 39F surpassing the previous low this month of 43 degrees. Norwood Airport recorded 35F while the low at Taunton Airport was 34F. The low at the Martha’s Vineyard Airport as reported by ASOS was 32F. Several other inland reporting stations on Martha’s Vineyard had low temperatures of 36F to 40F. Urban locations (Boston) and hilltops (high elevations) were much less cold than on Tuesday when Boston had a record low of 44 degrees. Here at the summit of Blue Hill we were 7 degrees warmer than 24 hours ago with a low of 47F after yesterday's 40F which came within 2 degrees of equaling the record low of 38F set in 1959. The sea-level atmospheric pressure reached close to 30.45 inches yesterday morning as the center of a big high pressure system moved right over us. This was the highest pressure here at the summit since way back in May. Today's Observations: 7 A.M. Weather: Clear, cirrus/cirrostratus layer distant SE Temperature: 51F; Dew Point: 41F; Wind: W at 8 kts, Sea-level pressure: 30.31 ins. Hg, rising then falling slightly Visibility: 85 miles 6-hr min. temp: 47F BHO SA 1155 CLR 85 265/51/41/2808/031/ CI/CS LYR DSNT SE/ 8/008 50005 10051 20047 10 A.M. Weather: Clear, cirrus/cirrostratus layer distant SSE Temperature: 64F; Dew Point: 42F; Wind: W at 9 kts, Sea-level pressure: 30.29 ins. Hg, falling slightly Visibility: 90 miles BHO SA 1455 CLR 90 258/64/42/2709/029/ CI/CS DSNT SSE 8/008 58007 1 P.M. Weather: Sky perfectly clear, SKC Temperature: 69F; Dew Point: 41F; Wind: W at 7 kts, Wind: Direction variable SSW-NW Sea-level pressure: 30.24 ins. Hg, falling then more rapidly Visibility: 90 miles 6-hr max. temp: 71F BHO SA 1755 CLR 90 239/69/41/2607/024/ SKC WND 20V32/ 58019 10071 20051 WEATHER SUMMARY FOR TUESDAY, SEPTEMBER 17, 2013 TEMPERATURE (DEGREES F) MAX.....60 NORMAL.....71 MIN.....40 NORMAL.....54 MEAN....50 NORMAL.....63 DEPARTURE FROM 30-YEAR NORMAL.....................-13 TOTAL DEPARTURE FOR THE MONTH.....................-15 [-1.1 DEGREES/DAY] COOLING DEGREE DAYS (SEASON JAN TO DEC) TOTAL COOLING UNITS FOR YESTERDAY..............0 DEPARTURE.........-2 TOTAL COOLING UNITS FOR THE MONTH.............54 DEPARTURE.........+8 TOTAL COOLING UNITS FOR THE SEASON...........694 DEPARTURE.......+111 TOTAL COOLING UNITS LAST SEASON TO DATE......764 DIFFERENCE.......-70 PEAK GUST AND AVERAGE WIND SPEED (MPH) PEAK WIND GUST FOR YESTERDAY..................27 NNE AT 7:55 A.M. AERO.......................27 NNE AT 7:55 A.M. * ASOS.......................28 N AT 1:53 A.M. DAVIS......................25 NNE AT 7:55 A.M. RMY 26 FASTEST MILE FOR YESTERDAY....................16 NNE AT 8:46 A.M. MAXIMUM 2-MINUTE ASOS AVERAGE.................17 NNE AT 8:40 A.M. MAXIMUM 2-MINUTE DAVIS AVERAGE................17 NNE AT 7:57 A.M. AVERAGE WIND SPEED AND DIRECTION.............9.0 N ASOS......................8.6 DAVIS.....................8.0 N [360 degrees] * 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..........3.52 DEPARTURE.............+1.35 ASOS..............3.63 TOTAL PRECIPITATION FOR THE YEAR..........41.53 DEPARTURE.............+4.34 ASOS..............N/A* *ASOS malfunctioned during storm on 2/8-9, leading to erroneous totals PRELIMINARY CLIMATE SUMMARY FOR SEPTEMBER 2013 CALENDAR DAY DATA DATA REPORTED: DATE: MAX/MIN/MEAN/DEP/PRECIP/SUN(MIN.)/SUN(%)/ PEAK GUST/AERO GUST AERO: Aerovane wind recording system gust RMY: RMY = R.M. Young wind gust recording system added 8/9/2011 TSTM: Thunderstorm day (thunder heard some time during day) ....: Data not yet available, records not finalized 9/1 76/67/72/+4/2.32/008/01 33 S AERO 39 MPH S RMY 38 TSTM 9/2 79/67/73/+5/0.43/056/07 30 SSE AERO 33 MPH SSE RMY N/A TSTM 9/3 79/61/70/+3/0.00/219/28 28 S AERO 29 MPH S RMY 30 TSTM 9/4 78/57/68/+1/0.00/733/94 24 W AERO 25 MPH W RMY 25 9/5 66/51/59/-8/0.08/179/23 20 NNE AERO 20 MPH NNE RMY 21 9/6 68/46/57/-10/0.00/751/97 18 WSW AERO 17 MPH WSW RMY N/A 9/7 78/51/65/-1/0.00/594/77 20 WSW AERO 21 MPH WSW RMY 21 9/8 74/50/62/-4/0.00/646/84 31 NW AERO 33 MPH NW RMY 32 9/9 69/47/58/-8/T/529/69 23 SW AERO 23 MPH SSW RMY N/A 9/10 73/56/65/0/0.03/007/01 30 S AERO 32 MPH S RMY 33 9/11 93/68/81/+16/0.00/654/86 25 SW AERO 27 MPH SW RMY N/A 9/12 85/66/76/+11/0.47/.../.. 32 S AERO 33 MPH S RMY 34 TSTM 9/13 79/58/69/+5/0.17/.../.. 24 NNW AERO 25 MPH NNW RMY 23 9/14 67/52/60/-4/0.00/.../.. 21 NW AERO 21 MPH NW RMY 21 9/15 70/48/59/-5/0.00/.../.. 17 WSW AERO 18 MPH WSW RMY 20 9/16 66/46/56/-7/0.02/.../.. 29 NNW AERO 31 MPH NNW RMY 30 9/17 60/40/50/-13/0.00/.../.. 27 NNE AERO 27 MPH NNE RMY 26 9/18 morning low temp: 47F; the normal low is now 54F DAILY RECORDS FOR SEPTEMBER 2013 9/1 - NEW DAILY RECORD MAXIMUM PRECIPITATION OF 2.32 INCHES; surpasses previous record of 1.60 inches set in 1927 9/11 - TIED DAILY RECORD MAXIMUM HIGH TEMPERATURE OF 93F; ties record of 93F set in 1983 DAILY EXTREMES Temperature and precipitation records back to 1885, and wind records back to 1940 (e = estimated): RECORDS FOR SEPTEMBER 18 HIGH 88F IN 1906 LOW 36F IN 1919 PRECIP 4.25 INCHES IN 1996 PEAK GUST 77e MPH WNW IN 1948 RECORDS FOR SEPTEMBER 19 HIGH 87F IN 1906,1983 LOW 37F IN 1929 PRECIP 3.69 INCHES IN 1936 PEAK GUST 55 MPH S IN 2012 TODAY'S REPORT PREPARED BY: Robert Skilling