You want the barometric pressure at your 'station' (QFE). Weather reporting entities get barometric pressure data from the nearest airport. These actually report 'altimeter' (QNH) but some report sea level pressure (QFF). For example, if you live near Burlington the current METAR looks like
KBTV 011549Z 13007KT 2SM -SN BKN017 BKN024 OVC036 M01/M04 A2979 RMK AO2 SLP092 P0001 T10061039
Here A2979 means QNH is 29.79 (1008.8 mb) while SLP092 means the station pressure reduced to sea level (by unfathomable rules) is 1009.2 mb) i.e. not much difference. Use either as either is representative of pressure at sea level). The ratio of pressure at 700 feet to that at sea level is 0.9750 so you can convert a QNH or QFF report to QFE by multiplying by that ratio. Thus, using the QFF value QFE = 1009.2*0.9750 = 983.9. The last step is to put the formula
" = 1013.25*(10^( 8.07131 - 1730.63/(233.426+ A1)))/760"
into a cell (other than A1) in an Excel spreadsheet. Now type temperatures ( °C) into cell A1 until the cell with formula reads 983.9 (or use the Solver find the value of cell A1 which does that). Doing that for 983.9 would give you a temperature of 99.19 °C as the temperature at which water would boil at 700 feet MSL if located near BTV at 15:49Z.
To convert mmHg to mB use mb = 1013.25*mmHg/29.92. To get the METAR from your nearest airport take the airport code (e.g. BTV), stick a K in front of it (KBTV) and do a search on 'KBTV METAR'.
You might want to look at wunderground.com/wundermap and interpolate barometer readings to determine the pressure in your area. Try to interpolate between airport or other 'official' stations. You may find an amateur station close to you but the odds that the guy has corrected his barometer correctly are pretty slim. Of course < 1°C isn't that much. It's probably not the source of your problem.