Local data

LSC data for Wed. 11 Feb. 2008 is posted in the image at right. the temperature reached a balmy 52.2 F (11.2C) at 14:45 in the afternoon. The dewpoint (purple line) rose consistently throughout the day as the air became more humid. The temperature (red line) fell and relative humidity (green line) rose abruptly at around 4 PM *(16:00 EST) . The dewpoint and temperature met at about 35 F as the relative humidity hit 100%, an indication of fog and precipitation.

The approach of the upcoming storm is announced by the increasingly sharp drop in pressure (blue line). The total drop in pressure appears to be about 15 mb for the day. Winds actually appear to have died down in the evening after peaking in the late afternoon.

Data from Littleton/Whitefield Airport, NH (HIE) confirms a high of 52.0 F and the onset of rain and fog at about 5 PM EST. A similar plunge in sealevel pressure is also observed. The rain gauge detected 0.10 inches of precip before 0Z (7PM EST).

Local precipitation

A close up of the situation over the northeast U.S. at 1Z Thursday 12 Feb, 2008 confirms a broad zone of overcast skies and light rain to the north of warm front cutting right across central New England and New York. In addition, Morrisville, VT (MVL) reports fog and Mount Washington, NH (MWN) reports freezing rain. Winds are either calm or from the southeast.

In contrast, behind the front in Massachusetts and Connecticut winds are southwesterly, with some stations actually report clear skies.

You link to the map of local stations to locate relevant stations.

February showers

Today's rain is associated with a low pressure system and associated warm front moving in from the southwest. On the surface analyses for 12 Z (7AM) Wednesday 11 February, 2008 (left) the low pressure system was located over the center of the U.S. A warm front extended northeastward into West Virginia. A south-southesterly flow ahead of the storm system (red arrows) transports warm, humid air from the Gulf towards the warm front. Meteorologists refer to this flow as a vapor channel. The humidity falls as precipitation to the north of the front (black circle). This is typical of of midlatitude winter storms. Light to moderate precipitation typically falls in broad regions north of warm fronts to the northeast of the low pressure center.

By 00Z Thursday 12 Feb. 2008, the storm center has moved into the Ohio valley. The vapor channel from the Gulf of Mexico is cut off by the cold front moving eastward across the southeastern states. Moist air from the Atlantic continues to stream northward ahead of the storm system (red arrows). Precipitation continues to fall ahead of the warm front (shown as a stationary front over northern New England (black circle).

This precipitation occurs because warm humid air overruns the cold air ahead of the front when it reaches the front. This leads to cloud formation and precipitation. This falls ahead of the front as frozen precipitation if the surface temperature is below freezing and rain of the surface is above freezing. See "Precipitation along warm front" tutorial for more information.