The trace at left shows the effect of radiative disequilibrium between solar and terrestrial radiation ( (i.e. the imbalance between the intensity of visible and infrared light) on daily temperature variations. Note that it is very similar to current conditions as the graph is valid for the equinoxes (March 21 and September 21).

• The green line shows the effect of solar radiation. It is only active after sunrise, peaks at noon, and dissappears after 6 PM.
• The purple line shows the intensity of terrestrial IR radiation. It closely follows that of surface temperature (red line) since the amount of IR emitted by the earth is directly related to its temperature (Stefan-Boltzman Law).
• The red shading shows the time of day when the incoming solar radiation is stronger than the outgoing longwave radiation (OLR). Because of this imbalance, the surface temperature increases during this period.
• The blue shading shows the time of day when OLR is more intense than the incoming solar radiation. At this time of day, the surface temperature decreases.
• Note that the peak temperature is reached when OLR and solar radiation are equal. This is usually about two hours after the solar noon (2 PM EST or 3PM EDT).
  
• Note that the temperature drops most quickly early in the eveing and gradually tapers off to a minimum just before sunrise.
  
• The temperature rises most quickly just after sunrise owing to the minimum in OLR intensity and the rapid increase in the intensity of solar radiation.

Note that the trace for LSC in the previous posting varies from the ideal situation depicted here. The cloud that pushed in around noon blocked out the sun, weakening the solar radiation and halting the temperature rise. The cloud also absorbs OLR, reemitting heat radiation back to the surface of earth early in the evening (see figure). This slows the dip in temperature early in the evening.

Sounding data for Albany, NY at 0Z 4 mar, 12Z 4 Mar shows that the daily temperature variation is in fact restricted to the very lowest layer of the atmosphere. At 0Z, the surface temperature at Albany is just about -8 C, whereas at 12 Z it has decreased to about -11 C. Note however, that above 950 mb, the temperature has barely budged. For example, at 950 mb the temperature remains constant at about -16 C.

This is typical of diurnal (daily) temperature fluctuations. These are restricted to a region of the troposphere called the boundary layer. Although the height of this layer can vary depending on weather conditions, it typically is restricted to below 850 mb. It's common to use temperature data from above this layer (usually 850 mb maps) to determine temperature trends based on temperature advection to remove the effect of the sun.

Data is taken from the University of Wyoming website.

The situation at 11 PM shows that winds have become calm over much of New England, with clears skies dominating the region as the high pressure system begins to dominate. Light winds and clear skies result in rapid temperature falls throughout the region. Where there is a weak wind, it tends to be westerly.

The time series below is for the last 24 hours at Littleton-Whitefield airport (click here for current conditions). Note that after 7 PM, with calm, clear conditions, that the temperature plummets by 26 degrees 15 F to -11 F as outgoing longwave radiation travels into outer space.

	Time EST (UTC)	Temperature F (C)	Dew Point F (C)	Pressure Inches (hPa)	Wind MPH	Weather
Latest	Midnight (5) Mar 05	-6.0 (-21.1)	-11.0 (-23.9)	30.26 (1024)	Calm
	11 PM (4) Mar 04	-2.9 (-19.4)	-9.0 (-22.8)	30.24 (1024)	Calm
	10 PM (3) Mar 04	-0.9 (-18.3)	-6.0 (-21.1)	30.23 (1023)	Calm
	9 PM (2) Mar 04	1.9 (-16.7)	-2.9 (-19.4)	30.22 (1023)	Calm
	8 PM (1) Mar 04	8.1 (-13.3)	1.0 (-17.2)	30.22 (1023)	Calm
	7 PM (0) Mar 04	15.1 (-9.4)	3.0 (-16.1)	30.2 (1022)	W 7
	6 PM (23) Mar 04	18.0 (-7.8)	5.0 (-15.0)	30.18 (1022)	NW 10
	5 PM (22) Mar 04	19.9 (-6.7)	3.9 (-15.6)	30.15 (1020)	WNW 15
	4 PM (21) Mar 04	19.9 (-6.7)	3.9 (-15.6)	30.14 (1020)	W 16
	3 PM (20) Mar 04	21.0 (-6.1)	3.9 (-15.6)	30.13 (1020)	WNW 16
	2 PM (19) Mar 04	19.9 (-6.7)	3.9 (-15.6)	30.14 (1020)	WNW 16
	1 PM (18) Mar 04	19.0 (-7.2)	5.0 (-15.0)	30.15 (1020)	W 10
	Noon (17) Mar 04	18.0 (-7.8)	3.0 (-16.1)	30.17 (1021)	W 12
	11 AM (16) Mar 04	16.0 (-8.9)	1.0 (-17.2)	30.19 (1022)	W 8
	10 AM (15) Mar 04	12.9 (-10.6)	-0.9 (-18.3)	30.21 (1023)	WNW 5
	9 AM (14) Mar 04	3.9 (-15.6)	-0.9 (-18.3)	30.22 (1023)	Calm
	8 AM (13) Mar 04	-9.9 (-23.3)	-11.9 (-24.4)	30.23 (1023)	Calm
	7 AM (12) Mar 04	-17.0 (-27.2)	-23.1 (-30.6)	30.23 (1023)	Calm
	6 AM (11) Mar 04	-18.0 (-27.8)	-23.1 (-30.6)	30.21 (1023)	Calm
	5 AM (10) Mar 04	-17.0 (-27.2)	-22.0 (-30.0)	30.2 (1022)	Calm
	4 AM (9) Mar 04	-15.0 (-26.1)	-22.0 (-30.0)	30.18 (1022)	Calm
	3 AM (8) Mar 04	-14.1 (-25.6)	-20.9 (-29.4)	30.18 (1022)	Calm
	2 AM (7) Mar 04	-14.1 (-25.6)	-18.9 (-28.3)	30.19 (1022)	Calm
Oldest	1 AM (6) Mar 04	-11.9 (-24.4)	-18.0 (-27.8)	30.19 (1022)	Calm
	Time EST (UTC)	Temperature F(C)	Dew Point F(C)	Pressure Inches(hPa)	Wind (MPH)	Weather

The image at left is for 15Z (10 AM EST) Wed. March 4, 2008. New England is under the influence of a high pressure system over Virginia and a low pressure system over Northern Labrador. Animation loops at archived sites show that these are stationary systems. Note that the counterclockwise flow around the low pressure system reaches into New England leading to north-northwesterly winds. Animation for earlier in the week (see link) shows that this is the same system that brought the northeast coast over a foot of snow.
A closer look at New England at 21Z confirms a trough (dashed orange line) swinging through from the north. This elongated region of weak low pressure extends southward form the low pressure system over Labrador and explains the decrease in pressure and snow showers onserved over LSC in the afternoon. Temperatures directly to the north of Vermont are not appreciably different, but temepratures further to the northwest are slightly colder (in the mid teens). To the west of Vermont in western New York State and Ontario temperatures are slightly warmer. A slight change in wind direction to the west could lead to warm advection.

Temperatue and weather at LSC weather station

Weather summary for Wed. March 4, 2009 at LSC indicates the following high and low
Hi temp: 22.2F (-5.4C) at 13:55
Low temp: -11.7 F (-24.3C) at 06:10

Overnight temperatures were falling continuously (blue) before the low at 6:10 AM shortly before sunrise. This indicates a relatively clear night in which outgoing longwave radiation (OLR) was able to radiate into outer space without clouds interfering.

The sharp 30 degree rise in temperatures during the morning hours (red) indicates strong solar warming associated with clear skies and higher noontime solar angles.

Finally, temperatures in the early afternoon (green) are relatively constant in the lower 20's after about noon . Indeed, a slight dip in temperatures can be observed at around noon. The pressure trace shows a very slight dip (about 2 or 3 mb) in the pressure trace.

Comparison to temperature and pressure data shows a clear morning with light winds and a sudden appearance of snow over Burke Mountain around noon. This corresponds to pressure fall and constant afternoon temperature. Click here to retrieve larger image at webcam archive.