Forecasting Tips: High & Low Temperatures Metr2413 March 12, 2004

Low Temperatures (not always overnight lows) Dependant mostly on radiational cooling; really a balance of many factors: Cloud cover – insulation vs. radiational cooling Moisture – Dew point can act as a lower boundary Topography – upsloping/downsloping winds Low level winds – vertical mixing Location – climate; proximity to bodies of water

Low Temps - Cloud Cover

Low Temps - Moisture

Busted…

Low Temps - Topography Steep topographic changes can influence adiabatic compression (downsloping – warming) or adiabatic expansion (upsloping – cooling) warming cooling Also affected are valleys and ridges: cooler air (higher density) due to radiational cooling at the surface can converge at the base of the valley – base=cooler, ridge=warmer

Pueblo, CO

Low Temps - Mixing Sustained overnight winds create turbulent mixing – allowing the boundary layer to maintain a well-mixed profile and suppressing some radiational cooling Overnight: look for low level jet (common in the Southern Plains) Daytime: look for strong radiational heating with a capped boundary layer

High Temperatures (not always during the daytime) Also a balance of many factors: Cloud cover – insulation vs. radiational heating Moisture – Surface energy budget effects Topography – upsloping/downsloping winds Low level winds – vertical mixing Location – climate; proximity to bodies of water

All about balance If you notice that your forecast area will likely experience upslope winds overnight (cooling), but also will have cloud cover (insulation), the two processes may balance each other. If you notice that your forecast area has a high dewpoint, but also a high about of clearing overnight, the radiational cooling may be slowed due to condensation (fog). Again, watch out for EOP/BOP highs and lows

Lab Assignment 9 (optional – 10pts) If you are participating in the LFC: Summarize your high and low temperature forecasts for Oklahoma City (KOKC): 1) Why was your reasoning behind your high/low temperature forecasts? 2) How correct were your numbers? If they were spot-on, explain why. If they were off, explain why, and don’t spare the details. In this assignment, details win points! If you are not in the LFC: Over the break, pick two consecutive days and make a high/low temperature forecast for KOKC. Verify and summarize your forecasts as described above. Once again, this assignment is optional, and is due on Friday, March 26.