Consider the following scenario... Computer models indicate that a deck of high

Question

Consider the following scenario... Computer models indicate that a deck of high clouds are due to move over Lexington, Kentucky, during the overnight hours of March 16. This forecast leads MOS (see to forecast a slightly warmer overnight low temperature (notice the temperature trend as the clouds move in). Assuming that there is high confidence in the dynamical model being correct with the timing and placement of these clouds, what can be said of the MOS low temperature forecast.

MOS always has trouble with nighttime clouds, regardless of the circumstances. The MOS forecast should be adjusted downwards by several degrees.

MOS always has trouble with nighttime clouds, regardless of the circumstances. The MOS forecast should be adjusted upwards by several degrees.

If this is a relatively common occurrence and the dynamical models are correct, then MOS will likely be accurate as well.

If the dynamical models are correct, then MOS will always be correct.

Because MOS is just using statistics, rather than dynamic equations, surface temperature forecasts are always highly suspect.

Focus your attention on the upper-right-hand panel on a 48-hour NAM prog (entire prog (Links to an external site.)Links to an external site.). Note that the prog is valid at 00Z. You may assume that weather conditions in the regions surrounding the points labeled on the map stayed pretty much the same all night. In light of this assumption, at which point would MOS prediction for the overnight low temperature likely be noticeably too low?

Point A

Point B

Point C

Point D

Point E

You are given the upper right-hand panels for the 96 and 120-hour GFS progs. Both are valid at 12Z. The model predicts that a steady high pressure system will only drift east over the Atlantic Ocean during the two days on which the progs are valid. Assume that you are a weather forecaster in Miami, Florida. You decide that MOS makes a reasonable forecast for the high temperature on the first day, but there's another computer glitch and MOS guidance for the second day becomes unavailable. So, you must choose an alternative method for forecasting the city's high temperature on the second day. Which of the following methods is the most logical choice?

climatology

modified persistence

persistence

850-mb method

darts

NAM MOS Forecast for KLEX LEXINGTON BLUEGRASS, KI 3/15/2013 0000 UTC KLEX NAM MOS GUIDANCE DT /MAR 15 HR 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 18 00 /MAR 16 MAR 17 59 51 60 38 48 TMP 38 37 37 46 55 59 56 54 54 54 54 58 57 54 49 46 43 41 39 44 41 DPT 30 30 30 33 38 41 43 45 47 48 48 49 47 46 44 42 40 38 36 39 37 CLD OV BK SC SC SC BK BK OV OV OV OV OV OV Ov oV oV OV OV OV OV OV WDR 19 18 19 22 24 23 17 19 22 23 23 25 28 34 02 03 06 05 08 03 05 WSP 07 07 09 10 10 10 04 07 13 13 14 15 11 09 07 06 04 04 09 08 09 P06 P12 206 212 T06 T12 SNW CIG 6 8 8 8 8 8 88 8 8 8 754 4 4 3 2 23 2 2 19 27 27 2 2 31 23 82 37 73 82 31 83 0/ 0 0/ 3 0/ 2 8/ 6 16 4 14/12 8/11 5/ 9 5/ 2 4/9 8/ 6 high clouds 0 1/ 3 27/15 OBV N N N N N N N N N N N N NN BR N BR BR BR N BR

Explanation / Answer

Explanation:

Ans 1. If this is a relatively common occurrence and the dynamical models are correct, then MOS will likely be accurate as well.

If at the daytime the sky is cloudy then the cloud reflects back some of the sunlight which will lower the temperature as less heat will reach the Earth but in the night heat emitted from the Earth get trapped by the cloud and increase the temperature.

Ans 2. It seems MOS prediction for the overnight low temperature likely be noticeably too low at point D

(It can be seen from the map that near to the point D there is a High-pressure area. High-pressure areas are associated with low temperature, as the cold wind because of its high density gets sinks and can produce a huge pressure. So as the point D is the closest to the High-pressure area that is why we can forecast very low temperature here.

Ans 3. The alternative forecasting method as a weather forecaster of Miami, Florida will be The Persistence Method.

Persistence method is the simplest method of weather forecasting. It says today's weather = tomorrow's weather, which means if it is a sunny day with 24oC then tomorrow will be also a sunny day with 24o C, also it works well if there is a slow change in weather pattern. Here in our case also the model is predicting a steady high-pressure system for the two days. This persistence method plays a very good role when it comes to forecasting the weather in the southern US.

Now if we want to talk about the Climatology method then it needs a huge amount of previous data from past for the same day, and it can only predict well if there are no outside factors, but due to climate change and global warming, our climate is changing day by day.

The 850-mb method will also not work well as it is not suitable for coastal regions and if there is differential advection (two or more air masses with a different direction, speed, source) is present.

The Darts method will not work also as it needs a huge algorithm and the data from the past. But due to the computer glitch, no data are available.

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