MET 3502(L) – Synoptic Meteorology
Fall 2015
Lab 13: Surface Low Development & Jet Stream Evolution
Due Tuesday, Dec. 1 at 11:00 AM (email to Margie before lecture starts).
Goals:
We will examine the evolution of features using the GFS model forecasts over the next five days, focusing on the area of
active weather over the Southern Plains and the tropical Eastern Pacific.
Part 1: Surface frontal development:
First, generate an animation (all contour plan view) of 2D > Pressure Reduced to MSL @msl. Load the same data as Lab
12 except for the 4-5 days starting today. Again, the data source is IDD Model Data > NCEP GFS 80 km CONUS model
data.
Second, plot a 250 hPa geopotential height field (contour plan view) for the same time period. Recall that the
geopotential_height @ isobaric is located under the 3D grid. Before you select create display, click on the level tab and
select only 250 hPa and fix the time to match the previous data that you loaded.
Question 1: Using your IDV maps, watch the formation of the surface front over the Southern Plains during the five day
forecast timeframe. Observe that there is a brief surface low that subsequently weakens. Why do we NOT get a welldefined surface low along the front in this case? In many cases we ask why a surface cyclone form – in this case we are
asking why doesn't it form. Hint: consider the optimal upper placing of the upper level feature to provide support for a
surface low, that we learned about in synoptic class. (also include an IDV image to help explain your answer)
Part 2: Polar and subtropical jet stream evolution
Examine the 300 mb, 250 mb, and 200 mb NCEP 000Z from the current run. At which level is the polar jet the strongest?
At which level is the subtropical jet strongest? Why?
For most of the forecast period, there is an upper high in the Pacific Northwest with a cutoff low below it. These
features are essentially stationary. What is the name for this type of blocking upper level pattern? This is one of the
upper air patterns that we reviewed in synoptics. Notice that repeated jet maxes move zonally underneath this feature
during the seven-day forecast 250_wind_ht loop, and when these jet maxes approach the polar jet, the confluence of
the two jets strengthens the jet max.
Now look at the surface layer params 1000_500_thickness at around 102 hours out. This shows a line of precipitation
over TX and OK. Compare this to the 250_wnd_ht and 850_temp_ht maps. What feature is at the 250 mb height
providing lift? What can be seen providing lift at the low level?
Looking at about four days out, what other feature could be adding upper level moisture to the features over the
Southern Plains, enhancing the rainfall? (Hint: think tropical).
Grading:
50%: Question 1
50%: Question 2