At the bottom of the map see:
12/24/2009 06UTC 048HR FCST VALID SAT 12/26/2009 06 UTC NCEP/NWS/NOAA
What does all this mean?
12/24/2009 06UTC= the date and time the map was produced.
048 FCST= indicates how many hours the forecast is valid. In this case, 48 hours.
VALID SAT 12/26/2009 06 UTC= This map is valid for 12/26/2009 at 06UTC.
NCEP,NWS,NOAA= Lists the branches of the government responsible for the forecasts.
WHAT DO WE SEE? It looks like there is a “mountain” along the
West coast of the United States and another “mountain off the East Coast. We call these mountains, “RIDGES”. They are pockets of warm air. In the central part of the United States there appears to be a deep valley in fact, it is deep “cut off low”. We call these valleys or deep lows in the upper air, “TROUGHS”. Find another trough off the west coast of the United States. These troughs are pockets of cold air.
WINDS: Winds on this map are indicated by a “shaft” which points into the direction from whence the wind comes. On the shaft, find lines and flags. A line represents a wind speed of 10 knots. One half line represents a wind speed of 5 knots. A flag represents a speed of 50 knots. For example, the upper level winds to the right of the “valley or trough” are blowing from the south or slightly southwest. The winds along the west coast are coming from the north. Notice the winds in the center of the troughs and ridges are very light and variable, meaning they can come from any direction.
SURFACE STORM MOVEMENT: Storms and precipitation (we call this weather) are carried by these upper air winds. We call these winds the “steering winds”. Weather on the surface moves “with” the winds at about one half the speed of the 500-millibar winds. For example, if the 500 millibar winds are blowing from the south at a speed of 80 knots, the storm and the accompanying precipitation will move towards the north at a speed of 40 knots. (VERY IMPORTANT)
VORTICITY: Notice the yellow and red coloring on the map? This indicates vorticity. Vorticity is a spinning, upward motion of air. Vorticity supports the intensification (strengthening or deepening) of storms. Yellow is moderate vorticity while red is strong vorticity. The brighter the red, the stronger the vorticity and the greater will be the intensification of the storm. See the very strong vorticity area near the Chicago area.
NOW LET’S TRY SOME REAL TIME FORECASTING.
MODEL ANALYSIS AND FORECASTS (UPPER AIR)
500 MB (18,000 FT)
Click on this: http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/
1. CLICK ON www.nco.ncep.noaa.gov LINK ABOVE. 2. CHOOSE MODEL-GFS 3. SELECT UPPER AIR PARAM.- 500_vort_ht 4. CHOOSE FORECAST HOUR- 000 5. CLICK ON THE "NEXT" BUTTON, THE MAP WILL ADVANCE 3 HOURS, CLICK NEXT AGAIN, THE MAP WILL ADVANCE ANOTHER 3 HOURS.
2. WHICH WAY WILL STORMS MOVE AND AT WHAT SPEED?
3. DO YOU SEE SOLID BLACK LINES? They are “height lines”. Oddly enough, they actually indicate the temperature of the atmosphere. The lower the number, the colder the air at 18,000 feet. For example, a reading of 570 over an area indicates it is much warmer than an area that has 540 over it.
4. DO YOU SEE WIND BARBS? These barbs indicate the wind speed and the direction from which the wind is blowing.
5. The flag indicates 50 knots, while each line represents 10 knots. A half flag equals 5 knots. If there were one flag and two lines, it would indicate a speed of 70 knots.( 50 knots for the flag and 20 knots for the two lines. (See wind chapter for further details). STORM SYSTEMS ON THE SURFACE WOULD MOVE AT A SPEED OF 35 KNOTS (1/2 THE SPEED OF THE 500 MB. WINDS. IF THE WINDS WERE FROM THE WEST, THE STORM WOULD BE MOVING TOWARDS THE EAST BEING PUSHED BY THE WESTERLY WINDS.
6. DO YOU SEE RED OR YELLOW AREAS? These areas indicate VORTICITY. (Vorticity is actually a spinning motion and supports the development of storms. Storms become much stronger & more severe when areas of vorticity approach them. Red areas of vorticity are stronger than yellow areas and thus would cause a storm to deepen much more rapidly. When vorticity is increasing, it is called Positive Vorticity Advection. (PVA)
7. From the “GFS” YOU WILL BE ABLE TO FORECAST THE WEATHER OUT 384 HOURS FOR YOUR AREA OR ANY AREA IN NORTH AMERICA. TRY IT! All the rules given to read the NAM apply to the GFS. The NAM , however, is sometimes more accurate for short term forecasts. (Next day). However, it is best to look at both the NAM and the GFS when making a forecast.