GFS 500 MB.
MODEL
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.
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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.