Q
Q' or Quadrature: The component of the complex signal that is 90 degrees out of phase with the inphase component. This component lies along the imaginary axis the complex plane.
QG: An abbreviation for quasigeostrophic.
Q-Vectors: Like the thermal wind, these are not physical realities (they do not exist). However, they arise mathematically from the Omega Equation and they help explain the results of physical processes in the atmosphere. Thus, they are useful diagnostic tools to forecasters. The divergence of the Q-Vectors through a layer depicts the synoptic scale vertical motions. Moreover, Q-vectors themselves, when they point from cold to warm air (when overlaying the thermal field on the Q-Vector field), it infers a tightening of the thermal gradient. This causes frontogensis (the generation of a front). If this frontogensis is strong enough, a low pressure may form.
QPF Discussion (PFD): This Meteorological Operations Division (MOD) forecast discussion is directed completely to explaining manual forecasts of areas in the contiguous 48 states expected to receive 1/4 inch or more precipitation during a 24-hour period. The manual forecasts are explained in terms of initial conditions and differences and/or similarities in the numerical model forecasts. General confidence in the manual forecast is expressed where it is appropriate and possible alternatives may be offered. This product is issued 3 times a day as described below:
1) Around 2 AM EST (3 AM EDT), a preliminary message is issued with a 24-hour forecast discussion valid from 7 AM EST (8 AM EDT) to 7 AM EST (8 AM EDT) the next day. This forecast
is a preliminary Day 1 QPF. This offers various field offices an opportunity to comment on or coordinate with Meteorological Operations Division (MOD) before the later QPF product is issued.
The AFOS accompanying graphic is 94Q and is identified as PRELIM DAY 1 on the graphic label.
2) The next message is issued around 6 AM EST (7 AM EDT). This
includes the DAY 1 QPF along with an updated 94Q graphic. In addition, this message
also contains a forecast valid from
7:00 AM EST (8 AM EDT) the next day to 7:00 AM EST (8
AM EDT) the day after next (Day 2 QPF) along with the accompanying graphic 98Q. This
narrative includes a coding of each
forecast isohyet for both Day 1 and Day 2. The
coded points are identified by degrees and tenths of latitude and longitude and are in a
clockwise direction around each isohyet. For points west
of 99.9 degrees west longitude, the leading 1 is
omitted from the coding.
3) Around 2 PM EST (3 PM EDT), a message updating the Day 2 forecast is
issued along with an updated 98Q. It is based on later data and numerical model
runs. Again, this narrative includes
the coded isohyets.
If for any reason the coded points are not available for the 7 AM EST (8 AM EDT) and the 2 PM EST (3 PM EDT) discussions, the message will be transmitted without them, and then retransmitted if they become available.
QPF (Quantitative Precipitation Forecast): A spatial and temporal precipitation forecast that will predict the potential amount of future precipitation for a specified region, or area.
QPFERD: NCEP Excessive Rainfall Discussion.
QPFHSD: NCEP Heavy Snow Discussion
QPFPFD: NCEP Precipitation Forecast Discussion
Quasi-stationary: Describes a low or high pressure area or a front that is nearly stationary.
