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Charts of analysis increments (e.g. real time example charts ) allow the user to see where the IFS model analysis has adjusted to observations. 

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In either case, the subsequent evolution of the forecast should be carefully monitored, or even treated with suspicion, as the instability in the structure of the IFS atmosphere transferrs downstream.  In some cases there can be jumpiness in the forecast conditions for several days later at locations well away from the initial differences.  For this reason it can help to inspect the analysis increment data before comitting to a forecast.

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Fig4.2.2:  Rapid growth of uncertainty (in the background forecasts of the Ensemble of Data Assimilations (EDA)) for PV on the surface where potential temperature=315K (shaded as scale).   Also shown are the CTRL forecast PV=2 on 315K (red contour) and 850hPa wind vectors, and ensemble mean precipitation (dots; size indicates rate).   Rapid growth of uncertainty can be associated with cyclogenesis and warm conveyor-belts.  Meso-scale convective systems (e.g. over USA) can also distort the upper flow significantly.  The ENS perturbations may not capture such rapid growth adequately and the upper flow may well become modified more than has been modelled with significant downstream differences at a later time in consequence.  It is helpful to note the development of energetic and fairly large convective systems or strong dynamic upslope motions in warm front conveyors and assess the possible impact on IFS performance.

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Fig4.2.6: 200hPa wind increments at 00UTC 26 Aug 2019.  The large differences over West Africa indicate that observations depart significantly from the IFS background based upon the forecast run 12hrs earlier. The structure of these increments implies that divergence is being "added" to the upper level flow. This is a relatively common occurrence in convective regions, and can be caused by there being insufficient upward net mass flux in the convecting area, which in turn may be because the model's convection is insufficiently vigorous and/or organised. MCS development commonly relates to this and is known to be a problematic area for the IFS.

_{Updated/Amended 09/02/20 - Additional information and examples.}

_{Updated/Amended 24/10/20 - amended chart links to open access.}