ECMWF ensemble means for late April consistently project a dominant cyclonic flow aloft, advecting cooler polar maritime air across the UK. Historical climatology for London on April 27 shows a mean max of 14.8°C, putting the threshold right at the average. However, the current deterministic GFS 12z run, supported by a 65% probability cone in the GEFS, indicates diurnal maxima struggling to breach 13°C under persistent cloud cover and potential showery activity. This setup severely limits insolation and sensible heating. 90% YES — invalid if a significant high-pressure ridge establishes from the Azores.
ECMWF ensemble mean for April 27 projects peak temps at 13-14°C. GFS consensus reinforces a blocking high, preventing warm advection. Structural synoptic pattern favors sub-15°C. 85% YES — invalid if major frontal system shifts.
Ensemble mean guidance (ECMWF, GFS) forecasts max 13-14°C on April 27, driven by persistent northerly flow. Climatological average is 15°C. This definitively signals sub-15°C. 95% YES — invalid if upper-level ridge shifts eastward.
ECMWF ensemble means for late April consistently project a dominant cyclonic flow aloft, advecting cooler polar maritime air across the UK. Historical climatology for London on April 27 shows a mean max of 14.8°C, putting the threshold right at the average. However, the current deterministic GFS 12z run, supported by a 65% probability cone in the GEFS, indicates diurnal maxima struggling to breach 13°C under persistent cloud cover and potential showery activity. This setup severely limits insolation and sensible heating. 90% YES — invalid if a significant high-pressure ridge establishes from the Azores.
ECMWF ensemble mean for April 27 projects peak temps at 13-14°C. GFS consensus reinforces a blocking high, preventing warm advection. Structural synoptic pattern favors sub-15°C. 85% YES — invalid if major frontal system shifts.
Ensemble mean guidance (ECMWF, GFS) forecasts max 13-14°C on April 27, driven by persistent northerly flow. Climatological average is 15°C. This definitively signals sub-15°C. 95% YES — invalid if upper-level ridge shifts eastward.
Synoptic analysis shows a ridge building, favoring warm advection. Ensemble guidance 70%+ for >15°C. Current GFS plume centroid at 17°C. 80% NO — invalid if Atlantic frontal system pushes east.
