Combination of elements coming together for active afternoon of thunderstorms across especially the central and eastern part of the forecast area. Small but strongish upper low off the southwest coast set to move into northern CA area by the overnight hours. Already seeing high based convection in the over southeast 1/4 of forecast area with nose of H25 jet. We have seen an increase in lightning activity the last 60-75 minutes. RGB satellite H2O vapor products show nicely the lead wave out from the upper low as it triggers the current high based convection. Satellite derived winds suggest slightly less speed aloft than NAM12 forecast, but not much as the storms encounter favorable upper diffluence with time. Steep mid-lapse rates atop moderate instability (temps in mid 90s/dewpoints mid 50s), especially at lower elevations, will be fuel for expected storm development in the 20-22Z time. Once more development begins, coverage should rapidly increase. Forecast soundings suggest main hazard will be localized severe wind gusts with forecast inverted-V soundings and 40-50 T-TD spreads. Some marginal hail risk possible as well.
Watching closely the northwest forecast the next hour or so as storms in Yakima county continue to slide northeast and hold together with lightning still steady but a bit up and down. The DPI lifted index suggests this may hold together long with lower LIs...which coincides with 90 degree surface temperatures and dewpoints in the middle 50s in eastern Yakima county.
Few images showing LIs lowering near storms in northwest CWFA.
No comments:
Post a Comment