Digger
03-22-2007, 05:02 PM
Summary: strong and cold system still on track for monday-tuesday with potential for 1-2 inches and locally more. Wild card is possible tap into atmospheric river now in place, with potential for precip as early as Sunday that will have to be watched, as well as more warm advection precip on Monday ahead of the trough.
Water vapor and SSMI imagery clearly show the jet has entrained moisture from the convection in the southwest. Much of this moisture will pound the Pacific Northwest over the next few days with inches of rain. By late Saturday into Sunday (24-25 March) the jet sags south enough to push some of this moisture very close to the area but the models continue to be rather sparse with any precipitation in this warm air ahead of the main system.
This initial moisture will have to be watched in the event the plume is more robust, and in fact the latest 12z GFS brings up to a third of an inch of rain just to the NW of the area on Sunday afternoon, then weakens the band as it drifts south, so stand by. If we assume that the initial moisture is not significant, our main event remains the aforementioned trough noted above that amplifies as it approaches the West Coast on Mon/26 Mar and then hits the area on Mon-Tue.
Everything still on track with this system to be a strong one with very cold air in the upper level low that should result in quite a bit of convective cold advection precipitation following trough passage near or just before 12z/Tue 27 Mar. Total precipitation amounts vary some, but the latest tendency has been to have the maximum right over the area, which is encouraging.
Overall the consensus among the various models is for a starting time for significant precipitation of 18-21z/Mon/26 Mar, with heavy precipitation by 00z/Tue that begins to taper off some after 06-09z/Tue with the trough passage. But as noted quite a bit of precip after trough passage, almost .7 inches in the 06z GFS run, through Tue night before ending around 12z Wed/28 Mar. The total precip in the 06z run was 2.17-2.25 near BLU, with the 00z run around 1.35 inches. Snow levels will lower way down behind the system witch could drop to 3000 feet or so on Tuesday.
The latest GFS is just coming in and as noted it brings more precipitation closer to the area on Sunday afternoon. Furthermore, on Mon/26 Mar this moisture consolidates and pushes into the area ahead of the main trough. This suggests the potential for a greater amount of warm sector precip than the models may be forecasting at this point. Then the winds shift to west with the trough passage, with a secondary max in the cold air advection the following afternoon, with precip ending by 06z/Wed.
Total precipitation from the event for the 12z GFS then is 2.7 inches at BLU to 3.5 to the northwest. So it still looks like a system worth watching with strong dynamics and good potential for over an inch of precipitation, eventual low snow levels, and locally higher precip amounts given strong orgraphic flow just ahead and behind the trough in an unstable atmosphere. Some remaining atmospheric river is possible, and there are signs the river now in place may be a factor in this storm if it hangs together, with the wild card whether the precip starts as early as Sunday.
Beyond this system models vary between a close call and a quick shot of over an inch with the next wave approaching out of the WNW for around Thu into Fri (29-30 Mar). The 12z GFS keeps pretty much all the precip to the north with this wave. In the latest GFS this system produces downstream ridging that forces the Thu/Fri wave to the north of the area.
Water vapor and SSMI imagery clearly show the jet has entrained moisture from the convection in the southwest. Much of this moisture will pound the Pacific Northwest over the next few days with inches of rain. By late Saturday into Sunday (24-25 March) the jet sags south enough to push some of this moisture very close to the area but the models continue to be rather sparse with any precipitation in this warm air ahead of the main system.
This initial moisture will have to be watched in the event the plume is more robust, and in fact the latest 12z GFS brings up to a third of an inch of rain just to the NW of the area on Sunday afternoon, then weakens the band as it drifts south, so stand by. If we assume that the initial moisture is not significant, our main event remains the aforementioned trough noted above that amplifies as it approaches the West Coast on Mon/26 Mar and then hits the area on Mon-Tue.
Everything still on track with this system to be a strong one with very cold air in the upper level low that should result in quite a bit of convective cold advection precipitation following trough passage near or just before 12z/Tue 27 Mar. Total precipitation amounts vary some, but the latest tendency has been to have the maximum right over the area, which is encouraging.
Overall the consensus among the various models is for a starting time for significant precipitation of 18-21z/Mon/26 Mar, with heavy precipitation by 00z/Tue that begins to taper off some after 06-09z/Tue with the trough passage. But as noted quite a bit of precip after trough passage, almost .7 inches in the 06z GFS run, through Tue night before ending around 12z Wed/28 Mar. The total precip in the 06z run was 2.17-2.25 near BLU, with the 00z run around 1.35 inches. Snow levels will lower way down behind the system witch could drop to 3000 feet or so on Tuesday.
The latest GFS is just coming in and as noted it brings more precipitation closer to the area on Sunday afternoon. Furthermore, on Mon/26 Mar this moisture consolidates and pushes into the area ahead of the main trough. This suggests the potential for a greater amount of warm sector precip than the models may be forecasting at this point. Then the winds shift to west with the trough passage, with a secondary max in the cold air advection the following afternoon, with precip ending by 06z/Wed.
Total precipitation from the event for the 12z GFS then is 2.7 inches at BLU to 3.5 to the northwest. So it still looks like a system worth watching with strong dynamics and good potential for over an inch of precipitation, eventual low snow levels, and locally higher precip amounts given strong orgraphic flow just ahead and behind the trough in an unstable atmosphere. Some remaining atmospheric river is possible, and there are signs the river now in place may be a factor in this storm if it hangs together, with the wild card whether the precip starts as early as Sunday.
Beyond this system models vary between a close call and a quick shot of over an inch with the next wave approaching out of the WNW for around Thu into Fri (29-30 Mar). The 12z GFS keeps pretty much all the precip to the north with this wave. In the latest GFS this system produces downstream ridging that forces the Thu/Fri wave to the north of the area.