HMT Forecast Wed 1/23/2008 2000UTC
Current system has given generous precip around 1" in the SAC area the past 24
hours with lighter amounts over the ARB, particularly above the snow line.
The GFS gives us about 0.5" of remaining precip with the current cutoff low,
mostly as it starts to kick out overnight Wednesday. The ESRL WRF-NMM continues
the precip longer than the GFS, with some light amounts up to 12Z Friday.
The next cutoff low is sliding down offshore on Thursday. This is a rather deep
system and interestingly it digs a bit southward towards Friday and starts to
entrain some tropical moisture just as it gets kicked out by the weekend
short wave. The GFS gives about 0.7" over the ARB between 00Z Friday and 06Z
Saturday. The precip then migrates westward in response to the southerly
elongation of the cutoff. The ESRL WRF-NMM keeps the Friday precip mainly to
the west of the ARB.
As the cutoff starts to kick out (albeit a bit slower in the ECMWF) and the
weekend short wave moves in we get and additional 2" between 00Z Sunday and
18Z Monday. We thus may reach the lower end of the IOP criteria. Access to
the tropical moisture will be somewhat limited once the previous system shunts
it more to the east. The initial southerly trajectory also increases upstream
orographic shielding of the plume. We will start out with warmer precip than
previously expected, with 850mb temps ranging from +4C down to -5C near the end.
The heaviest snow should be Sunday evening. The ECMWF shows a similar pattern
with this short wave.
In the longer range we will want to watch the system coming in about next
Tuesday to see how strong of an atmospheric river connection it will have. GFS
IWV plots show a moderate potential ATTM. We will have to see if it moves
southward into CA from WA/OR for a possible IOP.
Even longer term we may see an atmospheric river moving from BC down to CA
in the Feb 5-8 time frame.