The last few forecast discussions (FDs) from PHX have been interesting, since they have focussed on the evolution of moisture streams from the northwest interacting with a low-latitude plume from near Hawaii. An example of one of these is shown at bottom of this post.
I thought I'd take a look at the GEFS forecasts from 00 UTC last evening using both the experimental plume forecasts from NWS EMC and also from the Atmospheric River Portal at Plymouth State - see - http://jasoncordeira.weebly.com/ar-portal.html
The NWS plume forecasts at TUS for PW are shown above - PW jumps from around 0.25" to more than 0.50" (some members forecast values approaching 1.00") on Thursday and Friday. However, the plumes for QPF (below) are not very impressive at all for TUS - one member is out-of-sync with others and forecasts about 0.70" at the airport.
The AR Portal forecasts of the probability of Integrated Vapor Transport (IVT) greater than 250 kg/m/s are shown here. Forecast above is valid at 00 UTC on Wednesdayand indicates a fairly broad plume of moisture from just east of Hawaii into northern California. By 00 UTC on Friday the ensemble members have forecast a broadening, as well as a break off from the Hawaiian plume, and have high probabilities for important IVT over most of western US, including much of Arizona.
Bottom line this far out seems to be high confidence for much increased PW by end of week, but much less confidence (at least here in southern Arizona) in what this will mean for precipitation.
A portion of the FD from PHX issued early yesterday am is shown down at the bottom.
Friday and Saturday...
Models continue to
consolidate on a solution of developing a large
trof over
the region this period. The recent wave pattern evolution
upstream
across the Pacific the past few days, i.e. in the northern
branch of the
jetstream, supports a change toward troughiness over
the western states
including AZ on Friday. However confidence is low
on the amount of moisture/precipitation
with this system as the
southern branch of
the jetstream from Hawaii will merge with the
northern branch just
before landfall in AZ. Latest precip water
satellite imagery
detected a fairly wide plume of 1.50-2.00 inches
of precip water
associated with the southern branch near Hawaii, and
associated with a
disturbance that will merge with northern branch
jetstream next week.
Therefore confidence
in the amount of precip/storm
intensity is low
at the moment.
However confidence is high that some rainfall will
occur Friday through
early Saturday. Additionally, models are
forecasting a strong
low level westerly flow
across the coastal
mountain range of
southern CA that make enhance rain
shadow effects
over a large
portion of our southeast CA zones.
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