2006-12-04 Wx Discussion and Forecast
Forecast prepared by Chris Anderson, ESRL/GSD/FAB
2006-12-04 Synopsis
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Upper-level ridge resides over ARB. The amplitude has been reduced a bit by a shortwave crashing into WA, British Columbia. The next significant upper-level trough is passing south of the Aleutian Islands.
Current conditions in the ARB region
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Clear skies reported at 21 UTC. Tempreatures range from low 60s in the Valley to low 40s at higher elevation. Snow pack at Blue Canyon ETL site has been reduced to 4.5". Front is moving through southern OR.
0-72 hour forecast
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Weather will remain uninteresting until Friday. Dry frontal passage is expected tonight through tomorrow, resulting in a slight uptick in IPW values at Bedoga Bay.
>72 hour forecast
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Potent short wave forecasted to affect the ARB region on Friday, Dec 8. A wide swath of IPW >1.0" has moved into place ahead of this trough that is now situated south of the Aleutian Islands. UK and CMC move the wave westward at a slightly slower speed than GFS; whereas, the GFS ensemble is in near unison that precipitation will begin Friday, CMC and UK push it back to Friday night into Saturday.
From Hamill-Whitaker, probability of measurable, >0.5%, and >1.0" rain 00 UTC Dec 8 - 00 UTC Dec 9 (Friday) are >40%, ~25%, and ~15%. All but one GFS ensemble members have precipitation in the range of 0.5"-1.0" during that period. In the next 24-hour period, 00 UTC Dec 9 to 00 UTC Dec 10, pops for the same thresholds are 25%, 20%, and 10%. Pops during 00 UTC Dec 10 through 00 UTC Dec 11 are 35%, 30%, and 15%.
It appears more than one wave will affect the ARB Friday through Monday. The IPW values may not exceed 1.5", and, so, these are not expected to be extremely heavy rain events with 24-hour amounts more likely to be in the 0.5"-1.0" range and amounts >1.0" to be isolated. Most likely period of precipitation onset is Friday afternoon.