Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 08 2022 08:15:59 FOUS30 KWBC 080815 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 315 AM EST Thu Dec 08 2022 Day 1 Valid 12Z Thu Dec 08 2022 - 12Z Fri Dec 09 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Oravec Day 2 Valid 12Z Fri Dec 09 2022 - 12Z Sat Dec 10 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM FAR SOUTHWEST OREGON INTO NORTHWESTERN CALIFORNIA... There is fairly good agreement in the latest model guidance with the amplification of the upper trof off the Pac NW coast late Friday afternoon into the early hours of Saturday. This will strengthen the low level southwesterly flow into coastal sections from northwestern California into Oregon, with 850-700 mb moisture flux anomalies reaching 2 to 2.5+ standard deviations above the mean from far southwest Oregon into northwestern California. This will support heavy precipitation during the 0000-1200 UTC Saturday time period across the marginal risk area, with isolated hourly rates of .50"+ possible. The axis of anomalous onshore flow will, however, be fairly progressive to the southeast. This and only slightly above average precip values over the past week for northwest California will keep the risk level at marginal at best. There were no significant changes from the previous outlook for this period. Oravec Day 3 Valid 12Z Sat Dec 10 2022 - 12Z Sun Dec 11 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE CENTRAL CALIFORNIA COASTAL REGION... The amplifying mid to upper level trof off the Pac NW coast day 2 will continue to press southeastward day 3 across the coastal Pac NW and northern California. The axis of anomalous 850-700 mb moisture flux on the southeast side of this amplified trof will continue to press steadily southeastward, with values 3 to 4+ standard deviations above the mean affecting areas of central to southern California. This will support a period of heavy precipitation, especially through the Sierra and along the central California coastal range, with hourly rates topping near ..50"+/hour. Much of these regions have seen above average precip over the past few weeks. A marginal risk was confined to the coastal sections from the coast range north of San Francisco, south to approximately Santa Barbara where stream flow anomalies from the National Water Model indicate regions of much above normal to high flow from the above mentioned recent heavy precipitation. Additional heavy rains may result in isolated runoff issues, especially across recent burn scars. While heavy precip is also likely in the low elevation upslope of the Sierra, stream flows are mostly at or below average levels. For this reason and after collaboration with WFO STO, no risk area was denoted here. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7sSshiFeW0Bu6Ng8EqAkf4Z9B_BjfhxqT_A7Vjj7LGUl= IV-4D2gGgsPiLiskz7P7r053bclGD1KZRz6v7-xqBQLjD6U$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7sSshiFeW0Bu6Ng8EqAkf4Z9B_BjfhxqT_A7Vjj7LGUl= IV-4D2gGgsPiLiskz7P7r053bclGD1KZRz6v7-xqd4FuTqY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7sSshiFeW0Bu6Ng8EqAkf4Z9B_BjfhxqT_A7Vjj7LGUl= IV-4D2gGgsPiLiskz7P7r053bclGD1KZRz6v7-xqRnHKgjw$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .