Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Nov 04 2022 16:16:34 AWUS01 KWNH 041616 FFGMPD ORZ000-WAZ000-050015- Mesoscale Precipitation Discussion 1109 NWS Weather Prediction Center College Park MD 1215 PM EDT Fri Nov 04 2022 Areas affected...Western WA and Northwest OR Concerning...Heavy rainfall...Flash flooding possible Valid 041615Z - 050015Z SUMMARY...Strong atmospheric river conditions will impact western WA and northwest OR today with heavy rains continuing and gradually settling farther south with time. There will be a general increase in the threat of runoff problems and flooding as the rains persist. Some flash flooding and debris flow activity will be possible for the local burn scar areas. DISCUSSION...The latest GOES-17 satellite imagery in conjunction with radar shows a strong atmospheric river impacting large areas of the Pacific Northwest as a deep layer westerly fetch of Pacific moisture continues to round the western and northern periphery of the relatively flat subtropical ridge offshore of the West Coast. A look upstream over the central Pacific Ocean through the lens of the CIRA-ALPW plots show some notable subtropical origins to the moisture transport given proximity of a strong upper trough along 175W and deep southwest flow out ahead of it. Meanwhile, a strong upper trough is also seen settling southeast across the Gulf of Alaska and this will be helping to break down the ridge which will allow a cold front to eventually approach western WA by early this evening. While this is occurring, a warm front will continue to advance gradually east and inland across WA/OR today which will help drive heavy rains well inland into the higher terrain of the Cascades. A strengthening and very moist low-level jet of 50 to 60+ kts is expected to surge inland across the coastal ranges of western WA and northwest OR over the next several hours, with the belt of strongest moisture transport generally channeled across southwest WA, far northwest OR and into the southern WA Cascades. In fact, the latest consensus of guidance suggests IVT values will rise to in between 750 and 1000 kg/m/s in the 18Z and 00Z time frame across these areas, and actually edge above 1000 kg/m/s by 00Z for southwest WA as moisture gets particularly focused/concentrated ahead of the approaching offshore cold front. PWs are forecast to locally rise to near and just over 1.25 inches across this area. The aforementioned channel of strongest IVT values should correspond to the area of heaviest rainfall rates today, which are forecast to increase to 0.50" to 0.75"/hour in the 18Z to 00Z time frame, and may reach locally into the 0.75" to 1"/hour range for the favored west and southwest-facing slopes of the southern WA Cascades late this afternoon. Additional rainfall amounts going through 00Z of 2 to 4 inches are expected, with a couple of isolated heavier amounts possible. The persistence of heavy rainfall and the increase in rainfall rates today are expected to increase the threat of runoff problems and flooding. Additionally, there are several burn scars areas that will be sensitive to these heavy rains, including the Bolt Creek, Nakia Creek, and Siouxon burn areas. Some flash flooding and debris flow activity will be possible around these locations later today as the rainfall rates increase and persist. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6CFiFzoCHJuFr4R2r5iqQBFMgcfwFbGvrRD9cLwRMtsdk2__Da9SGYTpeH7qVR-j3BRl= WLQ8KMbzJ-hC7uGDjuWXG8E$ for graphic product... ATTN...WFO...OTX...PDT...PQR...SEW... ATTN...RFC...NWRFC...NWC... LAT...LON 48822199 48762145 48432120 47782104 47162103=20 46282117 45562138 44802166 44532201 44602253=20 45272246 45532266 45592302 45372323 44862340=20 44822396 45122416 46492420 47502447 48022478=20 48252465 48172401 47802330 47102291 47052247=20 47342208 48372219=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) .