Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Feb 24 2025 20:25:36 AWUS01 KWNH 242025 FFGMPD ORZ000-WAZ000-250815- Mesoscale Precipitation Discussion 0051 NWS Weather Prediction Center College Park MD 324 PM EST Mon Feb 24 2025 Areas affected...WA/OR Coastal Ranges into Cascades Concerning...Heavy rainfall Valid 242022Z - 250815Z SUMMARY...Areas of heavy rain will return to the WA and OR Coastal Ranges and downstream into the Cascades later today/tonight. While peak rainfall rates may reach/exceed 0.5 in/hr on an isolated basis, they are much more likely to remain in the 0.2 to 0.4 in/hr range. 12 hour rainfall of 1-2 inches, locally 3+ inches, is expected through 08Z. DISCUSSION...GOES West water vapor imagery at 20Z showed a well-defined closed low centered just west of 130W near 45N. This upper low had been strengthening this morning but appears to be nearing maturity. At the surface, an occluded cyclone was depicted through visible satellite imagery with the WPC 18Z surface analysis showing a central pressure of 978 mb and this intensity is likely close to peak strength. The triple point was located just near the mouth of the Columbia River and what is left of an earlier axis of warm advection precipitation was lifting north through central WA. Meanwhile, radar imagery showed a band of rain, associated with the approaching cold front, moving just past the Willamette Valley into the Cascades. The diffluent left exit region of a mid-upper level jet streak was also located over the lower Columbia River Valley, likely enhancing lift and enhancing precipitation intensity. Short term forecasts from the RAP suggest the closed low will maintain a similar intensity through about 03Z prior to filling as it moves toward southern Vancouver Island. The cold frontal band will continue to steadily move inland through 00Z, followed by a lull in precipitation intensity outside of instability driven showers due to steepening mid-level lapse rates tied to the approach of the closed low aloft. RAP forecasts show MLCAPE up to ~500 J/kg along the OR coast through the early overnight. As the deep low level low nears the coast, a period of strong 850 mb onshore flow is expected to be directed into the coast of northern OR into southern WA, with 850 mb wind speeds of 70-80 kt in the 03-09Z time frame from the SW to WSW. While snow levels will be dropping to ~3500 ft behind the cold front across the Pacific Northwest, the u-component of the 850 mb wind will be 60-70 kt into the Coastal Ranges and 30-45 kt into the Cascades with a strong orographic component and steady rainfall of 0.2 to 0.4 in/hr, locally up to 0.5 in/hr possible. While rainfall rates will not be exceptionally high, the addition of 1 to 2 more inches, perhaps as high as 3 inches through 08Z, is expected. Due to widespread 3 to 6 inch rainfall totals across the region over the past 48 hours, additional rainfall may bring additional localized concerns for runoff problems including small stream and urban flooding. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!55bhW1vo4IQzGsDuIMw_NE5Diu18eoFsJYr2p46l6W9gZLhpJIff3SS_BrqRHC7dYc7W= TAHvAhW86MrVVwQRIVZuG1s$ for graphic product... ATTN...WFO...PQR...SEW... ATTN...RFC...NWRFC...NWC... LAT...LON 47912425 47842399 47612365 47572333 47602310=20 47032293 46942263 47022225 46962195 46652177=20 46332188 45982181 45652168 45362178 44972186=20 44622201 44442224 44442248 44492262 44712279=20 44852288 44902310 44862327 44742334 44652339=20 44492349 44402379 44472410 44582428 44962430=20 45732423 46472429 47062450 47622455 47802452=20 =20=20=20=20=20=20=20=20=20=20=20=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .