Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Mar 23 2025 14:27:24 AWUS01 KWNH 231427 FFGMPD WAZ000-240230- Mesoscale Precipitation Discussion 0078 NWS Weather Prediction Center College Park MD 1026 AM EDT Sun Mar 23 2025 Areas affected...Northwest Washington.... Concerning...Heavy rainfall Valid 231430Z - 240230Z SUMMARY...Prolonged onshore moisture flux across Olympics and lower Foothills of northern WA Cascades may result in spots of 3-5" totals, given over .33"/hr average rates. Saturated grounds and some snow melt may increase run-off increasing stream flows. DISCUSSION...GOES-W WV suite depicts a strong upper-level jet across the northeast Pacific/southern Gulf of Alaska crossing central BC before extending southeast into the southern Canadian Rockies resulting in solid ridging across the Pacific Northwest with apex of the ridge just west of the coast. This allows for moderate divergence aloft across southwest BC/northern WA which is expected to persist through much of the day today allowing for solid westerly onshore, ascending flow into this divergent area.=20 The southern edge of a warm front has reached the NW WA coast and is aiding in the ascent/WAA which has started to increase over the last hour or so across the Olympics. Additionally, this leading pulse has brought increased low to mid-level moisture via a very broad atmospheric river plume with sfc-850mb LPW values in the ..5-.6" range with a dual core 850-700mb flow of .25-.3", though the northern plume/fetch is longer more directed toward southern Vancouver Island and the NW tip of WA. As a result, 1-1.2" total PWats are expected being fluxed with 35kts increasing to 50+kts toward 18-21z. Overall IVT values will increase from 400-450 kg/m/s currently peaking at 650-700 kg/m/s toward 21-00z...then leveling out around 500 kg/m/s for the rest of the evening into the overnight.=20=20 The plume's orientation will remain steady through this surge of moisture flux and favorably intersect the Olympic range with rates of .15"/hr currently to increase to near/just over .5"/hr in the best orographic ascent by 18z. The core of the flux will be north into southern Vancouver Island, but will then slide toward the northern WA Cascades through the late afternoon/early evening increasing rates of .25-.33", perhaps occasionally reaching .5"/hr at the peaks. The depth of warm air will result in freezing levels lifting above all but the highest peaks. This has a combination of those high rates but also rain upon snow.=20 Temperatures are not going to be significantly over freezing, so melt may be a bit slow, but will contribute to run-off. Soil saturation values are very high (or even 100% due to snow pack), so much of the water from rainfall will run-off too increasing potential for above average stream flow but not likely to rise fast enough for rapid-rise/flash flooding.=20=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7u5LhiU2H0T2GdeZ8a0qufxxSFrwQchurSmg0fp_8FpNZ0CDyOeeFItU1Ry6XEvV_GMI= UmW2gV4K632D0NIAFMNNgdA$ for graphic product... ATTN...WFO...SEW... ATTN...RFC...NWRFC...NWC... LAT...LON 49132248 49112172 48982125 48322116 47602148=20 47452178 48022208 48152248 48042298 47812312=20 47472321 47272338 47212383 47322417 47592451=20 47942466 48362485 48432447 48222370 48432313=20 48772304 49092285=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) .