Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jan 31 2024 08:58:56 AWUS01 KWNH 310858 FFGMPD CAZ000-ORZ000-312045- Mesoscale Precipitation Discussion 0041 NWS Weather Prediction Center College Park MD 358 AM EST Wed Jan 31 2024 Areas affected...southwestern OR into northwestern CA Concerning...Heavy rainfall...Flash flooding possible Valid 310857Z - 312045Z Summary...Rainfall intensity is expected to gradually increase early this morning across the West Coast with a focus over southwestern OR and northwestern CA. Hourly rainfall totals over 0.5 inches are expected to become more likely after 12Z with hourly totals near 1 inch possible near 18Z. Discussion...GOES West vapor imagery showed a highly wrapped up, strong and mature cyclone over the eastern Pacific, centered near 43N 136W at 08Z. 08Z infrared and surface observations placed the associated 963 mb surface low with an occluded/cold front extending outward from the low and approaching the West Coast with the triple point ~150 miles west of Cape Blanco, OR. Loops of TPW showed a long fetch (3000+ miles) of moisture with precipitable water values greater than 1 inch off of the northern CA and OR coast, extending back across the Hawaiian Islands with origins into the tropical central Pacific. Recent QMORPH2 and blended microwave-derived rain rate imagery showed 0.35 to 0.45 in/hr rain rates 100-150 miles west of the northern CA and southern OR coast=20 While no recent observed low level wind data was available offshore, special 00Z dropsonde data showed 70 kt at 850 mb near 40.7N 127.0W, in line with 00Z RAP/GFS analysis data. GOES West water vapor imagery also showed a powerful (170+ kt) zonally oriented jet near 33N between 140W and 160W with widely diffluent flow downstream along with a separate GOES West DMV measured 120-140 kt jet max oriented south to north above the triple point off of the Pacific Northwest. The occluded/cold front is expected to continue advancing toward the West Coast over the next 6-12 hours but with some slowing as the front nears the coast as the parent upper trough encounters large scale downstream ridging in place over the western U.S. Southerly to south-southwesterly 850-700 mb winds of 70-80 kt are forecast to combine with precipitable water values of 1.1 to 1.2 inches along the southern OR and northern CA coast with 00Z NAM/GFS forecast IVT values of 800-1000 (locally 1000+) kg/m/s just prior to 12Z with gradual weakening thereafter (as winds and moisture decrease later in the day), but remaining strong. While the primarily southerly flow (less favorable orographic ascent), a lack of appreciable instability and expected steady eastward translation of the IVT core will limit rainfall totals compared to a slower moving moisture axis, a period of intense rainfall is still expected later this morning. 00Z HREF members are in agreement with 0.5 in/hr rates becoming common across Curry and Humboldt (King Range) shortly after 12Z but increasing in areal extent and magnitude closer to 18Z with a focus across Humboldt County. Some hires model guidance indicates the potential for a narrow, mechanically forced line of heavier rain to approach with the cold front, with hourly totals near 1 inch near 18Z. Areas of moderate rain increasing to heavy rain through the morning should lead to localized 3 to 5 inch totals across Humboldt and Curry counties with 1 to 3 inches elsewhere through 20Z. However, the potential for higher rates may impact recent burn scars across northern CA into southwestern OR with flash flooding a concern. The axis of heavy rain is expected to weaken across southwestern OR and far northwestern CA between 18-21Z as the axis of heavy rainfall begins to translate southward down the CA coast. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4U-X3Q3uuLa3iJwZ-KG3f3XN5zemKc0n0pytWYUzFQ5RUDuOX5c2lJgwrVVE6GkqFapJ= ZoZLAqmctYXaN5lrKLh51sY$ for graphic product... ATTN...WFO...EKA...MFR...MTR...STO... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 43162429 43032384 42502351 41902303 40552283=20 39562276 39072263 38742219 38322251 38202303=20 38302343 38572404 39382474 40862527 42162539=20 42952496=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) .