Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 27 2023 08:34:57 FOUS30 KWBC 270834 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 333 AM EST Wed Dec 27 2023 Day 1 Valid 12Z Wed Dec 27 2023 - 12Z Thu Dec 28 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR NORTHERN CALIFORNIA AND SOUTHWEST OREGON, AS WELL AS FOR THE CENTRAL AND NORTHERN MID-ATLANTIC... ....Mid Atlantic... The latest guidance continues to depict increasing moisture advection within the lower levels through Wednesday evening before slowly drying as our surface low scoots northeastward. PW values up to 1 inch will be transporting onshore across the Mid-Atlantic and Northeast; which will be +2 standard deviations for late December. There's also plenty of ascent within the left exit region of a powerful jet off to the southwest thanks to a broad, closed upper low centered over the Midwest. Strong mid-level vorticity advection is expected to track overhead during the afternoon and evening allowing waves of moderate to heavy rainfall to impact the urban corridor of the Mid-Atlantic. Much of this region has increased soil saturation from recent rains that are more sensitive to additional rainfall, thus having lower thresholds for flash flooding concerns. Consensus persists with a swath of 1 to 2 inches for the highest amounts to focus over eastern Pennsylvania and parts of New Jersey. Most of the guidance suggests 1 to 2 inches for this part of the country. The latest guidance and WPC QPF showed increases in amounts over the Del-Mar-VA region. Locations along and northeast of I-95 from Baltimore up through Philadelphia into Northern NJ still are favored for the highest accumulations. The Marginal Risk was maintained, albeit with a few adjustments to reflect the latest trends. As such, The Marginal Risk area was extended southward into east-central Virginia while minor reshaping of the western and northern bounds were made to reflect the latest trends. ....West Coast... A lower intensity atmospheric river paired with a Pacific front will usher in scattered to widespread precipitation to the Pacific Northwest and northern California. Recent rains has increased the soil sensitivity thus reducing the amounts required to lead to local flooding concerns. The latest guidance keeps areal averages of 1 to 3 inches for this period. The Marginal Risk area that was already in effect was maintained for this period albeit with small adjustments to reflect the latest forecast. Campbell/Kleebauer Day 2 Valid 12Z Thu Dec 28 2023 - 12Z Fri Dec 29 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Campbell Day 3 Valid 12Z Fri Dec 29 2023 - 12Z Sat Dec 30 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR NORTHERN CALIFORNIA AND SOUTHWEST OREGON... The next front and surge of Pacific moisture is expected to approach the coast during this period spreading another round of rainfall over northern California and southwest Oregon. Most of the guidance depict areal averages of 1 to 3 inches along the coast, with the higher totals primarily between Eureka and San Francisco. The threat for excessive rainfall will continue to be elevated from recent rains therefore the Marginal Risk area was maintained. Minor expansions were made to the north and south. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4FMiO3T9M_JvS1gO3wG74mSaf27mr_ZksVIfTHb2I1Lf= --lVEpd5qp3Wp1Dyd_zK_hYaKvavX3_twya8yuGf4AohClg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4FMiO3T9M_JvS1gO3wG74mSaf27mr_ZksVIfTHb2I1Lf= --lVEpd5qp3Wp1Dyd_zK_hYaKvavX3_twya8yuGfbIwkkws$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4FMiO3T9M_JvS1gO3wG74mSaf27mr_ZksVIfTHb2I1Lf= --lVEpd5qp3Wp1Dyd_zK_hYaKvavX3_twya8yuGfuvGfjSc$=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) .