Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 28 2022 01:01:27 FOUS30 KWBC 280101 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 800 PM EST Tue Dec 27 2022 Day 1 Valid 01Z Wed Dec 28 2022 - 12Z Wed Dec 28 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTH-CENTRAL CALIFORNIA, MAINLY ALONG THE SOUTHWESTERN FOOTHILLS OF THE SIERRA NEVADA... Lift in association with the atmospheric river has diminished significantly this evening across the West Coast, as the jet stream aloft has begun to significantly fracture and weaken (compared to earlier today). This has resulted in an end to precipitation across much of north-central California (including the greater San Francisco metro area), while what is left of the anomalous moisture plume (PWs of 1.2-1.6 inches) is shunted southward into south-central and Southern California. The most impressive additional totals look to occur along the far southern slopes of the Sierra Nevada range (intersecting with the Sierra Madre range) in association with this moisture plume, where additional 11-hr totals (through 12z Weds) of 1-2" (perhaps locally as high as 3") may occur. The Slight risk was maintained (and extended a bit south) to encompass this relatively small area, whereas the Marginal risk was trimmed significantly in north-central CA (but maintained elsewhere as inherited). Rainfall has mostly tapered off across the northern fracture of the jet (northwest CA and coastal OR/WA), but occasional localized rates as high as 0.25-0.50"/hr are possible through the night. Churchill Day 2 Valid 12Z Wed Dec 28 2022 - 12Z Thu Dec 29 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF ARIZONA... ....2030Z Excessive Rainfall Outlook Discussion... Models still show a deep layer trough making its way inland which focuses the better moisture southward and eastward on Wednesday.=20 Maintained the Marginal Risk area without any changes given consistency of the big-scale picture and the anomalous nature of the moisture and moisture-transport into the region. Bann ....0830Z Excessive Rainfall Outlook Discussion... The flash flooding threat on Wednesday will remain temporally confined to the morning hours over portions of central and southern Arizona, as remnant moisture from the coastal atmospheric river event pushes through the Southwest along a strong cold front. PWATs may hover around an inch with anomalies between +2 to +3 standard deviations in southern/central Arizona Wednesday morning before quickly shifting southward and diminishing. The marginal risk area is cutoff on the northeastern edge along the Mogollon Rim and White Mountains, where light to moderate snowfall is expected. Kebede Day 3 Valid 12Z Thu Dec 29 2022 - 12Z Fri Dec 30 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE COASTAL RANGES OF SOUTHERN OREGON, NORTHERN CALIFORNIA AND PORTIONS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY... ....2030Z Excessive Rainfall Outlook... 12Z runs of the computer models suggested that the going forecast remains on track for both moisture returning northward into the Lower Mississippi Valley and another push of moisture coming into the western part of North America bringing renewed concerns for flash flooding. The previous outlook looked on track. Bann ....0830Z Excessive Rainfall Outlook... ....West... Flash flooding concerns return to the West Coast as a pair of low pressure systems arrive on Thursday. The first system will bring a round of rainfall to the coasts of the Pacific Northwest and northern/central California early Thursday morning. Rain rates should be between 0.1-0.25in/hr across the region with PWATs remaining modest at well below an inch. Forcing provided by a weak surface cold front won't help to enhance amounts, but higher totals will still be possible at elevation. The second round of precipitation will arrive with the entrance of another system later Thursday afternoon. Rain rates will be more substantial at around 0.5-1in/hr. PWATs between 0.75-1 inch should cause some flash flooding concerns over already well saturated soils, burn scars and in urban areas. ....Lower Mississippi Valley... An upper trough will move into the Great Plains on Wednesday leading to height falls and the return of southerly flow over the Gulf of Mexico and Mississippi Valley. Moist air advection will ensue with PWATs of between 1-1.5 inches flowing from the central Gulf coast up through the Mississippi Valley and into the Midwest. This moist/unstable airmass, overrunning a coastal warm front, a dry line and cold front to the west, will support convective initiation over the Gulf coast and inland areas, where rain rates may range between 0.25-1in/hr with locally higher amounts. The 00z GFS/UKMET and 06z NAM are in good agreement with the axis of heaviest precip footprint extending into the Midwest while the 00z EC/CMC keep their 24 hour totals confined to the central Gulf coast and ArkLaTex. Thus, the slight risk area is more of a reflection of the latest GFS/UK/NAM suite than that of the EC/CMC. The slight risk area is also consistent with the latest ensemble mean exceedance probabilities of 1 and 2 inches in 24 hours. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!99u8Y82Pq4NilQO6HkEVQsn2UMX_e2IYOOpQiQPz1dYI= eAxveRb5Rnu2SncEYcOcD-dXLZ9C8A0sZzrlmYyYaeAELUg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!99u8Y82Pq4NilQO6HkEVQsn2UMX_e2IYOOpQiQPz1dYI= eAxveRb5Rnu2SncEYcOcD-dXLZ9C8A0sZzrlmYyYfvd7ZlE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!99u8Y82Pq4NilQO6HkEVQsn2UMX_e2IYOOpQiQPz1dYI= eAxveRb5Rnu2SncEYcOcD-dXLZ9C8A0sZzrlmYyYMy9_AsI$=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) .