Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Wed Feb 14 2024 08:43:00 FOUS30 KWBC 140827 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 327 AM EST Wed Feb 14 2024 Day 1 Valid 12Z Wed Feb 14 2024 - 12Z Thu Feb 15 2024 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF SOUTHWEST OREGON & NORTHWEST CALIFORNIA... Portions of coastal OR and northwest CA... The southern lobe of an elongated mid to upper-level trough/closed low, now approaching 140W, should continue on an eastward trajectory and be near the Oregon/California border later this afternoon or early evening. While uncertainty remains in the evolution of this feature and its interaction with a developing closed low off of the Washington coast, the 00Z models continued to be in somewhat better agreement with the overall pattern evolution (a trend that began with the 12Z model cycle on Monday). Warm advection isentropic lift driven precipitation should be ongoing at the start of the period across northwest California that gradually expands in coverage to southwestern Oregon but the highest intensity rainfall should arrive with an occluded/cold front with the 14/00Z HREF indicating the probability of exceeding 0.5 in/hr rainfall at 10 to 30 percent near the coastal Oregon/California border by late morning and peaking 30 to 50 percent between Cape Mendocino and the Santa Lucia Range around 21Z. However, the progressive nature of the front and very weak instability (< 250 J/kg) should limit the duration/magnitude of these higher rates with localized 2-4 inch totals over the 24 hour period ending 12Z Thursday. The highest rainfall should focus along south to southwesterly facing slopes given a similar orientation of the low level wind. Across the northern foothills of the Sierra Nevada, there will be a narrow region below snow levels of 5,000 to 6,000 feet where locally heavy rain of 2-3 inches and brief rainfall rates over 0.5 in/hr will be possible. However, this inland region appears too low end for a Marginal at this time. Bann Day 2 Valid 12Z Thu Feb 15 2024 - 12Z Fri Feb 16 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Lower Rio Grande Valley of Southern TX... Low level moisture will return ahead of a shortwave trough in the southern stream...with precipitable water vales increasing into the 1.5 to 2.0 inch range across southern Texas by 12Z on Friday. The problem continues to be the lack of a low level boundary. Guidance is still able to generate some convection across parts of the Lower Rio Grande Valley with maximum QPF generally in the 1.5 to 2.5 inch range. Relatively dry antecedant conditions combined with a lack of better instability should limit any flooding potential. The area will continue to be monitored for changes with future forecast cycles. Otto/Bann Day 3 Valid 12Z Fri Feb 16 2024 - 12Z Sat Feb 17 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG AND NEAR THE LOWER TEXAS COAST ON FRIDAY... Continued amplification of the wave at mid-levels over northern Mexico during the period will push a cold front into the southern part of Texas and support showery conditions. The expectation is that a surface low will develop over portions of the western Gulf of Mexico and eventually focus the heavy rainfall away from land. Until that happens...deep moisture will be in place with precipitable water values in excess of 1.6 inches / some 2 to 3 standardized anomalies above climatology for this time of the year / with generally modest low level moisture transport into the region. Given that deterministic QPF is on the order of an inch or two...and the antecedent have been dry over an area of primarily agricultural land usage...it would appear that much of the area could handle the rain with limited exceptions in regions of poor drainage or in urban areas. Bann $$ --- SBBSecho 3.14-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/105) .