Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Nov 13 2025 23:46:10 FOUS30 KWBC 132345 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 645 PM EST Thu Nov 13 2025 Day 1 Valid 01Z Fri Nov 14 2025 - 12Z Fri Nov 14 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL & SOUTHERN CALIFORNIA... IVT values values will weaken slowly, though remaining strong,=20 while shifting through central and southern California, eventually reaching the western Transverse Ranges by 12Z Friday. Risk areas were trimmed from areas where heavy rainfall is ending or has ended. The 18Z HREF guidance continues to support high hourly rainfall=20 totals within the maximum axis of moisture transport, with amounts of 0.5-1" remaining possible overnight. Timing remains similar to=20 before with the axis of heaviest rainfall intensities impacting=20 the Transverse Ranges 09-12Z and a very slow fading of the heavy rainfall in the western foothills of the Sierra Nevada. With the=20 hourly amounts anticipated and local amounts of 3"+ probable for=20 the western Transverse ranges, coordinated with the LOX/Oxnard CA=20 forecast office to upgrade to a Slight Risk with this update. The=20 heavy rains would be most problematic in area burn scars. Roth Day 2 Valid 12Z Fri Nov 14 2025 - 12Z Sat Nov 15 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE TRANSVERSE RANGE OF SOUTHERN CALIFORNIA... ...2030 UTC UPDATE... Only some minor changes made to the slight risk area across the Transverse Range of Southern California. The previous slight risk area was extended approximately 40-50 miles farther to the east. This was to cover the slightly farther east axis of high HREF neighborhood probabilities for 2 and 3 inch+ totals during the day 2 period. Otherwise, no significant changes to the previous thinking below. Oravec ....Previous discussion... a front will continue to make southward progress toward the Transverse Ranges at the beginning of the forecast period, with strong onshore flow (around 25-35 knots at 850mb) continuing to foster upslope and orographically enhanced rainfall at 12Z Fri. Over time though, this flow will slacken partially due to the cutting off and retrograding mid/upper low west of the California coast. The heavy rainfall threat will lessen substantially during the day as a result, with only terrain- favored areas experiencing what should be an isolated risk of excessive rainfall. Slight Risk areas are maintained for this outlook per the previous forecast, but have been confined to portions of Santa Barbara and Ventura Counties for the morning rainfall activity. Late in the forecast period, models suggest another uptick in heavy rainfall potential approaching portions of the Los Angeles Basin and adjacent eastern Transverse and San Diego County Mountains. Timing on the onset of this activity is a bit uncertain, and the bulk of this second surge of rainfall should hold until D3/Sat. A Marginal Risk is maintained in these areas to address this secondary threat. Lastly, strong southwesterly flow will impinge upon the Olympics and Cascades for a second consecutive day Friday. This orographically enhanced heavy rain scenario will promote areas of an additional 1-2 inches of rainfall (with locally higher totals). With antecedent rainfall expected to fill area watersheds on D1/Thursday, the additional rainfall could cause isolated instances of flooding/flash flooding especially in sensitive and low-lying areas. A Marginal Risk area has been added to account for this threat. Cook Day 3 Valid 12Z Sat Nov 15 2025 - 12Z Sun Nov 16 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS A LARGE PART OF SOUTHERN CALIFORNIA... ....2030 UTC UPDATE... At the moment, no changes made to the previous slight risk areas across Southern California. There is still the potential for an upgrade to moderate across the Transverse Range. We will likely wait for this period to get more into the hi res time frame before making a final determination. Oravec ....Previous discussion... Strong onshore flow will redevelop across coastal ranges of southern California as a mid/upper low over (initially cutting off and retrograding over Pacific waters on D2/Fri) begins to advance slowly eastward during the forecast period. Models depict modest uncertainty with respect the timing of this system, however. Despite the uncertainty, south-southeasterly low-level flow will aid in advecting impressive moisture of tropical origin (with 1.5 inch PWAT values) toward both coastal areas and portions of the Lower Colorado River Valley. The combination of this moisture, orographic ascent, and eventual cooling aloft should result in several areas of heavy rainfall, with 2-4 inch totals expected (and locally higher amounts). Ordinarily, a setup like this would necessitate an upgrade to higher excessive rainfall probabilities and perhaps even a categorical upgrade particularly for the Transverse Ranges. Lingering uncertainties regarding timing of precipitation onset and typical difficulties in forecasting mesoscale phenomenon at 3-day timeframes are contributing factors to holding off on an upgrade at this time. An upgrade may be needed in later outlooks - especially with potential for heavy rainfall impacting a number of local burn scars north of the Los Angeles Metro area. Farther north and east, models depict a substantial increase in moistening and precipitation chances toward the southwestern Great Basin and Lower Colorado River Valley. There's some uncertainty regarding how moist the low-levels will get in these areas due model handling of the airmass over the northern Gulf of California. Relatively fast flow aloft will contribute to quick movement of convection also. A large area of Marginal and Slight Risk areas were maintained for this outlook, though any increases in low-level moistening/instability will likely result in an increase in flash flood potential that will need to be addressed with spatial expansions of risk areas. Cook Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!43ifjJ8VGs3bXYAL05ddYIYNnvYQzvZLtLEzX43So4Bb= ffy71WhKFEvQKGuUmZtMNaGmfUyqcBxUwwiIuTC-zvzlxAs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!43ifjJ8VGs3bXYAL05ddYIYNnvYQzvZLtLEzX43So4Bb= ffy71WhKFEvQKGuUmZtMNaGmfUyqcBxUwwiIuTC-2Z9Po_8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!43ifjJ8VGs3bXYAL05ddYIYNnvYQzvZLtLEzX43So4Bb= ffy71WhKFEvQKGuUmZtMNaGmfUyqcBxUwwiIuTC-b4Amzhg$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .