Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
452 FOUS30 KWBC 222349 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 649 PM EST Sat Feb 22 2025 Day 1 Valid 01Z Sun Feb 23 2025 - 12Z Sun Feb 23 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN WASHINGTON STATE AND OREGON... Pacific Northwest... The beginning of a multi-day atmospheric river/heavy rainfall event has begun. Precipitable water values of 0.75-1.25" should remain near coastal sections into Sunday morning. The combination of 50+ kts of 850 hPa inflow and 100 J/kg of MU CAPE initially are sufficient to support max hourly rainfall of 0.50-0.75" and max totals of 3-5" in favored terrain regions. See Mesoscale Precipitation Discussion 48 for more details on conditions expected through 0820 UTC. The greatest HREF neighborhood probabilities for .50"+/hr amounts were used to define the Marginal Risk area; no major changes were necessary. Snow levels will be quite high across the Pacific Northwest, with much of the precipitation falling as rain. This heavy rain, combined with snow melt will support isolated runoff issues. The higher hourly rates do not last for more than several hours. This combined with relatively dry antecedent conditions precluded a Slight Risk from consideration. Northwest Gulf Coast... Ongoing convection is on the wane, mostly shifting into the Gulf south of Louisiana, with local amounts of 2" occurring with hourly maximum rain amounts just exceeding 1". Instability has been on the decline as of late, but should build back up after 06z and reach a maximum near the Mouth of the Sabine River (TX/LA border with the Gulf) at 12z. Indications from the 18z HREF were for hourly rain totals of 0.5"+ in this region right at the end of the period/around sunrise on Sunday. While excessive rainfall/flash flooding cannot be completely ruled out, any instance appears to be singular at best, so no Marginal Risk areas were included in this update. Hourly rain totals to 1.5" with local amounts to 3" are possible in or near the vicinity of Galveston Island and High Island early Sunday morning. Roth Day 2 Valid 12Z Sun Feb 23 2025 - 12Z Mon Feb 24 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OREGON COAST INTO THE OLYMPIC RANGE AND OVER PORTIONS OF THE SOUTHERN WASHINGTON AND NORTHERN OREGON CASCADES... 19z Update: Forecast rainfall has increased further south over Oregon, and this warrants a southward expansion of the Slight risk along the Oregon coast and portions of the Oregon Cascades. Otherwise the forecast reasoning from below remains on track. Chenard ...Previous Discussion... The atmospheric river event that started day 1 into the Pacific Northwest will continue into day 2 as additional height falls embedded in the broad west southwest mid to upper level flow across the northeast Pacific move toward the Pacific Northwest. The second surge of high IVT values, 600-800 kg/m/s and anomalous PW and 850-700 mb moisture flux values, 2-4+ standard deviations above the mean will push back into the coastal Pac NW Sunday morning. This will support another day of widespread heavy rainfall totals of 1-2"+ and max totals in the 3-5"+ range in the favored terrain regions. Snow levels again will remain high across much of the Pac NW day 2 with much of the precip again falling as rain. With widespread two day totals in the 3-5"+ range and max totals 6-10" in favored terrain regions, increasing soil moisture and stream flow values will increase the risk of flooding. Given this, slight risk areas were added from the northern OR coast range, northward into the Olympic Range and over the southern WA Cascades. No significant changes to the marginal risk area inland across far northeast OR, far eastern WA state into northern ID and northwest MT. The anomalous PW values pushing into the Pac NW day 1 will move into the Northern Rockies day 2, with values 2-3+ standard deviations above the mean. Similar to areas across the Pac NW, snow levels will be very high day 2 with much of the precip falling as rain. Two day precip totals of 1-3" possible across northern Idaho into northwest Montana, combined with snow melt will support isolated runoff conditions developing. Oravec Day 3 Valid 12Z Mon Feb 24 2025 - 12Z Tue Feb 25 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN OREGON COAST RANGE INTO THE OLYMPIC RANGE AND OVER THE SOUTHERN WASHINGTON CASCADES... 19z Update: Not much change needed to the inherited risk areas as the forecast for Monday remains on track. A stronger shortwave and surface low will bring another round of moderate to locally heavy rainfall to northwest OR into western WA, warranting the continuation of the Slight risk areas. Still looks likely we will have organized convection push across southern FL Monday. Still some uncertainty on the details, but it does appear that at least some instability will try to work into southern FL, which combined with the strong dynamic forcing, could allow for locally excessive rainfall rates over urban areas. Chenard ...Previous Discussion... The next in the series of strong height falls in the broad west southwesterly mid to upper level flow across the northeast Pacific will push an amplifying trof into the Pac NW Monday. This third in the series will be stronger than the previous two and support a stronger surface low moving into the Olympic Peninsula/eastern Vancouver Island area Monday evening. 850-700 mb moisture flux values will again be anomalous..2-3+ standard deviations above the mean, but PW values not expected to be as anomalous as the days 1 and 2 events, generally around 1 standard deviation above the mean. This will result in slightly lower max IVT values, 500-600 kg/m/s impacting the coastal Pac NW day 3. Additional widespread heavy rains of 1-2" likely from the Olympics, south along the Oregon Coast Range and into the WA Cascades and northern OR Cascades. This will bring 3 day totals into the 7-10 inch range from the northern OR Coast Range into the Olympic Range and through much of the WA Cascades. Increasing soil moistures and stream flows will continue a flooding threat into day 3. Slight risks introduced day 2 were maintained day 3 across the southern WA Cascades and from the northern OR Coast Range and Olympic Range. ...Southeast Florida... While there are some timing differences among the latest suite of guidance, there is agreement on an amplifying upper trof across the western to central Gulf Monday and into the eastern Gulf by early Tuesday. Strengthening southerly to southwesterly low level flow off the Gulf will push anomalous PW and 850-700 mb moisture flux values, 2 to 3+ standard deviations above the mean, across South Florida early day 3. This will support the potential for an area of heavy rains to push across South Florida Monday into Monday evening, with timing differences evident between the 00Z EC, GFS and NAM which have detail differences with the amplitude of the upper trof. While confidence is not great with the details of the upper trof amplitude and resultant timing of the strongest UVVS, there is consensus for heavy rains to push across South Florida day 3. A marginal risk area was added for the urban areas of southeast coastal Florida from Miami to West Palm for the potential for isolated urban runoff issues. Oravec Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt