Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
148 FOUS30 KWBC 020103 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 903 PM EDT Sat Jun 1 2024 Day 1 Valid 01Z Sun Jun 02 2024 - 12Z Sun Jun 02 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE GULF COAST REGION BETWEEN THE UPPER TEXAS COAST AND FLORIDA PANHANDLE, ALONG WITH A PORTIONS OF THE SOUTHERN-CENTRAL PLAINS... ...0100 UTC Update... ...West Texas to south-central Texas, including much of the Hill Country... Have hoisted a relatively short term Slight Risk area across this region, owing to the rapid development/expansion of convection along the dry line in the Upper Rio Grande-West TX. Aiding to the organization and upscale growth is flat shortwave energy that will move into central and south-central TX later tonight. Currently (prior to sunset) robust deep-layer instability exists within the Slight Risk area, with mixed-layer CAPEs generally between 3000-4000 J/Kg. Moreover, an uptick in southeasterly low-level flow (20-25 kts at 850 mb) is helping to boost the 0-6km shear profile to 45+ knots. While largely a severe weather threat (several embedded supercells, with large hail and severe wind gusts as primary threats), the congealing of these convective clusters, again with multiple supercells, will also lead to intense short term rainfall rates, up to 2-3+ inches/hr underneath the strongest cells. Hurley ...2200 UTC Update... ...Upper Texas Coast to the Florida Panhandle... With this update we have removed the Moderate Risk across the western FL Panhandle, which received quite a bit of rain earlier this morning. While addition convection will be possible again later this evening/overnight, much of the latest guidance (including more recent HRRRs and 18Z HREF) has the bulk of the activity tracking south over the Gulf. Weak upper level difluence along with the E-SE progression of the upper level shortwave currently traversing the ArkLaTex will allow for more organized (widespread) convection this evening and overnight within the Slight Risk area. Dynamically, thermodynamically, and kinematically however the conditions aren`t overly favorable to support more than a Slight Risk ERO. Specifically, the low-level inflow is lacking somewhat (peak 850 mb winds ~20kts), though relative to the weak flow aloft (850-300 mb mean flow 20-25 kts), could allow for some backbuilding and thus some cell training. However given the weak mid-level lapse rates (<7.0 C/Km), expect a more substantial loss of deep- layer instability potential after sunset. This along with the modest moisture transport (with TPW and low-level moisture flux anomalies averaging 1 to 1.5 standard deviations above normal) will likely limit the areal extent of excessive rainfall/flash flooding following the loss of daytime heating. Hurley ...1600 UTC Update... ...Portions of the Central Plains... Guidance remains in relatively good agreement for this afternoon`s round of dry line convection to focus in southwest Kansas and the OK & TX Panhandles. Thus, while isolated storms are certainly possible further south, and especially along the Rio Grande, the isolated nature of the convection will limit the flash flooding. Areas along the immediate Rio Grande may have a higher risk as storms that form over the mountains of Mexico my drift across the river near Del Rio south to Eagle Pass. ...Ohio and Tennessee River Valleys... The inherited Slight was downgraded to a Marginal with this update in coordination with the impacted forecast offices. CAMs guidance trending downward and lack of instability has decreased the potential for flash flooding. Wegman Day 2 Valid 12Z Sun Jun 02 2024 - 12Z Mon Jun 03 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL AND NORTHERN PLAINS AS WELL AS THE WASHINGTON CASCADES AND SEATTLE METRO AND CENTRAL IDAHO MOUNTAINS... ...2030Z Update... ...Washington Cascades and Seattle Metro... A Slight Risk upgrade was introduced for the Washington Cascades and Seattle Metro Area with this update in coordination with SEA/Seattle, WA and PQR/Portland, OR forecast offices. An atmospheric river event is forecast to begin early Sunday morning, and continue into Monday. A plume of moisture associated with the atmospheric river will slam into the Cascades and coastal ranges, resulting in rainfall rates up to 1/2 inch per hour. Snowmelt will future add water to the streams and rivers draining the Cascades to Puget Sound. The area has been somewhat drier than normal lately, which will mitigate the flooding concerns a bit, but increase the "shock factor". The greatest flooding concerns are in areas with steep valleys/canyons, urban areas, burn scars, and other poor drainage areas. By Monday the rain should shift north largely into Canada, but there will be some lingering rainfall into the Olympics and Washington Cascades. ...Bitterroots and Salmon River Mountains north of the Salmon River... A Slight Risk upgrade was introduced in coordination with MSO/Missoula, MT forecast office. The same atmospheric river impacting the Washington Coast will continue inland into the mountains of eastern Washington and Idaho. Much of the moisture in this area will be beneficial and not result in many flooding concerns for eastern Washington and northern Idaho, but as the plume of moisture drifts south into the Bitterroots and Salmon River Mountains, well above average snowpack at the higher elevations with almost 9 inches of snow-water equivalent will be subject to the 1-3 inches of rain forecast for this area. This will result in snowmelt being a significant contributor to river and small stream rises draining those mountain ranges. Given the steepness of the terrain, the rises may be very fast, resulting in flash flooding. The rain will continue moving southward through late Sunday night into Monday, so the threat for flooding will shift south as time goes on. Given the drier antecedent conditions in the valleys, the lesser amounts of rain forecast for the Salmon River Mountains south of the Salmon River, Sawtooth, and southern Bitterroot Ranges should keep the flooding threat at Marginal until Day 3/Monday. ...Northern Plains... No significant changes were made to the ongoing Slight risk across the area. With the poor predictability of convection and relative similarity in the guidance in this area from run-to-run, the Slight looked good. See the previous discussion below for more. Wegman ...Previous Discussion... The focus for an excessive rainfall threat shifts into the northern and central plains on Sunday and Sunday night as a low amplitude trough makes its way out of the northern Rockies and tracks towards the western Great Lakes. Moisture transport into the region will be aided by strengthening low level flow over the plains which taps deeper moisture...with enough pooling ahead of an approaching cold front to boost precipitable water values into the 1.6 to 1.8 inch range by 03/00Z. The lift resulting from the mid level wave and the formation of 80 to 100 kt jet streak near the international border supporting initial development that spreads south into an increasingly unstable airmass with higher precipitable water values by Sunday evening. Maintained the Marginal risk area across the coastal regions of Washington and Oregon. 00Z numerical guidance shows a period of 12 hours or so with prolonged and sustained moisture transport from the eastern North Pacific Ocean directed normal to the coastal and Cascade ranges. IVT values peak in the 700 to 900 kg per meter per second range around 03/00Z and then weakens in the early morning hours on Monday. While atmospheric rivers are normally much of a consideration in summer...the upper level jet is quite anomalous with the u-component of the 500 mb flow being greater than 5 standardized anomalies greater than climatology helping boost precipitable water values to greater than an inch over the western half of Oregon and southwest Washington by 03/06Z (at or above the 90th percentile for this time of year) with 1.5 inch precipitable water values along the immediate Oregon coast by Sunday evening. That all gives support to the NBM and WPC QPF guidance of 1 to 3 inches...with the highest amounts in the west aspect of the Coastal Ranges and the Cascade Range...by the time that Day 2 ends at 03/12Z. Bann Day 3 Valid 12Z Mon Jun 03 2024 - 12Z Tue Jun 04 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL IDAHO MOUNTAINS... ...2030Z Update... ...Central Idaho Mountains... A Slight Risk upgrade was introduced in coordination with MSO/Missoula, MT; BOI/Boise, ID; and PIH/Pocatello, ID forecast offices. The atmospheric river ongoing from Day 2/Sunday will continue pressing slowly southward into the day on Monday. Rainfall amounts are not super impressive, generally between 1 and 2 inches in the area. However the rain will be falling on a well above average snowpack at the higher elevations of the Salmon River, Bitterroots, and Sawtooth ranges, and well as on the higher peaks in the area. The combination of rainfall and snowmelt will cause large rises on local area streams and creeks, as well as significant rises on area rivers. Any rainfall from Day 2 will begin raising river levels, and with most of the rain expected for the Slight Risk area on Day 3, the more significant flooding will occur into central Idaho on Monday. ...Washington Cascades and Olympics... There is expected to be a significant decrease in the amount of rainfall across this area on Monday as compared with Sunday. So while flooding may be ongoing at the start of the period, think the lesser amounts of rain closer to 1 inch should not add too much to any existing flooding, so a Marginal Risk remains in place in coordination with SEW/Seattle, WA forecast office. ...Mid-Mississippi Valley and the Ozarks... No major changes were made to the Marginal Risk in place across the region. The signals for heavy rain remain diffuse, and certainly lower than previous days, so the Marginal Risk, while over some saturated soils continues to look good. It`s quite possible that targeted Slights may be needed in this region with better model agreement and hopefully helpful CAMs guidance. Wegman ...Previous Discussion... Central U.S.... There is a Marginal Risk of excessive rainfall over a broad and rather unfocused area across the central U.S owing to weak and difficult to time shortwave energy ejecting out over the Plains ahead of largely zonal flow that gradually backs as broader height falls over the Rockies. The atmosphere over the plains will generally be moist enough to support locally heavy rainfall from any storms that form...but confidence was below average as to the placement and timing of the forcing. In the West... There is a Marginal Risk of excessive rainfall over portions of the northern Intermountain region as zonal flow draws deeper moisture inland that interacts with the terrain in the northern Intermountain region (especially parts of the Bitterroots and Sawtooth ranges). The resulting QPF is generally expected to be in the 1 to 1.5 inch range where the flow impacts the terrain...with spaghetti plots suggesting a low end chance for 2 inch totals. At the same time...weak shortwave ridging along the Washington/Oregon coast will lead to a decreasing risk of excessive rainfall as rainfall rates decrease and areal coverage diminishes with time. Bann 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