Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
195 FOUS30 KWBC 010101 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 901 PM EDT Sun Jun 30 2024 Day 1 Valid 01Z Mon Jul 01 2024 - 12Z Mon Jul 01 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEASTERN Virginia, NORTHEASTERN NORTH CAROLINA, SOUTHEASTERN ARIZONA, SOUTHWESTERN NEW MEXICO, AND SOUTHWESTERN COLORADO... ...01Z Update... A Slight Risk was added to portions of southeastern Virginia and northeastern North Carolina. With heavy rainfall having already occurred across portions of the region, guidance shows additional storms developing and moving across the region as a cold front slowly approaches from the northeast during the evening and overnight. HREF neighborhood probabilities, as well as recent runs of the HRRR, indicate an additional 2 inches or more can be expected across portions of the region, potentially elevating ongoing runoff concerns. In the Southwest, expanded the Slight Risk across a larger portion of southeastern Arizona and southwestern New Mexico, where showers and storms fueled by monsoonal moisture, will continue to produce areas of heavy rainfall and flash flooding into the evening. Elsewhere, made smaller adjustments to the previous outlook based on observations and recent hi-res guidance. Pereira ...16Z Update... ...Central Plains... In coordination with DDC/Dodge City, KS; ICT/Wichita, KS; and OUN/Norman, OK forecast offices, the Slight Risk for these areas was downgraded to a Marginal with this update. The ongoing MCS which caused numerous instances of flash flooding in southwest Kansas is slowly dissipating as is typical with the diurnal weakening of the LLJ. Thus, while there are a few pockets of greater than 1 inch per hour rainfall rates ongoing, the current and forecast trend over the next few hours is for continued weakening of the rainfall rates. For the rest of today into tonight, expect no more meaningful rainfall in this area. The expected development of a new MCS over northern KS and NE tonight will be entirely north of the heavy rainfall region from this morning, and thus not adding to any ongoing flash flooding. ...Southwest US... Monsoonal southerly flow of deep Pacific moisture continues across the Four Corners Region today. With maximum diurnal heating this afternoon, expect a renewed flareup of slow moving convection capable of rates to 1.5 inches per hour. Portions of southern Arizona have been hit repeatedly over consecutive afternoons with this same convection which will remain in roughly the same place. In similar fashion, the same moisture plume will advect north across much of Arizona and into southwest Colorado, where its meeting with the terrain there and some weak upper level support will cause a renewed round of showers and thunderstorms in this also hard-hit area this afternoon. Localized totals as high as 2 inches could likely cause additional flash flooding in the terrain and adjacent valleys of southwest Colorado, so the Slight remains in place with no changes. Wegman ...Previous Discussion... ...Southwest U.S... Moisture will continue to serge northward into parts of Arizona and New Mexico in broad anticyclonic flow around a mid- and upper-level ridge over the Southern Plains. Convective chances will be aided by mid-level height falls from the Pacific Northwest extending into the central Great Basin by evening. Any convection that develops should tap into an airmass characterized by precipitable water values in excess of an inch from eastern Utah and western Colorado to values approaching 2 in near the international border in southeast Arizona by evening (2 to 4 standardized anomalies above climatology and greater than the 95th climatological percentiles). The resulting instability should be enough to support some localized intense rainfall rates that pose a flash flooding risk...especially in complex terrain and over burn scars and normally dry washes. ...Eastern Seaboard to Florida Peninsula... A cold front associated with low pressure north of the international border will be moving into an anomalously moist airmass from the Mid-Atlantic region southward with precipitable water values expected to be as high as the 2.0 to 2.3 inch range in a 50 to 100 mile wide corridor from the Carolinas to the Florida panhandle by 01/00Z (approximately 3 standardize anomalies greater than climatology and near the 95th climatological percentile). The HREF focused its highest probability of 1- and 2-inch per hour rates and low-end probability of 1- and 3-hour rainfall exceeding flash flood guidance near the front given the moisture flux convergence. There was a similar region of higher probabilities extending along the Florida peninsula...presumably along sea breeze boundaries and interaction with a weak shortwave seen on water vapor imagery early this morning. ...Plains of Northeastern Montana... Convection capable of producing locally heavy rainfall is expected to develop later today as a shortwave moves from Washington/Oregon early in the period and eventually emerges east of the Rockies. Between falling surface pressures approaching from the west and surface high pressure over southern Canada moving south and east...surface dewpoints over the plains of northeast Montana should climb through the 50s in response to increasing moisture transport once a low level jet forms. Given expected rainfall amounts from what should be progressive storms...a Marginal is still sufficient. Bann Day 2 Valid 12Z Mon Jul 01 2024 - 12Z Tue Jul 02 2024 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE LOW COUNTRY OF SOUTH CAROLINA AND THE NORTH GEORGIA COAST... ...2030Z Update... ...Southeast US Atlantic Coast... In coordination with CHS/Charleston, SC forecast office, a Moderate Risk upgrade was introduced with this update. A cold front will become stationary as it stalls along the coast. Abnormally high PWATs on the order of 2 to 3 sigma above normal and above 2 inches will be in place along the coast on Monday. As this moisture runs into the stalling front, the slowing much cooler, drier air mass will hold the front in place from the north as the abundant moisture and instability moves into the front from the south. For more northern areas, the front is likely to continue east and therefore push the heaviest rain off the coast. Meanwhile for portions of the SC and GA coasts, the front will stall out largely perpendicular to the orientation of the front. This will allow for the convection that develops along that front to struggle ot move, while consistently being fed with moist, unstable air. Thus, the flash flooding threat has increased as the forecast for rainfall have also increased. Uncertainty remains with exactly where the front stalls out, as even a small eastward shift in the guidance would mean big changes (in the positive/drier direction) as all the heaviest rainfall occurs offshore. Nonetheless with some consistency that heavy rain ill fall along the coast, vulnerable urban centered in the area such as Charleston, SC and Savannah, GA may be adversely impacted with numerous flash floods, with some of them significant if that convection forms and stalls over those cities. Regardless, the heaviest rainfall rates of up to 3 inches per hour would support potential flash flooding most anywhere rates of that magnitude can occur for a significant period of time. ...Upper Midwest... Relatively few changes were made to the overall large Slight risk area across portions of the Upper Midwest. A low tracking in between will result in a relative minimum of rainfall over most of SD and west central MN, but in between 2 areas of greater rainfall, one over ND and northern MN and the second from northeast NE to western WI. Both areas are of concern for flash flooding due to very favorable antecedent soil moisture conditions from recent heavy rainfall. The area of greater concern is to the south from NE to WI, as both greater rainfall is expected here as these storms get "first dibs" at the flow of Gulf moisture moving in on the LLJ, and the flooding ongoing in this area is of greater magnitude than areas further north. Thus, this area is still in a higher-end Slight with a possibility for a MDT upgrade with future updates if QPF increases. For now as forecast rainfall remains similar to previous forecasts, no major changes were needed. Further north the Slight was extended back to the east to include the Arrowhead as the corridor across northern MN gets more rainfall than previous forecasts indicated. Due to also favorable antecedent conditions, widely scattered instances of flash flooding are expected. Wegman ...Previous Discussion... ...Upper Midwest/Northern Plains... The system that helps foster a risk of excessive rainfall on Day 1 will continue to propagate eastward during the period and a risk of excessive rainfall on Day 2 over portions of the Upper Midwest. With upwards of 12 hours of southerly winds drawing deep moisture into region...some storms will be able to produce locally intense rainfall rates and locally heavy rainfall amounts. The amounts...while actually fairly modest...could fall in areas recently soaked by heavy rainfall which has made some places hydrologically sensitive. The previously issued Slight Risk still captures the area and only minor changes were needed. ...SOUTHEAST US... Introduced a Slight Risk area along and near the coast from South Carolina into parts of Georgia. With the cold front sagging southward acting to focus convection and a fetch of post-frontal on-shore flow persisting into the afternoon...felt some enhanced chances for flooding/run-off problems existed. Elsewhere in the Southeast...deep moisture and weak flow south of the front will open the potential for disorganized convection to form along any boundary/outflow...so left a unfocused Marginal surrounding the Slight. ...Southwest US... Monsoonal moisture will be lingering over the Southwest (especially Arizona and New Mexico) that is drawn back north and east around an upper level ridge. Maintained a Marginal Risk at this point given the uncertainty of cloud-cover lingering from convection on Day 1 and its ramifications for when and where convection fires later in the day and how much subsidence there is in the wake of a wave moving north and east of Arizona...and the magnitude of dry air in the sub-cloud layer. Will be able to refine this later. Bann Day 3 Valid 12Z Tue Jul 02 2024 - 12Z Wed Jul 03 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE UPPER MIDWEST TO WESTERN GREAT LAKES... ...2030Z Update... ...Upper Midwest... No big changes were made with this update. Concerns are increasing in eastern Iowa and the surrounding areas from northern MO to southern WI as the same influx of moisture and instability results in training thunderstorms across this region. Antecedent conditions are also quite favorable to flash flooding due to recent heavy rainfall. In coordination with DVN/Davenport, IA forecast office, a Moderate risk was discussed as potential in future updates, but there`s still lots of time to review future model data to best determine impacts. Thus, a Moderate Risk will need to be considered with future updates. ...Southeast... A Marginal Risk area was introduced with this update targeting the Florida Panhandle, but extending into the Hilton Head Island area of far southern SC. This will be a continuation of the convection from the Day 2/Monday period for this area as the front gets a nudge on Tuesday towards the Gulf. Thus, overall rainfall amounts are expected to be lower than on Monday, but of course any continued rainfall at 12Z Tuesday may require an upgrade in areas hard hit from Monday night. Elsewhere, expect slow moving convection with plentiful Gulf moisture allowing for the potential for very high rainfall rates in the cores of the strongest storms. With less organization to the storms as compared with Monday, think the flash flooding threat is a bit lower. The greatest threat lies roughly from Hilton Head, SC southwest to Apalachicola, FL. ...Southwest... No big changes in the Southwest as the typical monsoonal storms form once again over AZ and NM, though minimal organization should prevent all but isolated flash flooding. Wegman ...Previous Discussion... ...Upper Midwest/Northern Plains to Western Lakes... Numerous showers and thunderstorms should be on-going ahead of an advancing cold front and associated impulse/wave aloft. There should be enough instability of support local downpours that may fall on ground still saturated from heavy to excessive rainfall recently. In addition to new or re-newed flooding from this batch of rainfall is the concern for on-going flooding to be aggravated. ...Southwest... Maintained the Marginal Risk area over the Southwest US on Tuesday...with some southern suppression of this moisture shown in line with the global guidance and decreased areal coverage of 1- and 2-inch contours from the QPF spaghetti plots. Will keep an eye open for trends in upcoming model cycles. 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