Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
511 FOUS30 KWBC 030049 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 849 PM EDT Sun Jun 2 2024 Day 1 Valid 01Z Mon Jun 03 2024 - 12Z Mon Jun 03 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS AS WELL AS PORTIONS OF THE PACIFIC NORTHWEST.... ...Southern Plains... 22Z update...Pared the Slight Risk area quite a bit on the west- northwest periphery based on the latest observational/convective trends (airmass having been worked over following the compact MCS). Meanwhile, have expanded the eastern extent of the Slight towards Shreveport and the ArkLaTex based on the highly favorable thermodynamic environment downstream of the aforementioned MCS and convectively-aided MCV. A broad area of 3000-4000+ ML CAPEs were noted across eastern TX and far western LA per the latest SPC mesoanalysis, with TPW in a non-convective environment between 1.75-2.00". Given the slow southeastward migration of these cells (~20kts), sub-hourly rainfall rates of 2+ inches underneath the strongest cells will foster a more enhanced risk for flash flooding within the Slight Risk area. For further details, please refer to Mesoscale Precipitation Discussion #376, which can be accessed from www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd.php. Hurley ...Previous Discussion... Introduced a Slight Risk across portions of the Southern Plains where increasingly deep southeast flow develops and interacts with a poorly defined boundary moving that move northward. Confidence in placement is below average but there are signals in various model runs that point to a better than Marginal chance for excessive rainfall given the moisture laden atmosphere and the passage of an upper level wave ejecting eastward from the southern Rockies during the afternoon. Bann ...Northern and Central Plains... 16Z update... Very minor tweaks were made to the western bounds of the Slight Risk area over eastern North Dakota, near the Nebraska/Kansas stateline and across central Iowa to reflect the latest trends for the global and hi-res guidance. Campbell ...Previous Discussion... The emergence of a low amplitude shortwave trough from the northern Rockies out over the adjacent western high plains this morning will set the stage for convection that produces locally heavy rainfall across parts of the northern and central plains later. Showers and thunderstorms should become more numerous across parts of the eastern Dakotas as a cold front becomes better defined and propagates across Minnesota and Iowa later. Model QPF shows convection building along the front as far south as Nebraska and Kansas during the evening. Accelerating southerly flow ahead of the cold front will draw deeper moisture into the area with precipitable water values ranging from roughly 1.3 inches along the international border to values approaching 1.75 inches across western Iowa/eastern Nebraska and northeast Kansas by 03/00Z should be aided aloft by divergence associated with a developing jet streak over the upper midwest late tonight/early Monday morning. Bann ...Pacific Northwest... 16Z update... Very minor adjustments/broadening of the Slight and Marginal Risk areas a bit eastward to account for increased QPF amount/coverage. Campbell ...Previous Discussion... There will be a growing threat for excessive rainfall over along the Coastal Range and Cascade Range from Washington and Oregon southward into the mountains of far northwest California as an anomalously strong mid and upper level jet usher in deep moisture throughout the day. While not normally a concern in the summer time...satellite imagery shows the moisture plume has its roots well into the subtropics in the central/western Pacific. With the arrival of strong onshore flow and precipitable water values that approach 1.5 inches along the immediate coast of Oregon by late this afternoon...IVT values at or above 700 kg per meter per second that is directed normal to the mountains for a rather prolonged period. Only change to the previous outlook was to bring the Slight Risk areas southward into the Coastal and Cascade ranges based on latest deterministic QPF amounts with isolated spots in the west facing terrain potentially receiving 4+ inch amounts due to the terrain influences and at least some possibility of enhanced rates from embedded convective elements. The combination of rainfall and snow-melt run-off from higher elevation has the potential for flooding or flash flooding. Latest numerical guidance brings an area of height falls...leading to the development of a trough axis...which reaches the west coast towards the end of the outlook period at 03/12Z. No modification was done to the changes coordinated farther inland by the previous shift. Bann Day 2 Valid 12Z Mon Jun 03 2024 - 12Z Tue Jun 04 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS AND THE NORTHERN ROCKIES... ...Plains... 21Z update... MCS moving through the Plains/Mississippi Valley could swiftly spread 2 to 4 inches across the region with isolated higher amounts possible. The latest trends have the placement of QPF further east across Missouri and Arkansas therefore the Slight Risk area expanded eastward into western Illinois and now encompasses more of eastern Missouri and Arkansas. Small adjustments were also made to the Marginal Risk area to cover more of extreme southeast Arkansas, northern Louisiana, and eastern Texas. Campbell The front which provided focus for showers and thunderstorms capable of producing heavy rainfall will continue eastward on Monday...extending from the western Great Lakes region southward into the central and southern plains by Monday afternoon. The front outruns better upper support and becomes less of a driving force for heavy to excessive rainfall...especially across the northern tier of states. The southern portion of the front should still be able to provide a mechanism for convective initiation. Exactly where continues to be a big challenge...with numerical guidance offering a wide range of possibilities, Introduced a Slight Risk area mainly across the central and southern Plains where an upper level trough moving out of the Southern Rockies should provide some upper level support. The vertical depth of this wave has been fairly limited but models were beginning to show increase its reach. Any convection that forms will be in a region with precipitable water values over 1.75 inches being drawn towards the front by southerly flow in excess of 30 knots. The GFS and CMC guidance fits the Slight risk area best but nothing to preclude the northern/western solution offered by the NAM. ...Central/Southeast Virginia... Raised a Marginal Risk from Richmond to Norfolk and surrounding locations for the potential for heavy rain developing near a weak surface frontal boundary. Some of the guidance suggests these storms could drop 2+ inches along the I-64 corridor that could result in localized urban flash ponding/flooding. Campbell ...Pacific Northwest and Rockies... 21Z update... Made minor reductions to the westward side of the Marginal Risk area near the Cascades in addition to a small nudge of the eastern boundary furtherer to the east. The latest guidance saw a small uptick in the QPF over north-central Idaho so in following that trend, the northern bound of the Slight Risk area was expanded northward. Campbell Saw little reason to make too many changes to the outlook area from Washington eastward Idaho and far western Montana as the flow of deeper moisture associated with the atmospheric river continues to push inland. The moisture fetch should eventually become disrupted by low amplitude ridging which leads to decreasing intensity and coverage from west to east. Until that happens...the combination of rainfall run- off...perhaps enhanced by snow melt...will continue. Bann Day 3 Valid 12Z Tue Jun 04 2024 - 12Z Wed Jun 05 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE NORTHERN AND CENTRAL PLAINS... 21Z update... A subtle broadening of the Slight Risk area was warranted over the Mid-Mississippi Valley/Plains portion of the region given the latest runs of guidance. Consensus stills favors to 3 inches for areal averages across the central part of the country. Isolated maximums of 4+ inches may be possible with any of these storms. Campbell As one cold front weakens as it progresses eastward...a second front takes shape and pushes southward/eastward on Tuesday in response to the sharpening of a northern stream trough on Tuesday. Low level flow is forecast to back once again and draw deeper moisture northward ahead of the on-coming front. It appears to be two mechanism for heavy rainfall...with the southern portion of the Slight Risk being aided by weak but important shortwaves supporting convection along the old front or other outflow boundary while the northern area was driven by the approaching front and upper level divergence/support from the developing synoptic scale system. Given the proximity of the two areas...confidence in placement was not high enough to warrant two separate areas so one broad Slight Risk was indicated. 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