Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jun 27 2023 16:01:05 FOUS30 KWBC 271600 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Tue Jun 27 2023 Day 1 Valid 16Z Tue Jun 27 2023 - 12Z Wed Jun 28 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST... ....16Z Update... A few areal adjustments were made to ongoing outlook areas based on updated 12Z hires guidance. Some relatively minor southward/eastward expansions were added to the SLGT and MRGL risks along the I-95 corridor in the Mid-Atlantic, but do better cover some of the urban areas from DC to Philadelphia and suburban New York City. Storms redeveloping this afternoon/early evening will pose a threat for some heavy downpours with the potential for rain rates of 1-2" per hour, with notable probabilities for locally heavy rainfall totals of 2-3" covering the SLGT risk area. The expectation is this should all occur in a relatively short timeframe later this afternoon. Much of this region is also more susceptible to heavy rainfall today given recent rain received both yesterday and over the past few days. Another adjustment was to the MRGL risk over portions of southern Kansas/northern Oklahoma. The current exception is for convection to organize into an MCS over the High Plains and track east-southeastward through the region. The progressive nature of the MCS will likely limit overall rainfall totals and duration, and FFGs do notably come up east of I-35, suggesting local conditions are less susceptible to a risk of any flash flooding. However, a quick 1-3" of rain is not out of the question, and would at least pose a risk for some minor ponding/flooding in more urban areas. Ongoing rainfall this morning may also contribute to a bit wetter antecedent conditions. Further adjustment east-southeastward of the risk area may be needed if confidence in the duration of the MCS increases and ongoing storms this morning contribute to more widespread rainfall in the region.=20 Finally, the MRGL risk in the Northern Rockies was also expanded westward into parts of central Idaho and adjacent far northeastern Oregon and southeastern Washington. Slow-moving thunderstorms later this afternoon translating around under the upper-level trough aloft will pose a risk for some locally heavy downpours. The probability of 2 and 5-year exceedance of ARI values was notable in the 12Z hires guidance. Putnam .....Previous Outlook... ....Northeast/Northern Mid-Atlantic... The upper low associated with widespread convection and moderate to heavy rainfall that developed across the eastern U.S. yesterday and continued into the overnight is forecast to transition to an open wave and begin to drift slowly eastward from the Great Lakes into the Northeast today. Ongoing convection over the Northeast and Mid-Atlantic is expected to wane and continue to move east through the remainder of the overnight. However, deep southerly flow ahead of the trough will continue to channel ample moisture and mid-level energy across the region, setting the stage for redeveloping showers and storms later today. PWs over 1.25 across the interior Mid-Atlantic/Northeast to over 1.5 along the coast, in addition to daytime heating, will help support showers and storms developing and becoming fairly widespread across the region during the afternoon. As the upper trough slows, there will once again be the potential for southwest to northeast training storms, raising the threat for heavy amounts and flash flooding. The 00Z HREF is again highlighting portions of eastern Pennsylvania, northern New Jersey, and the Catskill Mountain region of Upstate New York. Neighborhood probabilities indicate that locally heavy amounts of 2-3 inches are likely in the area. This includes some areas that were inundated with heavy amounts over the past 24-hours. Therefore, a Slight Risk was added to this region. ....Northern Rockies and Plains... A slow-moving trough in the West and sufficient moisture will support another day of showers and storms developing over the mountains of western Wyoming and Montana. Farther to the east, leading energy moving out of the trough, interacting with deepening moisture along a strengthening low level jet is expected to support showers and storms developing and moving east through the High Plains into parts of the Dakotas. Although widespread heavy amounts are not expected, locally heavy amounts may produce an isolated flash flooding threat, especially given the wet antecedent conditions across portions of the area. ....Southwestern Kansas/Northwestern Oklahoma... Storms are expected to begin to develop during the afternoon as mid-level energy emanating from the trough in the West moves over the downstream ridge and interacts with moisture deepening along a low level warm front. As the low level inflow into the front increases, guidance shows PWs increasing to at over above 1.75 inches near the Kansas-Oklahoma border. Merging cells, with some potential for backbuilding, may produce some locally heavy amounts and isolated flash flooding concerns before these developing storms are expected to consolidate and track progressively to the east. ....Northern Cascades... Ample moisture (PWs near an inch) and instability, along with weak flow aloft will once again support slow-moving storms, capable of producing locally heavy amounts. Heavy amounts that do occur may produce isolated flash flooding, especially across areas recently impacted by wildfires. Pereira Day 2 Valid 12Z Wed Jun 28 2023 - 12Z Thu Jun 29 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST, UPPER MIDWEST, AND THE NORTHERN ROCKIES... ....Northeast... An upper trough will continue linger over the Northeast, channeling both deep moisture and mid-level energy across portions of the region. Daytime heating is likely to help support additional showers and thunderstorms, with locally heavy amounts possible, especially across portions of eastern Upstate New York into New England. ....Upper Midwest... Mid-level energy emanating from the trough in the West, along with an amplifying trough approaching from the northwest over central Canada is expected to support an increasing chance for rain across portions of the region on Wednesday into early Thursday.=20 Deepening moisture (PWs increasing to around 1.5 inches), along with some potential for west-east training, may produce at least some locally heavy amounts from northern Minnesota to the western U.P. of Michigan. ....Northern Rockies... With an upper trough remaining positioned to the west and a relatively moist airmass still in place, isolated to scattered showers and storms are expected to develop once again across the region. These may produce locally heavy amounts and generate isolated flash flooding concerns, especially given the wet antecedent conditions. Pereira=20 Day 3 Valid 12Z Thu Jun 29 2023 - 12Z Fri Jun 30 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST AND FROM NORTHERN ROCKIES INTO CENTRAL PLAINS... ....Northeast... One more day of showers and storms, with locally heavy amounts possible, is expected for portions of northern New York and New England. The threat is expected to become more localized as the associated upper trough continues to weaken and finally begins to lift out ahead of a developing upper low moving across central Canada. ....Northern Rockies to the central Plains... Afternoon and evening thunderstorms will remain possible across portions of southwestern Montana and western Wyoming as an upper trough continues to slowly approach the region. Locally heavy rainfall amounts impacting areas already affected by above average rainfall over the past month may result in isolated flash flooding concerns. Meanwhile, mid-level energy ejecting east of out of the trough is expected to support showers and storms moving farther east out into the central Plains. With differences in the details, models are presenting a pretty good signal for training storms and heavy accumulations developing late Thursday into the overnight near a slow-moving boundary and axis of deeper moisture from southeastern Wyoming/northeastern Colorado into central Nebraska. Pereira=20 Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-fFmStMiwFUUjbNAHJC8V847HcM50DK5JJNbm9LS2TBR= 8dLd0Xbo6AsL1o9xmIN3YbkwBMvCrL-i722Vaz6k27Deqgo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-fFmStMiwFUUjbNAHJC8V847HcM50DK5JJNbm9LS2TBR= 8dLd0Xbo6AsL1o9xmIN3YbkwBMvCrL-i722Vaz6kWGxa44Y$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-fFmStMiwFUUjbNAHJC8V847HcM50DK5JJNbm9LS2TBR= 8dLd0Xbo6AsL1o9xmIN3YbkwBMvCrL-i722Vaz6k9-gHEZw$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .