SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Sat Jun 05 2021 Valid 052000Z - 061200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN NEW ENGLAND AND ALSO ACROSS PORTIONS OF THE NORTHERN PLAINS... ...SUMMARY... Severe thunderstorms are expected across portions of northern New England and the northern Plains this afternoon into tonight. Please refer to Mesoscale Discussion 854 for the latest thinking regarding convective trends and potential across northern New England. Elsewhere, the previous forecast remains on track and no significant changes have been made with this update. ..Bunting.. 06/05/2021 .PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Jun 05 2021/ ...Northern New England... A semi-amplified cyclonic belt of moderately strong westerlies will influence the region coincident with a warm/modestly moist air mass (upper 50s to low 60s F surface dewpoints) to the south of a southward-sagging cold front across Ontario and Quebec. Although some timing differences exist in short-term guidance, at least isolated to widely scattered thunderstorms are expected to develop and move into the region this afternoon via nearby Ontario/Quebec. Strong nearly unidirectional westerlies, accentuated by as much as 45-55 kt at 500 mb, will support well-organized fast east/southeastward-moving storms. This should mostly be in the form of multicellular/upscale-growing bands capable of wind damage, although wind profiles/buoyancy are supportive of some initial supercells capable of hail and possibly some tornado risk. It is conceivable that a few areas could have a multiple round of storms. The severe risk should diminish and/or shift off the coast of Maine by mid/late evening. ...Northern Plains including Montana/North Dakota... Height falls and strengthening west-southwesterly winds aloft will reach the northern High Plains by late this afternoon/evening in advance of an eastward-progressive shortwave trough over the Pacific Northwest early today. While the ambient air mass will not be overly moist across the region with surface dewpoints generally ranging from the mid 40s to mid 50s F, sufficient moisture will exist in the presence of steep lapse rates for around 300-800 J/kg MLCAPE across south-central/southeast Montana and 1000-1500 J/kg MLCAPE into North Dakota. Initial storm development/intensification of isolated to widely scattered thunderstorms is most likely to occur by mid/late afternoon across south-central toward east-central/southeast Montana, generally in vicinity of the where the southwest/northeast-oriented synoptic front interfaces with the higher terrain. Storms are likely to gradually increase in coverage and develop east-northeastward across eastern Montana toward North Dakota this evening along/north of the surface front and migratory surface wave. As strong winds overlie the frontal zone, 40+ kt effective shear will support the development of well-organized clusters and bands. Severe-caliber wind gusts can be expected along with some severe hail. At least some severe risk may persist across North Dakota into far northwest Minnesota during the late-evening/early overnight hours. ...South-central Texas/Edwards Plateau toward Southeast Texas... A conditional-type risk for a few strong to locally severe storms may exist this afternoon across the region on the southern periphery of the slow-moving upper low across Texas. While storm coverage is a bit uncertain and there will be a trend of post-wave subsidence where instability is greatest, it is conceivable that a few strong storms could materialize this afternoon coincident with locally moderate buoyancy and 25-35 kt effective shear. ...Southeast Louisiana and nearby Gulf Coast... Well to the east of the upper low across Texas, modestly enhanced low/mid-level winds and SRH will exist across the region. This could support a few stronger storms possibly with transient rotation near coastal areas. However, the prevalence of cloud cover/precipitation inland should limit the overall potential for severe storms. Read more LIVE: spc.noaa.gov
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