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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.

Saturday, July 9, 2022

SPC Jul 9, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0301 PM CDT Sat Jul 09 2022 Valid 092000Z - 101200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF CENTRAL MONTANA INTO CENTRAL NORTH DAKOTA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE NORTHERN PLAINS AND THE SOUTHEAST... ...SUMMARY... Scattered severe thunderstorms are expected later this afternoon through tonight across Montana into North Dakota, with damaging winds and large hail likely. Occasional damaging gusts will also be possible this afternoon/evening across parts of Alabama and Mississippi. ...20Z Update... Mostly minor adjustments were made to the outlook to reflect the latest observations or model guidance consensus. The one exception was to expand the Category 3/Enhanced risk into central ND. Some of the latest HRRR guidance members depict robust convection associated with a severe bow-echo MCS progressing into central parts of the state by 12Z. In the 06-12Z period, forecast soundings from several of the last RAP runs depict 9 C/km 700-500 mb lapse rates (and resultant 3500 J/kg MUCAPE), with considerable drying in the 800-600 mb layer. Despite a stable boundary layer, adequate evaporative cooling/ice melting should support strong enough downward momentum transport for an organized severe wind threat with the bow-echo MCS. ..Squitieri.. 07/09/2022 .PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Jul 09 2022/ ...MT/ND late this afternoon through tonight... Similar to the previous two days, midlevel shortwave troughs will move around the northwest periphery of the Four Corners midlevel high, from the interior Northwest across MT to ND through tonight. Despite overnight convection, boundary-layer dewpoints remain in the mid 50s to near the higher terrain in west/southwest MT (somewhat higher dewpoints across eastern MT). Steep midlevel lapse rates will again be replenished from the southwest, which in concert with daytime heating, will result in MLCAPE near 1500 J/kg this afternoon/evening. Deep-layer vertical shear will be fairly strong, with long hodographs and effective bulk shear in excess of 45 kt. Much like yesterday, scattered thunderstorm development is expected near or just after 21z, over and immediately northeast of the mountains in southwest MT. Some of these storms could develop supercell structures with an attendant threat for large hail of 2+ inches in diameter. Later this evening, some upscale growth into one or more clusters is expected, with an increase in the threat for damaging winds of 75+ mph. Embedded supercells will remain possible, especially on the southern flank of the convection, as the cluster(s) move eastward across ND tonight. ...Southeast into TX this afternoon/evening... Downstream from a midlevel high centered near the Four Corners, a broad zone of cyclonic flow aloft persists from the MS Valley to the Mid-Atlantic/Carolinas. Embedded perturbations within this cyclonic flow, enhanced by prior convection, will continue to move east-southeastward over the Southeast, as a surface cold front drifts slowly southward across VA/KY/TN/AR and north TX. Morning clouds/convection across north GA/northeast AL will produce weak outflow and differential heating zones that will drive afternoon thunderstorm development farther south and west from central AL into the Mid-South along the cold front. Hot afternoon temperatures of 95-100 F and boundary-layer dewpoints in the mid 70s will boost MLCAPE to 3000 J/kg or greater, with thunderstorm development expected by early-mid afternoon. Convection will likely grow upscale into a couple of clusters/lines and spread southward through late afternoon/evening. Though flow aloft will be weak, the large buoyancy and DCAPE near 1000 J/kg will support occasional damaging downbursts. Farther east, the morning convection across GA may persist into the afternoon while spreading southeastward, and additional storms are expected to form along the differential heating zone across the Piedmont, and along the cold front moving southward into NC. Vertical shear will remain rather weak (slightly stronger along the front in NC), and thermodynamic profiles from GA into the Carolinas will not be quite as supportive of downbursts compared to MS/AL. Thus, isolated strong/damaging outflow winds will be possible with multicell clusters this afternoon from GA into NC. Strong surface heating (afternoon temperatures well above 100 F) and inverted-v profiles along the slow-moving front across north TX will support the threat for high-based thunderstorms with isolated severe outflow winds for a few hours later this afternoon/evening. Read more CHECK UPDATE ZOOM GRAPHIC
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