Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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989 FXUS63 KMPX 170538 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 1238 AM CDT Mon Jun 17 2024 .KEY MESSAGES... - Showers and thunderstorms overnight, with elevated storms posing a risk for severe hail (1" or more). - Scattered showers & storms over the next few days with an increased risk of flooding due to training storms. Exact amounts will vary based on orientation of training thunderstorms. && .UPDATE... Issued at 811 PM CDT Sun Jun 16 2024 Collaborated with neighboring offices and WPC to issue a Flood Watch across the majority of central Minnesota along with St. Croix, Polk, and Barron counties in western Wisconsin. This Watch coincides with a rare Moderate Excessive Rainfall Outlook, which indicates a rich environment for potential flash flooding tomorrow. At this hour the atmosphere largely remains capped, as sampled by the 00z MPX RAOB, though there is plenty of CAPE stored aloft. Some of the hi-res models solutions have suggest isolated convection east of a boundary that is currently located across eastern Minnesota. The progression of the boundary will be a focus point over the next few hours for a few isolated to scattered storms, mainly across western Wisconsin. Widespread convection is then forecast to move into southwestern Minnesota overnight, with the heaviest rain expected across southern Minnesota. A Slight Risk for severe weather remains in place across much of the region, as a few instances of large hail or damaging wind gusts may accompany the heavy rain. Any storms that "train" over one location will pose a localized flood threat. As discussed below, the evolution of additional convection tomorrow remains somewhat uncertain, given that the heaviest rain will be tied to the northward advance of a warm front. Given the notable influx in moisture, the setup bears watching for constant regeneration/training of storms. && .DISCUSSION... Issued at 315 PM CDT Sun Jun 16 2024 Temperatures have struggled to realize the 90s so far this afternoon due to persistent cloud cover leftover from morning showers and storms, followed by enough strengthening of the upper level wave to continue to produce scattered to broken ceilings of cumulus through the afternoon. The warmest heat index as of 230pm sits in the low 90s in northern Scott County, so while the 95 threshold for the Advisory may verify briefly, we did not end up with the heat that was expected yesterday at this time. Despite this, the air outside is still quite humid and is not likely to change so plan accordingly if doing anything outdoors for the rest of the day. As we move through the overnight hours, another round of showers and thunderstorms is expected to develop as low to mid level warm air & moisture advection continues with an upper level wave producing a 1- 2 PVU PV anomaly shortwave as an upper level jet sits north of the MPX coverage area. The main player overnight will remain the low level jet with efficient moisture transport, with another round of late night thunder to contend with. Low level lapse rates are quite poor, however mid to upper level lapse rates are good enough such that a few storms could be capable of producing severe hail overnight. There is a degree of low level helicity such that some spinning lower level storms are also possible, however with the poor lapse rates and large moisture content, the tornado chances remain non-zero but also quite low. What is likely is another round of soaking rainfall equaling an additional inch or two across much of the area, with some isolated higher amounts depending on where the thunderstorms set up. Coupled with last night`s rainfall, we are quickly saturating our soils and swelling area water features such that flooding begins to become a larger concern this week. Tomorrow has quite a bit of uncertainty regarding what will happen especially for the second half of the day as it depends a considerable amount on how quickly the morning showers and storms push across the region. CAM guidance including the SPC HREF diminishes shower activity between roughly 13-15z, but keeps lighter showers and storms around throughout much of the day as CAMS continue to differ on placement and timing of further showers and storms. Should we trend towards the first line of showers exiting later by around 15z, it becomes less likely that we maintain an environment for stronger storms by the afternoon. However, most guidance continues to intensify the already blistering low level jet, with GFS/CFS deterministic solutions favoring a significant continued influx of low to mid level moisture and forcing. This jet will remain the focal point for additional showers and storms with the environment remaining static through much of Tuesday before the jet finally pushes over the Great Lakes by Wednesday morning. Although there are significant hydrologic concerns due to the anomalous PWAT values and multiple rounds of showers/storms, the positioning of the features has shifted enough over the last 12-24 hours within most of the guidance such that confidence in a specific area seeing enough to cause widespread flooding issues is low at this time. The main takeaway should be additional showers and storms are likely over the coming days, but unless we see multiple rounds training over a specific location, the flash flooding/areal flooding concerns are uncertain at best. River flooding is a different story, with enough rain falling over a large enough portion of the CWA that rises in area rivers will likely result in several new or upgraded river flood warnings over the coming days. A pattern shift mid-week with brief surface high pressure on the heels of the departing jet will give us a break from significant rainfall on Wednesday alongside a couple days of cooler temperatures, however deterministic guidance once again points to a strengthening low level jet amidst zonal to southwest flow aloft, once again favoring multiple rounds of scattered showers, thunderstorms, and areas of rainfall. Uncertainty will remain high given the scope of the short-term forecast and how that will end up modifying the overall environment later in the week. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1224 AM CDT Mon Jun 17 2024 The forecast remains on track as we await the arrival and persistence of widespread showers and storms today. A line of convection north of the frontal boundary is currently moving northeastward from southeastern SD, which is expected to fill in within the next few hours. Some of these initial storms could produce hail or strong gusts at times, but the main concern is heavy and prolonged periods of rainfall. These threats diminish throughout the day, but light rain could linger for some terminals in eastern Minnesota and western Wisconsin through late evening. Winds will gradually kick more southerly throughout the day as the front lifts north through the region. KMSP...Theme remains the same with rain/thunderstorms arriving around 09/10z depending on how quickly and how far south things develop. After a few hours of storms, more showery-like precipitation will follow. There is still uncertainty with how long these will stick around. Depending on coverage, it could be more like an on and off type of system which would last until late this evening/night. /OUTLOOK FOR KMSP/ TUE...VFR/MVFR, TSRA/SHRA likely, chc IFR. Wind S15-20G30-35kts. WED...VFR/MVFR, chc -TSRA/-SHRA. Wind N 5-10kts. THU...VFR/MVFR, chc -TSRA/-SHRA. Wind NE 5-10kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...Flood Watch from this afternoon through late Tuesday night for Anoka-Benton-Carver-Chippewa-Chisago-Dakota-Douglas- Hennepin-Isanti-Kanabec-Kandiyohi-McLeod-Meeker-Mille Lacs-Morrison-Pope-Ramsey-Renville-Scott-Sherburne-Sibley- Stearns-Stevens-Swift-Todd-Washington-Wright. WI...Flood Watch from this afternoon through late Tuesday night for Barron-Polk-St. Croix. && $$ UPDATE...Strus DISCUSSION...TDH AVIATION...BED