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Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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685 FXUS63 KMPX 150535 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 1235 AM CDT Sat Jun 15 2024 .KEY MESSAGES... - More widespread showers and thunderstorms likely Saturday and Saturday night with locally heavy rainfall possible. - An intense heat wave will build across the eastern third of the country next week with the Upper Midwest on its western periphery. This will mean periods of hot and humid conditions and multiple rounds of thunderstorms with the potential for severe weather and heavy rainfall. && .UPDATE... Issued at 820 PM CDT Fri Jun 14 2024 No major changes made to the forecast this evening, as the general theme remains on track. Regional water vapor imagery captures a region of broad ascent across the central Great Plains, east of shortwave trough. Showers and thunderstorms span from the Dakotas south into portions of Texas. Initial bands of showers lifting through SE South Dakota and NW Iowa may creep into SW Minnesota over the coming hours, but will likely struggle to hold together as they outrun upper-level support. However, this will not be the case as we fast forward into Saturday morning. Low-level moisture transport will increase ahead of the eastward shifting shortwave trough which will assist in saturating the notable low-level dry air sampled by the 00z MPX RAOB. Hi-res models have started to account for a slightly slower arrival of precipitation, which is not surprising given the conditions sampled this evening. As the morning rolls on, the expansive precipitation shield will lift northeast through the area. We feel this is likely more of a "soaking rain" event into Saturday afternoon, before the potential increases for convection later in the day. Speaking of which, CAMs have illustrated the potential for a brief lull in the precipitation across southern Minnesota late Saturday afternoon, prior to the redevelopment of scattered to widespread storms. It`s this convective activity that will feature the potential for an isolated instance of damaging winds or large hail, along with enhanced rainfall rates owing to a strengthening low-level jet and PWATs near 2". The QPF forecast remains on track, with 1-2" of rainfall possible for locations across south central Minnesota to western Wisconsin. && .DISCUSSION... Issued at 315 PM CDT Fri Jun 14 2024 Gorgeous afternoon continues across MN and western WI with temepratures ranging in the mid to upper 70s and and light winds. Satellite showing mainly widespread diurnal cu across much of MN/WI although a few bands of cirrostratus are beginning to make there way into southwestern MN. That area of cloud cover is part of the shortwave that will eject from the four corners region later tonight. As this shortwave approaches, a 40kt LLJ will increase moisture transport across the area. PWAT values are forecast to increase near 2.0" throughout Saturday and Saturday night. Forecast soundings continue to support an environment that is not conducive for strong convection initially, but more so highlighting the threat of moderate to heavy rainfall. Considering the track of this low pressure system`s core is progged across IA, southern/eastern MN and western WI have a favorable chance of seeing 1-2 inches of precip. Therefore a slight chance of excessive rainfall has been issued by the WPC for those areas. Behind the main more widespread rain late Saturday night, elevated instability alongside steeper lapse rates will increase. CAM guidance hint at the development of thunderstorms capable of producing a potential for hail. Another concern with these storms is the heightened flood risk on top of the rainfall just received earlier. For Sunday, to simply put it, its going to be hot and humid. The shortwave that provided all the rainfall will depart to the east and upper-level ridging takes hold. Guidance now showing with confidence that the thermal ridge off to our west will advect in overhead during the daytime hours. The aforementioned LLJ will not weaken and continue to bring only greater moisture transport up well into the the northern plains. Currently h925 temps showing a 25-27C increase which indicates surface highs will range in the lower 90s. Dew points will reach the lower 70s and force heat indices to 95-100 degrees. With each forecast run, heat headlines across the TC Metro may be necessary for Sunday. A frontal boundary will track across MN/WI sunday afternoon/evening. Forecast soundings continue to show an EML with steep lapse rates that should inhibit any convective development. However, should the frontal boundary be able to overtake the cap, we could see conditional risk of strong thunderstorms Sunday afternoon. The front will stall Sunday evening and the EML will begin to weaken at the same time the cap erodes. So some thunder potential remains and aligns with the SPC Convective Outlook Sunday evening. Flooding concerns will continue Sunday night as the LLJ increases to 50 kts and leading to training development along the frontal boundary. Next week`s forecast continues to look very active with several chances of rainfall and potentially severe weather. A trough over the CO Rockies will begin to lift Monday or Tuesday. At this time, numerous shortwaves will eject off of the broader trough providing continued rain/storm chances throughout next week. To our east, upper-level ridging will continue to deepen well into Quebec thus allowing for intense heat and humidity to reach the Great Lakes and the Ohio River Valley. Depending on the location of the western periphery of the ridge, some of the intense heat may encroach west into MN. Specific temperatures are still uncertain as confidence between ensemble members deviates but what is known is continued flooding concerns across the region given a strong LLJ and noticeably high PWATs. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1215 AM CDT Sat Jun 15 2024 Mid-high level cloudiness will continue to push in from the west overnight, as our rainmaker approaches NE from Nebraska this morning. Expect light rain associated with the initial precip shield to move into SW Minnesota early this morning (around 12z), and then gradually make its way northeastward throughout the morning. Winds will increase out of the southeast after sunrise and will generally persist at 10-15kts, gusting up to 20-25kts into the afternoon. Additional showers and thunderstorms will be possible heading into the afternoon/evening, which could result in lower visibilities at times. KMSP...No major changes to the forecast from 00z. Light winds from the southeast this morning, with increasing speeds heading into the afternoon. Light showers will reach the terminal by around 14z, becoming more persistent by about 16z. Rain will prevail much of the day, with an increasing chance for embedded t-storms to develop during the evening. Things will start to taper off heading into tomorrow morning, but lingering rain is likely until about 10/11z. /OUTLOOK FOR KMSP/ SUN...VFR. Slight chc TSRA/MVFR. Wind S 10-15 kts. MON...VFR with MVFR/TSRA possible. Wind SE 10-15G20 kts. TUE...VFR with MVFR/TSRA possible. Wind S 10-15G25 kts. && .HYDROLOGY... Issued at 315 PM CDT Fri Jun 14 2024 The extended period of heavy rainfall brings with it a potential return to river flooding in the 5-10 day period, extending to the end of the month on the mainstems. HEFS graphics show the potential threat nicely, and also show the degree of uncertainty with large ranges even within the blue "most likely" band by day 10. Factors that will determine flood severity (minor vs. moderate or worse) include how fast the rain falls...a number of 6-12 hour periods with less than an inch adding up to 3-5 inches is better than a couple of 2-3 inch events in a short period. We will also need to be wary of a boundary setting up with training storms moving from southwest to northeast over the same area. In summary, this scenario bears watching closely over the next week, with lots of uncertainty along the way. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ UPDATE...Strus DISCUSSION...Dunleavy AVIATION...BED HYDROLOGY...CCS