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Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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853 FXUS63 KFGF 141800 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 100 PM CDT Wed Aug 14 2024 .KEY MESSAGES... -Showers and thunderstorms will increase in coverage today and last into Thursday. Heavy rain and lightning are the main impacts. && .UPDATE... Issued at 100 PM CDT Wed Aug 14 2024 The initial cluster is lingering over the southern Red River Valley with less activity farther east. The more organized clusters/embedded thunderstorms remain along the theta-e axis in central ND and that is slowly moving northeast. Latest CAMs are doing a better job reflecting these trends, with activity eventually filling in as the mid level low begins to organize later this evening/overnight. RAP analysis continue to marginal/elevated instability along our west along with weaker shear and mode trends show this either holding as is or weakening in time this evening. Severe potential locally appears to be minimal, with skinny/marginal cores more likely than an organized severe threat. THere is a subset of CAMs that show an eventual linear MCS in SD moving "near" our southern CWA, however even those CAMs show less supportive environment for severe, so it will likely take some shifts in the surface pattern to suet up a threat for more organized severe locally. Worth monitoring in the 3hr mesoanalysis period, but right now confidence in severe is limited. Regarding heavy rain; latest HREF 6HR PMM has trended even lower versus the last update discussion further lowering confidence in excessive runoff potential outside an unlucky track of a thunderstorm over urban areas. UPDATE Issued at 1021 AM CDT Wed Aug 14 2024 A cluster of showers/embedded thunderstorms have spread into far southeast ND with isolated showers now along the Highway 2 corridor. More organized synoptic ascent doesn`t arrive until later this evening/overnight, so we are in a pattern with increasing deep moisture and smaller scale features leading to harder to predict evolution/coverage within our forecast area. Higher coverage is tending to be concentrated near several boundaries(more obvious in wind/theta-e fields) near our south and west of our CWA. At least for now HRRR (being a hot-start CAM) is reflecting near term trends, but beyond the morning I don`t have as much confidence in coverage/evolution. For now I`ve made adjustments to better reflect near term trends, and held off on any major adjustments beyond midday (blended previous forecast). Impacts in our area through midday are mainly moderate rain and isolated lightning activity. As the deeper moisture plume overspreads our area along with more organized ascent the threat for heavy rain increases, though HREF PMM doesn`t show values that raise concerns for our hydrological forecast area unless the higher end values fell in a short enough period of time over one of our towns/urban areas where there is poor drainage conditions lowering confidence in more than localized/minor impacts. Considering that, a watch is not being considered at this time. UPDATE Issued at 643 AM CDT Wed Aug 14 2024 Still many different scenarios for today rainfall evolution. There are some t-storms forming in central ND from Minot toward Dickinson and they are moving north-northeast. Movement of this activity this morning would keep majority of the activity west of Devils Lake unlike what 00z HREF had and what QPF is based on 12z-18z. Meanwhile something new is in the picture which is an area of showers moving north thru NE SD and this looks like will enter SE ND. This feature is more like what the 00z/06z High Resolution Canadian has but this model intensifies it over Jamestown today and has very little precip DVL region. So still no clearer in what path todays rainfall will take. Hence why we have pops in most areas thru today. && .DISCUSSION... Issued at 351 AM CDT Wed Aug 14 2024 ...Synopsis... 500 mb low moving slowly east/northeast thru west central/central Saskatchewan with one area of concentrated t-storms in that area. In our region though a second weaker upper low is over parts of Oregon/Idaho with a broad 500 mb ridge into Minnesota. This puts our area in southwest flow aloft and within this flow there are numerous short waves seen on water vapor this early morning. How these short waves move and bring development of showers/t-storms is the main forecast challenge. PWATS are near 2 inches in a zone over central SD/ND and this ribbon of deeper moisture slides slowly east today but basically remains in the Devils Lake-Jamestown-Bismarck region thru this evening. Thunderstorm/heavy rainfall situation today remains typically uncertain. HREF and various CAM guidance highlight what is the most likely scenario which is t-storms from NW SD or SE MT moving northeast and developing within this deeper moisture area toward Devils Lake during the course of the day. Latest HRRR backs off on timing and focuses it more into DVL region midday vs WPC/HREF had higher precipitation 12z-18z today. At this point and time, either scenario is just as likely. Not much development in central ND at 08z but as short wave from NW SD/NE MT moves northeast rapid development of t-storms may occur and bring the heavier rainfall this morning or wave is slower to move and slower to develop t-storms and main rain is midday or afternoon into Devils Lake area. Either way...idea is for the concentrated area of showers and t-storms in central ND into Devils Lake area to advance east in time into the Red River valley late today/this evening and into NW MN tonight...though with lower intensity rainfall. With high PWATS localized rain amounts 2-3+ inches are possible in the zone thru central ND into Devils Lake basin. Uncertainty is high enough though and also past 7 day NDAWN precipitation for the area shows little to no precipitation for most of the Devils Lake area. Thus feel going with a flood watch before storms form is not quite the way to go due to prior conditions have been mainly dry weather. Thursday will see 500 mb trough to our west slide over eastern Dakotas/Minnesota with Global Canadian and ECMWF developing a closed low aloft vs GFS is more progressive. 00z ECMWF remains more consistent from run to run and at this time favored in developing area of rain around the upper low into parts of E ND/RRV and much of northwest MN Thursday on backside of the upper low. Not a heavy rainfall but a general rain area. If more progressive GFS is right then rain area Thursday is less and ends as system moves east. Weekend into early next week shows an upper level ridge building into south central Canada and northern Plains. 00z operational GFS is a complete outlier compared to the 00z GFS ensemble and discounted at this time. It has an upper low in NW Ontario into Manitoba vs a ridge. Net weather result with a ridge would be temps more into the low 80s. Some risk of a shower/t-storm early and mid next week due to short waves moving. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 100 PM CDT Wed Aug 14 2024 Several cluster of showers are moving into southeast ND and west central MN, with larger areas of showers/embedded thunderstorms still over central ND which should eventually slide east. Eventually the system should fill in with numerous showers across eastern ND and northwest MN later this evening/tonight, but thunderstorm coverage remains a question for most sites. Winds initially are gusty from the southeast, but as the surface low shifts east tonight they will tend to become lighter and variable before north-northwest winds develop Thursday at KDVL by late morning. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...DJR DISCUSSION...Riddle AVIATION...DJR