Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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766 FXUS63 KBIS 210539 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 1239 AM CDT Fri Jun 21 2024 .KEY MESSAGES... - Isolated to scattered showers and thunderstorms possible tonight. - Patchy to areas of fog possible tonight, especially along and south of Interstate 94. - Widespread showers and scattered thunderstorms are expected on Friday, with a Marginal Risk (level 1 of 5) for isolated severe storms over portions of the far southwest and far south central. - Showers and thunderstorms will diminish through Saturday morning, with continued daily chances for showers and thunderstorms into the middle of next week. - Temperatures will continue warming through the weekend, with expected highs on Monday in the mid 80s to lower 90s. && .UPDATE... Issued at 1227 AM CDT Fri Jun 21 2024 We kept a slight chance for thunder in the northwest for a few hours with the ongoing convection over northeast Montana and southern Saskatchewan. It looks unlikely that convection will make it into ND but can`t rule it out. Otherwise we removed thunder from the forecast tonight and limited pops to slight chance. Cams have shower activity over SD too far north and think it`s unlikely it will make it into ND overnight, or possibly tomorrow in many areas as well, but we`ll get to that later. Updated text products will be transmitted shortly. UPDATE Issued at 955 PM CDT Thu Jun 20 2024 Mainly some minor updates to PoPs based on current radar trends were done late this evening. Showers and thunderstorm chances in southern portions were delayed until later tonight as a bulk of these showers are currently located in South Dakota. Also reduced thunderstorm chances in the northwest and north central through the late evening hours as storms in Montana have been diminishing as they approach the ND/MT border. With the sun now setting, the threat for severe weather through the rest of the night is low. There is some increasing confidence in fog development, mainly across the south, tonight especially if precipitation delays. For now kept mention of fog to patchy although something to monitor throughout the night. UPDATE Issued at 650 PM CDT Thu Jun 20 2024 Limited changes needed early this evening. Currently monitoring some thunderstorm in Montana, however, as these storms push east they appear to be weakening. That said, there still remains a window this evening of generally uncapped 1000 J/KG CAPE and 40 to 50 KTS of 0 to 6 KM shear across the northwest and north central. The lift along the boundary these storms could from on appears to be limited yet present. Thus there cold be an isolated strong to severe storm threat in these areas this evening. Otherwise look for isolated to scattered showers though the night. Hi-res models picking up on the potential for fog tonight into Friday morning, mainly along and south of Interstate 94. Winds may stay steady through the night which may hinder this, or help advect in increase moisture and help fog formation. For now have added in some patchy fog mention to account for this potential. && .DISCUSSION... Issued at 247 PM CDT Thu Jun 20 2024 Precipitation has been slow to arrive today, with very few radar returns in the northwest and southwest. There may be a few drops of rain reaching the ground in these areas, but it seems rather unlikely at this point. Surface high pressure dominates north of the International Border, with a weak pressure gradient across most of the state. Southwesterly flow aloft continues, with a weak embedded impulse moving through the flow to our south, across South Dakota. Convection is ongoing in that area, with the expectation that this convection won`t move north into North Dakota. The SPC has introduced a Marginal Risk (level 1 of 5) to eastern Montana, but this risk stops short of the North Dakotan border. As such, we can really just expect to see some showers and an occasional thunderstorm in the northwest and south today and tonight, with the greatest chances for thunder being in the northwest, aligned with a narrow corridor of MUCAPE near 1500 J/kg and 0-6 km bulk shear of around 40 to 50 kts. Severe weather is not anticipated at this time, though some storms that perfectly ride the CAPE boundary may see some small hail. After a brief break in precipitation overnight, chances begin to move back into the area from the south on Friday. An upper level trough positioned across Alberta is expected to dive south through Friday, helping drive some more embedded shortwaves across the Northern Plains. A surface low across eastern Wyoming and western South Dakota is expected to deepen and track northeastward through Friday, helping push that precipitation northward. At the moment, chances for precipitation range from 40 to 70 percent, with the highest chances expected during the late evening and early overnight period. Similar to today, we are anticipating most of this to be showery, with some isolated thunderstorms. However, this time the SPC has outlined a Marginal Risk (level 1 of 5) for the very far southwestern corner of the state, as well as right along much of the border with South Dakota. There`s a very narrow corridor of MUCAPE near 1500 J/kg in this area, combined with 0-6 km bulk shear values nearing 50 kts. The setup just outside of our area is a bit more potent, which may result in greater chances of storms forming outside of our area, riding the CAPE boundary and intensifying as it approaches our border, and briefly being able to sustain itself and potentially strengthen once they enter North Dakota. However, given how borderline the event is to begin with, the chances for anything being severe within our area is still rather low, but also still non- zero. Given the quick reduction in instability and shear as you move east, any thunderstorm that forms across much of the rest of our area is not expected to become severe. As the aforementioned upper level trough continues moving east, we are expected to enter a slightly drier and warmer pattern, with a fairly pronounced ridge building into our west. While temperatures today and Friday are expected to be slightly below normal, we can expect to see a quick warmup into the mid 80s and lower 90s by Monday, which is also expected to be the warmest day of the forecast period. Chances for precipitation will be on and off, with 15 to 30 percent chances for showers and thunderstorms on Monday, and 10 to 15 percent chances for showers each subsequent day. Due to how warm it will be, and with the continued southerly flow bringing in decent moisture over the next few days, instability values will support at least isolated thunderstorms associated with these showers each day. The shortwaves embedded within the upper level flow that will bring these chances each day are not very strong, given the more west- northwesterly flow aloft, so the exact positioning and timing of these waves of precipitation are not well resolved from Monday onward. Tuesday will see a slight reduction in temperatures, dropping into the upper 70s to lower 80s, and with the upper level pattern remaining largely the same, these high temperatures are expected to remain consistently within this range through at least the end of next week. NBM spreads are somewhat high, owing to the confidence in this pattern holding true, so we can expect to see similar conditions from Tuesday onward to at least next Friday. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1227 AM CDT Fri Jun 21 2024 MVFR to possibly IFR ceilings and possibly some MVFR vsbys south. MVFR cigs to begin the 06Z TAF period at KDIK, otherwise VFR. MVFR ceilings are expected to lift north from SD into North Dakota through the overnight hours and expect MVFR to at times IFR ceilings through much of the day Friday. Shower and possible thunderstorm activity will also lift north into ND, but there is much uncertainty as to whether this will make it up to the TAF sites. Convection could also track west to east over the southern TAF sites during the day Friday. For now, kept only a period of VCTS and some VCSH as uncertainty in timing is high. Also kept ceilings mainly MVFR for not although guidance shows widespread IFR. IFR vsbys are possible, but WSUP IFR probabilities are generally around 30 percent along the I-94 corridor. Genially an easterly surface flow is expected through the TAF period. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...TWH DISCUSSION...Besson AVIATION...TWH