Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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479 FXUS63 KBIS 201950 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 250 PM CDT Thu Jun 20 2024 .KEY MESSAGES... - Chances for showers and thunderstorms will increase through this afternoon and evening. A stronger storm with small hail and gusty winds will be possible across the northwest this evening. - 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. && .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 /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1232 PM CDT Thu Jun 20 2024 Some rather dense cumulus have begun to develop across the south, bringing MVFR ceilings to KBIS and KDIK, with some forming just to the south of KJMS. Across the north, mostly clear skies are present, with some additional, less expansive cumulus across the north central. Generally southwesterly winds will prevail through the day, before shifting overnight to become more southeasterly. Some showers and potentially a thunderstorm may develop across the northwest near KXWA tonight, though confidence is rather low. Clouds will recede south through the late evening, before a more widespread MVFR/IFR deck builds in from the south early Friday morning. More rain is expected with this, bringing about showers and reduced visibilities to KBIS, KDIK, and KJMS by 09z. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Besson AVIATION...Besson