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Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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824 FXUS63 KBIS 291147 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 647 AM CDT Sat Jun 29 2024 .KEY MESSAGES... - Clouds will gradually clear through the day today, with highs in the 60s across the area. - There is a Slight Risk (level 2 of 5) for severe thunderstorms across parts of the west Sunday night after sunset. The main hazards are hail up to quarter size, and wind gusts up to 60 mph. - Breezy winds are expected Sunday, with the strongest winds in the southwest. - There is also a Slight Risk (level 2 of 5) for severe thunderstorms across south central North Dakota on Monday. && .UPDATE... Issued at 647 AM CDT Sat Jun 29 2024 No significant changes were needed with this update. Low clouds remain well-entrenched across much of the area, especially over southwestern ND where there`s a subtle upslope component to the wind field. However, satellite imagery reveals clearing starting near the Canadian border and guidance continues to support this spreading southward through the area by midday. All we did with this update was blend observed trends into the existing forecast. && .DISCUSSION... Issued at 358 AM CDT Sat Jun 29 2024 Surface low pressure to our east has helped maintain a deck of low clouds across essentially our entire area this morning, slowly moving southeast as the surface low and upper level trough move off to the east. Some areas of light rain and drizzle are occasionally being reported, especially below the lowest cloud decks, along with some areas of patchy fog. As such, we`ve continued the low chances for precipitation and patchy fog across much of the area, mostly centered across the central portions of the state, dissipating through the early morning hours. On the back side of this surface low, some areas in the James River Valley may see some continued gusty winds through the morning, decreasing through the daytime hours as the low pushes east, and as surface high pressure begins sliding into the area from the west. Through the day today, we can expect to see a gradual clearing of clouds from north to south, and a gradual calming of winds from west to east. As the aforementioned trough moves east into the Great Lakes region, a ridge positioned over the Rockies will move east into the Northern Plains, along with a surface high, bringing about these generally calmer and clearer conditions. Though with the continued northwesterly flow aloft throughout the day, temperatures aren`t expected to warm up much at all, with forecast highs largely in the 60s today. Sunday appears to be a bit more active, as the upper level ridge is not expected to persist across our area for long. By mid-day Sunday, the axis of the ridge will be positioned across the area, along with the 850mb thermal ridge beginning to nudge into the west. The surface high pressure will have moved out of our area, with a deepening surface low across Wyoming beginning to build against the high to our east. As a result, we can expect to see warmer temperatures and breezy conditions across the entire area, with the highest winds expected in the southwest where the surface pressure gradient is expected to be the highest. The ECMWF EFI currently has highlighted that area with a value of around 0.8, which helps further increase confidence in the windy conditions there, potentially warranting a Wind Advisory in that area. Heading into Sunday night, we may see our next round of strong to severe storms, mostly across the west. The SPC has maintained a Slight Risk (level 2 of 5) for portions of western North Dakota, while the rest of western and portions of central North Dakota is outlined in a Marginal Risk (level 1 of 5) for severe weather. Ahead of the deepening surface low, moisture will be advected into the northern High Plains, with some parts of western North Dakota seeing dew points approaching 60 degrees. However, given the strength of the cap across the west as indicated by model soundings, convection will be limited during the afternoon and evening hours, despite the presence of somewhat low instability (roughly around 1000 J/kg of MLCAPE). The main threat with the convection Sunday night will come much later, after sunset, as confidence has increased in the 850 mb nocturnal low level jet (LLJ) strengthening quite a bit in the early overnight period. With the ongoing convection expected across eastern Montana moving into the area from the west, this LLJ could help maintain these storms as they move through, carrying the threat for large hail and damaging winds. Storm mode remains a bit uncertain given how conditional this threat is, but if some of these storms can congeal into an MCS, significant wind gusts could become the main concern, especially along the nose of the LLJ. With the environment quickly becoming less supportive of severe storm development with eastward extent, storms should begin to weaken relatively quickly as they move east. All in all, the main takeaway is that this threat will be heavily dependent on the formation of storms to the west of our area, the true strength of the nocturnal LLJ, and the overcoming of the cap. If storms do get going, they could definitely become severe, but the main concern will be if they can get going in the first place. Given the uncertainty, our current thoughts for the hazards are wind gusts up to 60 mph, and hail up to 1 inch in diameter. After Sunday, we can expect to see a continuation of the active pattern, with near daily chances for showers and thunderstorms through the work week. Flow aloft will mostly be zonal, with embedded shortwaves passing through the area each day. On Monday, the previously mentioned trough and associated surface low are expected to continue strengthening and moving east across the central Plains, helping funnel even more moisture north towards the area. The SPC has outlined portions of our south central in a Slight Risk for Monday, as well as a Marginal Risk for much of the rest of our area, as a cold front associated with this surface low sweeps across the region. While still a bit far out, deterministic guidance does suggest ample instability and deep layer shear, which would support the development of a few strong to severe storms. We`ll need to continue keeping an eye on how this situation develops. One of the main limiting factors, at least for our area, will be the effects of the earlier convection on the atmosphere. As a result, this set up is once again rather conditional, depending quite a bit on how the convection Sunday night goes. Regardless, temperatures will remain right around normal for this time of year, with highs generally in the 70s and lower 80s. Long range guidance tentatively suggests ridging, drying, and warming for next weekend, with an increase in temperatures. However, NBM spreads are still rather large this far out. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 647 AM CDT Sat Jun 29 2024 Widespread MVFR to IFR ceilings and occasional MVFR to IFR visibility in BR will continue early this morning over most of western and central ND. However, clearing is still expected from north to south today, and VFR conditions are forecast to prevail after 18 UTC and continuing through the remainder of the TAF cycle. North winds will gradually diminish today, though they will gust to around 25 kt at KJMS this morning. Winds will become light area-wide by 00 UTC and turn southeast overnight. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...CJS DISCUSSION...Besson AVIATION...CJS