####018007617#### FXUS63 KBIS 041327 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 827 AM CDT Sat May 4 2024 .KEY MESSAGES... - Low to medium chances (20 to 40 percent) for rain showers will diminish this morning across the far north central. More isolated showers (~20 percent chance) are possible this afternoon across the north central and northeast. - Expect warmer highs today through Monday before we cool back into normal to below normal categories for most of the work week. - Gusty southeast winds are likely Sunday through Monday. Sustained winds up to 35 mph will be possible with gusts to 50 mph. - Chances for rain return late Sunday evening and continue through the work week. The wettest period will be Monday through Tuesday when most of western and central North Dakota will see high chances (70 to 90 percent) of rain. && .UPDATE... Issued at 825 AM CDT Sat May 4 2024 For mid-morning update main change was to address the persistant low clouds that continue to drop south through the area, which are now starting to nudge into south central North Dakota. On the west side, advancement has slowed down some, while towards the east clouds continue to move right along. Therefore, have adjusted cloud grids to address this advancement. UPDATE Issued at 613 AM CDT Sat May 4 2024 For the most part, the weather is fairly quiet across western and central North Dakota this Saturday morning. We have seen a little bit of patchy fog develop across the far north, so we did go ahead and add mention of this here until 15z. Otherwise, no major changes were needed for this update. && .DISCUSSION... Issued at 347 AM CDT Sat May 4 2024 At the mid to upper levels, a trough axis currently sits over central North Dakota and will continue to move east through the morning as a western ridge starts to approach. Given the upper level forcing of the trough, a few rain showers (20 to 40 percent chance) will remain possible across the far north central, mainly north of the Highway 2 corridor. Surface high pressure will move in today as the western ridge nudges closer. Clouds should diminish from southwest to northeast through the day and into the evening. We may see enough diurnal heating and synoptic forcing for a few more isolated showers across the north central and northeast this afternoon (~20 percent chance). This activity should diminish rather quickly around and after sunset given the loss of heating. Highs will be a bit warmer today than in previous days, ranging from the lower 50s to lower 60s. Areas that clear out earlier today may end up a touch warmer. The ridge axis then crosses the state on Sunday, which will lead to even warmer temperatures and a mostly sunny sky. Highs will range from the lower 60s around the Turtle Mountains, to the lower 70s southwest. That being said, the surface pressure gradient will tighten as a longwave trough approaches and a surface low deepens significantly over northern Wyoming. This gradient coupled with strong pressure falls and steep lapse rates will lead to gusty winds out of the southeast. The latest NAM/NAM Nest soundings have come in a bit stronger with winds at the top of the mixed layer Sunday and Sunday night. For now it appears that the strongest winds will be across the southwest and south central where forecast soundings suggest the potential for up to 50 knots at the top of the mixed layer. Elsewhere across the west, we could see 40 to 45 knots at the top of the mixed layer. All that being said, it certainly appears that we will see higher winds than we usually see in these southeasterly flow setups with some sustained values up to 35 mph and gusts up to 50 mph. Wind headlines will likely be needed in future shifts. As the longwave trough approaches Sunday night, the aforementioned surface low will move out of northern Wyoming and into eastern Montana. An initial shortwave impulse will overspread the low and we will see increasing chances of rain across the west by the late evening hours. Several waves will then move around the base of the potent trough and eject into the northern Plains through the day on Monday as it takes on a negative tilt. Another surface low moves into western South Dakota by mid to late Monday morning and then deepens (sub 985 mb?) as it lifts into western or central North Dakota by the late afternoon or early evening. By then, the system is forecast to become stacked and nearly stationary or even retrograde back into eastern Montana Tuesday into Wednesday. Cluster analysis suggests that two distinct scenarios have started to show themselves and at the moment it appears that each scenario has about a 50/50 chance of happening. One scenario would have the main low ending up in northeast Montana and the other would have the low ending up somewhere across southwest North Dakota. Scenario one would lead to the heaviest precipitation being mainly over eastern Montana with a more pronounced dry slot over central North Dakota. The second scenario would lead to some heavier rain across the west (especially the southwest) and maybe a less pronounced dry slot. No matter the scenario, it does appear that we will at least see some dry slotting somewhere across the central with the James River Valley and vicinity being the most likely area. Regarding thunderstorm potential on Monday, CSU Machine- Learning guidance still suggests low chances for severe weather in the afternoon and evening, but the signal continues to weaken given meager instability in the forecast. Shear will be strong and we could see some pockets of MUCAPE up to 500 J/kg or so. Thus, a few strong storms may not be out of the question but the severe threat continues to appear low. The upper low remains stalled out over the northern Plains through at least midweek before it washes out or moves out towards the end of the week (models are having a tough time deciding how this low predictability pattern evolves mid to late week). This will mean more highs in the normal to below normal categories (mainly in the lower 50s to lower 60s) Tuesday through the rest of the week and continued chances for rain. The period for heaviest rainfall will be Monday and Tuesday but the highest NBM probabilities for an inch or greater have shifted to the west, now maximized over portions of central and eastern Montana. That being said, 72-hour NBM probabilities (ending 12z Thursday) for an inch or greater still range from 40 to 60 percent across much of the west and central. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 613 AM CDT Sat May 4 2024 A band of MVFR to IFR stratus will continue to spread across northern North Dakota this morning. KMOT and KXWA will likely see MVFR ceilings until late this morning or early afternoon while KJMS may see a period of MVFR ceilings this afternoon. KXWA may also see brief ceiling reductions into IFR categories over the next few hours. KDIK and KBIS should remain in VFR conditions through the period. A few isolated showers may once again develop across the north central and northeast Saturday afternoon. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...JJS DISCUSSION...ZH AVIATION...ZH