Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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364 FXUS63 KBIS 292330 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 630 PM CDT Sat Jun 29 2024 .KEY MESSAGES... - 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 630 PM CDT Sat Jun 29 2024 No forecast adjustments were made at the time of this update. Fair-weather cumulus has begun to degrade across across the west and south, with a deck of high-level clouds starting to encroach into the northwest out of northeastern Montana and southern Saskatchewan. Winds remain generally light and out of the north, though have some sites have become increasingly variable as winds continue to diminish this evening. The forecast remains on track. && .DISCUSSION... Issued at 255 PM CDT Sat Jun 29 2024 A seasonably cool late June day continues today, as a broad high pressure is centered over North Dakota and has been filtering in cooler air through the day. Widespread cloud cover associated with an exiting surface low and attendant upper shortwave has been quite slow to exit, and still extends across much of southwest and south central North Dakota. North of this stratus, fair weather cumulus has developed, which will diminish later this evening with the loss of (rather limited) daytime heating. Highs will be in the 60s across the area. Cool and quiet tonight, with lows in the mid 40s to lower 50s. Sunday is forecast to be warmer and more active, as a shallow ridge quickly builds over the Northern Rockies before flattening as an embedded wave moves through later on Sunday. Southerly return flow will boost highs back into the lower 70s to lower 80s, with dew points around 60 degrees in southwest North Dakota. With the approaching wave, a surface low is progged to deepen over northern Wyoming and move east/northeast. The tightening surface gradient should produce breezy southeast winds across the entire forecast area, and strong winds across the southwest, closer to the center of the low. There is some uncertainty on if winds will be advisory-level but will likely be close. High-res guidance is relatively consistent on scattered convection developing off the higher terrain in Montana late in the afternoon and through the evening, moving east towards North Dakota. The main concern is that with a stronger thermal ridge in place across western North Dakota, capping will be too strong for convection to overcome. However, a low- level jet in place could potentially be enough for strong to severe convection to sustain itself as it crosses the state line into an environment characterized by up to 1000 J/kg of bouyancy and 35-45 knots of bulk shear. The 12Z HREF has a few max UH tracks crossing into western North Dakota late Sunday evening around midnight, but the more likely threat is west of the forecast area. SPC continues a Day 2 Slight Risk (level 2 of 5) focused on parts of western North Dakota, with a decreasing risk to the east. Our threat message remains consistent, with expected hazards being hail up to the size of quarters and wind gusts up to 60 mph. To start the work week, a deepening upper trough and closed low will continue pushing east into the central CONUS on top of a relatively moist airmass. CSU machine learning and SPC are both highlighting parts of the central and eastern Dakotas for severe thunderstorm potential ahead of the trough base and attendant front that are expected to move through Monday afternoon and evening. The expectation is that this potential will likely be dependent on what happens Sunday night into Monday morning, and if that lessens the higher threat ceiling for convection on Monday. For now, deterministic guidance is advertising a narrow plume of instability around 1500 J/kg, and with seasonably strong bulk shear around 50 knots, it would be a sufficient environment for strong to severe storms to develop. The work week looks relatively consistent, temperature wise, with highs generally from the mid 70s to mid 80s. Persistent cyclonic flow aloft is expected to continue the active pattern we`ve been in, with on and off chances of showers and thunderstorms through the work week. Currently, the highest blended POPs are during the day on the Fourth of July, so will have to watch how precip chances trend through the next couple of days. NBM 25th/75th percentile spreads are showing modest confidence in the coolest temperatures late this week before a warming trend through the weekend. This is from general consensus in ensemble guidance for a broad upper ridge to develop across the western CONUS late next week. However, it is worth noting that there is a small cluster of ensemble members, around 15 percent, that has the ridge axis much further to the east. NBM percentile temperature spreads aren`t too large for this amount of lead time, generally around 10 degrees, but a shift of tails on the cooler side does indicate a fair amount of ensemble members advertising highs cooler than the 25th percentile. The question then becomes whether temperatures are near normal, in the lower 80s, or above normal, in the mid to upper 80s. NBM precipitation probabilities are noticeably lower this weekend into next week than they have been recently, so there are some signs of a drier period setting up. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 630 PM CDT Sat Jun 29 2024 VFR ceilings and visibility are anticipated at all terminals throughout the 00Z TAF period. Fair-weather cumulus clouds linger over the south early this evening will continue to diminish over the next few hours, with a mid to high level deck of scattered to broken clouds anticipated to push into the northwest and north central through this evening and overnight, gradually dipping drifting south through the early morning on Sunday. Winds are generally light and out of the north, but will turn southeasterly through the late evening hours. The approach of a low pressure system our of the southwest will promote increasing windy conditions across western and central North Dakota through the late morning and afternoon, with speeds approaching 20 MPH and gusts up to 30 MPH at most terminals. The terminals of KBIS and KDIK are forecast to experience the strongest winds, with sustained speeds of approaching 25 MPH and gusts approaching 35 MPH. Beyond the end the TAF period, chances for showers and thunderstorms will increase across the area, starting in the west. Strong to severe thunderstorms will be possible across the west, including the terminals of KDIK and KXWA, Sunday evening and early Sunday night. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Adam DISCUSSION...Jones AVIATION...Adam