Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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695 FXUS63 KBIS 290553 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 1253 AM CDT Wed May 29 2024 .KEY MESSAGES... - Severe storms are possible Wednesday later in the afternoon and early evening mainly west of Highway 83. Hail up to the size of ping pong balls, 70 mph winds, and a tornado or two are the primary threats. - With this storm complex, there is a 90 percent chance or greater of a wetting rain (a tenth of an inch or more) for all of western through central ND, including the James River Valley. - Breezy to windy conditions are expected Wednesday, especially in the southwest and south central portions where winds could gust up to 45 MPH. - Temperatures remaining near to slightly above average through the weekend. Shower and thunderstorm chances will also continue (mainly 20 to 40 percent), with a minimum Saturday. && .UPDATE... Issued at 1253 AM CDT Wed May 29 2024 The forecast remains on track. UPDATE Issued at 948 PM CDT Tue May 28 2024 Once again only minor changes were made to tonight`s forecast, with east-southeast flow becoming established as of mid evening and observed trends supporting lows in the 40s F. We continue evaluating the Wednesday late afternoon and evening severe storm risk, but one signal that`s becoming apparent is the potential may be confined to far western North Dakota, mainly along/west of the Highway 22 corridor. We expect significant capping aloft further east owing to marginal low-level moisture return. The environment in far western ND will also only have effective- layer shear ranging from 20 to 30 kt, and as a result, we expect multicellular to only transient supercell structures. There will also be a trend toward a linear mode Wednesday evening as deep- layer shear vectors become parallel to the surface front. The hazard ceiling will be somewhat restrained given these factors. Moreover, recent guidance suggests less low-level SRH than past simulations (now limited below 100 m2/s2 in most output). Given that and marginal deep-layer shear for sustained supercells, along with a tendency toward linear modes, it appears that any tornado risk may be even more limited than earlier thought. If those trends continue in the full suite of 00 UTC guidance, we may remove the tornado mention from our outlook messaging. Our messaged hail size (up to ping pong balls) and wind gusts (up to 70 mph) remain supported by the expected environment and mode. UPDATE Issued at 629 PM CDT Tue May 28 2024 No significant changes were needed with this update. Diurnally- driven cumulus will fade as mixing subsides with the approach of sunset. Surface ridging is located near a Langdon to Carrington and Ellendale line as of early evening, and will slowly move to the east overnight, causing winds to become southeasterly in all areas by about 06 UTC. Afternoon dewpoints are mainly in the 40s F, supporting the going forecast of lows in the 40s F tonight. && .DISCUSSION... Issued at 330 PM CDT Tue May 28 2024 Surface high will exit through tonight, while ridge aloft is found. The result will be mainly clear and dry conditions. An increased surface gradient will shift winds to the southeast, and they may become breezy across the west. This increase in winds should limited the fog threat tonight. Temperatures tonight will generally be in the 40s. If temperatures can trend toward the NBM10th percentile, then some patchy frost is possible in the east. This is not in the forecast, but important to note as some areas trended this way for this morning. Something to monitor. Wednesday will see this increased gradient will be found across much of the CWA through Wednesday. This could bring breezy to windy conditions across the forecast area. Pressure falls through the day and lack of upper level support creates just enough lack of confidence to hold off on a wind advisory for now. That being the case, there is a strong low level jet that develops in the southwest and southcentral for Wednesday. If these winds can mix down, then gusts 45 MPH are possible as well as sustained winds around 30 mph. High temperatures from this southerly flow will warm into the 70s for Wednesday, perhaps some lower 80s. SPC has maintained a slight risk for severe weather later in the day Wednesday through Wednesday night. The forecast is overall very similar to last night. The threat is conditional, and more so on the timing of everything along with some weak capping issues. Low lee of the northern rockies still looks to set up with a cold front pushing through sometime overnight. The moist gulf southerly flow will increase dewpoints and instability Wednesday afternoon into the evening. CAPE will be abundant in over 2000 J/KG in some areas. However, the stronger overall shear looks to be found on the back end of the front, with 0 to 6 KM shear in the warm sector forecast to be 25 to 35 knots. These storms could maybe tap into higher amounts of shear at the 0 to 8 KM level though. The strong low level jet could contribute to stronger 0 to 1 KM and 0 to 3 KM shear. This could also bring some adequate helicity to the lower levels, although the higher values of this are in the 0 to 3 KM layer. This is shown in some hodographs, with veering in the atmosphere not starting right away and be slightly elevated. One last thing to note is the 0 to 6 KM shear vector is more parallel to the expected surface trough and front. This could make more discrete cells tougher to come by. Given the uncertainty, there still remains enough of a threat and window for severe weather Wednesday afternoon through the evening, diminishing in the overnight hours. Abundant CAPE and enough shear with some rotating storms possible will maintain the hail threat to ping pong. A more organized storm or supercell could produce an isolated golf ball sized hail. Large DCAPE and increasing 0 to 3 KM shear will maintain wind gust threat up to 70 MPH. There still remains an isolated tornado threat if a more discrete cell can get going before the front moves through. Heavy rain is also possible with any storm that develops as Pwat values are in the 90th percentile and over an inch. Cold front then takes over showers and thunderstorms sometime Wednesday night and pushes everything eastward through Thursday. A breezy westerly wind may be found on Thursday, with temperatures cooler and in the 60s. There could also be some shower and thunderstorm chances in the north. A broad trough over the region could bring more showers and thunderstorm chances on Friday. A lack of instability will limit the severe weather threat. Unsettled westerly flow then looks to be found through the weekend. Chances for showers and thunderstorms will be isolated on Saturday, then could return to scattered on Sunday. Temperatures look to warm each day, with highs approaching 80 degrees on Sunday. Friday morning could see some cooler low temperatures, with the weekend looking to see lows more near normal. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1253 AM CDT Wed May 29 2024 Southeasterly winds will pick up through the remainder of the night and during the day Wednesday. This will result in breezy to windy conditions across the entire area with some gusts up to 45 kts possible in portions of the far southwest. Otherwise, VFR ceilings and visibility will prevail through most of the TAF period. However, by mid to late afternoon Wednesday, showers and thunderstorms will begin entering western North Dakota mostly from Montana. Thunderstorm confidence is high in the western two tiers of counties during the evening. Therefore, added TSRA to the Williston and Dickinson TAFs towards the end of the period. Per usual, reduced ceilings and visibility are possible with any thunderstorms that develop. And with these storms, gusty and erratic winds in excess of 50 kts are one of the main threats. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Telken DISCUSSION...Anglin AVIATION...Telken