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Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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872 FXUS63 KFGF 280331 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 1031 PM CDT Thu Jun 27 2024 .KEY MESSAGES... - There is a level 1 out of 5 risk for severe thunderstorms for all of eastern North Dakota tonight. - There is a level 1 out of 5 risk for severe thunderstorms across the region Friday afternoon and evening. - There is a low chance for severe thunderstorms again Monday across the region. && .UPDATE... Issued at 948 PM CDT Thu Jun 27 2024 Showers and Thunderstorms continue to push across the area this evening. The severe risk continues for the Devils Lake Basin, but appears to be losing steam. Forecast remains on track. UPDATE Issued at 635 PM CDT Thu Jun 27 2024 Severe weather is starting to our west in western and central North Dakota. Currently in our area, we have majority showers and some embedded thunderstorms moving through. The severe weather should become elevated into this evening as it approaches our area, but the Devils Lake Basin is under a level 1 out of 5 (marginal) risk for severe storms so not out of the question we could have a few. Forecast remains on track. && .DISCUSSION... Issued at 247 PM CDT Thu Jun 27 2024 ...Synopsis... Ridging is propagating eastward, with a mid/upper low propagating eastward from the Pacific NW. Ensemble guidance in good agreement depicting the upper level pattern to remain progressive through the period. Ensemble members do show variances with timing, track, strength of each passing mid level trough and associated surface low/front evolution which leads to variances in timing, location, and magnitude of any severe impacts or heavy rain. Temperatures vary with passing shortwave ridges/troughs with a tendency for below average temperatures at time (notably this weekend behind the trough on Friday). Each passing trough carries at least some potential for severe thunderstorms, with details tied to the mentioned uncertainties. ...Severe threat overnight... Mid-level warm air advection currently propagating into the region leading to scattered showers. Instability is very weak, so not much for thunder at this point, although do anticipate at least isolated thunder at times. This activity will continue to move northeast into the evening hours. The more widespread coverage overnight will be associated with stronger 850mb WAA associated with a stronger low level jet. With this stronger forcing, SPC indicates the marginal risk for severe severe storms (at least for eastern North Dakota), although instability quickly wanes after sunset - and forcing arrives after sunset. Given lack of instability most convection will be weaker, although strength of forcing and strong deep layer shear will lead to a stronger storm or two. Primary threats remain hail, and wind where momentum transfer of heavy rain/elevated downdrafts can mix down higher gusts in the higher low level shear environment. Will also need to monitor for stronger wake low winds as the convection tonight propagates eastward - the latest runs of the HRRR indicate this potential. At this point predictability is very low - especially considering the weaker nature of the anticipated convection. ...Severe threat Friday afternoon/evening... Deformation zone is favored by latest trends to shift north through Friday morning towards the US/Canada border, lingering into the afternoon. A mid level dry slot is shown to allow for clearing across much of the region. Latest guidance in good agreement indicating the main axis of instability will be east of the CWA by mid-afternoon. However, there is a signal for MLCAPE up to 1000 J/KG along and just ahead of an inverted trough which connects back toward the mid-upper low which will still be approaching from the west. This will tend to be in a post frontal shear environment (backing low levels) but deep layer shear remains high (top heavy shear profiles). Due to the strong effective shear we could see low topped supercell development. If clearing and enough instability builds along and ahead of the inverted trough, low level vorticity along with stronger low level lapse rates/CAPE and slower propagating frontal boundary could lead to a conditional tornado threat. Given lower freezing levels, hail up to 1.5 or so inches also would be a threat. ...Severe threat Monday.... Another mid/upper wave follows a very similar track and evolution as the system Friday, with a period of widespread showers or embedded thunderstorms. There is a signal for a deeper warm sector building into our region within most clusters, and higher probs for SB CAPE to exceed 1000 J/KG during the peak heating/diurnally favored period of the afternoon/evening. CSU GEFS based machine learning (15-30% severe probs) are supported by 100% chance for greater than 55 NBM CWASP and 50-60% probability for NBM CWASP values exceeding 65. That aligns with a threat for isolated to scattered severe convection. This is still farther out, so details/impacts are still inherently uncertain. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1031 PM CDT Thu Jun 27 2024 MVFR to IFR and eventually LIFR conditions expected through tonight into Friday evening. With the TSRA moving through, ceilings are forecasted to drop to around 005 into Friday morning and remain there for the TAF period. Winds will lessen to around 10 knots, but before then they will be gusting up to 20 - 25kts and sustained around 15 kts. Winds will shift into Saturday morning, but that is outside the current TAF period. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...AH DISCUSSION...TG AVIATION...AH