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Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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555 FXUS63 KFGF 011146 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 646 AM CDT Mon Jul 1 2024 .KEY MESSAGES... - There is a level 1 out of 5 risk for severe thunderstorms this afternoon and evening across much of the forecast area, with a level 2 out of 5 risk for severe thunderstorms along and south of Interstate 94. - A system is expected to bring numerous showers and thunderstorms to parts of the Northern Plains on Independence Day, with a low chance for severe thunderstorms. && .UPDATE... Issued at 645 AM CDT Mon Jul 1 2024 There is one cluster of showers/thunderstorms in northeast ND (higher coverage), with isolated showers/thunderstorms near our far eastern counties (Beltrami/Lake of the Woods). This matches trends from CAMs and earlier HREF mean. Some adjustments to refine coverage are necessary, the general forecast remains on track this morning with a likely delay in new development for some locations (namely south) until midday or early afternoon. && .DISCUSSION... Issued at 404 AM CDT Mon Jul 1 2024 ...Synopsis... Large scale flow remains progressive across the Northern Plains, with a series of mid level shortwave troughs. This larger scale pattern shows strong consensus in ensembles, with variances in specific tracks and strength of some of the waves and surface features. The strongest/most organized mid level waves are today and another on Thursday (Independence Day Holiday), with less organized/more diffuse forcing between these waves keeping shower/thunderstorm chances. There is a larger spread in the evolution of the large scale pattern late next weekend and early next week, with a subset of clusters favoring more amplified ridging versus a larger percentage of ensembles favoring NW flow over our region. Overall, temperatures are favored to trend back towards seasonal averages through the week, with a much larger spread in highs by next week (chance for above normal temperatures). ...Today... Initial showers that developed early this morning have been associated with an axis of 700MB WAA within SW flow ahead of the main mid level trough (still located over the Northern Rockies). A cluster of showers and embedded thunderstorms (a few stronger) are shown by CAMs to arrive in our northwest later this morning, but the severe threat should be delayed due to narrower limited CAPE profiles locally. Strong low level moisture advection is underway and additional isolated-scattered shower/thunderstorms may develop within less organized forcing through the day before the main wave approaches and a strengthening LLJ organizes activity into larger areas of showers and thunderstorms this evening (evolution well represented by all HREF members). Widespread rain totals exceeding 0.5" should be expected (particularly this evening/overnight) with a strong signal in HREF PMM for one or more swaths of 1-2" rainfall (strongest signal north). Hydrological this wouldn`t be enough for excessive runoff/flash flooding in our area outside of urban areas with poor drainage, though additional/eventual rises on rivers would be possible. As surface low pressure deepens southeast BL flow may increase and there is a signal in some guidance for near advisory winds across the southern RRV, though mixing heights appear limited due to a strong elevated inversion/warm nose and persistent stratus. This stratus stable layer also plays a role in limiting potential impacts from deeper convection that may develop this afternoon and evening. Parcel traces remain very elevated and while elevated CAPE does increase as the LLJ builds east (along with strong deep layer shear) the potential for surface based parcels is not reflected and DCAPE is minimal (well under 500 J/KG). This raises the possibility that most activity will tend to be heavier rain with a few stronger cores supporting large hail to around 1". Wet downbursts can`t be ruled out though considering the shear profiles, especially if there are any linear segments that become orthogonal to higher shear vectors. This may be less prevalent due to the stable low levels, limiting confidence/coverage for our area in a wind threat. ...Independence Day Rain and Severe Threat... The system Thursday continues to show good agreement in timing and broader track at 500/700MB. However, the specific strength/evolution and exact track all shift surface features and create higher spread in potential rain totals and any severe potential. There is still a low chance for severe storms (5% probs on CSU GEFS based machine learning), but little confidence in those types of details at this range. Despite the variances, there is still a strong signal for showers and thunderstorms during the afternoon/evening period which even if not severe could impact Independence Day festivities. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 645 AM CDT Mon Jul 1 2024 Initially showers and isolated thunderstorms are primarily in far northeast ND (towards KDVL) and north central MN towards KBJI, however this activity should gradually increase in coverage along with MVFR and IFR stratus midday into the afternoon. Widespread rain and embedded/scattered thunderstorms then overspread eastern ND and northwest MN this evening gradually transitioning east thorugh the late TAF period. VFR may return after 07-10Z in ND, with lower conditions lingering longer in MN based on current guidance. Where heavier rain showers or strong thunderstorms develop LIFR conditions can`t be ruled out late this afternoon into the evening, though anticipating timing of impacts is difficult due to limited coverage/chances. Southeast winds increase as low pressure continues to deepen today, and gusts may exceed 35kt at times in the southern Red River Valley during the afternoon. Winds eventually shift to the south-southwest then west, decreasing below 12kt, as low pressure pushes east tonight. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...DJR DISCUSSION...DJR AVIATION...DJR