FXUS63 KBIS 051416 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 916 AM CDT Mon Aug 5 2024 .KEY MESSAGES... - Widespread showers are expected across central and eastern North Dakota through the morning, with a few thunderstorms along and south of Interstate 94. Localized heavy rainfall of at least one inch is possible. - Below normal temperatures are expected through the upcoming week, especially today when highs will mainly be in the 60s. - Another round of widespread showers and scattered thunderstorms is expected across the forecast area late Tuesday through Wednesday. && .UPDATE... Issued at 914 AM CDT Mon Aug 5 2024 The forecast has been updated to reflect the most recent observed and modeled trends, resulting in minimal changes to the overall forecast messaging. The most notable changes to PoPs were to 1) spread higher percentages farther north, 2) lower percentages more quickly from west to east across the south, and 3) lower percentages to around 40 to 50 from northwest to central North Dakota this afternoon, where coverage of light rain is expected to be more of a scattered nature. Sky cover was increased, especially for the morning, and current satellite imagery suggests it may need to be increased further this afternoon as well. If there is no sunshine until very late in the afternoon, southern climate sites could set record cold maximum temperatures for the day, which are 62 at Dickinson, 64 at Bismarck, and 69 at Jamestown. Beyond the near-term period, patchy fog was added to the forecast for southern North Dakota tonight through mid Tuesday morning. Models that simulate visibility are inconsistent on the areas that are most likely to see fog, but surface ridging with low dewpoint depressions around sunset across the south should provide favorable conditions for fog formation. UPDATE Issued at 705 AM CDT Mon Aug 5 2024 No major updates to the forecast were made at the time of this update. Widespread showers are present over western and central North Dakota this morning. A few thunderstorms are present across the south, with a roughly east to west orientated line of training thunderstorms beginning to develop over an area of FG forcing across the south central. A broad deck of mid levels is moving across the forecast area, while an area of low stratus is beginning to develop across the west. Winds remain generally northeasterly, from 5 to 15 knots, while temperatures are broadly in the mid 50s to lower 60s. The forecast remains on track. && .DISCUSSION... Issued at 415 AM CDT Mon Aug 5 2024 Today, the approach of a shortwave down the overall northwesterly flow pattern will promote widespread chances for showers. An area of 850-700 mb FG forcing is present across our southern counties, along the northern edge of a low level jet across South Dakota. This forcing, paired with WAA punted northward from the jet, will promote a banded of non-severe thunderstorms to develop across our southern counties this morning, generally south of the I-94 corridor. With the westerly steering flow parallel to the roughly west to east orientation of this FG forcing and, CAMs have picked on these thunderstorms training across much of the south through the late morning period. These training storms, paired with high PWATs exceeding 1.50+ across the south this morning, there is some potential for localized excessive rainfall over portions of south central North Dakota this morning. Deterministic rainfall through this afternoon across our our southern counties range generally from around 0.50" to 1.25" over the area south of I-94, with the highest amounts in excess of 1.00" found in the southern James River Valley. These amount are generally in line with the 00Z run of the HREF, with the highest 6 hour probability-matched mean up to 1.50" found over Logan, McIntosh, LaMoure, and Dickey counties from 7 AM to 1 PM CDT. With these amounts excessive rainfall concerns are very limited at this time, but will have to continue to monitor localized rainfall amounts over this area through the morning hours. Precipitation is expected to begin tapering off and exit the area as the low level jet is displaced further eastward by the intrusion of surface high pressure from the southern Canadian prairies, along with the FG forcing diminishing through the afternoon. With the shortwave aiding the continued flattening of the upper level ridge lingering over the western CONUS, high temperatures are anticipated to broadly be below seasonable normals this afternoon, from the lower 60s to the lower 70s. Winds are generally expected to be out east to northeast through the day today, with somewhat breezier conditions in the southern James River Valley this afternoon with sustained speeds forecast from 20 to 25 mph. The sky will remain mostly cloudy through the day today, but cloud cover will begin to diminish overnight from east to west. Northwesterly flow will be re-established late Monday and overnight into Tuesday as the shortwave dissipates into the general pattern. Ahead of the southward dive of a closing Pacific Northwestern upper level low, the ridge is expected to briefly reamplify over the northern Plains on Tuesday. With this re-amplification temperatures will be somewhat warmer, though still seasonably cool, with highs forecast from the mid 70s over much of the forecast area, to the lower 80s in the far southwest. Late Tuesday afternoon, synoptic scale forcing from the closed low now over the Canadian Prairies will again promote widespread chances (40 to 60%) for showers and thunderstorms over much of western and central North Dakota through the overnight period. Current CAMs do show a few clusters of ongoing convection being pushed out of eastern Montana into our western counties Tuesday evening. With strong deep layer shear currently expected across western North Dakota late Tuesday. As things currently stand, SPC has a Marginal risk (level 1 of 5) over a small portion of southwestern North Dakota for Day 2 (Day 2), with CSU Machine Learning highlighting a similar area, as the axis of better instability is progged to remain to our west at this time. Showers and scattered thunderstorms are expected to continue through much of the day Wednesday as the synoptic forcing continues to break over the northern Plains. Though the primary axis of instability is expected to penetrate further eastward into our area Wednesday afternoon, with current model MUCAPE values from 1000 to 2000 J/KG found in the southwestern and central North Dakota, deep layer shear is also anticipated to diminished by this period. As things currently stand, SPC has place portions of southwestern and central North Dakota into a Marginal risk (level 1 of 5) for Wednesday. Otherwise, temperatures on Wednesday will again be cooler as the upper level low moves eastward over Saskatchewan and again flattens the ridge, with highs forecast from the upper 60s northeast to the upper 70s southwest. The upper level low over the Canadian Prairies will slowly progress south and eastward through the remainder of the workweek, and will continue to promote seasonably cool temperatures, as well as modest daily chances (10 to 20 percent) for showers through Friday, generally in the far southwest. Highs anticipated to remain below seasonable normals through the end of the week, forecast broadly in the mid 60s to lower 70s Thursday and Friday, then broadly in the 70s through the weekend. By late Saturday and into Sunday, the further eastward progression of the upper level low will see its influence begin to diminish. There is some fairly good agreement for this far out amongst ensemble members on the landfall of a Pacific trough onto the West Coast, which would allow to ridge to again re- amplify. In such a scenario, temperatures would be be anticipated to begin a gradual warming trend back toward seasonable normals beyond the end of the forecast period. This scenario is reflected by the CPC's 8-14 Day Temperature Outlook, which has the forecast area leaning toward near normal temperatures for the August 12th-18th time period. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 705 AM CDT Mon Aug 5 2024 Showers and thunderstorms are present over the forecast to begin the TAF period. MVFR to IFR ceilings are present at the terminals of KBIS, KXWA, KDIK,with KXWA and KDIK occasionally dropping to LIFR ceilings. MVFR will move over KJMS later this afternoon. Ceilings are anticipated to lift back to VFR ceilings late this afternoon and evening, before again dropping across west near the end of the TAF period, including at the terminals of KDIK and KXWA. Otherwise, all other terminals are expected to remain at VFR ceilings and visibilities through the end of the TAF period. Some scattered thunderstorms are expected to develop across the south through the morning, mainly in the vicinity of KBIS through the mid morning. Winds are generally forecast to be east northeasterly from around 10 to 15 knots, with gusts up to 20 to 25 knots possible at KJMS and KXWA. Where thunderstorms do develop, gusty and erratic winds are anticipated. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Hollan DISCUSSION...Adam AVIATION...Adam