Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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437 FXUS63 KBIS 201808 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 108 PM CDT Mon May 20 2024 .KEY MESSAGES... - Temperatures will trend near to below normal this week, with highs in the upper 50s to around 70 and lows in the mid 30s to upper 40s. - Medium to high chances for rain in the James River Valley tonight through Tuesday, with lower chances elsewhere. - Medium to high chances for showers and a few thunderstorms across all of western and central North Dakota Thursday through Friday. && .UPDATE... Issued at 104 PM CDT Mon May 20 2024 A quiet afternoon continues across western and central North Dakota. Some diurnal cumulus will remain possible through the afternoon across the central and east with a mostly clear sky over the west. UPDATE Issued at 934 AM CDT Mon May 20 2024 Fog has mostly lifted across the area but a few patches may linger for another hour or so. Otherwise, the forecast remains relatively quiet this morning. No major changes were needed for this update other than to blend in the latest observations to the forecast. UPDATE Issued at 654 AM CDT Mon May 20 2024 Patchy fog has developed across portions of the state early this morning. The greatest impacts in our forecast area have been across the Prairie Pothole region and southern James River Valley, and southwest Williams County including the Williston Airport, where visibility has fallen below one quarter mile. The fog should lift between 8 and 9 AM CDT. && .DISCUSSION... Issued at 351 AM CDT Mon May 20 2024 Surface low pressure is located between Mobridge and Aberdeen, South Dakota early this morning, with the parent mid/upper level wave back to the northwest from southeast Saskatchewan into northwest North Dakota. The wave continues to produce scattered showers across northwest and north central North Dakota, which are forecast to diminish and lift northeastward into southwest Manitoba through the morning. Some parts of southwest and central North Dakota that have remained cloud free for most of the night have seen temperatures drop into the upper and even mid 30s. This includes Golden Valley, western Slope, and western Bowman Counties, as well as areas from around Beulah/Hazen to Garrison, Max, and Velva. Patchy frost could develop in these areas early this morning. Aside from the morning showers dissipating in the far north, a mostly dry day is expected. Some models bring high based showers into far south central and southeast North Dakota later this afternoon and evening along a band of mid level frontogenesis. Given forecast cloud bases around 10-15 kft (aside from diurnal cumulus), this will likely manifest as virga. Elsewhere, cyclonic southwest flow aloft could generate some light isolated to widely scattered showers this afternoon and evening, with the highest chance of occurrence (albeit still quite low) in the northwest. Highs this afternoon are expected to be in the 60s. A progressive shortwave over the western CONUS will force the development of a Colorado low late tonight, with strong model consensus on a northeast track into southern Minnesota on Tuesday. Most of the rain from the wrap-around deformation band will miss our forecast area, but the southern James River Valley could get clipped with a few tenths of an inch. The synoptic pattern looks to remain active thereafter, but stronger forcing is forecast to avoid the Northern Plains through Wednesday. Nevertheless, some weaker disturbances could generate a few showers at times Tuesday through Wednesday. But most locations are likely to remain dry through the middle of the week. The NBM keeps temperatures slightly below normal over this time period, with highs in the 60s and lows in the upper 30s to mid 40s. However, should any overnight period end up with light winds and a clear sky, temperatures could fall closer to freezing. Tuesday night looks to the have the greatest frost potential at this time, with surface ridging forecast over the western half of the state. A much stronger wave is forecast to dig into the Northern Plains Thursday into Friday. The greatest ensemble spread is on the timing of this system, with latitudinal displacement being a secondary source of uncertainty. 00 UTC ensemble cluster analysis appears to favor a slower and slightly more northward progression by a ratio of 3:2, and this scenario is heavily weighted by the ECMWF and Canadian ensembles. The GEFS dominates the southern and quicker solution, though its parent deterministic model now more closely aligns with the former. Some parts of western and central North Dakota are likely to receive at least a few to several tenths of an inch of rain from this system, with the NBM showing a 40 to 60 percent chance of exceeding half an inch across the entire state. Depending on the timing and track of the system, there could be a strong to severe storm risk. This appears more likely should the slower progression come to fruition, though weak moisture return in the warm sector could be a limiting factor. Daytime temperatures over this two-day period are likely to be slightly cooler, especially Friday when forecast highs are only in the mid 50s to lower 60s, but overnight lows could be kept in the 40s by the increased cloud cover. Ensemble guidance then hints at a slight warming trend for the holiday weekend that ensemble mean height fields show could feature another shortwave passage Sunday into Memorial Day. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 104 PM CDT Mon May 20 2024 VFR conditions are expected through the period. A few isolated to scattered showers may be possible across the far south towards the very end of the period but confidence is low that these showers will move over any particular site. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...ZH DISCUSSION...Hollan AVIATION...ZH