Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
247 FXUS63 KBIS 181955 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 255 PM CDT Wed Sep 18 2024 .KEY MESSAGES... - Strong winds are forecast from this afternoon through Thursday evening, with sustained winds up to 30 mph at times. - Showers and thunderstorms are possible (40-60% chance) across western and northern North Dakota this evening through tonight. - A cooling trend is forecast for the end of the week, with highs in the 60s by the weekend. && .DISCUSSION... Issued at 255 PM CDT Wed Sep 18 2024 The expansive, stacked low pressure system that brought us our thunderstorms earlier this morning sits across eastern Montana today, with a large band of precipitation wrapping around it. Across western and central North Dakota, skies have cleared out, allowing for some heating and drying to occur. Highs today range from the mid 70s to lower 80s. Southerly winds continue to increase as the low slides eastward, tightening the surface pressure gradient and allowing for sustained wind speeds around 20-25 mph, gusting up to 30-35 mph, especially across the southern tiers of counties. At the moment, winds are not necessarily exceeding advisory criteria, but there is the potential for some areas to see isolated speeds right around the lower threshold of advisory criteria. Wrap-around precipitation may begin to nose into the southwest in the afternoon hours, which may potentially help limit the mixing at the surface, so there is no Wind Advisory out at this time. We will continue to monitor winds throughout the day, in case the mixing begins to overperform. This precipitation should then continue to expand to the northeast as the surface low tracks to the northeast into southern Saskatchewan, bringing about 40-70% chances for showers and an occasional thunderstorm to much of the west and north through the evening and through the overnight hours. Portions of the south central also see some near critical fire weather conditions, given the increased wind speeds and minimum relative humidity values around 20-23%, but our live herbaceous fuel moisture values in that area exceed 130%, helping limit much of the concern for critical fire weather. As the aforementioned low continues moving northeast, wind speeds will remain breezy overnight, with the wind direction becoming more southwesterly, before becoming entirely westerly by Thursday morning. Along the nose of the precipitation band moving into our far southeast, winds are expected to increase in speed, with portions of Bowman, Adams, and Slope counties potentially seeing sustained wind speeds above 30 mph for a time. There is the potential for these winds to remain elevated long enough for a Wind Advisory, so we will have to keep a close eye on how the forecast evolves in that area. Some forecast soundings indicate stronger winds aloft (30-35 kts) mixing down to around 500-700 ft for a few hours in that area, which could certainly support some stronger winds there. The EFI for wind speeds does indicate parts of the southwest as potential areas for strong winds, but the shift of tails remains further west and out of our area. Some models, including the HREF, also suggest wind speeds dying out overnight before they really establish themselves in our area. All in all, it is a somewhat strange setup that will need to be closely monitored through the rest of the evening. Otherwise, overnight lows will mostly remain within the 50s. Through the day Thursday, the low pressure system will transit to our north, resulting in continued breezy winds from the west. Chances for showers and thunderstorms (mostly 25-50%) will slowly cross the northern counties, before eventually lifting north into Canada by Thursday evening. Wind speeds will once again remain close to advisory criteria but staying just below, mostly across the far south and far northwest. Given the strong influence from the low, high temperatures will be a bit cooler tomorrow than they are today, with highs mostly in the upper 60s to mid 70s. Very brief upper level ridging will help bring highs back into the upper 70s to lower 80s Friday. With the low finally moving entirely out of our region, winds should decrease across the area. Friday should remain mostly dry under the influence of the ridge, with very low chances (roughly 15-20%) for showers in the evening. Through the weekend, models suggest a large trough digging down across the Canadian Prairies, with the trough axis positioned just to the north of the International Border. As a result, upper level flow becomes more westerly, bringing about cooler temperatures to the state. High temperatures on Saturday and Sunday mostly remain in the 60s, with overnight lows in the low 40s. Some areas in the west may see lows in the upper 30s as well. Long range guidance has shifted flow to be more westerly as opposed to southwesterly over the past few runs, so chances for precipitation through the weekend has decreased quite a bit, with only portions of the southeast seeing 15% chances for rain. These dry conditions are forecast to continue into next week, where cluster analysis suggests the beginning of a warming and drying trend, with upper level ridging building into the western CONUS. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1234 PM CDT Wed Sep 18 2024 VFR conditions are present across all terminals this afternoon. A low pressure system sits across eastern Montana, forecast to move northeast through the rest of the day. Wrap-around precipitation is forecast to arrive in the southwest, which will increase cloud coverage and lower ceilings to around MVFR criteria. These ceilings, along with increased chances for showers, will arrive at KDIK and KXWA around 21z, expanding northeast and impacting KMOT around 00z. Breezy southerly winds are present, with sustained wind speeds from 15 to 20 kts persisting through the TAF period. These winds will shift southwesterly late tonight, becoming more westerly Thursday morning. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Besson AVIATION...Besson