FXUS63 KBIS 040956 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 456 AM CDT Fri Oct 4 2024 .KEY MESSAGES... - A Freeze Warning is in effect for northern North Dakota through early this morning. - It continues to look like Saturday will be very windy, with near-critical to critical fire weather conditions expected over portions of western and central North Dakota. - A High Wind Watch remains in effect for western and much of central North Dakota. A Fire Weather Watch remains in effect for a good portion of western and south central North Dakota. - Very little to no measurable precipitation is expected through most of next week. && .DISCUSSION... Issued at 252 AM CDT Fri Oct 4 2024 Currently, high pressure was situated over southern Minnesota and extended west into the central Dakotas. It was mostly clear across the region with some thin high level cloudiness tracking east from eastern Montana into the Dakotas. Temperatures were in the lower 30s to lower 40s. For today, the freeze warning continues through 9 AM. No plans to change this. NDAWN mesonet is showing a pretty good area of lows in the lower to mid 30s attim along and north of the Highway 2 corridor, with some readings down into the upper 20s. Farther south more hit and miss areas in the lower to mid 30s. It will a breezy to windy this afternoon with southerly winds generally 15 to 25 mph west 20 to 30 mph central. There are a few areas of near advisory to advisory criteria winds over the south central but given the small areal extent and short duration (2-3 hours) will hold off on issuing a small wind advisory. Will pass this along though to the day shift to monitor. Winds drop off this evening but will pick up after midnight as shortwave trough currently over the eastern Pacific races east across the Northern/Canadian Rockies and closes off a stacked low pressure system over Southern Saskatchewan Saturday morning and propagates into southeast Manitoba by 00 UTC Sunday. This will bring an associated strong cold front west to east across the forecast area Saturday morning, with strong gradient winds remaining over the areas through the day and into Saturday evening. The NAEFS SA page indicates strong winds of 50kts at 85H and 60kts at 70H over northwest ND around 18 UTC Saturday and tracking into north central-northeast ND by 00 UTC Sunday. The 12Z 10/3 ECMWF EFI shows probabilities of winds and wind gusts have increased from yesterday with probabilities of 0.9 or higher over the northern half of the CWA. The wind gust shift of tails is at 2 around the Turtle Mountains, which indicates at least some probability for a higher scale event. Looking at the NBM 4.2 data the probability of a 24 HR 10m Max Wind Gust of 55 mph or greater is pretty much above 80 percent along and north of the Highway 200 corridor and near 100 percent over portions of the northwest and far north central. The probabilities drop off South of Hwy 200 and are pretty much highest over the normally high areas as you get south of I-94. Similar to yesterday there looks to be a strong initial surge as the cold front moves into western ND in the pre-dawn hours. The isallobaric component is quite strong and is aligned well with the strongest push of cold advection with this initial surge. The problem is that it's pushing through the forecast area at an unfavorable time. However you do see an initial bump of steep lapse rates move through, but it looks like it's ever so slightly trailing the strong cold advection and isallobaric component. It seem then that we will get an initial surge of strong winds across all of western and central ND with the cold front. The RAP shows that the initial surge would be strongest over the western third of ND, and then wash out a bit as it pushes into central ND. It's possible that that winds here could be at or above HWW criteria (especially west) but it's reasonable to assume that it won't be for a long duration, maybe 2-3 hours at best. As the strong gradient winds develop during the day and lapse rates increase in the late morning through the afternoon, we get more into a mix down scenario, and the question transitions to where will the best potential be for strong winds aloft to mix down to the surface. An educated guess would be that the north would be favored over the south half of the CWA. With this in mind we did extend the High Wind Watch east through Rolette, Pierce, Wells and Foster counties. This was in collaboration with FGF which added a HWW to the Devils Lake Basin. Although the southern portion of the CWA, lets say the I-94 corridor and south seems to be the are of most uncertainty for HWW criteria winds, but with the initial surge and strong winds still present at the top of the mixed layer Saturday afternoon, we will continue keep the southwest and south central in the High Wind Watch. The James River Valley was not in the initial watch and we will keep them out. A Wind Advisory will be needed everywhere that does not get upgraded to a High Wind Warning. After Saturday, confidence remains high in a warming trend into next week, although ensemble temperature spreads increase a little bit towards the latter half of the week. NBM forecasts for Tuesday and onwards are generally on the higher end of the 25th/75th ensemble spread. However, with an impressive ridge for October and dry conditions, this seems more than reasonable. Bottom line is that temperatures next week should return to the 70s for highs, with many locations potentially reaching the 80s during mid-week. Fortunately, winds are favored to remain fairly light overall next week, which should help limit otherwise increasing fire weather concerns && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1205 AM CDT Fri Oct 4 2024 VFR conditions are expected through the 06Z TAF period. LLWS at all sites late in the TAF period. Mostly clear skies with only some thin high clouds and a couple patches of mid clouds here and there through the 06Z TAF period. Light surface flow will increase later this morning and will be southerly generally 15 to 25 knots this afternoon. Winds diminish little early evening with strong winds aloft and LLWS developing 02-04 UTC at all TAF sites. && .FIRE WEATHER... Issued at 252 AM CDT Fri Oct 4 2024 Near critical fire weather conditions are expected over southwest and south central North Dakota, including the James River Valley. Strong southerly winds will develop over southern North Dakota by this afternoon. The strong winds, combined with afternoon highs in the mid 60s to mid 70s and minimum relative humidities of 20 to 30 percent will result in near critical fire weather conditions, mainly along and south of the I-94 corridor. The strongest winds are expected to be over south central North Dakota, along and either side of the Missouri River Valley. Winds will not be as strong as you go east into the James River Valley, and west into far southwest ND. However the minimum relative humidities are expected to be lower in these areas (20 to 25 percent). Humidities over the south central, where winds are expected to be strongest, are forecast to be more in the mid 20s to lower 30s. Although the strongest winds and lowest humidities do not overlap, they are close enough for a near critical category today. One concern today is the forecast temperatures over the south central, where winds are forecast to be strongest. At Bismarck, NBM ensemble spread is quite small (25th percentile of 71 and 75th percentile of 73) and the deterministic value is 71. Our concern is that temperatures could overperform. We already used the NBM50th percentile to increase temperatures a little over the south central. Generally a straight south wind is not conducive form warm temperatures but just looking at the source region today in the central Plains, it looks pretty dry. The normally more humid air down south doesn't look to be too humid, so there is a concern that forecast high could be a little low, and the dewpoints a little too high. If this would be the case, it's possible we could see a few hours of critical fire weather conditions in the south central. Will pass this along to the day shift to monitor. Critical fire weather conditions are possible on Saturday. Saturday looks to be more of a cut and dry case as far as strong winds. Most of western and central North Dakota will see winds around 30 mph (south) to around 40 mph (north) Saturday afternoon with the potential for gusts of 50 to 60 mph over the entire area. The lowest relative humidities will be along the South Dakota border (20 to 25 percent) and the highest will be along the International Border (35 percent northwest to 50 percent Turtle Mountains). Because winds are expected to be so strong, the number of red flag hours is expected to range from around 3 to 8 hours, mainly south and west of Lake Sakakawea and the Missouri river. We kept the Fire Weather Watch for the same area, but it's possible it could be expanded perhaps a county or so north and east of the Lake and the Missouri. Temperatures will be cooler with highs mostly in the 60s, which could be a limiting factor. Again will pass along to the day shift to scrutinize. && .BIS WATCHES/WARNINGS/ADVISORIES... Freeze Warning until 9 AM CDT /8 AM MDT/ this morning for NDZ001>005-009>013-017>019-021. High Wind Watch from late tonight through Saturday evening for NDZ001-002-009-010-017-018-031>033-040-041-043-044. High Wind Watch from Saturday morning through late Saturday night for NDZ003>005-011>013-019>023-025-034>036-042-045>047- 050. Fire Weather Watch from Saturday morning through Saturday evening for NDZ009-017>020-031>034-040>046. && $$ DISCUSSION...TWH AVIATION...TWH FIRE WEATHER...TWH