Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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899 FXUS63 KBIS 070618 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 118 AM CDT Tue May 7 2024 .KEY MESSAGES... - Widespread showers are expected across western and northern North Dakota on Tuesday, with isolated to scattered showers south central into the James River Valley. - Strong westerly winds are expected along and south of Highway 12 in far southwest North Dakota on Tuesday. - A transition to warmer and drier weather is expected for the end of the work week. && .UPDATE... Issued at 117 AM CDT Tue May 7 2024 At 1 AM CDT, surface and upper air analyses show a nearly stacked low pressure over northwest South Dakota. Dry slotting across much of southern North Dakota is now evident on both radar and satellite imagery, with scattered showers across areas mainly north of Highway 200. Very little, if any lightning has been observed over the past few hours, and current SPC mesoanalysis paints only a few hundred J/kg of MUCAPE over west central North Dakota. Thunderstorm chances have limited to 20 percent or less with this update. Other minor forecast changes included blending the latest NBM and high- resolution ensemble PoP projections through Tuesday afternoon. UPDATE Issued at 921 PM CDT Mon May 6 2024 Will allow the wind advisory to expire with this product issuance. The majority of wind gusts the past couple of hours have been below 40 mph, and should remain so for the rest of tonight. Also updated POPs based on latest radar and near term trends, using a blend of the RAP/NBM and current location of precipitation returns. Expect wrap around showers to then fill back in eastward Tuesday morning and during the day as the low shifts slowly east-northeast, with the better chances west and north. UPDATE Issued at 753 PM CDT Mon May 6 2024 Will allow the severe thunderstorm watch to expire as scheduled. Still around 500-1000 MLCAPE in southwest ND, though wind shear is only 20-25 knots so the severe threat has ended for this evening. UPDATE Issued at 640 PM CDT Mon May 6 2024 The risk for severe thunderstorms remains across far southwestern North Dakota through early this evening. Surface low is centered over northwestern South Dakota, with its associated warm front now orientated west/northwest to east/southeast across northwest into north central SD. Convective updrafts continue to spawn north of the front over my far southwest, but have lost their earlier organization as instability has weakened and will continue to do so over the next hour or two. Will keep the Watch as is with this product issuance, but fully anticipate dropping the watch before its expiration at 01Z (8pm central, 7pm mountain). Farther east, scattered convection has developed between the Missouri River and the James River Valley the past few hours, and will continue as an embedded wave rotates around the upper low and lifts north across the eastern Dakotas. Do not expect any severe weather for this area with limited instability present. Will maintain the wind advisory for now, but will look to trim off counties or expire altogether over the next couple of hours if winds remain below criteria. && .DISCUSSION... Issued at 318 PM CDT Mon May 6 2024 Currently, a surface low sits across western South Dakota and northeastern Wyoming, with an attendant warm front oriented northwest to southeast across roughly the same area. Some windy conditions are still present across much of central and eastern portions of the state, with the highest measured sustained winds around 25 to 35 mph. As such, the current Wind Advisories will continue as planned, expiring at midnight CDT. Some showers are also making their way north through the central parts of the state, with an occasional rumble of thunder possible. These showers should remain rather tame, as the instability in this area is not too strong. Temperatures should max out in the mid 50s to lower 60s today, with overnight lows in the 40s to 50s. The previously mentioned warm front is slowly moving roughly north, along with the surface low, which is fueling the development of some strong storms in western South Dakota. As the afternoon progresses, this front will move north towards North Dakota, bringing along with it the potential for continued severe storm development along it. As a result, parts of southwestern and portions of far south central North Dakota are currently under a Severe Thunderstorm Watch until 8 PM CDT (7 PM MDT), as well as a Marginal Risk (level 1 of 5) from the SPC. The main hazards expected with this event will be winds up to 60 mph, large hail up to quarter size, and the potential for a tornado or two. While the ingredients are certainly supportive of strong storm development, our main concern with this setup is whether or not the instability will remain in our area for long enough to get anything going. The most recent deterministic analysis of SBCAPE suggests a narrow corridor focused along and moving with the warm front, with values maxing out around 1500 to 2000 J/kg. However, as soon as this corridor of instability moves into Bowman and Adams counties, it begins to weaken rather quickly, nearly dissipating entirely around 8 or 9 PM. 0 to 1 km shear values ahead of the front are forecast to be around 20 to 30 kts, which combined with forecasted 0 to 1 km SRH values of 150 to 300 m2/s2, help support the possibility of a tornado or two, albeit being weak and short lived tornados. Modest mid level lapse rates are expected to be present as well, but once again, the timeframe is rather short for all of these ingredients to line up, and as such, the overall severe threat is expected to be short lived as well. Overnight and into Tuesday, this large low pressure system is expected to move further north into North Dakota, before weakening and moving southeast into the Great Lakes region through the second half of the week. Wrap around moisture will bring continued showers to the area through tonight and Tuesday, with chances tapering off into Wednesday. Current probabilistic guidance suggests portions of far western North Dakota will see a 50 to 60% chance of exceeding 1.00" of rain through Wednesday morning, with those chances dropping to around 10% in central North Dakota. Chances for exceeding 0.50" of rain in the same timeframe are in the 60 to 80% range for almost the entire area. Rainfall totals continue to slightly decrease with each subsequent model run, but overall, the chances for receiving precipitation remain in the 40 to 70% range for a majority of the area. Temperatures Tuesday will be a bit lower than today, with highs mainly in the 50s to lower 60s. After this wet period, long range guidance suggests the start of a drying and warming period, as signs point towards the development of a large ridge across the western CONUS, building east into the Great Plains through the end of the week and into the weekend. High temperatures are forecast to warm into the upper 60s and lower 70s by Thursday, continuing through the weekend. Current NBM spreads for temperatures on Thursday and Friday are pretty tight, suggesting increased confidence in a warm and dry end to the work week. Following that, while temperatures are expected to remain warm, the spread increases as a result of guidance beginning to disagree with the synoptic flow pattern heading into the weekend. However, warmer temperatures in general are expected to continue regardless of the outcome. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 117 AM CDT Tue May 7 2024 A low pressure center will continue to spin over western and central North Dakota through the forecast period. Precipitation/visibility: Most terminals should see a break in persistent rainfall overnight. During the day Tuesday, rain should fill back in across western and northern North Dakota, with more isolated to scattered shower activity across south central and southeast North Dakota. A few flashes of lightning cannot be completely ruled out, but the probability for TS is very low. Visibility could be reduced to MVFR/IFR levels in heavier showers. Ceilings: Parts of southern North Dakota will see some breaks in low ceilings overnight, and this trend may continue at KJMS into Tuesday morning. Otherwise, the overall expectation is for MVFR/IFR ceilings to prevail. Wind: Central North Dakota will continue to see strong east- southeast winds overnight into Tuesday morning, with a gradual decrease in intensity Tuesday afternoon and evening. Northwest North Dakota will have easterly winds around 10 kts overnight, turning slight to the northeast and increasing to around 15 kts with gusts to 25 kts Tuesday afternoon. For most of southwest North Dakota, expect easterly winds around 10 kts overnight, gradually turning to the north and then west during the day Tuesday. The far southwest corner of the state, primarily Bowman County, will see much stronger westerly winds on Tuesday, with sustained speeds up to 50 kts and gusts to 45 kts. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Hollan DISCUSSION...Besson AVIATION...Hollan