334 FXUS65 KRIW 201527 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 927 AM MDT Wed May 20 2026 .KEY MESSAGES... - Mostly virga showers, and a few rumbles of thunder, are forecast across the western Mountains and the Bighorn, Wind River, and Upper Green River Basins from 1PM to 8PM today. Gusty downdrafts up to 50 mph will be possible even in the absence of rain. - Rain chances (80% to 90%) quickly increase across northwest Wyoming after sunset tonight. Rain showers and thunderstorms become widespread across the state Thursday. - Light snow is expected across the western and northern mountains and Yellowstone National Park Thursday morning and potentially around Lander and Casper Mountain by Thursday night. - High confidence in warm temperatures Saturday through Memorial Day, with highs in the 70s and 80s. Low shower potential Sunday and Monday afternoons. && .DISCUSSION... Issued at 110 AM MDT Wed May 20 2026 The warming trend continues today, but temperatures will still be below normal for central and southern portions of the CWA. Eastern portions of the Bighorn Basin will have near normal highs near 70F. Virga showers will be more widespread across the CWA this afternoon, as winds aloft back to the west-southwest through the day. Most of the showers will develop over the western mountains and move over the Bighorn, Wind River and Upper Green River Basins through the afternoon. Wind gusts up to 45 mph will be possible with these showers, as dewpoint depressions will range between 30 and 50 degrees. Winds outside of any potential outflow will be light, 20 mph or less. Precipitation chances will become more focused over northwestern portions tonight as the storm drops southward, gradually pushing east and south into the Bighorn Basin, the western valleys and the Upper Green River Basin through the overnight hours. Snow levels will be as high as 9500 ft early in the evening and drop to around 7000 ft by 12Z Thursday. The associated cold front with this incoming storm system will drop southward over the CWA through the overnight hours as well, extending along a Casper-to-Riverton-to Kemmerer line by 12Z Thursday. The front will then slowly push through Natrona and Sweetwater counties through the rest of the morning, with a leeside low developing over northeast portions of WY by 18Z. The aforementioned area of precipitation will continue to move over the CWA through the rest of the day. Model trends have warmed the associated 700mb cold pool that pushes through the Bighorn and Wind River Basins during the afternoon and are now forecasted to be around minus 4C/minus 5C (snow levels as low as 6000 ft). Areas along and north of a Meeteetse-to-Lovell line could still see rain changing over to snow after 18Z. However, precipitation looks to end during the afternoon along a Jackson-to-Cody-to-Lovell line as drier air begins to advect in from the northwest behind the storm. Similar conditions could occur at Lander by 00Z with a greater chance for accumulating snow. There will be an added upslope component, aided by a potential 700mb low moving along the Divide between 00Z and 06Z. This could be enough to dynamically cool the column and lead to snow for the Lander Foothills. Current forecast is for conditions to quickly dry out from west to east through the overnight hours Thursday night, but if the storm slows down precipitation could continue over central and southern portions through 12Z Friday. Initial snowfall amounts of 6 to 8 inches are forecasted over the Absaroka, Wind River and the northern half of the Bighorn Mountains, with up to 4 inches over the Tetons, Gros Ventres and portions of Yellowstone. Temperatures rebound quickly on Friday, with a chance for showers over the far western mountains again in the afternoon as a weak shortwave moves over the area. Afternoon showers and possible thunderstorms will be possible over the holiday weekend as highs reach the middle to upper 80s by Monday. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 430 AM MDT Wed May 20 2026 West of the Divide...KJAC/KRKS/KPNA/KBPI Terminals Northwest flow aloft backs to the west as a shortwave drops south toward the forecast area late this afternoon. Weak showers develop over the mountains between 19Z and 21Z and move east into the basins and valleys around KJAC and KBPI. Any impacts would be brief and confidence is not high enough to include PROB30, with KJAC being the most likely terminal. Shortwave energy and deeper moisture reaches northwest Wyoming around KJAC by 06Z, so a PROB30 group has been added beginning at 04Z. In general, cloud cover increases and begins to slowly lower after 00Z. Wednesday afternoon westerly surface wind 10-18kts decreases to 7- 10kts around 01Z. Mountain tops occasionally obscured after 18Z as a result of the developing showers. Obscurations will lower over northwest Wyoming after 04Z, spreading southward through the rest of the TAF period with the increasing precipitation. East of the Divide...KCPR/KCOD/KRIW/KLND/KWRL Terminals All terminals to be VFR through the forecast period. Weak showers develop over the Absaroka and Wind River Mountains between 19Z and 21Z and slowly track east into the basins during the afternoon. Impacts are likely to be confined to gusty outflow wind 25-35kt, with convection around KCOD the most likely to produce these gusts. Otherwise, KCPR to see 10-18kt westerly wind during the day with occasional late day westerly wind 9-13kt at KRIW and KLND. The arrival of more robust shortwave energy in northwest Wyoming leads to a better chance of light rain showers at KCOD by 06Z. This shortwave will begin to push a cold front accompanied by northerly surface wind through the Bighorn Basin after about 03Z and reaching KCPR and KRIW around 06Z and 07Z, respectively. Mountain tops obscured after 00Z in the Absaroka Range, spreading to the Wind River and Bighorn Mountains between 09Z and 12Z Thursday. Please see the Aviation Weather Center and/or CWSU ZLC and ZDV for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...LaVoie AVIATION...CNJ/LaVoie  650 FXUS63 KFGF 201538 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 1038 AM CDT Wed May 20 2026 .KEY MESSAGES... - Near critical fire weather conditions are forecast in eastern North Dakota this afternoon. - Next chance for widespread rain comes Friday and Saturday, with overall light amounts under half an inch and very low chance for thunder. && .UPDATE... Issued at 1021 AM CDT Wed May 20 2026 Main update to adjust Key Message away from freezing temperatures as temperatures have risen above freezing. Near critical fire weather conditions are forecast today in eastern North Dakota as southerly winds increase this afternoon 20-30 mph coupled with relative humidity values around 30 percent and lingering dry fuels. Patchy shallow fog this morning has also since diminished. UPDATE Issued at 644 AM CDT Wed May 20 2026 We went ahead and issued an SPS for patchy dense fog as observations are starting to become more frequent, but webcams still show the shallow and isolated nature of it. With sunrise ongoing, the expectation is for things to clear out over the next few hours. UPDATE Issued at 950 PM CDT Tue May 19 2026 Some guidance is beginning to hint at fog potential along the the eastern edge of the valley tonight once winds go calm with soundings ranging from a 3-5 degree dewpoint spread to a full on low level inversion and ground fog. Unsure whether clear skies prevail with the calm winds or if patchy ground fog develops but even with a worst case scenario would expect isolated pockets as low as a 1/4 to 1/2 mile with more widespread 1-2 mile vis from Fergus Falls north to Hallock and Crookston. Would say that is about a 30% chance. && .DISCUSSION... Issued at 212 PM CDT Tue May 19 2026 ...Synopsis... Upper trough axis currently over the Red River Valley will pull east into the western Great Lakes tonight. The high pressure centered over the western Plains currently will shift into the upper midwest tonight. Another trough will be digging into the Rockies tomorrow night into Thursday, so westerly flow will quickly shift back to southwesterly. The upper trough to our west splits into a northern and southern branch, and ensemble members vary a bit on how exactly they handle it as it moves east. Most solutions do push the trough east over the weekend, with ridging building into the Plains by Memorial Day. Details such as precipitation timing and placement with the trough are low confidence, but there seems to be good agreement on below average temperatures becoming near to above average by the end of the period. ...Frost and freeze headlines... Clouds should clear out as the upper trough moves east, and with high pressure overhead, winds will become light and variable overnight. There will be a good setup for radiational cooling, and dew points currently in the low 30s over southern Manitoba should be down in our area by tonight. Temps should drop to near or below the freezing mark in most locations, with a 60 to 90 percent chance of 32 or lower for much of eastern ND into northwestern MN. Probabilities of less than 32 are much lower for some reason in west central MN from Elbow Lake up to Detroit Lakes, with chances 20 percent or less.Kept Grant, Otter Tail, and western Becker as frost advisory but have the rest of the CWA in a Freeze Warning. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 615 AM CDT Wed May 20 2026 Shallow fog this morning will improve fairly quickly and within the next 2 hours, giving way to VFR conditions. Winds will initially be light and variable this morning but will increase from the south towards the afternoon hours. Once this occurs, winds will remain elevated through the end of the TAF period, with the highest speeds generally in eastern North Dakota, decreasing as you head further east. No other aviation impacts are expected at this time. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...CJ/Perroux/TT DISCUSSION...JR AVIATION...Perroux  713 FXUS63 KBIS 201540 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 1040 AM CDT Wed May 20 2026 .KEY MESSAGES... - Low to medium chances for showers and isolated thunderstorms across western and north central North Dakota late this afternoon through the evening, then medium to high chances across the western half of the state Thursday through Friday. - Temperatures remain closer to normal through Friday, then warm to well above normal by the end of the holiday weekend. && .UPDATE... Issued at 1034 AM CDT Wed May 20 2026 An upper level wave moves across the northwest this morning mainly with sprinkles expected. No major updates needed at this time, the forecast remains on track. UPDATE Issued at 649 AM CDT Wed May 20 2026 The forecast remains in good shape. Temperatures in the Frost Advisory have mostly risen into the upper 30s to mid 40s, but there are still a handful of locations in the mid 30s scattered throughout the advisory, so will just let it continue for now. && .DISCUSSION... Issued at 438 AM CDT Wed May 20 2026 Early morning surface analysis shows high pressure from the Red River through Lower Missouri River Valleys, with a low pressure trough along the Alberta-Saskatchewan border into northeast Montana. Flow aloft is turning more zonal as a transient mid level ridge precedes a shortwave digging down the Canadian Rockies. The placement of the surface high has allowed temperatures to fall to near or below freezing across the eastern half of the state. Meanwhile, an increase in southerly return flow is keeping temperatures above freezing in the western half of the state, except in a few low- lying, sheltered spots. The Freeze Warning and Frost Advisory remain in good shape. A weak shortwave that appears to be embedded in the mid level ridge is producing light showers aloft, little of which is reaching the ground on account of a very dry low level layer of air. A slight chance of sprinkles remains in the forecast as this feature crosses northern North Dakota this morning. A southeastward advancement of the upstream surface trough will squeeze the pressure gradient over central North Dakota later this morning and afternoon, increasing winds to near 30 mph and gusting to 40 mph. But temperatures are forecast to be much warmer today, with highs ranging from the mid 60s east to mid 70s west. This could lead to near-critical fire weather conditions in parts of western and central North Dakota this afternoon, but the lowest RH of around 20 percent in the southwest is not forecast to overlap with the strongest winds between Highways 83 and 281. By late afternoon today, mid level DCVA is forecast to spread into western North Dakota ahead of a closed low circulation spinning over southwest Saskatchewan. At the surface, a low pressure with an attendant warm front to the east, dryline to the south, and cold front to the southwest is forecast to enter northwest North Dakota at a similar time. CAMs are in agreement on widespread shower and thunderstorm activity initiating closer to the cold front in eastern Montana this afternoon, but also indicate a lower degree of coverage developing into western and north central North Dakota by early evening. There is potential for up to 500 J/kg of CAPE to build just ahead of the dryline, but models are fairly consistent in keeping the buoyancy displaced downstream of stronger shear, and HRRR/RAP soundings show a skinny CAPE profile with equilibrium levels only approaching 25,000 ft. Stronger convection is therefore highly unlikely late this afternoon and evening, but the inverted-v thermodynamic profiles could support gusty winds. Showers and storms are forecast to gradually dissipate late this evening into tonight, which will have milder low temperatures in the upper 30s to mid 40s. On Thursday, the mid/upper level trough axis is forecast to reorient itself and deepen from southern Saskatchewan to northern Utah, inducing lee cyclogenesis with an inverted surface trough extending northward through the western Dakotas. The inverted surface trough will be the focal axis for high chances of showers Thursday afternoon through Thursday night. There is still some uncertainty on the placement of the inverted trough and associated maximum QPF, but the range has narrowed in scope to as far west as the Montana border and as far east as a line roughly from the Turtle Mountains to the Standing Rock Reservation. The NBM places its averaged maximum QPF axis from around Hettinger to Stanley, with high chances of exceeding 0.25" and low to medium chances of exceeding 0.5". But embedded thunderstorms along a ribbon of up to 1000 J/kg CAPE could produce locally higher amounts, as indicated by the HREF localized probability-matched mean QPF showing pockets of 1-2". Training convection, high deep-layer RH, and precipitable water approaching 75th-90th climatological percentile values near 1 inch could also contribute to enhanced rainfall rates on a localized basis. The mid/upper trough is forecast to pivot into the High Plains on Friday with two distinct vort maxima over southeast Saskatchewan and northeast Colorado, respectively. Numerous showers are likely to persist along the inverted surface trough on Friday, which may only shift slightly to the east. But there is a much lower risk for thunderstorms on Friday as guidance is showing little to no CAPE. There are several potential outcomes for multi-day rain totals depending on how much or little the inverted surface trough shifts around. If it remains nearly stationary all the way through Friday, there could be a narrow corridor of +1 inch amounts surrounded by widespread amounts under a quarter of an inch. If the inverted trough does shift eastward, there could be a broader area or perhaps two separate areas of around half an inch. The latest NBM shows a narrow axis of medium chances (50 to 60 percent) for exceeding half an inch of rain Thursday through Friday night from Hettinger to just west of Minot, with low chances (10 to 20 percent) for exceeding 1 inch. Temperatures will remain closer to normal Thursday and Friday, although showers and associated cloud cover could cause some deviations. Friday in particular looks like a day where a large portion of the area could see cooler daytime temperatures under persistent clouds and shower activity. Overnight temperatures are forecast to remain well above freezing, with only parts of southwest North Dakota having a low chance of falling into the mid 30s Friday night. A significant warm up continues to be strongly favored by ensemble guidance through the holiday weekend as there is now increasing ensemble agreement on mean ridging over the central CONUS. The NBM shows moderate to low spread given the forecast time range with highs in the mid 70s to mid 80s on Sunday and around 80 to 90 degrees on Memorial Day. Chances for rain under this pattern are low, but there could be some shortwaves traversing the top of the ridge over the Northern Plains before the ridge becomes more amplified. Above normal temperatures of highs in the mid 70s to upper 80s are favored to continue through the middle of next week, with increasing uncertainty in the eastward progression of the central CONUS ridge as a stronger wave digs down from the Gulf of Alaska. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 649 AM CDT Wed May 20 2026 VFR conditions are mostly expected through the forecast period. A few sprinkles are possible across northwest and north central North Dakota this morning, with no impacts to aviation. From mid afternoon through this evening, scattered showers and isolated thunderstorms are forecast to develop over western and central North Dakota. Heavier showers and storms could produce brief downpours with IFR visibility and gusty winds. Outside of showers and storms, southerly winds will increase over central North Dakota this morning and afternoon, with sustained speeds reaching 20-30 kts and gusts as high as 35 kts. In western North Dakota, expect southerly winds around 15 kts this morning, becoming more southwesterly around 10-15 kts through the afternoon. A period of low-level wind shear is expected at KMOT early this morning. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Hollan/Johnson DISCUSSION...Hollan AVIATION...Hollan