Area Forecast Discussion
Issued by NWS Billings, MT
Issued by NWS Billings, MT
207 FXUS65 KBYZ 212301 AFDBYZ Area Forecast Discussion...Updated National Weather Service Billings MT 501 PM MDT Tue May 21 2024 .UPDATE... The Winter Storm Warning for the Northern Big Horns has been cancelled. A few snow showers may linger up there this evening, but additional accumulations will be light and local. We will be assessing the need for additional winter storm highlights for the Northern Big Horns for Wed night through Thursday. BT && .DISCUSSION... Through Wednesday night... Upper trough continued to move E through the forecast area per water vapor imagery. Highest surface-based CAPE was 500 J/kg from KBIL E and SE. Bulk Effective Shear was less than 30 kt and PWAT`s were around average. Scattered showers and isolated thunderstorms were moving across much of the area at 21Z. 20-40% chances of showers with isolated thunderstorms will continue over the area this afternoon into early evening. PoPs decrease after 03Z to 20% from KBIL E and NE. It will then be dry into early Wednesday. As for snow in the NE Bighorns, web cams showed it was fairly light, with heavier snow falling S of Burgess Junction. Will keep the Warning going until 6 PM MDT. Low temps will be a few degrees below normal. For Wednesday, weak upper ridging will shift E of the area, while SW flow and upper diffluence increase over western areas in the afternoon. Temps will be from the low 60s W to around 70 SE. SREF did not show much in the way of CAPE, but had greater than 30 kt of Bulk Effective Shear in the afternoon and evening. Models also showed breezy conditions for KLVM, so boosted gusts toward the NBM 90th percentile. Cold front will push S through much of the area in the afternoon. There will be a 20% chance of rain and mountain snow in the W during the late morning. PoPs then increase from W to E in the afternoon and evening for areas of rain with some thunderstorms. There will be rain and snow in the mountains. Highest PoPs will be W of KBIL at 80-100%. Areas in the far SE looked dry through the evening as a surface low moves through SE MT and central/E WY. PoPs continue to increase for most areas late Wed. night, with the exception of the far eastern counties where it will remain dry. Models had upper low centered over NW WY by 12Z Thursday. Snow levels decrease to 5000-6000` W of KBIL. Precipitation type will be rain with a few thunderstorms in the lower elevations. Some snow is possible in the foothills but Red Lodge looks like rain at this point. There was only a 20% chance of any snow in Red Lodge. QPF amounts will be highest N and NW of KBIL, and there was a 30-40% chance of at least a half an inch of precipitation from Judith Gap to K6S0 to KLVM Wed. night. Snow will start to pile up in the mountains, especially over the Crazys where up to a foot is possible over the highest peaks. Continued the Winter Storm Watch that begins Wed. evening and goes through Thursday evening. Arthur Thursday through Tuesday... The long term will see a split flow northern hemispheric pattern with a high wave count. This will set the stage for an active long term with multiple precipitation chances and temperatures swings. Thursday will start of with an upper wave and deepening low over Wyoming bringing precipitation. Looking at soundings, there is a deep moist layer to near 300mb creating a long and skinny atmospheric profile. This should lead to efficient cold rain processes with PWAT values near 0.75in. Temperatures Thursday morning will be in the low to mid 30s across the region with atmospheric profiles almost entirely below freezing leading to the possibility of some snow flakes on the ground. Accumulations and impacts are not expected. Rain will continue to fall until around 09Z Friday as the low moves off to the east and upper level winds turn more westerly. WPC clusters are in good agreement that much of the region will receive over 0.5 inches of rain Thursday. NBM gives most of the region a 30-50% chance of getting over 1in of rain with the highest totals being in areas favorable for upslope with a north wind. During this time snow levels will generally be around 6,000ft. The Beartooth and Bighorn mountains have a 20-40% chance of getting over 1ft of snow with the Crazies having a 50-80% chance. There is more uncertainty in the Sunday system as the clusters disagree as to how the pattern will look. About 50% of models are showing a weaker wave with precipitation amounts around 0.25 inches or less and 50% of models showing a stronger wave and precipitation values 0.3 inches or more. Snow levels will be closer to 7,000ft this round with the mountains having a 20-40% chance for 6 inches of snow. Temperatures will be cool Thursday with upper troughing keeping temperatures in the 40s and 50s. Friday and Saturday, shortwave ridging takes over raising temperatures into the 60s and low 70s. Sunday will see upper troughing return cooling temperatures back into the 60s. Monday and Tuesday see the return of upper ridging and downsloped flow bringing temperatures into the 70s to near 80 for some by Tuesday. Torgerson && .AVIATION... Isolated to scattered showers with a few thunderstorms will occur over the area through early evening. Conditions will be MVFR to IFR in the precipitation. A few showers will linger from KBIL N and E late in the evening. Areas of mountain obscuration will decrease through the evening. Expect VFR late tonight into Wednesday morning, before showers and thunderstorms become more numerous Wed. afternoon, mainly W of KBIL. MVFR to IFR is expected in showers and thunderstorms. Mountain obscurations will increase Wed. afternoon. Arthur && .PRELIMINARY POINT TEMP/POPS... Tdy Wed Thu Fri Sat Sun Mon ------------------------------------------------------- BIL 064 043/065 042/049 035/065 043/070 045/061 044/072 3/R 32/R 8+/T 42/R 14/T 66/T 32/R LVM 061 039/061 038/047 032/062 039/064 039/058 039/070 2/T 27/T 9+/T 33/T 16/T 65/T 21/U HDN 064 040/069 041/052 034/066 041/072 044/064 043/072 3/T 21/B 6+/T 62/R 12/T 66/T 32/R MLS 064 041/069 043/053 036/062 042/071 047/065 045/071 2/T 21/B 39/T 62/R 11/B 45/T 42/R 4BQ 062 040/070 044/057 035/062 040/071 047/065 044/069 3/R 21/U 18/T 72/R 11/B 35/T 42/R BHK 063 038/070 040/058 033/060 038/071 043/064 042/068 1/B 21/U 28/R 72/R 11/B 35/T 33/R SHR 058 035/066 038/053 031/062 037/070 041/061 041/069 4/T 21/B 49/T 61/U 11/B 45/T 42/T && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...Winter Storm Watch remains in effect from Wednesday evening through Thursday evening FOR ZONES 67-68. WY...None. && $$ weather.gov/billings