Area Forecast Discussion

KEY MESSAGES

- Scattered thunderstorms mainly southern mountains this evening, then most of area Wednesday & Thursday. Storms could produce very heavy rainfall and gusty winds.

- Thunderstorms have the potential to create very heavy rainfall over burn scars Wednesday evening. Plan ahead if recreating near any burn scars. - This weekend into early next week is looking hotter & drier; a return of triple digit heat expected (starting Friday). Fire danger may increase.

DISCUSSION

Through next Tuesday...

Band of very elevated warm frontal light showers continues to clip Fallon County, but this activity should exit our area soon. Mesoanalysis shows pwats have risen to 1-1.2" and this will lead to convection developing over the southern mountains by around 21z. Easterly winds and "cooler" temps will keep instability capped across lower elevations, and without any real forcing expect today's activity to remain confined to the high terrain. Tonight, with a southeasterly LLJ, most CAMs show some weak storms over far southeast MT, which may linger to sunrise tomorrow. Today's storms will be capable of producing heavy rain and erratic gusts, but should remain sub-severe w/ bulk shear of 20kts or less.

Wednesday looks like the moistest day of the week w/ pwats closer to 1.5". Also, there is a distinct wave that is expected to emerge from the northern great basin and track thru the region late tomorrow through tomorrow night. Again, severe wx is not expected per weak shear, but very heavy rain and erratic winds (wet microbursts possible) are risks. Storm coverage should be greatest near mountains & foothills, and storm motion will be slow, so have issued a Flood Watch for potential flash flooding across the SW/S (along and south of a line from Livingston to Columbus to Lodge Grass). Burn scars such as Robertson Draw, East Side and Elk will be particularly susceptible to flash flooding w/ debris flows. Timing of the Watch is from 1pm to 2am.

Wet thunderstorm activity will continue Thursday but the air mass will begin to turn drier behind the exiting shortwave. Still a risk of heavy rain but not to the extent of Wednesday. WPC has southern portions of the region highlighted for a low risk of excessive rain each of the next two days. Stay alert if you have outdoor/recreation plans. Temps tomorrow and Thursday will remain seasonable with highs mostly mid 80s to lower 90s.

The air mass will turn notably drier by Friday as the exiting wave scours out the deep monsoonal moisture in place. That said, pwats will still be near to slightly above normal, so there remains a slight (10-20%) chance of higher based t-storms each day through the first part of next week. However, the main story is the strong ridge expected to bring hotter & drier conditions starting Friday. Mixed west winds look to be breezy on Friday, with deep mixing expected to push temps back to triple digits. Along with humidities in the teens, would expect fire concerns to be on the increase again after about of week of elevated RHs. Triple digit highs are likely again Saturday, though with less wind. The Sunday/Monday time period may see a brief flattening of the ridge and possible weak cold front, thus something to monitor with regard to fire weather/wind. Overall, the longwave pattern thru next week favors above normal heights and temperatures.

For those following the July 25th drama, the odd (and meaningless) fact that the Billings airport has never reached 100F on this date going back to 1934, confidence is growing that the site will finally reach triple digits. Current forecast for Billings is 103F, which would easily break the old record of 98F set on four occasions. The wildcard is smoke and high cloud cover, which could hold temps back slightly. Stay tuned.

JKL

AVIATION

Showers and thunderstorms will increase this evening over the southern mountains and foothills, moving from west to east into the overnight hours. The highest chance (30-50%) is over the mountains and along the MT/WY border. Localized visibility reductions due pockets of heavy rain are possible under any showers or storms. Wildfire smoke from the Pacific NW may produce slant range visibility reductions at times, but surface visibility reductions are not expected. Archer/STP

PRELIMINARY POINT TEMP/POPS

Wed Thu Fri Sat Sun Mon Tue ----------------------------------------------------------- BIL 065/089 067/092 066/102 068/102 069/100 067/096 068/097 21/U 44/T 11/G 21/G 21/U 21/U 20/U LVM 057/085 057/091 058/098 059/098 059/096 057/095 058/095 14/T 64/T 10/U 11/N 22/T 22/T 22/T HDN 063/092 064/092 062/102 064/104 066/102 066/099 067/099 21/U 44/T 00/G 21/G 20/G 11/U 21/U MLS 064/091 066/093 066/104 069/105 072/102 069/100 070/100 20/U 11/B 00/G 10/G 21/G 11/U 21/U 4BQ 064/088 065/089 065/101 068/103 070/101 070/099 070/099 40/U 54/T 10/G 11/G 21/G 11/U 32/T BHK 059/086 060/091 062/102 066/105 068/102 065/099 066/099 10/U 11/B 10/G 11/G 11/G 11/U 21/U SHR 060/087 061/086 059/100 063/100 065/099 064/095 064/096 34/T 67/T 10/U 01/U 11/U 12/T 22/T

BYZ WATCHES / WARNINGS / ADVISORIES

MT...Flood Watch in effect from Wednesday afternoon through late Wednesday night FOR ZONES 56-64>67-138-139-169>171. WY...Flood Watch in effect from Wednesday afternoon through late Wednesday night FOR ZONES 198-199.