Area Forecast Discussion

KEY MESSAGES

- Hot and dry into Wednesday. Elevated fire weather concerns. Expect rises on streams and rivers due to mountain snowmelt.

- Impactful weather system likely late Wednesday into Friday. Impacts include strong winds, precipitation (rain and snow), and cooler temperatures.

- Late week weather system could impact travel and recreation. Hazardous cool and wet conditions could also impact young livestock.

DISCUSSION

Today through Monday...

Elevated fire concerns continue into Wednesday as warm and mostly dry conditions continue under upper level ridging. Highs will be in the 70s to upper 80s and minimum relative humidity in the teens for many locations today and Wednesday. Winds today will be breezy at times west of Billings, with gusts out of the south to southwest of 25 to 35 mph. Wednesday will see stronger, more widespread gusts ahead of a system moving in late Wednesday/early Thursday, with gusts of 35 to 50 mph from Billings west and 25 to 35 mph across the rest of the region. One limiting factor for grass fire concerns is that green up is well underway for some locations. Regardless, take care not to cause a spark! Additionally, with these above normal temperatures, mountain snowmelt will increase and lead to rises on streams and rivers, although no flooding is expected.

Before the next system, a subtle wave rounding the ridge will bring some elevated moisture (PWATs 150-180% of normal over the west) into the area late this afternoon and evening. With this, an isolated shower or two is possible (10 to 20 percent chance), particularly over the mountains, but very dry air near the surface will limit the amount of precipitation that makes it to the ground.

Late Wednesday through Friday, a spring storm system will move through the region, dropping highs into the 40s by Friday. Models continue to disagree on the exact track and speed of this system, but confidence is high in a change to cooler and wetter weather. The first option for how this system develops is a slower track across the region before the upper low stalls over North Dakota, with energy wrapping around and continuing precip over the central and eastern portions of the region. The result of this option would be the highest precip totals falling near the Dakota border and a longer period of strong winds on Thursday from Billings east. A second option is a faster track that lifts the upper low northeast into Canada, which would bring more precip to western portions of the region (and much less to eastern portions) and favor the mountains and foothills as energy wraps around Thursday into Friday. Winds would still be strong with the second option, but during a shorter window. One area of concern is eastern Montana, where dynamic cooling from the low pressure system may allow rain to switch over to snow more quickly, and with the stronger winds, may result in blowing snow impacts.

Considering the above options, there is currently a 30-60% chance for a gust greater than 60 mph Thursday, highest over far eastern Montana and north-central Wyoming. For precip, there is a a 50-80% chance of at least 0.5" over the mountains, foothills, and higher hills, and a 25-50% chance of the same over the plains. Precip will fall as all snow over the mountains, with a 60-80% chance of at least 8". Over the plains, precip will begin as rain, gradually switching to snow. Given daytime high temps remaining above freezing, little to no accumulating snow is expected, outside of the higher hills and foothills, and will mostly be on grassy surfaces.

Into early next week, conditions look to remain cooler and unsettled, with highs generally in the 40s and 50s. Archer

AVIATION

Wildfire smoke from the East Fire (just south of Red Lodge) is spreading eastward with the prevailing winds. Occasional reductions of slant range visibility are possible near Sheridan as a result. Otherwise, VFR will prevail across the region under strong high pressure aloft. Mixed SW winds will gust 25-35 knots at KLVM Tuesday afternoon.

Isolated high based convection is beginning to show up this evening, developing over the southern mountains and moving north across the western half of the forecast area through 07z. Main impact from this activity will be the potential for erratic stronger wind gusts of 35 to 45kts near any cells. This could impact KBIL/KSHR from 00z-07z this evening. At this time the potential is too low to mention in the TAFs, but will reconsider with subsequent TAF issuance if this activity continues to show in the models. Chambers/JKL

PRELIMINARY POINT TEMP/POPS

Tdy Wed Thu Fri Sat Sun Mon ------------------------------------------------------- BIL 086 053/079 041/049 030/045 027/049 028/050 030/055 0/U 14/W 87/W 34/J 11/B 12/W 22/W LVM 080 047/068 035/045 025/040 020/046 023/048 027/053 0/B 14/W 98/W 66/J 21/B 12/J 22/W HDN 086 050/083 039/049 029/046 026/049 025/051 028/056 0/B 14/W 88/W 35/J 22/J 12/W 22/W MLS 085 054/086 038/048 029/042 025/044 025/048 027/052 0/U 12/W 78/W 23/J 11/B 12/W 11/B 4BQ 084 055/084 039/049 029/042 026/046 025/048 029/052 0/U 01/N 58/W 23/J 11/B 12/W 22/W BHK 084 050/086 038/049 026/041 022/041 022/045 025/049 0/U 01/B 38/W 32/J 11/B 12/J 22/J SHR 082 048/078 036/049 024/042 020/046 021/047 026/052 0/B 12/W 68/W 56/J 32/J 23/W 22/W

BYZ WATCHES / WARNINGS / ADVISORIES

MT...None. WY...None.