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KEY MESSAGES

- Warm temperatures above normal and mostly clear skies into Friday.

- Friday will be monitored for any Fire Wx concerns as a ridge breaks down and cold front moves through.

- Overcast skies, possible precipitation, and low temperatures anticipated this weekend and into Monday. Isolated snow possible at higher elevations.

DISCUSSION

Synoptic Setup: Forecast begins with relatively zonal to NW flow from Montana through the PCNW and across SW Canada. To the S, hot high pressure sits over the desert southwest with a ridge building into the Intermountain West. Farther West a highly amplified trough is working its way into the Gulf of Alaska.

Today through Thursday night: Zonal to NW flow remains relatively intact with temps remaining 5 to 15 degrees above normal with relatively dry conditions. There is a small chance (5-15%) during this time that any fires over the PCNW could begin to pool smoke across Montana for light haze, but current HRRR and RAP Smoke models suggest that it will not make it to eastern MT at all. Meanwhile, the Intermountain West ridge will drift east and the crest will start to bump up against MT zonal/NW flow while the Gulf of Alaska trough behind it will begin slamming up against the PCNW coast.

Friday: Ridge crest will move across eastern Montana raising temps to 10 to 20 degrees above normal with highs into the 70s and 80s. Downslope winds could begin to lower RH a bit more than normal as well here leading to possible fire weather concerns. Currently winds speeds seem just under criteria. This ridge will continue be monitored for breakdown timing and any increase in wind speed. Meanwhile, the PCNW trough will smash into the large ridge and break apart with the southern section digging S into the lower Intermountain west and southern California while the northern part progresses eastward allowing cool Canadian air to fill in behind it on the Plains.

Friday night into Monday: Newly minted SW flow regime will drag a cold front across Montana Friday night and lead to some pacific moisture increasing into the region. By Saturday to Saturday night rains showers will begin to form as highs drop into the 40s and 50s by Sunday or nearly 20 degrees below normal. Expect a strong NW t N wind behind this frontal passage Saturday and Saturday night. Lows are suggesting that snow may be possible overnight Sunday night at higher elevations but totals will be less than an inch if it snows at all. Also, warm ground should melt off any accumulations. Cooler, wetter periods hold through about Monday before beginning to clear out.

Forecasts beyond Sunday come into question as ensemble data moves out of phase with each other. In addition, the southern Prairie ridge to the east appears to become persistent enough to block forward progress of the southern flow which may means the cooler conditions stay a bit longer but dry conditions could return to Montana Monday evening through about mid-week. Expect these periods to change in future updates. So, low confidence.

FORECAST CONFIDENCE & DEVIATIONS:

- No changes from NBM.

- There is moderate to high confidence (50-70%) in frontal timing Friday night/Saturday morning.

- There is high confidence (80-100%) in warmer temperatures through Friday and cooler temps this weekend.

- There is moderate to high confidence (50-80%) in any precipitation occuring between Saturday night and Monday morning.

AVIATION

LAST UPDATED: 0400Z

FLIGHT CAT RANGE: VFR

LLWS: There is a small chance(30-60%) for a couple hours of low level winds shear now through 12Z for KGGW, KOLF and KSDY.

DISCUSSION: SCT/BKN mid-to-high clouds will persist through the cycle.

WINDS: Light and variable through mid morning. NBecoming N late moring thorugh the afternoon. Then transitioning back to variable this evening through tonight.

/GAH

GGW WATCHES/WARNINGS/ADVISORIES

None.