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KEY MESSAGES

- A few scattered strong to severe thunderstorms are part of the story this evening. Another chance for showers and storms is expected tomorrow evening, and then another in the north is possible on Wednesday.

- Temperatures look to warm up to near to above normal by the middle of the week as highs push back into the mid and upper 80s.

DISCUSSION

WEATHER PATTERN OVERVIEW: There are some scattered showers moving across the north currently. The models have some disagreement about storm location and intensity, but the main possibilities are these. An isolated strong to severe storm may occur with the ongoing activity in a few hours from now, a strong storm may start in eastern Alberta and move into the area by late afternoon, showers in the north will slowly move south and remain below severe limits, or the boundary moving southward and the higher terrain will work together to initiate a strong storm across the south. The best chance is from 3pm until 10pm. CAPE/Shear profiles in the presence of steep low level lapse rates and wide afternoon dew point depressions paint a scenario depicting isolated severe storms with wind gusts to 60 mph. This is shown well in the HREF ensemble guidance and high resolution model solutions.

The next shortwave trough will track through the region on Tuesday evening into Wednesday for additional opportunities for convection. Ensembles then show height rises over NE Montana as the U.S. Western CONUS upper level ridge amplifies and becomes more pronounced. This should push daytime high temperatures for the second half of the week back toward near or above normal.

FORECAST CONFIDENCE & DEVIATIONS: The main deviation was to PoPs to fill in the splotchy gaps in the NBM through tomorrow evening.

There is moderate confidence in storm location and strength through tomorrow evening.

There is low to moderate confidence in showers and storms occurring in the northern one third of the area on Wednesday afternoon.

There is high confidence in mainly dry weather for Thursday and Friday.

There is low confidence in the late week ridge on when it will break down.

AVIATION

LAST UPDATE: Monday August 17 at 1830Z.

FLIGHT CAT RANGE: VFR, MVFR in thunderstorms.

DISCUSSION: A shortwave trough will provide the necessary support for scattered showers and thunderstorms today between 21Z and 04Z. A few storms may be severe with wind being the main concern. There is low to moderate confidence of scattered showers at times overnight, and then again after 21Z Tuesday to bring slight reductions in visibility (remaining above 5 miles).

WINDS: Northwest at 6 to 12 knots becoming light and variable after 00Z. Look for gusty and shifting winds near storms. A few storms may produce severe wind gusts to 60 mph.

GGW WATCHES/WARNINGS/ADVISORIES

None.