textproduct: Great Falls

KEY MESSAGES

- Daily chances for afternoon and evening showers and thunderstorms through at least Saturday. - Some strong to severe thunderstorms are possible Thursday with locally gusty winds, hail and intense rainfall.

- Seasonable temperatures today warm back to afternoon temperatures in the 90s by early this weekend.

DISCUSSION

A broad mid-upper level ridge remains in place over much of the US. The ridge center expands/shifts westward some by the weekend as as and upper level trough in the eastern Pacific lifts northward along its periphery into BC. A south to southwesterly mid-level flow around the ridge maintains a stream of anomalous atmospheric moisture from the SW US across the Northern Rockies into the upcoming weekend with some indications of the deeper moisture being shunted east by Sun/Mon as an upper level system moving through western Canada temporarily flattens the northern periphery of the ridge.

Today will be the coolest (but still seasonably warm) of recent and upcoming days with considerable cloud-cover streaming across the region and even some patchy fog early this morning across mainly north-central MT. Convection will be somewhat inhibited today by the more extensive cloud-cover and lack of any larger scale forcing, but a few widely scattered showers and thunderstorms may still develop from terrain heating this afternoon. The upper level trough lifting toward BC tomorrow will provide some larger scale lift for a more widespread coverage of showers and thunderstorms Thursday afternoon/evening. The increased flow aloft will provide enough shear to support some strong to severe thunderstorms late Thursday with isolated strong winds and hail, while the deep moisture still in place will bring a risk locally intense rainfall with some some storms. At this point models are not focusing on any particular area for heaviest rainfall but coverage of thunderstorms is likely to be greatest across central and southwest MT vs areas to the north.

A daily risk for showers and thunderstorms continues through at least Saturday with lower confidence in the coverage or intensity of storms with less forcing available. Temperatures also warm back up as the ridge nudges westward by the end of the week with widespread maximum temperatures in the 90s likely again by Friday and Saturday. Hoenisch

AVIATION

15/06Z TAF Period

Chances of showers and thunderstorms will exit over the next few hours, though could threaten KHVR and KLWT until 0700-0800 UTC. Low MVFR, possibly IFR, ceilings are expected to develop overnight tonight at KGTF and KLWT. Confidence is a bit lower at KHVR, but bases of 1-2 kft AGL are more likely than not Wednesday morning. These ceilings are expected to gradually lift and then scatter through the morning. Showers and (weaker) thunderstorms are forecast to develop late morning into the afternoon. Brief downpours and gusty winds are the main threats. Dry weather is then forecast by Wednesday evening across the area along with continued light/variable winds.

PRELIMINARY POINT TEMPS/POPS

GTF 83 59 88 60 / 30 10 20 30 CTB 80 57 84 59 / 30 30 20 20 HLN 86 62 90 63 / 40 20 30 50 BZN 86 57 90 59 / 70 30 20 20 WYS 83 49 87 50 / 40 40 30 20 DLN 85 55 89 57 / 50 20 20 20 HVR 82 59 89 61 / 50 20 0 20 LWT 77 54 84 56 / 60 30 30 40

TFX WATCHES/WARNINGS/ADVISORIES

None.