textproduct: Great Falls

KEY MESSAGES

- Thunderstorms across central MT this afternoon and evening may produce locally heavy rainfall, damaging winds and hail.

- Moisture circulating across the Northern Rockies and MT will maintain daily chances for showers and thunderstorms through the upcoming weekend.

DISCUSSION

The Northern Rockies and MT remain on the NW periphery of an expansive mid-upper level ridge centered on the N-central CONUS. A plume of subtropical sourced mid-upper level moisture circulating around the back side of the ridge will continue to deepen today with lower level easterly flow bringing dewpoints in the 50s to around 60 to central/north-central MT overnight. An embedded mid- level shortwave and upper level jet disturbance lifting out of northern CA will help to trigger and organize thunderstorm development across SW MT this afternoon with stronger cells tracking N/NE through central MT and eastern portions of n-central MT this evening. The presence of deep moisture and moderate shear will support some strong to severe thunderstorms with strong winds and hail possible in addition to localized heavy rainfall as storms peak in intensity early this evening.

The flow of anomalous moisture across the area looks to remain in place through the upcoming weekend, maintaining a daily chance for showers and thunderstorms. Cloud-cover on Wednesday will result in temperatures closer to seasonal averages and may inhibit instability and result in a lower coverage of showers/storms. Differences in the timing of embedded disturbances and the extent cloud-cover and instability leads to lower confidence in specific details beyond Wednesday. Hoenisch

AVIATION

14/12Z TAF Period

A few light showers continue to track northeastward early this morning from near KGTF to KHVR. Otherwise mainly mid to higher level clouds stream across the area with VFR conditions through early this afternoon. Showers and thunderstorms develop across southwest MT this afternoon and track northeast across central MT and portions of north-central MT through this evening. Strongest storms are likely across central MT in the vicinity of KHLN-KGTF- KLWT, which may bring brief MVFR along with very heavy rain and isolated strong winds and hail. Hoenisch

HYDROLOGY

A Flash Flood Watch remains in place for much of central MT and adjoining areas for this afternoon and evening. High-resolution model ensembles are in fairly good agreement focusing stronger convection and potential for intense rainfall rates along an axis from southern Lewis and Clark County east across the Big/Little Belts, Judith Basin and Fergus counties where there is 50-80% probability of 1hr rainfall rates exceeding .50" and 30-50% probability for localized hourly rates exceeding 1". This puts the Horse Gulch burn scar at risk for flash flooding as well as other areas that may see these types of intense rainfall rates. Storms are expected to have reasonably quick motion, which may help to keep intense rainfall rates relatively brief but still impactful. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 90 60 82 59 / 30 80 40 30 CTB 80 57 79 57 / 20 50 50 20 HLN 91 63 86 63 / 30 60 40 50 BZN 94 59 86 57 / 20 40 40 70 WYS 94 53 85 50 / 10 10 40 40 DLN 90 57 86 55 / 30 20 40 40 HVR 93 61 83 58 / 20 70 40 40 LWT 92 56 79 54 / 20 70 40 50

TFX WATCHES/WARNINGS/ADVISORIES

Flood Watch from 3 PM MDT this afternoon through this evening for Bears Paw Mountains and Southern Blaine-Big Belt, Bridger and Castle Mountains-Canyon Ferry Area-Cascade County below 5000ft-Elkhorn and Boulder Mountains-Fergus County below 4500ft- Gallatin Valley-Gallatin and Madison County Mountains and Centennial Mountains-Gates of the Mountains-Helena Valley-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains- Meagher County Valleys-Missouri Headwaters-Snowy and Judith Mountains-Southern High Plains-Southern Rocky Mountain Front- Upper Blackfoot and MacDonald Pass-Western and Central Chouteau County.