406 FXUS65 KTFX 101115 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 515 AM MDT Mon Jun 10 2019 ...Aviation Section Updated... .SYNOPSIS... A weak disturbance will bring isolated to scattered showers and thunderstorms to North Central Montana during the daylight hours today, with the best coverage of these showers and storms being focused over the central mountains. High temperatures will remain below to near normal across the region, with breezy west to northwest winds developing during the afternoon hours. Another shot of showers and storms is possible Tuesday morning and early afternoon across North Central Montana. && .DISCUSSION... Today through Tuesday night...no major forecast concerns or impacts expected, outside of some lightning with thunderstorm activity. Subtle H500 shortwave was cresting the ridge axis over West Central British Columbia early this morning, and will dive southeast within a northwest flow regime and across the Northern Rockies by this afternoon before sliding further southeast into the Northern High Plains by this evening. Accompanying the shortwave this afternoon/evening as it crosses the Northern Rockies will be a H500 jet maximum of 40-60kts, with its favorable left exit region (which is ideal for synoptic scale divergence and subsequent ascent) crossing North Central Montana. This increasing synoptic scale ascent combined with a relatively moist (PWATs near normal at around 0.5") northwest flow regime and some limited diurnal heating (due to increasing mid- to upper clouds), will help to spark off isolated to scattered showers and thunderstorms over the plains of North Central Montana late this morning and through the evening hours tonight. Over the higher terrain in North Central Montana, especially over the Central Montana mountains (i.e. Big and Little Belt, Snowy, Judith, Moccasin, and Highwood), numerous showers and storms are expected this afternoon thanks to enhanced lifting from orographic effects. Severe thunderstorms are not anticipated today (despite impressive 0-6km bulk shear of 40-60kts) due to a lack of instability, which will be very marginal at best. Areal coverage and intensity of the showers/storms will slowly dissipate through the evening hours tonight, with a brief break expected during the morning hours on Tuesday. H500 ridge will continue to build over the Pacific Coasts of the CONUS/Canada during the day today, and gradually slide east towards the Northern Rockies tonight and into the day on Tuesday. As the ridge slides east on Tuesday, large scale subsidence will begin to overspread the region, especially during the late afternoon hours on Tuesday. Despite the advancement of the upper level ridge towards the region, lingering northwest flow aloft (which will still be relatively moist) and diurnal heating should once again spark off isolated to scattered showers (possibly a thunderstorm or two) over North Central Montana during the late morning and early afternoon hours. This shower activity will then decrease in coverage during the late afternoon hours as the aforementioned large scale subsidence overspreads the region from west to east. Both high and low temperatures throughout the timeframe will generally be below to near normal, with breezy west to northwest winds during the afternoon/early evening hours (especially across North Central Montana). - Moldan Wednesday through next Monday... An upper level ridge with axis along the west coast migrates inland and flattens Wednesday and Thursday. This is followed by a series of generally weak shortwave disturbances moving through an open westerly flow aloft across the western US late this week into early next week. Daytime temperatures will peak on Thursday around 10-15 degrees above seasonal averages with most lower elevation locations reaching the 80s. We will see the chances for precipitation increase beginning Thursday and continuing through the weekend, and at this point it looks generally convective and diurnally driven (afternoon and evening showers and thunderstorms). The specific timing of these disturbances is still unknown and will dictate when periods of more widespread showers and thunderstorms occur late this week into the weekend. While its still very early to diagnose any storm threats late this week into the weekend, flow aloft looks rather weak at times, suggesting the potential for locally heavy rain, which will continue to be monitored. Hoenisch && .AVIATION... Updated 515 AM MDT Mon Jun 10 2019 (12Z Mon TAFs) VFR conditions are expected throughout the duration of the 1012/1112 TAF period, but ceilings are and will continue to lower as mid-level moisture associated with an upper level disturbance dives southeast across the region today. As the upper level disturbance crosses the region, expect isolated to scattered showers/storms to develop over the plains of North Central Montana by the late morning/early afternoon hours, with numerous showers/storms being focused over the higher terrain (especially over the mountains of Central Montana. While VFR conditions are expected throughout the TAF period, any shower/storm could produce brief periods of MVFR. In addition to the threats for showers and storms, expect diurnal mixing to bring another period of breezy west to northwest winds to most terminals from the late morning and into the early evening hours today. - Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 70 48 71 48 / 20 20 10 0 CTB 68 45 71 45 / 20 20 10 0 HLN 71 48 75 48 / 20 20 10 0 BZN 68 44 72 43 / 20 20 10 0 WEY 63 35 66 35 / 20 20 10 0 DLN 71 43 73 45 / 10 10 0 0 HVR 74 46 73 45 / 20 20 10 0 LWT 65 45 66 43 / 20 30 20 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls