772 FXUS65 KTFX 231650 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1050 AM MDT Thu May 23 2019 .SYNOPSIS... After a mostly dry and sunny day today for most of the region, a series of disturbances will bring more unsettled weather with slightly cooler than normal temperatures through much of the holiday weekend. The first one will spread scattered showers northeast over the part of the region along and east of a Dillon to Havre line this afternoon into tonight, which will linger into Friday. Disturbances will then move south through the area Friday through Sunday, bringing a good chance of showers and thunderstorms each day, with the strongest thunderstorms likely occurring on Saturday. Weak high pressure may bring drier conditions for Monday. && .Morning Update... Large scale troughing pattern remains in place across the western third of the CONUS this morning, with closed mid- and upper level lows (currently as of 10:30am MDT) spinning over the Great Basin. The aforementioned disturbance will quickly lift northeast into North Central Wyoming this evening and then into East Central Montana by Friday morning. The progression of this disturbance will continue to promote moist and unstable low to upper level easterly flow across the Northern Rockies, which combined with increasing synoptic ascent from south to north across Southwest and Central Montana should spark off showers and even a few isolated thunderstorms through tonight (with the best chance for thunderstorms coming this afternoon along and south of the I-90 corridor). Further to the north across North Central Montana, sunny skies so far this morning have allowed temperatures to rise into the mid-50s to low 60s already, which is within 5 degrees of todays convective temperatures. With continued diurnal warming and increasing synoptic ascent (albeit weaker than across Southwest and Central Montana), expect a fairly wide areal coverage of cumulus clouds to develop near the noon hour today across North Central Montana, with increasing cloud cover from south to north as the disturbance lifts northeast throughout the remainder of the day. Enough lift/forcing is expected in conjuction with mid-level moisture for a few showers/sprinkles this afternoon/evening over North Central Montana, with the best chance for showers existing along and east of a Great Falls to Havre line. With respect to the morning update, tweaked high temperatures and PoPs a little this morning, but no major changes were made to the on-going forecast. - Moldan && .AVIATION... Updated 530 AM MDT Thu May 23 2019 (12Z TAFs) VFR conditions are generally expected over the forecast area for at least the next 24 hours, with a few possible exceptions noted below. North Central and Central Montana will remain mostly clear through at least 18Z. However, a disturbance will spread the mid clouds and scattered showers over Southwest Montana northeast over the parts of Central and North Central Montana mainly along and east of a KDLN-KLWT line after 18Z, but more so after 00Z, when occasional MVFR conditions will be possible with showers. Mid level easterly winds will cause low level wind shear over Southwest Montana until they mix down to the surface across the entire forecast area after 16Z. Coulston && .PREV DISCUSSION... /ISSUED 530 AM MDT Thu May 23 2019/ Today through Saturday Night... The first part of the Memorial Day holiday weekend will gradually become quite unsettled with slightly cooler than normal temperatures through this period. A disturbance will eject from the low pressure trough over the western United States and move from the Great Basin today into Eastern Montana tonight into Friday. This will spread cloudiness and scattered showers northeast over the area, mainly along and east of a Dillon to Havre line, for this afternoon through the day on Friday. A few thunderstorms will also be possible this afternoon and early evening, but mainly over far Southwest Montana. The cloudy skies will keep the southwest about 10 to 15 degrees below normal, but the clearer northern plains will likely warm to near normal again today. Another disturbance will move south out of southwest Canada and into the Pacific Northwest on Friday on the back side of the low pressure trough, which will spread scattered showers over the remainder of the forecast area. Weak instability with warming temperatures should also help generate a few thunderstorms there. A low pressure area will then move south along the Pacific coast on Saturday and merge with the Pacific Northwest disturbance, putting the forecast area under an unstable and diffluent southerly flow aloft with a good tap into Pacific moisture. This flow will also help move a warm front north into the area. The instability, lift, and moisture from the flow and the focusing mechanism of the front will bring a very good chance for showers and thunderstorms to the entire area Saturday into Saturday night. Looks like heavy rain and small hail will be the main threats. Coulston Sunday through Thursday... Unsettled conditions should continue into Sunday, but there may be a break in the weather for Memorial Day itself. The low pressure area will dig south into the southwestern United States on Sunday. This will help drag a disturbance and associated cold front south out of Canada over the forecast area, bringing another good chance of showers and thunderstorms, as well as temperatures of around 10 degrees below normal. The latest forecast model runs now move this low pressure area more so to the east over the Four-Corners region on Monday, rather than previously moving it northeast into the central Great Plains. This will bring a better chance that weak high pressure ridging will move into Montana from the northwest, so have decreased the chance for additional showers and thunderstorms, as temperatures remain up to 10 degrees below normal. There is still some uncertainty as to whether the day will be completely dry, so have kept at least some mention of precipitation in the forecast for now. A drier northwesterly flow aloft for Tuesday through Thursday will allow temperatures to warm back closer to normal, with the main chance for additional showers occurring during the afternoon and early evening due to weak instability caused by daytime heating. Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 64 40 63 42 / 20 20 20 20 CTB 67 39 64 42 / 10 20 20 20 HLN 61 41 64 42 / 30 20 30 30 BZN 56 38 62 38 / 20 50 30 40 WEY 48 31 51 32 / 60 50 70 60 DLN 55 35 59 38 / 30 30 60 60 HVR 70 43 66 43 / 10 20 10 0 LWT 58 39 57 38 / 20 40 40 10 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls