368 FXUS65 KTFX 130451 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1050 PM MDT Mon Jun 12 2017 Updated Aviation Discussion .SYNOPSIS... An upper level disturbance will move northward into the region tonight and reside over Central MT on Tuesday. As a result...showers and thunderstorms this evening will become a more widespread rainfall overnight and on Tuesday morning. The rain will gradually diminish from west to east on Wednesday morning. && .DISCUSSION... Tonight through Tuesday night...The main upper level low is currently over Idaho this afternoon and is expected to slowly move northeastward tonight through Tuesday. Showers/thunderstorms are developing in the Southwest. Some storms could be near/or severe in portions of Southwest MT this evening...but it looks too isolated to have a watch at this time. The rain shifts northward overnight...overspreading much of North Central MT. The main concern is the WRF model brings in the dry slot to areas along and east of Great Falls during the morning hours on Tue...allowing for several dry hours. The rain does wrap back around late Tue afternoon as the upper level low starts to pull away. Thus I leaned more towards this solution. Precip amounts are adjusted down a touch...but still widespread 1 to 2 inches...with isolated 3 inch amounts in the mountains possible. Brusda Wednesday through Monday...Scattered showers with a few thunderstorms, gusty westerly winds, and temperatures slightly cooler than normal will linger over the plains of North Central Montana on Wednesday in the wake of the exiting upper low. Montana will then be under the influence of a moderate westerly flow aloft for the remainder of the period, which will keep temperatures near to slightly above normal with occasionally gusty westerly surface winds. Generally weak disturbances will pass over the forecast area, mainly bringing scattered showers to the mountains. However, a slightly stronger disturbance will bring a good chance of showers and thunderstorms to the area Friday afternoon through Saturday evening. There is some discrepancy regarding precipitation on Monday, as the GFS model has at least scattered coverage, while the ECMWF keeps things dry. A blend of models leans toward a mention of precipitation, so will go with that for now and analyze later model runs for possible adjustments. Regardless, the models agree to have temperatures warm to around 5 degrees above normal Sunday into Monday. Overall, though, no significant weather systems are expected through the period with only minor temperature variation. Coulston && .AVIATION... Updated 0500Z. Weakening thunderstorms will continue to push northward across north central MT late this evening while an area of widespread rain continues across much of central MT, pivoting around and upper level low tracking from SE ID into S Central MT by Tuesday morning. Widespread rain and MVFR/IFR conditions will persist through the night across much of the region with some drier air working into eastern areas Tuesday morning. As the low continues NE across eastern MT on Tuesday, rain and additional MVFR/IFR conditions will again spread SE across much of central and SW MT Tuesday afternoon. Hoenisch && .HYDROLOGY... A flood watch continues for Southwest MT for this evening through Tuesday night for the potential of flash flooding tonight...then areal flooding Tue/Tue night. The main rivers of concern in Southwest MT are the Big Hole River near Melrose with this river rising to near/above flood stage by Wednesday...and the Jefferson River near Three Forks rising to near/above flood stage by Thursday. Over Central MT...I delayed the flood watch until Midnight...but the potential for flooding is still possible Tue/Tue night. The Dearborn River is expected to rise near flood stage by Wednesday. There is a chance for some flooding problems on small streams and creeks later tonight through Wednesday morning across all of Central and Southwest MT...depending on where the heavy rain develops. Brusda && .PRELIMINARY POINT TEMPS/POPS... GTF 50 59 48 67 / 80 90 90 20 CTB 52 58 47 65 / 50 90 80 20 HLN 49 55 45 70 / 90 90 80 10 BZN 43 55 40 68 / 70 80 80 10 WEY 34 47 33 58 / 50 90 60 10 DLN 41 55 38 65 / 100 100 40 0 HVR 55 69 50 69 / 50 50 70 60 LWT 44 61 45 64 / 80 60 70 40 && .TFX WATCHES/WARNINGS/ADVISORIES... Flood Watch through late Tuesday night Beaverhead...Gallatin... Madison. Flood Watch from midnight MDT tonight through late Tuesday night Broadwater...Cascade...Central and Southern Lewis and Clark... Chouteau...Eastern Teton...Fergus...Jefferson...Judith Basin... Meagher...Southern Rocky Mountain Front. && $$ weather.gov/greatfalls