741 FXUS65 KTFX 101147 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 545 AM MDT Mon Apr 10 2017 Updated Aviation Discussion .DISCUSSION... Today through Wednesday...Satellite imagery early this morning shows a compact upper level low over SD/NB with deformation axis extending NW across eastern MT and the next upper level trough from the Pacific moving onto the WA/OR coast. Weak upper level ridge sandwiched between these features drifts east across MT this morning for generally dry conditions through mid-day. Areas of fog that developed overnight across portions of N-central MT will dissipate by late morning. Shortwave currently moving onto the Pacific NW coast moves rapidly inland today, lifting NE across NW MT this afternoon and evening with an associated surface cold front moving east across the forecast area by this evening. Scattered showers are anticipated to develop and move NE across SW and Central MT this afternoon and evening as the airmass destabilizes. Instability is rather weak but some isolated lightning is possible with some of the convective showers this afternoon and evening, though main impact from this activity will likely be a period of gusty winds in conjunction with the frontal passage. Surface low develops in southern AB tonight as the shortwave energy emerges east of the Canadian Rockies and tracks east into SK Tuesday. Breezy west winds will continue through Tuesday with a shift to NW/N winds likely occurring Tuesday night as the surface low moves east across SK and a cooler airmass slides south in its wake from AB into N-central MT. Low level NE/E flow then persists through Wednesday while upper level flow backs from W to SW as the next Pacific trough moves onto the west coast. Expect increasing cloud-cover Wednesday across the region with some showers developing over western and SW portions of the forecast area by Wednesday afternoon. Hoenisch Wednesday night through Monday...The medium range period will feature semi-permanent troughing over the eastern Pacific, with multiple shortwaves cutting through the NRN Rockies / NRN High Plains, aided by an active jet stream. The models are in general agreement through about Saturday, but then begin to diverge. It should be noted that in these active/progressive patterns, the models may generally agree on larger-scale features (ie. troughs, shortwaves), but differ more regarding timing of fronts, placement of precip, etc. With that in mind, it is expected that a Pacific cold front will cross the area sometime Thursday/Thursday evening. The timing of the front will be important in how unstable it can get. For now, still thinking the best chance of seeing any thunderstorms will be eastern sections of central MT (ie. from Stanford to Lewistown) and I limited any mention of thunder to those areas for now. Ahead of the front, much of the area may actually remain capped, limiting any shower/t-storm potential until the front, itself, arrives. Along and just behind the front, a band of showers will likely impact much of the area. A second front is then expected to move through on Friday, potentially bringing a period of stronger winds across central Montana. Given better model agreement this morning, I upped the wind some across central MT Friday/Friday night, although at this time the wind still looks to remain below High Wind Warning criteria. In the wake of that front, the Easter Weekend may start dry and seasonably cool. However, by SUN/MON, the models hint at another spring storm system potentially impacting parts of the area, possibly similar to the system that just moved through the area. Too early to speculate on precip amounts/impacts, but something to watch in the coming days. Martin && .AVIATION... Updated 1145Z Upper level high pressure ridge shifts across the region this morning for mainly clear skies and VFR conditions into early this afternoon with the exception of some patchy fog in the KHVR area early this morning. Pacific weather system and associated cold front moves into western MT this afternoon, sweeping east across N-central and SW MT between 21z and 03z. Winds increase from the S/SW this afternoon ahead of the front and shift to westerly with the frontal passage this afternoon/evening. Scattered showers will accompany the frontal passage, potentially bringing a brief period of MVFR conditions. Gusty winds will accompany and follow the frontal passage this evening. Skies clear quickly behind the front this evening for a return to VFR conditions. Hoenisch && .HYDROLOGY... 24hr precipitation totals yesterday exceeded 1.25 inches at several observation points in Cascade, Judith Basin, and Fergus Counties. A combination of spotter and SNOTEL reports suggest that snow accumulation may have peaked at mid slope elevations. Daytime warming today and over the next few days may contribute to a rapid snowmelt runoff into small creeks across central MT, or at least areas of standing water in fields and ditches. The Judith River and its tributaries, including Big Spring Creek and Beaver Creek near Lewistown as well as tributaries of Belt creek, including Otter Creek near Raynesford, appear to be the most likely candidates for high flows from snowmelt. Nothing reported or observed, but will continue to monitor closely for rises on small streams and creeks in central Montana. && .PRELIMINARY POINT TEMPS/POPS... GTF 50 27 52 30 / 30 20 0 10 CTB 50 30 49 28 / 10 10 10 0 HLN 53 29 54 33 / 40 20 10 20 BZN 52 26 53 33 / 30 30 10 20 WEY 38 18 41 27 / 40 30 10 30 DLN 48 25 51 32 / 30 20 10 30 HVR 57 31 55 29 / 0 20 10 0 LWT 48 23 50 28 / 10 40 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ weather.gov/greatfalls