Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/30/20

Area Forecast Discussion
National Weather Service Great Falls MT
755 PM MDT Sun Mar 29 2020 .UPDATE... With evening upon us, temperatures are cooling and convective clouds are dissipating. Expect some mountain showers to continue tonight. The inherited forecast is handling the meteorological situation well; therefore, no changes will be made to the forecast, at this time. - Fogleman .SYNOPSIS... Mild and breezy conditions continue through Monday, along with scattered rain and mountain snow showers. Temperatures turn colder starting Monday night, then remain well below average through the remainder of the week. Periods of heavy, wet snow Monday night into Tuesday morning could slow travel over mountain passes, and across much of Western and Southwest Montana. Additional periods of snow are likely through early Thursday. && .DISCUSSION... Skies have been mostly clear today as a shortwave ridge aloft moves away through eastern Montana, aside from some mountain cumulus and higher clouds associated with a Chinook arch. Surface temperatures this afternoon have exceeded the convective temperature indicated by the 12Z GTF sounding. Thus, with weak instability, scattered cumulus are beginning to grow across much of the region. SPC and short-term model guidance indicate there is adequate instability to support a few rumbles of thunder through the rest of this afternoon. As well, a combination of deep layer mixing and a moderate surface pressure gradient are producing noticeably breezy west-southwest winds. Most of the remaining shower activity will decline in coverage overnight, yielding another fair and mild day for Monday. However, we should expect increasing clouds, continuing southwest winds, and re-developing rain and mountain snow showers Monday afternoon. A strong Pacific cold front is poised to cross the Continental Divide late Monday evening. This will bring falling temperatures into Tuesday, and of course, falling snow levels as well. The combination of low level convergence along the front, strong height falls, and divergence aloft will support a band of potentially heavy snow spreading along and over the Divide into Southwest Montana early Tuesday morning. Initial precipitation will melt on roads, but as temperatures fall and rain changes to snow, roads are likely to turn icy with additional snow accumulation continuing Tuesday morning. Given potential impacts to travel along I-15 south of Helena and along I-90 in Southwest Montana, Winter Weather Advisories are posted from Monday evening through noon Tuesday. While impacts to travel will be lessened with daytime heating, temperature advection will continue to maintain colder temperatures, so the advisory may need to be extended in time as additional rounds of snow continue. -PN A re-enforcing cold front will advance from Canada Tuesday afternoon and across North Central Montana, reaching Central Montana by Wednesday morning. This cold front will likely bring a period of moderate precipitation, this time to North Central and Central Montana, especially to the mountains. Temperatures behind this re- enforcing cold front will fall quickly Tuesday afternoon and night, generally from the upper 30s/low 40s to teens/20s. Additional winter weather advisories may need to be expanded in time and area to cover ongoing winter weather impacts. Wednesday through next Sunday...well below normal temperatures will be experienced across the region from Wednesday through Thursday, with daytime highs running 10 to 20 degrees below normal. Additional precipitation chances will also be possible over this timeframe, with light snow accumulations over lower elevations and higher amounts in the mountains. Broad upper level troughing looks to hangout over a large portion of the Western CONUS/Canada to end the work week and into the weekend, with a slight moderation in temperatures. - Moldan && .AVIATION... Updated 606 PM MDT Sun Mar 29 2020 (30/00Z TAF Period) Begin this TAF period with VFR conditions at all airfields. Expect KCTB, KHLN, KBZN and KWYS to fall into the MVFR range, with possible IFR/LIFR conditions at KWYS. Mountain obscurations are forecast. Additionally, aircraft icing will become an impact to aviation. Periods of gusty winds will effect light aircraft especially near mountains and in passes. LLWS conditions are forecast at KCTB. Expect the associated TURBC. - Fogleman && .PRELIMINARY POINT TEMPS/POPS... GTF 31 58 31 46 / 20 20 50 40 CTB 29 51 26 37 / 10 30 20 50 HLN 30 57 29 44 / 30 30 90 60 BZN 29 54 29 43 / 10 10 80 80 WYS 19 40 23 36 / 30 50 80 90 DLN 29 48 30 41 / 20 20 80 80 HVR 34 60 32 45 / 0 10 30 20 LWT 31 54 30 42 / 20 10 40 50 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 6 PM Monday to noon MDT Tuesday above 4500 feet for Central and Southern Lewis and Clark... Northern Rocky Mountain Front...Southern Rocky Mountain Front. Winter Weather Advisory from 9 PM Monday to noon MDT Tuesday Beaverhead...Gallatin...Jefferson...Madison. && $$