Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/11/20

Area Forecast Discussion
National Weather Service Great Falls MT
838 PM MDT Mon Aug 10 2020 .UPDATE... No update is needed this evening. && .SYNOPSIS... High temperatures will warm above climatological norms by Tuesday across the entire Northern Rockies, with dry and breezy conditions expected to accompany these warming temperatures. Critical Fire Weather Conditions are expected across the entire forecast region due to these breezy and dry conditions from Tuesday afternoon through Wednesday evening. && .AVIATION... 455 PM MDT Mon Aug 10 2020 (11/00Z TAF Period) VFR conditions continue throughout this TAF period. A narrow corridor of showers and isolated thunderstorms will be encountered through mid-evening between KEKS and KWYS in association with a weak surface boundary, but neither terminal should be impacted except for perhaps some light southerly outflow winds and KEKS. Evening winds gusting to 30 knots along The Rocky Mountain Front and up to 22 knots will diminish through 02z-03z along the adjacent plains and parts of central and southwest Montana, which will cause aviation impacts to light aircraft flying near mountains and in passes. Refer to for more detailed regional aviation weather and hazard information. NOTE: Amendments not scheduled for Ennis (KEKS) due to ongoing runway closure. && .FIRE WEATHER... Red Flag Warnings have been issued for all fire weather zones across portions of Southwest, Central, and North Central Montana from Tuesday afternoon through Wednesday evening. The Fire Weather Watch has therefore been canceled for these zones. Confidence has increased that periods of Critical Fire Weather conditions (i.e. breezy winds and low relative humidity values) will be observed from Tuesday afternoon through Wednesday evening across all fire weather zones. This will be especially true during the mid-to-late afternoon through early evening hours on both Tuesday and Wednesday when deep mixing will transport strong mid-level winds down to the surface and the driest conditions will be experienced. Confidence is very high the afternoon relative humidity values will fall below 20 percent across all fire weather zones, with some locations over the plains of Central and North Central Montana potentially nearing 10 percent. While winds over the timeframe are forecast to be near the low end of the Red Flag Warning threshold, recent events (including non-Red Flag Warning days) have shown that observed winds have been over- performing (higher than the forecast). With this in mind, confidence in even these minimum thresholds for Red Flag Warning winds being reached was high enough to upgrade the Fire Weather Watch. While relative humidity values will rise above 20 percent during the overnight hours on Tuesday at all elevations, moisture recovery at the mid-slopes and ridgetops will be poor. This combined with continued breezy winds at these elevations (lower elevations will likely decouple and be less than 15 mph) will continue to lead to critical fire weather conditions. While outside of the Great Falls Fire Weather area of responsibility, isolated thunderstorms across Southwest Montana near the Idaho/Wyoming borders Wednesday afternoon could produce additional gusty/erratic winds, frequent lightning, and very little rainfall. For this reason, have inserted "dry thunderstorm" wording for these areas on Wednesday in collaboration with the Storm Prediction Central and WFO Missoula. - Moldan && .PREV DISCUSSION... /ISSUED 455 PM MDT Mon Aug 10 2020/ Rest of this afternoon through Wednesday...Weak ridging over the Northern Rockies will help to maintain dry (low relative humidity), clear/sunny, and breezy conditions throughout the period. A weak disturbance rippling over the ridge axis may help to spark off an isolated shower or thunderstorm over far Southwest Montana this afternoon and early this evening, with this activity expected to remain south of the I-90 corridor and near the Idaho/Wyoming borders. Temperatures will warm to above normal Tuesday and Tuesday night as the ridging amplifies (save for those cold valleys at night where a decoupled boundary layer and dry conditions as of late will let temperatures cool to below normal), but a deepening low pressure trough over the Pacific Northwest coast will increase the flow aloft and shift it more so out of the southwest. Very dry air with gusty surface winds will increase the threat for critical fire weather conditions from Tuesday afternoon through Wednesday evening (please read the Fire Weather section for more details). The trough will then move from over the Pacific Northwest Wednesday morning to over the Northern Rockies by Wednesday afternoon, all the while a weak cold front pushes through the forecast area on Wednesday dropping temperatures near to slightly below normal. Despite continued dry conditions in the low levels, the mid to upper level airmass will likely become unstable enough to support an isolated chance for thunderstorms across much of the area by Wednesday afternoon and evening. - Moldan/Coulston Thursday through next Monday... The low pressure trough will weaken somewhat as it moves over Montana Thursday into Friday, leaving the forecast area under a cyclonic westerly flow aloft. This will keep temperatures slightly below normal with a chance for showers and thunderstorms and continued breezy westerly winds. High pressure ridging will then build back into the area, which will keep the area dry as temperatures warm back above normal by Monday. - Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 52 90 53 84 / 0 0 0 0 CTB 49 85 48 77 / 0 0 0 0 HLN 53 90 53 87 / 0 0 0 10 BZN 46 89 48 88 / 0 0 0 10 WYS 38 81 39 80 / 10 0 10 30 DLN 48 85 49 83 / 10 0 0 10 HVR 53 92 53 87 / 0 0 10 0 LWT 51 87 52 87 / 0 10 10 10 && .TFX WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from noon Tuesday to 9 PM MDT Wednesday Central and Eastern Lewis and Clark National Forest Areas...Chouteau and Fergus Counties...Deerlodge/Western Beaverhead National Forest... Eastern Beaverhead National Forest...Eastern Glacier/Toole/Central/Eastern Pondera/Liberty...Helena and Townsend Ranger Districts of the Helena National Forest...Hill and Blaine Counties...Lewis and Clark National Forest Rocky Mountain District-Rocky Mountain Front...Lincoln Ranger District of the Helena National Forest. Fire Weather Watch from Wednesday afternoon through Thursday evening Gallatin National Forest. && $$