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 weather.gov/zlc 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.
&&
$$
http://www.weather.gov/greatfalls