Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/16/20
Area Forecast Discussion
National Weather Service Great Falls MT
628 PM MDT Mon Jun 15 2020
.SYNOPSIS...
Expect the next couple of days to be cool and wet, as a North
Pacific Low passes through the region. Temperatures will range
about 10 to 15 degrees below average, with widespread rain and
mountain snow forecast. Additionally, there is a chance for
afternoon and evening thunderstorms, especially on Tuesday.
&&
.DISCUSSION...
Rest of the afternoon through Wednesday...primary concern throughout
the period will be rainfall and snowfall amounts across Southwest,
Central, and North Central Montana.
A strong storm will impact the Northern Rockies over the next 48
hours, bringing widespread rain and mountain snow to the CWA. As of
this afternoon (21z Monday), H500 trough was digging into the
Pacific Northwest, with a closed low off of the southwest coast of
British Columbia. This H500 trough and closed low will continue to
dig southeast towards the Central Rockies into the day on Wednesday,
with the H500 closed low crossing Central Idaho/Southwest Montana
during the Tuesday night timeframe. As the main trough/closed low
digs southeast, an embedded shortwave within the southwest/south
flow regime will lift northeast and across the Northern Rockies this
afternoon and through the overnight hours. Expect precipitation
chances to increase and expand in areal coverage from southwest to
northeast through tonight and into the day on Tuesday. Precipitation
amounts with this first wave, which will be primarily in the form
of rain, will generally range from less than 0.25" across North
Central, 0.25" to 0.5" across Central, and 0.5" to 1" over Southwest
Montana. As the upper level low approaches the region Tuesday
afternoon/night, expect snow levels to fall to around 5000-5500 feet
across Southwest and Central Montana, aided by not only the cold air
aloft advecting east but also dynamical cooling. This second wave of
precipitation will bring additional precipitation amounts of 0.25"
to 0.75" to North Central and 0.75" to 1.5" Central/Southwest
Montana from Tuesday night through Wednesday. Snowfall amounts above
5000 feet across Southwest and portions of Central Montana could
approach 8", with amounts potentially exceeding 12" above 7500 feet.
Given the potential impacts to transportation and backcountry
recreation from Tuesday night through Wednesday morning, decided to
issue a Winter Storm Watch given the potential for some areas along
the Continental Divide to potentially approach warning level
impacts. Biggest concern with the accumulating snow will be impacts
to travel on I-15 in Jefferson County, I-90 over Homestake Pass, US
12 over MacDonald Pass, and the remaining high elevation roadways.
In addition to travel, the heavy and wet snow will create hazardous
conditions for backcountry recreation, along with the potential
damage to vegetation with foliage which could cause power outages or
property damage. - Moldan
Thursday and Friday...A trough continues to dominate the area.
Upstream, a ridge axis stretches from the eastern Canadian
Northwest Territories into the Pacific Ocean 30N Latitude and 150W
longitude. The Treasure state is located with the trough axis
overhead, and with the northwesterly upper level flow along the
leading edge of the upstream ridge approaching from the west.
Expect cooler temperatures to continue, with precipitation
lingering, especially along the Hi-Line. Widespread afternoon and
evening thunderstorms are forecast, Thursday and Friday.
Saturday through Monday...Ridging dominates the weekend weather,
and beyond. With perturbations passing through the upper level
flow, and warming temperatures, afternoon and evening
thunderstorms are possible, especially on Saturday. Sunday and
Monday looks to be more dry, under the influence of the subsidence
and drying of high pressure, Sunday and Monday, are forecast to be
warm and dry, with Monday`s afternoon highs ranging in the mid to
upper 80s.
- Fogleman
&&
.AVIATION...
Updated 628 PM MDT Mon Jun 15 2020 (16/00Z TAF Period)
Expect widespread MVFR conditions and mountain obscuration during
this TAF period. Aircraft icing conditions are forecast. Periods of
gusty winds are forecast, especially during the first few hours of
these TAFs. The Northern Rocky Mountain Front and its immediately
adjacent plains are expected to experience gusty winds throughout
the period. With the strongest airfield winds listed as 30KTS, the
greatest impact will be to light aircraft. Expect the associated
turbulence. Tomorrow afternoon and evening, expect thunderstorm
activity to occur across southwest Montana and as far north as KHLN.
For detailed aviation hazard forecast information, please see:
aviationweather.gov/icing
aviationweather.gov/turbulence
aviationweather.gov/convection
- Fogleman
NOTE: Amendments not scheduled for Ennis (KEKS) due to ongoing
runway closure.
&&
.HYDROLOGY...
The current forecast has about 1 to 3 inches of rain falling over
the higher elevations of Central and Southwest Montana tonight
through Wednesday. With snow expected at elevations above 5000
feet, where precipitation amounts will be the highest, some runoff
should be reduced in the short term. Some flooding issues could
develop in burn scar areas or if mountain runoff is more
significant. River flooding is not expected, at this time;
however, backcountry streams and creeks may experience rises and
possible flooding in response to the coming precipitation and snow
melt. We will continue to monitor, and highlights will be issued,
as necessary.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 48 63 47 58 / 80 70 80 80
CTB 43 63 46 61 / 20 40 50 80
HLN 48 61 44 56 / 90 90 100 90
BZN 47 57 41 51 / 90 100 100 90
WYS 39 50 31 44 / 100 100 90 90
DLN 46 56 35 51 / 90 100 100 80
HVR 51 68 49 63 / 50 60 30 80
LWT 47 59 44 55 / 60 80 70 90
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Tuesday evening through Wednesday
morning above 5000 feet for Beaverhead...Central and Southern
Lewis and Clark...Gallatin...Jefferson...Madison.
&&
$$
http://www.weather.gov/greatfalls