Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/30/22
Area Forecast Discussion
National Weather Service Great Falls MT
744 PM MDT Sun May 29 2022
.SYNOPSIS...
Cool and unsettled conditions persist through Memorial Day,
especially for central and southwest Montana. Numerous showers and a
few thunderstorms continue into this evening, especially for central
and southwestern areas. More widespread rain and high mountain snow
then becomes established tonight into early Monday, heaviest for the
southwest and over and near the central mountain ranges.
Temperatures warm closer to normal by mid-week as drier conditions
settle in.
&&
.UPDATE...
A moist and generally north northeasterly flow favors precipitation,
especially, along northward and eastward facing slopes. A few
thunderstorms pass across the area. Inherited forecast is
performing, nicely; therefore, no updates are made, at this time.
- Fogleman
&&
.DISCUSSION...
Rest of this Afternoon through Monday night...
The entire Northwest US resides under a large-scale upper trough,
with embedded closed lows centered over Vancouver Island and
southern Idaho. Most of the Great Falls CWA lies within weak upper
flow within the upper trough caused by weak positive vorticity
advection and deformation from weakly diverging flow aloft. Broad
synoptic lift combined with low stability and plentiful moisture
support areas of rain and high-elevation snow, with scattered
showers outside of the more concentrated areas of precipitation. The
heaviest precipitation is occurring primarily over southwest Montana
where most of these features are occurring concurrent with one
another.
The upper trough will continue to trek eastward over the next couple
of days, bringing widespread precipitation along its northern
periphery. Showers and a few thunderstorms will become more numerous
over Central/Southwest MT through this afternoon as moist east to
northeasterly flow converges around the approaching low pressure
area. Precipitation intensity and occurrence will quickly diminish
going toward the eastern and northeastern portions of the CWA. The
main precipitation shield retreats to the southwest tonight, but
does return back to central/north-central areas by Monday morning,
especially for the eastern and northern slopes and foothills of the
Front Range mountains. Ensemble guidance places the greatest chances
for rainfall amounts in excess of 1.00" over the higher terrain
south of I-90 while amounts in the 0.25-0.75" range are most likely
for much of Central MT and the lower elevations of the southwest.
Storm totals drop off sharply going northeastward through North-
central MT, with little to no additional precipitation expected for
the central and eastern portions of the Hi-line, especially after
this afternoon/evening.
Snow levels lower to around 7000-ft today with the cooler
northeasterly flow aloft moving in and could possibly fall to some
valley floors above 6,000-ft elevation for a period late tonight
through Monday morning. Snow accumulation in excess of 4 inches will
generally be limited to areas above 7000 ft with higher mountain
peaks south of Interstate 90 potentially seeing local accumulations
of 1 foot or more. There are some concerns that mountain passes in
these areas could see a brief period moderate snowfall and slushy
roadway accumulations late tonight into Monday morning, but no
winter weather products are planned due to lower confidence in this
occurring combined with the brief window of opportunity. The steady
precipitation diminishes from north to south by Monday evening,
though lingering shower activity may persist into Tuesday morning.
Afternoon temperatures cool to the 50s and 60s today and fall
further on Memorial Day, when temperatures in the 40s and 50s for
much of the day across much of the area, except warmer 60s for
northeastern areas.
Tuesday through next Sunday...
The upper level low responsible for the cool and wet conditions
weakens significantly into a broad low-amplitude trough over Montana
before moving east Wednesday, with a trend toward drier conditions
and moderating temperatures during this time. However, weak
troughing and colder air aloft will remain over the Northern Rockies
through Wednesday and few showers and thunderstorms cannot be ruled
with the lingering instability in the area. Transient ridging will
keep much of Thursday dry, but weak disturbances streaming ahead of
another Pacific trough increases the day to day chance for showers
and possible thunderstorms Friday through Sunday.
-RCG/CC
&&
.AVIATION...
620 PM MDT Sun May 29 2022 (30/00Z TAF period)
Expect periods of MVFR conditions at all airfields during this TAF
period. KWYS spends much of this forecast period in IFR/near IFR
conditions due to low ceiling. Expect mountain obscuration and poor
visibility through valleys in precipitation and fog/mist. Gusty
northerly winds impact light aircraft that may wish to fly through
north-south oriented mountain valleys/passes. Funneled winds along
with low ceilings and poor visibility favor hazardous flying
conditions.
- Fogleman
Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.
&&
.HYDROLOGY...
Rivers and streams continue to rise as the snowpack at higher
elevations continues to slowly melt out. While significant
precipitation is occurring over southwest Montana, especially
areas south of Interstate 90, rapid rises into flood stage are
not expected as snow levels will fall to as low as 6500-ft
elevation tonight, which will help to draw out the amount of time
that precipitation and snowmelt enter the Missouri River
headwaters.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 43 56 43 61 / 60 80 50 10
CTB 41 54 38 60 / 60 60 20 0
HLN 45 56 43 63 / 80 90 50 10
BZN 42 54 39 58 / 90 90 70 20
WYS 33 46 32 52 / 100 80 60 50
DLN 38 50 39 55 / 90 70 50 20
HVR 45 64 40 66 / 10 30 20 0
LWT 41 54 40 58 / 40 80 70 10
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
http://www.weather.gov/greatfalls