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