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Office: TFX

FXUS65 KTFX 200518
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1017 PM MST Mon Feb 19 2018

UPDATED AVIATION SECTION

.SYNOPSIS...

A few flurries or brief light snow showers could linger across
northern and central portions through this evening...while the
remainder of the areas sees partly cloudy...cold...and dry
conditions. Bitterly cold temperatures and dangerous wind chills
are then expected for tonight for much of the area. See the Wind
Chill Advisories for the latest details. Southwest winds will
bring a slight warming trend for Tuesday...with below normal
temperatures overall still expected. Mainly dry conditions are
also expected...with some light snow possible across the southwest
and portions of the Hi-Line.

&&

.UPDATE...

Satellite and radar imagery, as well as the latest short term
models, suggest that cloud cover and the risk for light snow
were somewhat overstated in the afternoon forecast package. As
such, I have updated to reduce cloud cover and PoPs tonight
through Tuesday. Have also made some minor changes to overnight
low temperatures and hourly diurnal temperature trends using
observations and short term model consensus tools. Main risk for
tonight continues to be bitterly cold wind chills across north-
central and central Montana. Current batch of advisories appear to
be on-track and do not anticipate any further updates this
evening. mpj

&&

.AVIATION...
Updated 0517Z.

A dominant area of high pressure remains in control of the weather
across the area early this morning leading to VFR conditions for all
terminals. Areas of low clouds continue to spread slowly to the
southeast across south-central MT impacting HLN, EKS and BZN
terminals with CIG's ranging between 030 and 070. Another area of
patchy low to mid-level clouds continue across GTF to HVR but should
not last too long after daybreak. Otherwise, no major or impactful
weather conditions are expected throughout the period. KLG

&&

.PREV DISCUSSION...
/ISSUED 420 PM MST Mon Feb 19 2018/

Tonight through Tuesday....Large mid level low continues to
progress across the WY area while a broad tough remains over the
region. Stuck in this trough is a decent amount of moisture
bringing areas of clouds and flurries/light snow to the northern
half of the CWA...with cold and partly clear conditions elsewhere.
Expect these clouds and flurry chances to linger though the
evening hours until the trough moves out and a sfc high moves
south out of Canada. With this high will come very cold air. As
this high stall across the south...west to southwest flow will
increase just enough to cause dangerous wind chills for central
and northern areas. There remains some uncertainty on the strength
of the winds and tonight's low temperatures. The lows tonight
will depend greatly on if this remnant moisture exits tonight and
can bring clear skies. Temperatures will plummet in this
scenario. Even if the skies don't clear...temperatures will still
drop to below zero readings. Decided to issue a Wind Chill
Advisory for those areas with the best wind and cold potential.
Some of these areas are close to Wind Chill Warning
criteria...however...confidence was not high enough to issue.
Southwest MT will also be bitterly cold tonight...however...the
stalled high pressure will limit winds needed for any highlights.
Still can't rule out very cold wind chills and it will need to be
monitored. Tuesday then sees a slight warming trend with the
mentioned southwest winds. Temperatures will still be below normal
with highs only in the single digits to teens above zero. Overall
dry conditions are expected for Tuesday...although some lingering
light snow is possible in the southwest...and some scattered
light snow showers are possible in the north from a weak clipper
system in northwest flow. Anglin

Tuesday Night through Sunday...A deep, positively-tilted low
pressure trough will remain over the western and central United
States through this period, keeping the forecast area generally
under a northwesterly flow aloft. A series of disturbances will
move through this flow, bringing a chance of snow mainly to the
western and southwest Montana mountains...with only slight chances
across the valleys and plains as the disturbances move through.
Some breezy winds may also accompany these disturbances...perhaps
bringing some areas of blowing snow. These winds should help
bring a gradual warming to the area, but temperatures will only
warm from around 20 degrees below normal for Tuesday
night/Wednesday to around 5 to 10 degrees below normal by Saturday
night/Sunday. The strongest disturbance of the long term is
forecast to move south along the Pacific coast, which will focus
the best precipitation there. However, the greatest chance for
(what is currently forecast to be) light snow over the entire
forecast area will be during the upcoming weekend, as a
broad disturbance and cold front moves northwest to southeast
over Montana. Widespread light to perhaps moderate snow is
possible from Saturday into Sunday. Accumulations and impacts are
hard to nail down at this point as a westerly component to the
disturbance could bring hindering downslope flow to some areas.
Stay tuned to future updates for the latest details on this
developing system. Coulston/Anglin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF -18  13 -12  16 /  10  10  10  20
CTB -19  15 -15  14 /  10  10  20  10
HLN -14  13  -8  18 /  10  10  10  10
BZN -18  10  -9  16 /  20  10  10  20
WEY -27   8 -17  13 /  20  10  20  20
DLN -20  12  -8  13 /  10  10  20  20
HVR -20   8 -16   8 /  10  10  20  20
LWT -18  11 -11  16 /  20   0  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory until noon MST Tuesday Blaine...Cascade...
Chouteau...Eastern Glacier...Eastern Pondera...Eastern Teton...
Hill...Liberty...Toole.

Wind Chill Advisory until noon MST Tuesday Fergus...Judith
Basin...Meagher.

Wind Chill Advisory until noon MST Tuesday Central and Southern
Lewis and Clark...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.

&&

$$

http://www.weather.gov/greatfalls



Office: MSO FXUS65 KMSO 192124 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 224 PM MST Mon Feb 19 2018 ...BITTERLY COLD TONIGHT... .DISCUSSION...Snow showers are winding down across central Idaho today, with very light snow expected to continue through this evening. Last night was very cold with some locations in western Montana reaching 20 to 35 below zero! Tonight is expected to be another cold one, with many locations dropping below zero in western Montana and into the single digits in central Idaho. Normally in this situation the actual low temperatures will depend heavily on how much cloud cover remains over the area. Models indicate mostly dry air aloft, but not the excessively dry air that makes it a sure thing. And today's satellite imagery is showing the development of some low clouds in area valleys. By the numbers it is a very difficult forecast, but whether it's 10, 20, or 30 degrees below zero, it is going to be very cold. A light northerly or northwesterly flow will remain over the Northern Rockies through the end of the week. Temperatures will remain quite cold, though will slowly warm from day to day, with highs across the region reaching the upper 20s to low 30s by Friday. Typically under this type of pattern, light snow showers will develop each day, but will not accumulate much, if they do develop. Long range forecast models remain in good agreement with another active pattern developing over the Northern Rockies by this weekend, and likely persisting into the first part of next week. Most locations will likely remain cold enough for snow, however, it's too early to tell where the heavier precipitation develops. Though, widespread snow accumulations look likely for the mountains and valleys. && .AVIATION...Some low and mid level clouds are hanging around and may cause some very light snow showers, especially around the mountains. Thin stratus is the most likely restriction to from at any terminals tonight. The main regional terminals including KGPI, KMSO, and KBTM are expected to be below zero tonight, with KBTM being colder than 20 below zero. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$
Office: BYZ FXUS65 KBYZ 200552 AFDBYZ Area Forecast Discussion...Updated National Weather Service Billings MT 1052 PM MST Mon Feb 19 2018 .UPDATE... Quick update to temperatures and cloud cover late this evening. Areas from Billings west have seen considerable clearing in the past few hours allowing temperatures to plunge into the teens and 20s below zero already. Harlowton currently at -20. Some mid clouds lingering int he Livingston and Big Timber areas but those areas are well into the teens below zero as well. With back edge of thin cloud cover at Billings and already around -7 degrees lowered temperatures to around -17 degrees at the airport, and will probably go several degrees colder on the west end. Adjusted cloud cover lower as we go through the night to go along with current trends and latest model thoughts. Chambers && .SHORT TERM...valid for Tue and Wed... Light snow continued across portions of southeast Montana into the mid afternoon with areas of flurries as far west as Yellowstone County. Dynamic support aloft will continue to slide slowly southeast this evening and overnight. So we look for precipitation winding down from west to east overnight. The southeast corner up into Fallon county are the only areas which may see around an additional inch of snow from late afternoon through the night. Other locations will see flurries to maybe a dusting of new snow tonight. The trof axis finally slides by us Tuesday morning. Our main forecast issue is potential wind chills early tomorrow. Model progs are slow to dissolve the cloud cover overnight, but do suggest sky cover will begin to break up toward 12Z in the western CWA. At that time we see winds shift to the southwest late tonight and pick up a bit hitting 7-12 kts. As a result, it appears wind chills by sunrise may be 20 to 30 below zero over our western CWA. Course this is an issue for children waiting for buses etc. We will issue a wind chill advisory from midnight to noon Tuesday for these areas. Areas further east will have less wind and air temperatures may not bottom out thanks to lingering low clouds. Highs on Tuesday will be mainly single digits above zero. Lower elevations will remain dry Tuesday through Wednesday. However, the flow aloft remains cyclonic and proggs show some energy dropping south out of Canada into the Northern Rockies. This may generate some snow showers over our western mountains Tuesday night into Wednesday, but this should be of little relative impact or accumulation. Look for another cold night Tuesday night and highs on Wednesday still only in the single digits and teens. BT .LONG TERM...valid for Thu...Fri...Sat...Sun...Mon... Only minor changes to the extended forecast this afternoon, as mainly dry conditions and below average temperatures persist through the latter portions of workweek. Several reinforcing trofs in western CONUS will keep high temperatures from rising very quickly through the work week, only reaching mid 20s by Friday. Meanwhile, low temps a few degrees above and below zero are expected through Friday. Temps will Jump into the mid 30s on Saturday, as downslope flow develops ahead of an approaching weather maker for Sunday evening and Monday. Western mountains looks good for additional snow into the Cooke City area through the latter portions of the workweek, as moisture continues to stream into the region. Models continue to advertise mainly dry conditions over the lower elevations until Sunday/Monday time frame. Would not be surprised to see a few light snow showers slipping off the mountains at times, but would not anything of significance. AAG && .AVIATION... MVFR to IFR conditions are expected to continue to improve to VFR from northwest to southeast through the evening as the storm system moves out of the area. Cloud cover may be slow to clear, and could hang around in the east through mid day Tuesday, although VFR conditions should prevail before that point. AAG/Reimer && .PRELIMINARY POINT TEMP/POPS... Tue Wed Thu Fri Sat Sun Mon ----------------------------------------------------------- BIL 917/006 910/013 907/020 901/027 012/034 016/033 013/034 11/U 01/B 01/U 11/U 12/J 22/S 21/B LVM 917/010 905/017 901/023 005/029 016/036 018/034 015/036 11/U 01/B 11/B 11/B 13/J 43/S 22/S HDN 916/006 914/012 909/020 907/025 007/033 012/031 009/034 21/U 00/B 00/U 11/U 01/B 22/S 21/B MLS 910/003 916/007 912/014 909/018 004/027 007/025 005/029 31/B 00/U 00/U 10/U 01/B 11/B 21/B 4BQ 911/003 918/011 911/018 907/023 006/030 011/029 009/033 41/B 00/U 01/U 11/U 01/B 11/B 21/B BHK 909/003 914/009 911/018 908/018 005/028 009/026 004/029 61/B 00/U 00/U 10/U 01/B 11/N 21/B SHR 915/006 917/013 909/021 906/027 006/033 012/032 008/034 31/B 00/U 01/U 11/U 01/B 21/B 21/B && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...Wind Chill Advisory in effect until noon MST Tuesday FOR ZONES 28-29-34-35-40>42-63-65-66. WY...None. && $$ weather.gov/billings
Office: GGW FXUS65 KGGW 200154 AAA AFDGGW Area Forecast Discussion...UPDATED National Weather Service Glasgow MT 654 PM MST Mon Feb 19 2018 .DISCUSSION... Evening update: Mainly to increase PoPs across our SE zones and to drop temperatures across our NW zones. Even though winds are expected to remain light tonight through early Tuesday morning, any sudden increase in winds up to around just 10 mph will justify the wind chill advisory in place. Expecting conditions to improve after sunrise. BMickelson Previous discussion: Upper low pressure trough to swinging through central and eastern Montana through 18z Tuesday. Look for areas of light snow mainly east of a line from Winnett to Malta through Tuesday morning as this trough moves east. Cold conditions can be expected Tuesday through Thursday mornings with lows from 10 to 20 degrees below zero and very low wind chills readings from 20 to 35 below zero. Wind chill advisory is in effect from 10 pm this evening to 11 am Tuesday morning. Weak upper trough to remain over the western states this week with an upper level high pressure ridge over the Canadian rockies. This pattern will help continue to support the push of cold arctic air southward into the region. Some temperature moderation expected late in the week as the upper level high pressure ridge over the Canadian Rockies flattens in response to a strong low pressure trough pushing into the Gulf of Alaska. This pattern change will allow a fetch of warmer air to push SE across the northern Canadian Rockies and into the plains of eastern Montana. The next chance for snow will be this weekend as a weather system moves into the Pacific NW and into British Columbia, with short wave troughs coming out of that system and moving east across the plains of eastern Montana. The forecast confidence of the predicted timing of these shortwave troughs is still low. TEC && .AVIATION... FLIGHT CAT: VFR for KGGW and KOLF. IFR for KSDY and KGDV in light snow and ceilings around 2000 ft. Widespread VFR to return later Tuesday morning. SYNOPSIS: An upper level trough moving east across NE MT will push east into the Dakotas after 18Z Tuesday with CIGS and VSBY restrictions due to clouds and light snow improving through Tuesday. Wind: Light and variable winds overnight becoming 6 to 12 kts from the west Tuesday afternoon. TEC/BLM && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Wind Chill Advisory from 10 PM this evening to 11 AM MST Tuesday for Central and Southeast Phillips...Central and Southern Valley...Daniels...Dawson...Eastern Roosevelt...Garfield... McCone...Northern Phillips...Northern Valley...Petroleum... Prairie...Richland...Sheridan...Southwest Phillips...Western Roosevelt...Wibaux. && $$ weather.gov/glasgow