498
FXUS65 KTFX 181710
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1110 AM MDT MON MAY 18 2026
AVIATION SECTION UPDATED.
KEY MESSAGES
- MAINLY MOUNTAIN SHOWERS TODAY, WITH DRY AND COOL CONDITIONS
ELSEWHERE.
- ANOTHER COLD NIGHT IS IN STORE TONIGHT ACROSS THE VALLEYS OF
SOUTHWEST AND CENTRAL MONTANA, WITH A HIGH CHANCE FOR A HARD
FREEZE.
- TEMPERATURES MODERATE THROUGH REST OF THE WORK WEEK, BUT DAILY
CHANCES FOR SHOWERS EXIST.
UPDATE
/ISSUED 645 AM MDT MON MAY 18 2026/
LINGERING NORTHERLY FLOW ALOFT HAS RESULTED IN A FEW AREAS OF MORE
PERSISTENT UPSLOPE SNOW IN A FEW MOUNTAIN AREAS. THE ONLY CHANGE
THIS MORNING WAS TO INCREASE PROBABILITY OF PRECIP AND SNOW
AMOUNTS IN THESE AREAS THROUGH THE REMAINDER OF THE MORNING.
PRECIPITATION BECOMES MORE SHOWERY IN NATURE THIS AFTERNOON AS
DAYTIME HEATING ENSUES, AND LARGELY LOOKS TO BE CONFINED TO THE
MOUNTAINS AND ADJACENT AREAS. -AM
DISCUSSION
/ISSUED 645 AM MDT MON MAY 18 2026/
- METEOROLOGICAL OVERVIEW:
ONE FINAL DAY OF WELL BELOW NORMAL TEMPERATURES CAN BE EXPECTED AS
COOL, CYCLONIC NORTHWEST FLOW PREVAILS OVER THE NORTHERN ROCKIES,
WITH ADDITIONAL OPPORTUNITIES FOR PREDOMINATELY MOUNTAIN
PRECIPITATION, ESPECIALLY ALONG THE ROCKY MOUNTAIN FRONT. BY THIS
AFTERNOON UPPER LEVEL RIDGING OVER THE EASTERN PACIFIC WILL BEGIN TO
AMPLIFY, WITH OVERALL RISING HEIGHTS ACROSS MUCH OF THE WESTERN
CONUS. WHILE THIS RIDGE WILL AMPLIFY OVER THE EASTERN PACIFIC IT
WILL FAIL TO BUILD EAST AND OVER THE NORTHERN ROCKIES THROUGH THE
WORK WEEK, WHICH WILL HELP TO KEEP SOUTHWEST THROUGH NORTH CENTRAL
MONTANA BENEATH CONTINUED NORTHWEST FLOW ALOFT. WHILE TEMPERATURES
WILL MODERATE BENEATH THE RISING HEIGHTS ALOFT THERE WILL BE DAILY
CHANCES FOR SHOWERS AND STORMS THROUGHOUT THE WORK WEEK, ESPECIALLY
FROM WEDNESDAY MORNING THROUGH THURSDAY MORNING WHEN A COMPACT
SHORTWAVE DIVES SOUTHEAST AND OVER THE NORTHERN ROCKIES WITHIN THE
AFOREMENTIONED NORTHWEST FLOW ALOFT. THIS SHORTWAVE LOOKS TO BRING
THE BEST CHANCE FOR WIDESPREAD PRECIPITATION THIS WEEK, WITH MOST
LOWER ELEVATIONS SEEING LIGHT RAINFALL UP TO 0.10" AND THE MOUNTAINS
SEEING BETWEEN 0.10" TO 0.25". THE EXCEPTION TO THIS WILL BE THE
NORTHERLY UPSLOPE AREAS OF CENTRAL MONTANA, ISLAND RANGES OF CENTRAL
MONTANA, AND CONTINENTAL DIVIDE WHERE PRECIPITATION AMOUNTS OF
BETWEEN 0.10" TO 0.25" AND 0.25" TO 0.50" ARE POSSIBLE FOR PLAIN AND
MOUNTAIN LOCATIONS, RESPECTIVELY. THIS WEEKEND THE UPPER LEVEL FLOW
WILL BECOME QUASI-ZONAL, WHICH WILL LEAD TO INCREASING SURFACE WINDS
AND WARMING TEMPERATURES, WITH MOST LOCATIONS CLIMBING ABOVE TO WELL
ABOVE NORMAL. - MOLDAN
- FORECAST CONFIDENCE & SCENARIOS:
COLD TEMPERATURES TONIGHT...
UPPER LEVEL RIDGING BUILDING IN OVER THE NORTHERN ROCKIES COMBINED
WITH OVERALL LIGHT SURFACE WINDS AND MOSTLY CLEAR SKIES WILL SETUP
IDEAL RADIATIONAL COOLING PROCESSES ACROSS MUCH OF SOUTHWEST THROUGH
NORTH CENTRAL MONTANA TONIGHT, WITH THE EXCEPTION OF THE IMMEDIATE
ROCKY MOUNTAIN FRONT WHERE SOUTHWEST SURFACE WIND WILL BE JUST
STRONG ENOUGH TO INHIBIT SURFACE DECOUPLING. WITH BELOW NORMAL
TEMPERATURES ALREADY IN PLACE THANKS TO THIS WEEKENDS DISTURBANCE
TEMPERATURES WILL COOL EFFICIENT TONIGHT; WITH A 50% OR GREATER
CHANCE THAT VALUES FALL BELOW FREEZING ACROSS MOST LOCATIONS AND 70%
OR GREATER CHANCE FOR A HARD FREEZE ACROSS MOST VALLEY LOCATIONS IN
SOUTHWEST AND CENTRAL MONTANA. THOSE WITH EARLY SEASON GARDENING
INTEREST SHOULD BE PREPARED TO TAKE PROTECTIVE MEASURE FOR SENSITIVE
VEGETATION.
BELOW IS THE NBM5.0 PROBABILITIES FOR CERTAIN TEMPERATURES FOR
SELECT LOCATIONS ACROSS NORTH CENTRAL, CENTRAL, AND SOUTHWEST
MONTANA TONIGHT.
LOW TEMPERATURE PROBABILITIES
LOCATION <36F | <32F | <28F
BROWNING 100% | 55% | <5%
CUT BANK 95% | 60% | 20%
HAVRE 100% | 80% | 40%
GREAT FALLS 95% | 60% | 25%
LEWISTOWN 100% | 100% | 85%
HELENA 85% | 45% | 5%
BOZEMAN 100% | 100% | 85%
DILLON 100% | 100% | 70%
ENNIS 100% | 100% | 90%
WEST YELLOWSTONE 100% | 100% | 100%
GUSTY WINDS AND CHOPPY WATER THIS MEMORIAL DAY WEEKEND...
INCREASING SOUTH TO WEST SURFACE WINDS OVER THE HOLIDAY WEEKEND,
SPECIFICALLY ON SUNDAY AND MONDAY, IS LIKELY TO LEAD TO CHOPPY
WATER CONDITIONS ON AREA LAKES, RESERVOIRS, AND LONG FETCHES OF
RIVERS. NBM5.0 PROBABILITIES FOR WIND GUSTS IN EXCESS OF 40 MPH
ACROSS MOST OF SOUTHWEST THROUGH NORTH CENTRAL MONTANA RANGE FROM A
20-40% CHANCE ON SUNDAY AND BETWEEN A 40-60% CHANCE ON MONDAY, WITH
THE EXCEPTION OF THE ROCKY MOUNTAIN FRONT WHERE A 40-75% CHANCE
EXISTS BOTH DAYS. THOSE WITH PLANS TO RECREATE ON WATERWAYS SHOULD
BE PREPARED FOR CHOPPY CONDITIONS, ESPECIALLY CONSIDERING THAT LOCAL
WATERWAYS WILL BE SIGNIFICANTLY COLDER THAN THE AMBIENT AIR
TEMPERATURE DUE TO SNOWMELT. THESE CHOPPY CONDITIONS AND COLD WATER
TEMPERATURES WILL CREATE AN INCREASED RISK FOR DROWNING SHOULD A
PERSON FALL INTO THE WATER WITHOUT PROPER SAFETY EQUIPMENT. -
MOLDAN
AVIATION
18/18Z TAF PERIOD
PRIMARY CONCERN THIS TAF PERIOD WILL BE FOR LOW-VFR OR MVFR CEILINGS
AT TIMES THROUGH THE AFTERNOON. ADDITIONALLY, NUMEROUS SHOWERS LOOK
TO DEVELOP THIS AFTERNOON, MOSTLY NEAR TERRAIN, WHICH WILL BE
CAPABLE OF BRIEF CIG/VIS REDUCTIONS AND BRIEFLY GUSTY WINDS AT
TERMINALS IN CLOSE PROXIMITY TO MOUNTAINS. MOUNTAINS WILL BE
OBSCURED AT TIMES THROUGH THE EVENING WHERE SHOWERS FORM.
CLOUDS BEGIN TO CLEAR TONIGHT, WHICH PAIRED LIGHT WINDS, WILL YIELD
AN OPPORTUNITY FOR FOG BY TUESDAY MORNING. CONFIDENCE IN THIS FOG
DEVELOPING AT ANY SPECIFIC TERMINAL WAS TOO LOW TO WARRANT MENTION
IN TAFS AT THIS TIME, HOWEVER. -AM
PRELIMINARY POINT TEMPS/POPS
GTF 52 29 63 40 / 10 0 30 10
CTB 54 31 63 38 / 20 10 20 10
HLN 55 29 62 38 / 10 10 20 0
BZN 51 22 60 34 / 10 0 10 0
WYS 41 16 51 24 / 10 10 20 0
DLN 48 23 60 30 / 10 10 20 0
HVR 54 26 66 41 / 10 0 50 10
LWT 46 23 59 36 / 40 0 30 0
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
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