289
FXUS65 KTFX 201102
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
502 AM MDT TUE OCT 20 2026
AVIATION SECTION UPDATED.
KEY MESSAGES
- TEMPERATURES WILL BE A ROLLER COASTER OVER THE NEXT SEVERAL
DAYS WITH A MID-WEEK WARMUP FOLLOWED BY ANOTHER DROP TO NEAR OR
SLIGHTLY BELOW SEASONAL AVERAGES FOR THE WEEKEND.
- RAIN AND MOUNTAIN SNOW WILL OVERSPREAD THE REGION FRIDAY INTO SATURDAY
BRINGING HEALTHY LIQUID PRECIPITATION TO LOWER ELEVATIONS AND
ACCUMULATING SNOWFALL ABOVE 4KFT.
- GUSTY WINDS DEVELOP ACROSS THE AREA FRIDAY AFTERNOON INTO EARLY
SATURDAY MORNING. HIGHEST GUSTS WILL BE ACROSS CENTRAL MT AND
THE HI-LINE.
DISCUSSION
/ISSUED 1234 AM MDT TUE OCT 20 2026/
- METEOROLOGICAL OVERVIEW:
WEAK ZONAL FLOW ALOFT ACROSS NORTH-MONTANA AND WEAK SOUTHERLY FLOW
OVER SW MONTANA WILL KEEP CONDITIONS RELATIVELY QUIET ON TUESDAY,
WITH TEMPERATURES COOLING TO NEAR-SEASONAL AVERAGES. ISOLATED, LIGHT
SHOWERS REMAIN POSSIBLE NEAR THE IDAHO BORDER, BUT DRY CONDITIONS
WILL PREVAIL EVERYWHERE ELSE.
ON WEDNESDAY, AN UPPER-LEVEL LOW SETTLES ALONG THE CALIFORNIA COAST,
INCREASING OUR SOUTHWESTERLY FLOW ALOFT OVER SW MONTANA WHILE ZONAL
FLOW PERSISTS ACROSS NORTH-CENTRAL MT. STRENGTHENED WARM AIR
ADVECTION WITH THE SOUTHWESTERLY REGIME WILL REBOUND HIGH
TEMPERATURES BACK TO WELL ABOVE SEASONAL AVERAGES. MOSTLY DRY
CONDITIONS WILL CONTINUE ACROSS THE PLAINS, THOUGH WEAK MOISTURE
ADVECTION SUPPORTS A LOW CHANCE FOR A SHOWER OR TWO ALONG THE ID/MT
BORDER.
AN ACTIVE SYNOPTIC PATTERN ARRIVES LATE IN THE WEEK, AS THE PACIFIC
LOW PRESSURE EJECT INLAND, AND BEGINS TO PHASE WITH THE DIGGING
TROUGH EMERGING OUT OF CANADA. A WEAK COLD FRONT WILL PASS THROUGH
THE REGION THURSDAY NIGHT INTO FRIDAY MORNING, HELPING INITIATE
WIDESPREAD PRECIPITATION THAT PERSISTS THROUGH EARLY SATURDAY.
THIS SYSTEM WILL BE FAIRLY HEAVY IN MOISTURE WITH HIGH CONFIDENCE IN
A LARGE AREA SEEING OVER 0.5" OF LIQUID PRECIPITATION. AN AXIS OF
HEAVIER AMOUNTS IS LIKELY ACROSS SOUTHWEST AND CENTRAL MONTANA WHERE
AREAS COULD SEE OVER 1" OF QPF. PRECIPITATION WILL BEGIN WITH HIGH
SNOW LEVEL THURSDAY NIGHT (ABOVE 6KFT). DURING THE HEAVIEST PERIOD
OF PRECIP ON FRIDAY MORNING, DIABATIC AND DYNAMIC COOLING WILL HELP
PULL LEVELS DOWN TOWARDS 5KFT, TRANSITIONING MUCH OF THE MOUNTAIN
RAN TO ACCUMULATION SNOW. AS THE PRIMARY DEFORMATION AXIS AND
MOISTURE DEPART FRIDAY NIGHT INTO SATURDAY, ADDITIONAL COLD AIR
ADVECTS IN LOWERING SNOW LEVELS BELOW 4KFT. HOWEVER, MID-LEVEL
DRYING WILL QUICK CUT OFF PRECIPITATION RATES, LIMITING LOW-
ELEVATION ACCUMULATION POTENTIAL. SIMULTANEOUSLY, A TIGHTENING
SURFACE PRESSURE GRADIENT AND INCREASING LOW-LEVEL LAPSE RATES WILL
HELP TAP THE STRONGER 700MB FLOW ON FRIDAY BRINGING GUSTY WINDS
ACROSS THE REGION.
- FORECAST CONFIDENCE & SCENARIOS:
CONFIDENCE IS MODERATE TO HIGH REGARDING ELEVATED POST-FRONTAL WINDS
ON FRIDAY. THE PROBABILITY FOR GUSTS REACHING OR EXCEEDING 45MPH IS
40-60% ACROSS THE HI-LINE AND CENTRAL PLAINS, ACROSS THE RMF AND
CENTRAL ISLAND RANGES THAT RISES UP TO 50-70%.
FOR SNOWFALL, CONFIDENCE IS MEDIUM FOR ACCUMULATION SNOWFALL ABOVE
4KFT, WITH A 35-55% CHANCE OF EXCEEDING 2 INCHES ESPECIALLY ACROSS
THE RMF AND CENTRAL ISLAND RANGES. FOR ELEVATIONS BELOW 4KFT, THE
PROBABILITY OF EXCEEDING 1" IS LARGELY UNDER 10%. THE MAIN QUESTION
MARK FOR THE WEEKEND STORM CENTERS ON HOW LONG MOISTURE WANTS TO
HANG AROUND AS SNOW LEVEL DROP FURTHER ESPECIALLY WITH THE PHASING
OF THE LOW AND TROUGH.
-SCENARIO 1: THE LOW PHASES AND SWINGS THROUGH MORE PROGRESSIVELY,
MOISTURE EXITS RAPIDLY BEFORE SNOW LEVELS FALL BELOW 4KFT, CONFINING
ACCUMULATION SNOW TO THE MOUNTAINS AND PASSES WHILE VALLEY FLOORS
SEE RAIN ENDED AS NON ACCUMULATION "MOOD-FLAKES" WITH NO IMPACTS.
-SCENARIO 2: THE LOW/TROUGH PHASING IS SLOWER, BOTH DELAYING THE
PROGRESSION OF THE TROUGHING BUT ALSO ALLOWING DEFORMATION
MOISTURE TO LINGER ACROSS THE AREA WHILE COLD AIR DRIVES SNOW
LEVELS DOWN TOWARDS 3KFT. THIS WILL INTRODUCE A WINDOW FOR A MORE
PERSISTENT BUT LIGHT SNOWFALL ACROSS LOWER ELEVATIONS. THAT BEING
SAID, WARM GROUND TEMPERATURES AND HOURS OF RAIN PROCEEDING THE
POTENTIAL CHANGE WOULD RESTRICT ANY OF THIS TO ELEVATED SURFACE IF
ANY AT ALL.
-JR
AVIATION
20/12Z TAF PERIOD
VFR CONDITIONS WILL PREVAIL AT ALL TERMINALS DURING THIS TAF PERIOD
WITH LIGHT AND VARIABLE WINDS AND HIGH-LEVEL CLOUDS AROUND. -IG
PRELIMINARY POINT TEMPS/POPS
GTF 57 36 71 44 / 0 0 0 0
CTB 56 30 66 38 / 0 0 0 0
HLN 62 34 66 40 / 0 0 0 0
BZN 63 33 65 37 / 0 0 0 0
WYS 59 27 60 28 / 10 10 10 10
DLN 63 35 64 37 / 0 0 10 0
HVR 61 32 68 37 / 0 0 0 0
LWT 58 34 70 44 / 0 0 0 0
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
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