428
FXUS65 KTFX 211956
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
156 PM MDT THU MAY 21 2026
KEY MESSAGES
- ISOLATED SHOWERS DIMINISH THIS EVENING.
- TRENDING WARMER AND DRIER INTO THE WEEKEND.
- UNSETTLED AGAIN EARLY NEXT WEEK.
DISCUSSION
- METEOROLOGICAL OVERVIEW:
UPPER LEVEL TROUGHING PIVOTING THROUGH THE NORTHERN AND CENTRAL
ROCKIES IS RESULTING IN A COOL NORTHERLY FLOW ALOFT THIS AFTERNOON
ACROSS THE REGION. GIVEN THE COMBINATION OF COOLER AIR ALOFT AND
SUFFICIENT CLEARING, THERE IS ENOUGH SUPPORT FOR AT LEAST WIDELY
SCATTERED SHOWERS THROUGH THE REMAINDER OF THE AFTERNOON AND EARLY
EVENING, PRIMARILY ALONG AND EAST OF I-15. THE SHALLOW NATURE OF THE
INSTABILITY SHOULD KEEP THE POTENTIAL FOR LIGHTNING LOW, THOUGH A
STRIKE CANNOT BE COMPLETELY RULES OUT IN THE STRONGEST SHOWER.
A BRIEF STRETCH OF RIDGING ATTEMPTS TO BUILD IN FROM THE WEST
TOMORROW, THOUGH THE NORTHWESTERLY FLOW THAT DEVELOPS STILL APPEARS
TO HAVE A MARGINALLY CYCLONIC NATURE TO IT. THIS LOOKS TO RESULT IN
AT LEAST ISOLATED SHOWERS DEVELOPING IN THE AFTERNOON AND EARLY
EVENING, WITH GREATEST COVERAGE NEAR TERRAIN.
A DRIER ZONAL FLOW THEN DEVELOPS FOR THE WEEKEND. THE MAIN TAKEAWAY
FOR SATURDAY AND SUNDAY WILL BE FOR A DRIER STRETCH WITH WARMING
TEMPERATURES. THE ZONAL FLOW ALOFT WILL ALSO RESULT IN SOME GUSTY
WINDS AT TIMES, MOST FAVORED IN THE AFTERNOON. THOSE RECREATING ON
THE WATER SHOULD KEEP THE GUSTIER WINDS IN MIND. ADDITIONALLY, EVEN
THOUGH THE AIR TEMPERATURES WILL BE QUITE WARM BY SUNDAY, WATER
TEMPERATURES ARE STILL QUITE COOL, WHICH WILL ALSO POSE A RISK TO
THOSE NOT PREPARED FOR THE CONDITIONS.
BY MONDAY UPPER LEVEL TROUGHING BEGINS TO NUDGE IN FROM THE EASTERN
PACIFIC OVER THE PACIFIC NW. THERE REMAINS CONSIDERABLE UNCERTAINTY
WITH RESPECT TO HOW QUICKLY THIS TROUGHING MOVES IN, IN ADDITION TO
ITS PROGRESSION ONCE IT DOES ENCROACH UPON THE NORTHERN ROCKIES. THE
MAIN TAKEAWAY FOR MEMORIAL DAY THROUGH MID-WEEK WILL BE FOR ACTIVE
WEATHER ACROSS THE REGION. -AM
- FORECAST CONFIDENCE & SCENARIOS:
THE MAIN, AND MOST IMPACTFUL SOURCE OF UNCERTAINTY IS RELATED TO THE
PROGRESSION OF UPPER LEVEL TROUGHING ACROSS THE PACIFIC NW AND
NORTHERN ROCKIES EARLY NEXT WEEK. THE RISK FOR THUNDERSTORMS WILL
INCREASE AS EARLY AS MONDAY AFTERNOON, AS SOUTHWESTERLY FLOW AHEAD
OF THE TROUGHING OVERSPREADS THE REGION.
CONFIDENCE DECREASES FURTHER INTO TUESDAY, AS THERE IS A ROUGH SPLIT
BETWEEN ENSEMBLE MEMBERS THAT CUTOFF THE TROUGH, OR AT THE VERY
LEAST ALLOW IT TO DIG SIGNIFICANTLY AND SLOW ITS OVERALL PROGRESSION
AND MEMBERS THAT KEEP AN OPEN WAVE AND PROGRESS THINGS THROUGH
QUICKER. THIS PLAYS A SIGNIFICANT ROLE IN WHETHER THE RISK FOR
THUNDERSTORMS WILL LINGER INTO A SECOND AFTERNOON, OR IF
PRECIPITATION ACROSS THE REGION WILL BE MORE STRATIFORM IN NATURE
ALONG AND BEHIND A COLD FRONT INTO TUESDAY. TRENDS WILL BE MONITORED
FOR CHANGES IN CONFIDENCE LEVELS IN EITHER SCENARIO. -AM
AVIATION
21/18Z TAF PERIOD
SCATTERED LIGHT SHOWERS HAVE BEGUN TO DECREASE ACROSS THE REGION,
DISSIPATING BY THIS EVENING. VFR CONDITIONS WILL PREVAIL FOR ALL
TERMINALS THROUGH THIS TAF PERIOD, ALTHOUGH MVFR CONDITIONS ARE
POSSIBLE WITH THE PASSING OF ONE OF THESE LIGHT SHOWERS. BY AROUND
03Z 5/21, WINDS BECOME LIGHT AND VARIABLE FOR ALL TERMINALS.
PRELIMINARY POINT TEMPS/POPS
GTF 36 68 41 76 / 10 10 10 0
CTB 34 67 39 74 / 0 20 20 0
HLN 35 68 40 75 / 10 10 10 0
BZN 29 65 36 74 / 10 10 10 0
WYS 22 59 29 68 / 0 20 20 0
DLN 31 65 37 76 / 0 10 20 0
HVR 34 70 39 79 / 10 0 0 0
LWT 33 63 38 73 / 10 10 10 0
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
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