117
FXUS65 KTFX 200522
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1120 PM MDT TUE OCT 19 2021
AVIATION SECTION UPDATED.
SYNOPSIS
FOG IS POSSIBLE IN SOME VALLEYS OF SOUTHWEST AND CENTRAL MONTANA
TONIGHT, ALONG WITH THE IMMEDIATE PLAINS EAST OF THE ROCKY
MOUNTAIN FRONT. LOW TEMPERATURES ARE EXPECTED TO FALL INTO THE
MID-20S TO LOW 30S ACROSS THE REGION, WITH CLEAR TO MOSTLY CLEAR
SKIES.
UPDATE
SKIES CONTINUE TO CLEAR OUT THIS EVENING AS A DISTURBANCE OVER
WYOMING CONTINUES TO MOVE EASTWARD. BIGGEST CONCERN TONIGHT WILL
BE THE POTENTIAL FOR FOG TO DEVELOP OVER THE PLAINS, ESPECIALLY
ALONG THE ROCKY MOUNTAIN FRONT AND OTHER AREAS ACROSS THE PLAINS
AS EASTERLY WINDS UPSLOPE OVERNIGHT TONIGHT. LUDWIG
AVIATION
1120 PM MDT TUE OCT 19 2021 (20/06Z TAF PERIOD)
AS A WEATHER SYSTEM MOVES EAST OVER WYOMING THIS EVENING, EXPECT
SKIES TO CONTINUE TO REMAIN CLEAR THROUGH THE OVERNIGHT AT MOST
TERMINALS. THE EXCEPTIONS TO THIS WILL BE IN THE KWYS VICINITY AS
SOME LOW CLOUDS LINGER, RESULTING IN INTERMITTENT LIFR CONDITIONS,
AS WELL AS PARTS OF THE NORTH-CENTRAL PLAINS, WHERE SOME FOG OR LOW
STRATUS WILL BE POSSIBLE, PARTICULARLY IN THE VICINITY OF KCTB.
OTHERWISE, VFR CONDITIONS ARE EXPECTED, EVEN AS SOME HIGH CLOUDS
FILTER BACK INTO THE AREA TOMORROW. LUDWIG
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PREV DISCUSSION
/ISSUED 545 PM MDT TUE OCT 19 2021/
REST OF TODAY THROUGH TONIGHT...PRIMARY CONCERN WILL BE POTENTIAL
FOR FOG DEVELOPMENT LATE THIS EVENING THROUGH THE MORNING HOURS ON
WEDNESDAY.
REX BLOCK OVER THE ROCKIES IS SLOWLY BEGINNING TO BREAK DOWN AS A
H500 LONGWAVE TROUGH OVER THE EASTERN PACIFIC BEGINS TO APPROACH THE
WESTERN CONUS. LOW LEVEL STRATUS, THANKS IN PART TO LOW LEVEL
NORTHEAST TO EASTERLY UPSLOPE FLOW, WAS FINALLY ERODING ACROSS
CENTRAL AND NORTH CENTRAL MONTANA EARLY THIS AFTERNOON. EXPECT CLOUD
COVER ACROSS THE ENTIRE NORTHERN ROCKIES TO CONTINUE ERODE/SLIDE
EAST THROUGH THE REMAINDER OF THE DAY, LEADING TO CLEAR TO MOSTLY
CLEAR SKIES FOR MUCH OF THE OVERNIGHT HOURS. WHILE SURFACE WINDS
WILL BEGIN TO TURN MORE SOUTHEASTERLY THROUGH THE REMAINDER OF THE
DAY AND INCREASE OVER THE PLAINS OF CENTRAL AND NORTH CENTRAL
MONTANA DUE TO A STRENGTHENING LOW LEVEL JET (I.E. H850 WINDS
INCREASING FROM 5-15KTS TO 15-30KTS), MOST VALLEYS OF SOUTHWEST AND
CENTRAL MONTANA WILL DECOUPLE THIS EVENING. THESE DECOUPLED VALLEYS
COMBINED WITH CLEARING SKIES AND ANTECEDENT LOW LEVEL MOISTURE WILL
CREATE THE POTENTIAL FOR FOG DEVELOPMENT, MOST NOTABLY IN THE
HELENA, SMITH, GALLATIN, HEBGEN VALLEYS AND ALONG THE ROCKY MOUNTAIN
FRONT WEST OF I-15 FROM GREAT FALLS TO CUT BANK. WILL NEED TO
MONITOR THE POTENTIAL NEED FOR DENSE FOG ADVISORIES IN THESE
LOCATIONS AS SOME MODELS ARE SUGGESTING VISIBILITIES BELOW 1/4MILE,
BUT FOR NOW HAVE REFRAINED FROM ISSUING ANY HIGHLIGHTS. OTHERWISE,
EXPECT ANOTHER COOL NIGHT WITH LOWS FALLING INTO THE MID-20S TO LOW
30S. - MOLDAN
WEDNESDAY THROUGH NEXT TUESDAY... A DEEPENING LOW PRESSURE TROUGH
OFF THE PACIFIC COAST WILL PUT THE AREA UNDER MORE OF A
SOUTHWESTERLY FLOW ALOFT ON WEDNESDAY. A SHORTWAVE TROUGH WILL
EJECT FROM THIS TROUGH AND MOVE OVER THE AREA WEDNESDAY INTO
WEDNESDAY NIGHT, BRINGING A CHANCE OF PRECIPITATION TO THE
MOUNTAINS ALONG AND WEST OF THE CONTINENTAL DIVIDE; HOWEVER,
SOUTHERLY WINDS WILL KEEP MOST OF THE AREA DRY WITH SLIGHTLY
ABOVE NORMAL TEMPERATURES. A WEAK HIGH PRESSURE RIDGE WILL THEN
MOVE IN BEHIND THE SHORTWAVE AND AHEAD OF THE LARGE-SCALE TROUGH,
WHICH WILL KEEP THE AREA DRY WITH TEMPERATURES UP TO 10 DEGREES
ABOVE NORMAL THURSDAY INTO FRIDAY. THE PACIFIC TROUGH WILL
BROADEN AND SPREAD EAST INTO THE ROCKIES FRIDAY THROUGH TUESDAY,
WHICH WILL KEEP THE FORECAST AREA UNDER MORE OF AN UNSETTLED
PATTERN, BUT WITH SLIGHTLY ABOVE NORMAL TEMPERATURES. AS A
RESULT, THERE WILL BE A GOOD CHANCE OF MOUNTAIN SNOW AND RAIN EACH
DAY, WITH SNOW ACCUMULATIONS LIKELY REMAINING ABOVE MOUNTAIN PASS
LEVEL. HOWEVER, WINDS SHOULD REMAIN MORE SOUTHWESTERLY AND
DOWNSLOPING OVER THE PLAINS, WHICH WILL LIMIT PRECIPITATION THERE.
-COULSTON
PRELIMINARY POINT TEMPS/POPS
GTF 29 61 38 63 / 0 0 0 0
CTB 28 56 34 60 / 0 0 10 0
HLN 32 63 37 65 / 0 10 10 0
BZN 28 59 33 63 / 0 0 0 0
WYS 25 48 29 50 / 20 10 0 0
DLN 32 54 33 59 / 0 0 0 0
HVR 27 58 33 64 / 0 0 0 0
LWT 27 58 36 62 / 0 0 0 0
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
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