FXUS65 KTFX 170927
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
327 AM MDT SAT MAY 17 2008
.DISCUSSION...
MAIN CONCERNS THROUGH THIS WEEKEND WILL BE WARM TEMPERATURES...THE
POTENTIAL FOR SMALL STREAM AND TRIBUTARY FLOODING...AND FIRE
WEATHER POTENTIAL ON SUNDAY. THE PERSISTENT RIDGE OF HIGH PRESSURE
WILL BECOME MORE POSITIVELY TILTED EARLY THIS WEEKEND...INCREASING
WARM AIR ADVECTION THROUGHOUT MUCH OF THE LOWER/MID-LEVELS ACROSS
THE FORECAST AREA. AS A RESULT...TEMPERATURES TODAY ARE EXPECTED
TO BE SEVERAL DEGREES WARMER THAN YESTERDAY. HOWEVER...HOW MUCH
WARMER IS IN QUESTION...AS THE PRIMARY RIDGE AXIS WILL RESIDE WELL
TO THE WEST OF THE REGION...WITH NORTHWESTERLY UPPER LEVEL FLOW
OVER THE FORECAST AREA. MODEL GUIDANCE CONTINUES TO TREND TOWARD
SLIGHTLY LESS WARM CONDITIONS ACROSS THE REGION. FOR A QUICK
COMPARISON...850 MB TEMPS AT KGTF WERE AROUND 20C AROUND 00Z
SATURDAY...AND FORECAST SOUNDING SHOW 850 MB TEMPS AROUND 00Z
SUNDAY BETWEEN 23C AND 24C. GIVEN SUFFICIENT MIXING...THIS
TRANSLATES TO SURFACE HIGH TEMPS TODAY NO MORE THAN 9F WARMER THAN
HIGH TEMPS YESTERDAY...AND THUS MAINLY MIDDLE AND UPPER 80S ACROSS
THE PLAINS AND VALLEYS. ACCORDINGLY...POTENTIAL FOR WIDESPREAD
RECORD-BREAKING HIGH TEMPS TODAY HAS DIMINISHED SOMEWHAT. AT THE
SAME TIME...A PACIFIC TROUGH WILL CONTINUE PROGRESSING EASTWARD
THIS WEEKEND...ACTING TO DE-AMPLIFY THE RIDGE. THIS TROUGH WILL
BECOME DISORGANIZED...EJECTING SEVERAL SHORTWAVE TROUGHS EASTWARD
THROUGH THE UPPER LEVEL JET STREAM NEAR THE INTERNATIONAL BORDER.
AS A RESULT...LEE CYCLOGENESIS WILL BEGIN THIS AFTERNOON...AS
SURFACE WINDS BECOME WESTERLY. WESTERLY WINDS WILL INCREASE IN
SPEED TONIGHT...ELEVATING LOW TEMPS TONIGHT. LOW TEMPS TONIGHT MAY
STRUGGLE TO FALL BELOW 60 AT SOME LOCALES. WINDS WILL BE STRONGEST ON
SUNDAY WHEN THE MAGNITUDE OF THE LOW-LEVEL PRESSURE GRADIENT IS
STEEPEST...RESULTING IN SOME FIRE WEATHER CONCERN OVER NORTH
CENTRAL MONTANA. NO FIRE WEATHER HIGHLIGHTS ARE PLANNED AT THIS
TIME...AS AFTERNOON RELATIVE HUMIDITIES ARE EXPECTED TO BE
MARGINAL...ONLY FALLING TO NEAR 20 PERCENT...AND FUEL MOISTURE
WILL BE SUFFICIENT TO MITIGATE FIRE WEATHER CONCERNS. ON
SUNDAY...THE 850 MB THERMAL RIDGE WILL TRANSLATE EASTWARD AS THE
UPPER LEVEL JET STREAM CONTINUES TO BE SITUATED FROM NORTHWEST TO
SOUTHEAST ACROSS THE FORECAST AREA. THE WARMEST TEMPERATURES ON
SUNDAY ARE EXPECTED IN EASTERN PORTIONS OF THE FORECAST AREA...BUT
THE OVERALL DE-AMPLIFICATION OF THE RIDGE AT THIS POINT WOULD
AGAIN DIMINISH THE THREAT FOR WIDESPREAD RECORD-BREAKING HIGH
TEMPS ON SUNDAY. A SIMILAR SITUATION IS EXPECTED ON MONDAY...BUT
WITH SLIGHTLY COOLER TEMPERATURES IN RESPONSE TO INCREASING
CLOUDINESS WITH INCREASING MID/UPPER-LEVEL MOISTURE. AN ISOLATED
SHOWER/THUNDERSTORM CANNOT BE COMPLETELY RULED OUT SUNDAY AND
MONDAY AFTERNOON OVER NORTHEASTERN PORTIONS OF THE FORECAST AREA
AND/OR OVER THE HIGHER TERRAIN OF SOUTHWEST MONTANA...WHERE WEAK
AFTERNOON INSTABILITY MAY EXIST. THE WARM TEMPERATURES WILL RESULT
IN HYDROLOGY CONCERNS FROM SNOW MELT...WHICH ARE ADDRESSED BELOW.
COHEN
MONDAY NIGHT THROUGH THURSDAY NIGHT...EXPECT A MAJOR CHANGE IN THE
WEATHER PATTERN DURING THIS PERIOD...AS A RETURN TO WETTER AND
COOLER CONDITIONS DEVELOP. A PACIFIC COLD FRONT WILL MOVE THROUGH
THE REGION ON TUESDAY...BRINGING IN COOLER AIR AND A CHANCE FOR
SHOWERS/THUNDERSTORMS ACROSS THE REGION AS THE COLD FRONT MOVES
THROUGH. EXPECT WINDY CONDITIONS AND MILD TEMPERATURES AHEAD OF THE
FRONT...BUT GRADUALLY COOLING TEMPERATURES ARE EXPECTED BEHIND THE
FRONT. THE CHANCES FOR SHOWERS CONTINUE ON WEDNESDAY...ESPECIALLY
OVER SOUTHWEST MONTANA. A STRONGER AND SLOW MOVING AREA OF LOW
PRESSURE WILL MOVE THROUGH THE REGION FROM WEDNESDAY NIGHT THROUGH
THURSDAY NIGHT. EXPECT INCREASING CHANCES FOR PRECIP...WITH PRECIP
CHANCES BECOMING LIKELY IN THE MOUNTAINS. TEMPERATURES WILL COOL TO
BELOW SEASONAL NORMALS...WITH AFTERNOON HIGHS GENERALLY 10 TO 15
DEGREES BELOW NORMAL FOR WEDNESDAY AND THURSDAY. ADDITIONALLY...SNOW
LEVELS WILL CONTINUE TO FALL...LOWERING TO NEAR 6000 FEET AT TIMES
DURING THE OVERNIGHT HOURS. BRUSDA
FRIDAY AND SATURDAY...LATEST LONG RANGE FORECAST MODELS ARE IN
REASONABLY GOOD AGREEMENT THROUGH THE EXTENDED PERIODS. A DEEP LOW
PRESSURE IS EXPECTED TO REMAIN OVER THE REGION CAUSING SCATTERED
SHOWERS AND COOLER BELOW SEASONAL TEMPERATURES FOR MUCH OF THE
STATE. SAUCIER
&&
.AVIATION...
UPDATED 0455Z.
VFR CONDITIONS WILL CONTINUE ACROSS NORTH CENTRAL AND SOUTHWEST
MONTANA THROUGH AT LEAST SATURDAY. AN UPPER LEVEL RIDGE OF HIGH
PRESSURE OVER THE PACIFIC COAST STATES WILL CONTINUE THE GENERALLY
DRY NORTHWEST FLOW ALOFT. SKIES WILL BE MOSTLY CLEAR WITH ONLY A FEW
HIGH CLOUDS PASSING THROUGH THE AREA. LIGHT WINDS TONIGHT ACROSS
NORTH CENTRAL MONTANA WILL BECOME MORE BREEZY AND WESTERLY SATURDAY
AFTERNOON AS A SURFACE TROUGH FORMS TO THE LEE OF THE ROCKIES.
COULSTON
&&
.HYDROLOGY...
UNSEASONABLY WARM TEMPERATURES THIS WEEKEND WILL RESULT IN A RAPID
INCREASE IN SNOW MELT. CURRENT LIQUID EQUIVALENTS FOR THE SNOW PACK
INFLUENCING MANY BASINS ACROSS THE FORECAST AREA ARE GENERALLY 10 TO
20 INCHES...AND SLIGHTLY ABOVE CLIMATOLOGICAL AVERAGES. THUS...RISING
WATER LEVELS AND THE THREAT FOR FLOODING WILL EXIST IN THE VICINITY
OF SMALL STREAMS AND TRIBUTARIES THIS WEEKEND. THE FLOOD WATCH FOR
PORTIONS OF THE FORECAST AREA REMAINS IN EFFECT THROUGH SUNDAY
AFTERNOON. THE TWO MEDICINE RIVER 10 MILES SOUTH OF BROWNING IS
ALREADY NEARLY WITHIN ONE HALF FOOT OF FLOOD STAGE...AND A FLOOD
ADVISORY FOR SMALL STREAMS WILL BE IN EFFECT FOR THIS REGION.
ADDITIONAL ADVISORIES...OR POSSIBLY WARNINGS...MAY BECOME REQUIRED
THIS WEEKEND. FOR THE MAJOR RIVERS...WATER LEVELS ARE EXPECTED TO
RISE THIS WEEKEND...BUT NO FLOODING IS CURRENTLY ANTICIPATED.
COHEN
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 87 60 85 55 / 0 0 0 0
CTB 86 58 84 50 / 0 0 0 0
HLN 90 61 86 58 / 0 0 0 0
BZN 86 50 87 51 / 0 0 0 0
WEY 74 42 75 42 / 0 0 0 0
DLN 85 51 85 48 / 0 0 0 0
HVR 87 54 87 50 / 0 0 0 0
LWT 82 49 85 50 / 0 0 0 0
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH THROUGH SUNDAY AFTERNOON FOR MTZ008-009-012-014-015-
048-050-052>055.
&&
$$
SHORT TERM...COHEN
LONG TERM...BRUSDA/SAUCIER
AVIATION...COULSTON
WEATHER.GOV/GREATFALLS
