Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 022024
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
224 PM MDT WED SEP 2 2015

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH FRIDAY...
A WARM TO HOT AND MAINLY DRY AFTERNOON LOOKS TO CONTINUE ACROSS
NORTHEAST MONTANA. RADAR INDICATES SOME WEAK SHOWER ACTIVITY
APPROACHING FROM THE SOUTH AT THIS TIME...BUT MESOSCALE MODEL
GUIDANCE MOSTLY KEEPS THIS THREAT TO THE SOUTH. WILL MONITOR OVER
THE NEXT FEW HOURS...BUT MOST PLACES SHOULD REMAIN DRY.

A BROAD PACIFIC TROUGH WILL DEEPEN AND TRANSLATE EAST OVER THE
WESTERN CONUS...PUMPING IN AN ABUNDANCE OF MOISTURE AS IT DOES SO.
HEIGHT FALLS AND CLOUD COVER WILL RESULT IN COOLER TEMPERATURES
FOR THURSDAY AND FRIDAY...AND THE TROUGH WILL ENHANCE DYNAMIC
FORCING FOR ASCENT. EXPECT INCREASING SHOWERS AND THUNDERSTORMS
EACH DAY AS THE TROUGH ADVANCES. MALIAWCO


.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...

THE WET PATTERN CONTINUES INTO THE WEEKEND. FRIDAY EVENING THE
WEST COAST TROUGH DESCENDS FURTHER SOUTH INTO CALIFORNIA. THE
TROUGH PICKS UP ADDITIONAL PACIFIC MOISTURE EJECTING IT NORTHEAST
INTO THE ROCKIES. THEN BEGINNING SATURDAY THE TROUGH LIFTS
NORTHEAST MOVING INTO MONTANA ON SUNDAY. MODELS ARE SHOWING QUITE
A BIT OF ENTRAINED QPF.

SATURDAY...THE FRONTAL BOUNDARY...BETWEEN THE HOT AIR-MASS IN THE
EAST AND THE COOL AIR MASS IN THE WEST...WILL RUN NE TO SW ACROSS
MONTANA. THIS WILL PROVIDE THE FOCUS FOR THE OVERRUNNING MOISTURE
TO PRODUCE RAIN SHOWERS AND THUNDERSTORMS. A BLEND OF MODELS
SUGGESTS SOME AREAS COULD SEE AN INCH OF RAIN OR MORE.

SATURDAY NIGHT/SUNDAY...MODELS AGREE WITH THE NOW FAST MOVING STORM
STACKING UP THE LOW CENTERS AS IT SLIPS INTO THE EASTERN MONTANA.
WHERE MODELS DIFFER IS HOW FAST THE STORM MOVES NORTH INTO CANADA.
THE RESULT COULD BE SIGNIFICANT DRY-SLOTTING WHICH COULD CUT OFF
THE RAIN BY SUNDAY AFTERNOON...BUT NOT BEFORE ADDITIONAL HEAVY
RAIN FALLS...POSSIBLY ANOTHER INCH OR MORE. SUNDAY ALSO LOOKS TO
BE QUITE WINDY AND MUCH COOLER...AROUND 15F BELOW NORMAL.

MONDAY AND BEYOND...THE WIND CONTINUES MONDAY AND TEMPERATURES
COULD FURTHER FALL TO AROUND 20F BELOW NORMAL. THEN MODELS SHOW
ANOTHER TROUGH ROTATING ACROSS THE DIVIDE AND THROUGH THE
AREA...MAINTAINING THE COOL CONDITIONS THROUGH MID-WEEK. THIS
TROUGH WILL NOT BE QUITE AS WET...BUT COULD BRING ADDITIONAL
SCATTERED LIGHT RAIN. LOOKING BEYOND THE PERIOD...BY THE END OF
NEXT WEEK MODELS TEND TO AGREE WITH HIGH PRESSURE DEVELOPING OFF
THE WEST COAST AND WARMER AIR STARTING TO DRIFT BACK NORTH INTO
MONTANA WITH DRY CONDITIONS AND A RETURN TO AT LEAST NORMAL OR
SLIGHTLY ABOVE TEMPERATURES.

CONFIDENCE IS HIGH FOR WEEKEND GENERAL WET AND COOL. CONFIDENCE IS
LOWER WHEN IT COMES TO LOCATING WHERE THE RAIN WILL BE HEAVY OR
LIGHT. THEREFORE WITH CONTINUING TIMING AND LOCATION
DIFFERENCES...GRIDS WELL REPRESENT EXPECTED CONDITIONS. THE FEW
GRID EDITS WERE TO DEEMPASIZE THUNDER. ALSO EDITS WERE MADE FOR
COORDINATION PURPOSES.

SCT

PREVIOUS DISCUSSION...
SYNOPTIC SET UP... LONG RANGE BEGINS WITH A SMALL DIFFERENCE IN
MODELS WHICH IS QUICKLY EVOLVING APART IN MODELS. AREAS OF
SIMILARITY RESIDE ON THE HOT HIGH PRESSURE OVER THE FOUR CORNERS
WITH A RIDGE RUNNING INTO THE DAKOTAS AND ONTARIO. A LARGE COLD
TROUGH RUNS FROM NORTHERN ALBERTA THROUGH SOUTHERN BRITISH
COLUMBIA AND THEN CHANGES ITS BASE PLACEMENT DEPENDING ON MODEL.
GEM AND GFS DROP THE BASE OF THE TROUGH OVER NORTHERN CALIFORNIA
WHILE THE EC AND DGEX PLACE THE LOW FARTHER NORTH OVER THE
PACIFIC NORTHWEST.

FRIDAY NIGHT THROUGH SUNDAY NIGHT... DIFFERENCES BETWEEN THE
MODEL SETS IN THE BASE OF THE TROUGH TO THE WEST ARE SUBTLE AT
THIS RANGE BUT LEAD TO DOWNRIGHT CHAOS UPSTREAM IN SOUTHWEST FLOW
LOCATED OVER NORTHEAST MONTANA. DIFFERENCES IN MODEL QPF BASED ON
PLACEMENT OF THE DOWNSTREAM JETS VARY FROM A QUARTER INCH TO 4
INCHES OVER 60 HOURS. CURRENTLY THE BULK OF THE PRECIPITATION
LOOKS TO FALL OVER SATURDAY NIGHT AND SUNDAY WHEN THE BASE OF THE
SYNOPTIC TROUGH ITSELF MOVES THROUGH AND A TROWAL MAY/OR MAY NOT
SET UP BEHIND IT. A CLOSED LOW WILL ALSO FORM AT THE SURFACE
SOMEWHERE BETWEEN SOUTHERN MONTANA AND SOUTHERN SASKATCHEWAN.
THIS WIDE SPREAD OF RANGE MEANS THAT SURFACE WIND DIRECTIONS AND
SPEEDS ARE VERY MUCH SUBJECT TO CHANGE OVER THE NEXT FEW FORECAST
CYCLES. REGARDLESS OF THESE PLACEMENT PROBLEMS COOLER CONDITIONS
WITH AT LEAST LIMITED EXTENDED RAIN IS ANTICIPATED DURING THESE
PERIODS. CONFIDENCE IS BELOW AVERAGE.

MONDAY ONWARD... AS THE BASE OF THE TROUGH EXITS THE AREA COOL
ZONAL FLOW WILL TAKE OVER. EXPECT CONDITIONS TO REMAIN DRY WITH A
SLIGHT WARMING TREND. GAH



&&

.AVIATION...

A LEE SIDE SURFACE TROUGH SLIDES INTO NORTHEAST MONTANA
TODAY...FOLLOWED CLOSELY BY A COLD FRONT TONIGHT.

SOUTHERLY WINDS WILL RELAX AND BECOME VARIABLE LATER TODAY. THEN
AS THE SURFACE TROUGH MOVES INTO THE DAKOTAS...WIND BEHIND THE
TROUGH WILL STRENGTHEN AND BECOME NORTHERLY TONIGHT AND THURSDAY.

THE MAIN EFFECT OF THE COLD FRONT WILL BE TO INCREASE SKY COVER
TODAY THROUGH THURSDAY. THE PATTERN WILL REMAIN MOSTLY DRY.
HOWEVER BOTH GFS AND NAM PRODUCE LIGHT RAIN ALONG THE FRONTAL
BOUNDARY AS IS DRIFTS EAST LATE TONIGHT AND THURSDAY. NOT
EXPECTING MUCH IN THE WAY OF MEASURABLE RAIN..BUT IT COULD
TEMPORARILY LOWER CEILINGS AND VISIBILITIES.

SCT


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

WEATHER.GOV/GLASGOW



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