Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 190347
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
947 PM MDT SAT APR 18 2015

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH MONDAY...
UPDATE...
RADAR RETURNS ACROSS THE REGION ARE MAINLY VIRGA AT THIS
POINT...SO EXPECTING A MAINLY DRY OVERNIGHT PERIOD. COLD AIR
ADVECTION WILL CONTINUE TO DRIVE GUSTY WINDS ACROSS THE REGION
OVERNIGHT...SO WILL LEAVE THE LAKE WIND ADVISORY IN EFFECT UNTIL
3 AM. HIGH RESOLUTION MODEL GUIDANCE POINTS TO A 9 TO 12 HOUR LULL
IN WINDS AFTER MIDNIGHT THROUGH SUNDAY MORNING...AND SO WILL
WRESTLE WITH THE IDEA OF CANCELLING EARLY IF THAT COMES TO
FRUITION. THE OTHER OPTION WILL BE TO EVENTUALLY EXTEND THE
ADVISORY OUT THROUGH SUNDAY EVENING AS GUSTY NORTHWEST WINDS AGAIN
LOOK TO AFFECT RECREATIONAL ACTIVITIES...IN PARTICULAR NEAR THE
DAM. THE WEST END OF THE LAKE LOOKS TO HAVE MORE MARGINAL
CONDITIONS ON SUNDAY AT THIS POINT. MALIAWCO

PREVIOUS DISCUSSION...

THE INTERACTION OF THE LARGE CLOSED LOW PRESSURE SYSTEM CENTERED
OVER EASTERN COLORADO AND THE UPPER-LEVEL TROUGH FROM THE NORTHERN
ROCKIES HAS SET OFF THUNDERSTORMS STRETCHED ACROSS NEARLY THE
ENTIRE LENGTH OF THE HIGH PLAINS REGION. MOST OF THE FORECAST
ATTENTION WAS DIRECTED TOWARD THE IMMEDIATE NEAR SHORT TERM WITH
THE STRONGER N/NW WINDS ASSOCIATED WITH THE COLD FRONTAL PASSAGE
TODAY AND POSSIBLE FIRE WEATHER CONCERNS. SEE FIRE WEATHER
DISCUSSION BELOW.

THE COLD FRONT HAD PUSHED THROUGH OUR ENTIRE CWA BY 20Z. SOME OF
OUR MORE WIND-PRONE AREAS ARE SEEING WINDS IN THE 35G45 MPH RANGE
WHILE MOST OTHER LOCATIONS HAVE 25G35 MPH WINDS. LAKE WIND
ADVISORY IS WELL COVERED. FOR NOW...CHOSE NOT TO ALTER THE CURRENT
LAKE WIND ADVISORY TO AVOID PUBLIC CONFUSION. AS THE UPPER-LEVEL
TROUGH AXIS PASSES OVER NORTHEAST MONTANA...THE POST-FRONTAL
SURFACE WINDS ARE EXPECTED TO DIMINISH BELOW 15 KTS SUNDAY
MORNING. NOT EXPECTING AN INCREASE IN WINDS AGAIN UNTIL THE NW
FLOW ALOFT BECOMES ESTABLISH OVER THE REGION SUNDAY AFTERNOON. AND
EVEN THEN...THAT INCREASE IN WINDS MAY BE JUST MARGINAL ENOUGH AND
MORE EMPHASIZED OVER OUR EASTERN ZONES...THAT THERE STILL REMAINS
SOME UNCERTAINTY WHETHER ANOTHER LAKE WIND ADVISORY WOULD BE
NEEDED. WOULD LIKE TO HAVE THE NEXT SHIFT LOOK AGAIN AT THE LATEST
UPDATED MODEL DATA TONIGHT FOR THAT DECISION.

THAT NW FLOW ALOFT STAYS WITH US FOR THE REMAINDER OF THE FORECAST
PERIOD...KEEPING THE COLDER AIR OVER OUR NE ZONES AND ALLOWING
SOME WARMER AIR TO SNEAK BACK INTO OUR SW ZONES EVER SO GRADUALLY.

SUNDAY AND SUNDAY AFTERNOON...MODELS ARE INDICATING SOME GENERAL
AGREEMENT FOR SOME VERY LIGHT PRECIP/QPF FOR THOSE E/NE ZONES BUT
THEIR DEPICTION OF IT SEEMS MORE REMINISCENT OF VIRGA SHOWERS OR
SPRINKLES...SO CHOSE TO DECREASE POPS BELOW SLIGHT CHANCE LEVELS
FOR THE MOST PART TO REFLECT THIS THINKING. BMICKELSON

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...
NO SIGNIFICANT CHANGES MADE TO THE GOING FORECAST. LITTLE MODEL
CHANGE EARLY IN THE PERIOD WITH LARGE CLOSED LOW SETTLING OVER
ONTARIO AND HIGH AMPLITUDE RIDGE OVER CENTRAL CANADA. UNCERTAINTY
INCREASING FOR LATE IN THE WEEK AND INTO THE WEEKEND WITH MODEL
DIFFERENCES IN BRINGING SHORTWAVES ACROSS THE NORTHERN ROCKIES AND
UNDERCUTTING THE RIDGE...SO HELD OFF ON ANY FORECAST CHANGES.
EBERT

PREVIOUS LONG TERM DISCUSSION...NORTHWEST FLOW ALOFT WILL PREVAIL
TUESDAY AND WEDNESDAY WITH AN UPPER LOW OVER ONTARIO AND AS UPPER
RIDGE OVER ALBERTA AND WESTERN MONTANA. NORTHEAST MONTANA WILL SEE
MILD AND DRY WEATHER AS THE SHORTWAVES IN THE NW FLOW ALOFT STAY
WELL TO THE EAST.

SOME MODEL DIFFERENCES WITHIN THE BLOCKING PATTERN SHOW UP ON
THURSDAY AS THE GFS IS STRONGER THAN THE ECMWF WITH A BACK DOOR
COLD FRONT THAT MOVES INTO THE FORECAST AREA.

FRIDAY AND SATURDAY...THE HIGH AMPLITUDE RIDGE REMAINS A BLOCKING
FEATURE OVER EASTERN MONTANA BUT MODELS DIFFER ON HANDLING A
DIGGING UPPER TROUGH TO THE WEST THAT COULD BRING SOME SHOWERS TO
CENTRAL AND SOUTHERN MONTANA WITH THE HELP OF EASTERLY UPSLOPE
FLOW. FORRESTER

&&

.AVIATION...
VFR.

CLOUDS: SCATTERED MID-LEVEL CLOUDS FROM 8-12K AGL TONIGHT WILL
GIVE WAY TO A BROKEN DECK OF 5K CLOUDS SUNDAY.

WINDS: NW AT 10-15 KTS TONIGHT THEN INCREASE TO ABOUT 20-25 KTS BY
SUNDAY AFTERNOON. TFJ

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
LAKE WIND ADVISORY UNTIL 3 AM MDT SUNDAY FOR FORT PECK LAKE FOR
CENTRAL AND SOUTHEAST PHILLIPS...CENTRAL AND SOUTHERN VALLEY...
GARFIELD...MCCONE...PETROLEUM.

&&

$$

WEATHER.GOV/GLASGOW





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