Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 020256
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
856 PM MDT FRI AUG 1 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SUNDAY...
UPDATE...A LINE OF THUNDERSTORMS IN THE FAR NORTHEASTERN SECTION
OF THE FORECAST AREA WILL CONTINUE TO DISSIPATE AS THEY MOVE
TOWARDS THE NORTH DAKOTA BORDER. OTHERWISE ANOTHER FAIR AND MILD
SUMMER NIGHT IN-STORE FOR NORTHEAST MONTANA. SLIGHT ADJUSTMENTS
MADE TO DEAL WITH THE EVENING CONVECTION AND TEMPERATURES.    PROTON

PREVIOUS DISCUSSION...A WEAK SURFACE LOW PRESSURE CENTER REMAINS ANCHORED OVER
SOUTHEAST MONTANA...DIRECTING EASTERLY WINDS OVER OUR EASTERN
ZONES AND NORTHERLY WINDS OVER OUR WESTERN ZONES...NONE OF WHICH
ARE OF GREAT CONSEQUENCE AS MOST LOCATIONS ARE SHOWING LIGHT WINDS
OCCASIONALLY GUSTY UP TO 12 OR 13 KNOTS AT MOST WITH PEAK HEATING.

THIS REPEAT PATTERN WE HAVE BEEN STUCK IN LATELY WILL CONTINUE FOR
JUST A FEW MORE DAYS. SYNOPTIC RIDGE OF HIGH PRESSURE OVER THE
WESTERN STATES WITH STRONG DAYTIME HEATING OF THE SURFACE LAYER
SETTING OFF THUNDERSTORMS DURING THE MID-AFTERNOON HOURS INITIALLY
OFF THE HIGHER TERRAIN THE PROGRESSING OVER OTHER PORTIONS OF
NORTHEAST MONTANA THROUGH THE EARLY EVENING HOURS. HARDLY ANY
EFFECTIVE BULK SHEAR AVAILABLE TO STRENGTHEN MOST OF THESE
STORMS...SO THEY MOVE SLOWLY AND COLLAPSE UNDER THEIR OWN WEIGHT
AND PRODUCE OUTFLOW WINDS GUSTING 30 TO 40 MPH AT TIMES.

TONIGHT...A STRONGER STORM FROM CENTRAL SASKATCHEWAN IS PROGGED TO
DESCEND SOUTHEASTWARD AND JUST KISS THE NORTHEAST CORNER OF
SHERIDAN COUNTY. MOST EVERY OTHER DIURNALLY-DRIVEN STORM WILL BE
OF LESSER IMPACT...WITH LIGHTNING BEING THE MAIN THREAT. THIS
ACTIVITY IS BEING DRIVEN BY A VERY SMALL-SCALE DISTURBANCE
EMBEDDED WITHIN THE NORTHWEST FLOW ALOFT OVER NORTHEAST MONTANA.

SATURDAY...THE RIDGE BOUNCES BACK A BIT...BUT IT IS FLATTENED
SOMEWHAT BY AN APPROACHING SHORT-WAVE DISTURBANCE FROM THE WEST.
THIS IS NOT EXPECTED TO PRODUCE MUCH MORE THAN VIRGA SHOWERS
BEYOND THE EAST AND WEST EDGES OF OUR CWA.

BY SUNDAY...THE FLOW TURNS A BIT MORE NORTHWESTERLY WHILE AN
EMBEDDED SHORT WAVE DISTURBANCE BRINGS MORE WIDESPREAD SHOWERS AND
THUNDERSTORMS FROM THE NORTHWEST. I CHOSE TO RAISE POPS HERE TO
SHOW THE INCREASE IN CONFIDENCE AND COVERAGE COMPARED TO THE ISOLATED
NATURE OF THE PRECIPITATION WE HAVE BEEN RECEIVING LATELY.
BMICKELSON

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...

THERE IS AN INCREASED CHANCE FOR RAIN SHOWERS AND THUNDERSTORMS
NEXT WEEK. A PERSISTENT LOW WILL CONTINUE TO BE PARKED OVER THE
GULF OF ALASKA THAT WILL DRIVE PACIFIC MOISTURE OVER THE RIDGE.
LATE IN THE WEEKEND A SHORTWAVE LOW OFF SOUTHERN CALIFORNIA MOVES
ONSHORE AND WILL BE PICKED UP BY THE UPPER FLOW. THIS SHORTWAVE
SYSTEM WILL RIDE UP THROUGH THE ROCKIES...FLATTENING THE RIDGE.
THE LOW...WHICH PICKED UP PACIFIC MOISTURE...WILL SEND WEAK FRONTS
ACROSS NORTHEAST MONTANA...WHICH MODELS SUGGEST HAS WEAK TO
MODERATE CONVECTIVE INSTABILITY. THEREFORE...DUE TO INCREASING
MODEL CONSISTENCY CONCERNING THIS WAVE...INCREASED POPS TO CHANCE
FOR MID-WEEK. WHILE LATEST EC AND GFS BOTH AGREE IN GENERAL WITH
THE MODERATELY UNSETTLED PATTERN...BUT DO NOT YET AGREE WITH
TIMING OR LOCATION. SCT

PREVIOUS DISCUSSION...
A WEAK QUASI-ZONAL FLOW ALOFT IS EXPECTED EARLY NEXT WEEK AS
UPPER RIDGE CONTINUES TO BREAK DOWN. THERE WILL BE A SLOW MOVING
LOW PRESSURE SYSTEM ACROSS EASTERN MONTANA THAT WILL DRIFT INTO
THE DAKOTAS MONDAY NIGHT. A MIXTURE OF WEAK SHORTWAVES...EITHER
PACIFIC AND/OR MONSOONAL MOISTURE AND UNSTABLE AIR MASS WILL ALLOW
FOR CHANCES FOR THUNDERSTORMS.

THEN...A WEAK SHORTWAVE IN THE ZONAL FLOW ALOFT IS EXPECT ON
TUESDAY. THE ECMWF IS SLOWER THAN THE GFS WITH THE SYSTEM AND
THE MODELS ARE SHOWING SOME RUN TO RUN DIFFERENCES. CONDITIONS
LOOK FAVORABLE FOR AT LEAST A FEW THUNDERSTORMS ON TUESDAY AND
POSSIBLY WEDNESDAY.

ECMWF MAINTAINS THE IDEA OF AN UPPER RIDGE THURSDAY AND FRIDAY
WITH THE GFS FAVORS A MORE MOIST NW FLOW ALOFT. WILL MAINTAIN DRY
FORECAST FOR NOW AS SEE WHERE FUTURE MODEL RUNS TAKE THE FORECAST.
FORRESTER

&&

.AVIATION...
A BRIEF SHOWER OR THUNDERSTORM IS POSSIBLE BEFORE 06Z AT KSDY.
OTHERWISE EXPECT MAINLY VFR CONDITIONS TONIGHT WITH WINDS UNDER 10
KTS OUT OF THE NORTHEAST. MALIAWCO

&&

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

&&

$$

WEATHER.GOV/GLASGOW





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