Area Forecast Discussion
Issued by NWS Glasgow, MT

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000
FXUS65 KGGW 180135
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
735 PM MDT THU APR 17 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SATURDAY...
A MOIST FLOW HAS MOVED INTO THE AREA THIS EVENING ON THE BACKSIDE OF
A SHORTWAVE RIDGE. RADAR ECHOES HAVE BEEN INCREASING AND MODELS ARE
SHOWING A DECENT POSSIBILITY OF 0.05" ACCUMULATING ACROSS THE
CENTRAL AND NE ZONES TONIGHT. SILENT OR SLIGHT CHANCE POPS WERE
RAISED SLIGHTLY. REST OF FORECAST WAS LARGELY LEFT UNTOUCHED. JAMBA

PREVIOUS SHORT TERM DISCUSSION...
SHORTWAVE TROF PUSHING INTO THE PACIFIC NORTHWEST WILL SWING
ACROSS THE NORTHERN ROCKIES AND INTO MONTANA THROUGH FRIDAY NIGHT.
WARM FRONT/LEE TROF EDGING SLOWLY EASTWARD TODAY WILL BECOME QUASI
STATIONARY TONIGHT WITH WARM AIR CONTINUING TO STREAM NORTHWARD IN
ADVANCE OF THE UPPER WAVE. BEST CHANCE OF SHOWERS WILL BE WITH THE
COLD FRONT THAT CROSSES THE REGION FRIDAY AFTERNOON AND EVENING.
SHOWERS MAY CONTINUE INTO SATURDAY MORNING ACROSS THE FAR NORTH
WITH COLD AIR WRAPPING INTO THE STATE.

SYSTEM MOVES EAST BY SATURDAY AFTERNOON WITH RIDGE REBOUNDING OVER
THE STATE. EBERT

.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
THE LONG RANGE IS ON TRACK DEPICTING A SHORTWAVE RIDGE SATURDAY
NIGHT TRANSLATING EAST FOR SUNDAY AS A SHORTWAVE TRACKS ACROSS THE
INTERNATIONAL BORDER. THERE MAY BE ENOUGH DYNAMIC FORCING FOR A
SHOWER SO WILL MAINTAIN SLIGHT CHANCE POPS.

UPPER LEVEL RIDGING IS THEN EXPECTED TO DOMINATE AS INDICATED BY
EXCELLENT MODEL CONSENSUS FOR MONDAY AND INTO EARLY NEXT WEEK.
THIS WILL DRIVE LARGE SCALE SUBSIDENCE AND THUS DRY CONDITIONS
ACROSS THE NORTHERN PLAINS AND WARMER TEMPERATURES.

A LARGE TROUGH WILL THEN BECOME CARVED OUT BY THE 500MB HEIGHT
FIELD ACROSS THE WESTERN CONUS BY TUESDAY NIGHT AND TRANSLATE
EASTWARD THROUGH THE MIDWEEK...SWITCHING THE FLOW ALOFT AROUND
FROM THE SOUTHWEST ACROSS THE NORTHERN PLAINS. ENSEMBLE FORECASTS
SHOW SOMEWHAT LOWER PROBABILITIES FOR 0.25 INCHES OF QPF ACROSS
THE CWA BUT CONSIDERING IT IS STILL NEARLY A WEEK AWAY THE OVERALL
AGREEMENT IS STILL CONSIDERABLE ENOUGH TO MAINTAIN HIGH CHANCE
POPS. IN ANY EVENT...THERE WILL BE ENOUGH DYNAMIC LIFT WITH THIS
SYSTEM AND PLENTY OF PACIFIC MOISTURE THAT A WIDESPREAD WETTING
RAIN IS LOOKING MORE LIKELY. ADDITIONALLY...ENOUGH INSTABILITY MAY
EXIST IN THE SOUTHEASTERN ZONES TO INITIATE THUNDERSTORMS. WILL
EXPECT TO REFINE THE DETAILS OF THIS SYSTEM IN THE COMING DAYS AS
THE ECMWF HAS BEEN SOMEWHAT FURTHER NORTH WITH THE TRACK THAN THE
GFS. MALIAWCO
PREVIOUS LONG TERM DISCUSSION...
SYNOPTIC SET UP...A SHORTWAVE TROUGH IS EXITING THE AREA OVER THE
UPPER MISSISSIPPI VALLEY AND MANITOBA. A LARGE RIDGE RUNS UP HIGH
PLAINS OF MONTANA AND ALBERTA AND THEN TIPS OVER WEST ACROSS
NORTHERN BRITISH COLUMBIA AND THE GULF OF ALASKA. A SHORTWAVE EXIST
S OVER THE PACIFIC NORTHWEST WHILE AN EVEN LARGE TROUGH OF COLD
AIR IS JUST SOUTH OF THE GULF OF ALASKA RIDGE RUNNING UP INTO THE
BEARING SEA.

SATURDAY NIGHT THROUGH SUNDAY... THE RIDGE WILL FLATTEN AND THE WEAK
SHORTWAVE WILL PASS JUST NORTH OF THE CWA SKIRTING THE
INTERNATIONAL BORDER. A SLIGHT CHANCE FOR SPILL OVER PRECIP IS
POSSIBLE IF THE SHORTWAVE MOVES SLIGHTLY FARTHER SOUTH.

SUNDAY NIGHT THROUGH TUESDAY... RIDGE WILL RE-AMPLIFY ACROSS THE
REGION WITH THE EXITING SHORTWAVE. EXPECT DRY CONDITIONS OUT WITH
A WEAK DOWN-SLOPING EFFECT ON MONDAY. HIGH TEMPERATURES WILL RISE
INTO THE 60S AND 70S HELPING TO DESTABILIZE THE SURFACE LAYER A
BIT MORE.

TUESDAY NIGHT ONWARD...SURPRISINGLY...MODELS STILL SEEM TO BE
HOLDING TOGETHER DURING THESE PERIODS WITH FAIRLY WELL MATCHED
SYNOPTIC FEATURES FROM RUN TO RUN AND MODEL TO MODEL. THE MAIN
PLAYER IS THE LARGE TROUGH OVER THE BEARING SEA AND GULF OF ALASKA
DROPPING DOWN OVER THE WESTERN THIRD OF THE CONUS. MODELS HAVE
NOT FULLY RESOLVED THE BASE/SOUTHERN COMPONENT OF THIS
TROUGH...HOWEVER THEY DO APPEAR TO BREAK THE NORTHERN HALF INTO A
WIND UP LOW OVER EASTERN MONTANA AND SOUTHERN SASKATCHEWAN. A
STRONG JET LADDENED WITH PACIFIC MOISTURE WILL PUMP INTO THIS LOW BRINGING
INCREASED CHANCES FOR PRECIPITATION TO NORTHEAST MONTANA IN
MULTIPLE MODELS. FOR THIS REASON...RAISED POPS CONSIDERABLY ABOVE
THE NORMAL CLIMO OF 15 TO 20 PERCENT DURING THESE PERIODS. GAH


&&

.AVIATION...

EXPECT VFR CEILINGS TO PREVAIL FOR ALL TAF SITES THROUGHOUT THE
ENTIRE TAF CYCLE. A FEW ISOLATED SHOWERS ARE POSSIBLE OVERNIGHT BUT
SCATTERED SHOWERS ARE EXPECTED FRIDAY. SOUTHEAST WINDS OF 10 TO 15
KTS WILL CONTINUE THROUGH FRIDAY. MALIAWCO/BMICKELSON


&&

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

&&

$$

WEATHER.GOV/GLASGOW




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