Area Forecast Discussion
Issued by NWS Glasgow, MT

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000
FXUS65 KGGW 212039
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
239 PM MDT THU AUG 21 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SATURDAY...
A SIGNIFICANT STORM SYSTEM IS DUE TO ARRIVE THIS WEEKEND WITH A
SOAKING RAIN. WINDY CONDITIONS ARE EXPECTED SATURDAY.

ANOTHER BAND OF SHOWERS ARE MOVING INTO THE CENTRAL ZONES THIS
AFTERNOON AS DISTURBANCES HAVE PERIODICALLY MOVED NORTHEAST THROUGH
THE AREA. AN UPPER TROUGH WILL DIG TO OUR WEST AS A STRONG
DISTURBANCE DROPS INTO WASHINGTON STATE. THE UPPER LOW WILL CLOSE
OFF OVER THE PACIFIC NW TONIGHT THEN DRIFT THROUGH THE
NORTHERN/CENTRAL ROCKIES FRIDAY AND SATURDAY. THE CLOSED NATURE OF
THIS SYSTEM WOULD FAVOR A SLOWER MODEL SOLUTION.

RAINSHOWERS SHOULD DISSIPATE EARLY THIS EVENING WITH THE LOSS OF
DAYTIME HEATING. WITH THE SYSTEM CLOSING OFF...NE MT MAY ENJOY A
PERIOD OF RELATIVE DRYNESS THROUGH TOMORROW...ESPECIALLY THE NE
ZONES.

THEN FRIDAY NIGHT AND SATURDAY...THE SYSTEM BEGINS TO THROW A RAIN
SHIELD OUR WAY FROM THE SW. A SOAKING RAIN IS EXPECTED FOR MOST
AREAS SATURDAY BUT PROXIMITY TO A DRY SLOT TO THE SOUTH MAY THROW IN
CONVECTIVE ELEMENTS INTO THE MIX. SINCE SOILS STARTED OUT
RELATIVELY DRY PRIOR TO THIS EVENT...WIDESPREAD FLOODING IS NOT
ANTICIPATED. BUT BRIEF PERIODS OF HEAVY RAIN COULD SWELL
CREEKS/STREAMS. TFJ


.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...

THE EXTENDED MODELS INITIALLY AGREE WITH GENERAL FEATURES BUT
STILL STRUGGLE WITH DETAILS DUE TO THE DISPLACEMENT OF THE LOW
CENTERS BETWEEN EACH MODEL. THIS IS SIGNIFICANT SINCE IT WILL
DETERMINE WHEN AND WHERE THERE WILL BE RAIN DUE TO THE PLACEMENT
OF THE DRY SINKING AIR BEHIND THE LOW CENTER THAT COULD POSSIBLY
CUT OFF MOST MOISTURE AROUND SUNDAY EVENING. THERE IS ANOTHER
PERIOD NEAR THE END OF NEXT WEEK WHERE THE 00Z MODELS DIFFERED
WITH THE TIMING AND AMPLITUDE WITH THE NEXT TROUGH. HOWEVER BOTH
12Z MODELS CONVERGE ON A MORE SHALLOW LONG WAVE TROUGH BY THURSDAY
EVENING. SCT

FEW CHANGES IN THE EARLY PERIOD SINCE THE RAIN IDEA COMES ACROSS
ELL. ALTHOUGH WITH THE LATEST EC AND NAM...MADE POPS MORE
WIDESPREAD SUNDAY/SUNDAY EVE. LATER IN THE WEEK THE UNCERTAINTY
CONTINUES...THEREFORE FEW OTHER CHANGES WERE MADE. SCT

PREVIOUS DISCUSSION...
STEADY PERIODS OF RAIN CAN BE EXPECTED TO BE ONGOING ACROSS THE
CWA WITH THE UPPER LEVEL TROUGH AXIS DIRECTLY OVER NORTHEAST
MONTANA SATURDAY NIGHT TO START OFF THE EXTENDED PERIOD. 21/00Z
GUIDANCE INDICATES THAT THE LOW WILL CLOSE OFF AS IT TRANSLATES
NORTHEAST ON SUNDAY...ALLOWING THE STEADY RAIN TO TAPER OFF FROM
SOUTHWEST TO NORTHEAST. SREF PLUMES SHOW DECREASING MUCAPE AND
SHEAR THROUGH THE WEEKEND AND SO LEFT OUT MENTION OF THUNDER AS
WRAP AROUND MOISTURE LIFTS OUT OF THE AREA.

MONDAY AND MONDAY NIGHT...AS THE CLOSED LOW PUSHES INTO CENTRAL
SASKATCHEWAN AND MANITOBA...ANOTHER SHORTWAVE APPROACHES IN
NORTHWEST FLOW ALOFT FROM THE PACIFIC NORTHWEST WITH A DEEPENING
TROUGH ONCE AGAIN TO INFLUENCE MONTANA. THERE ARE DIFFERENCES IN
THE WAY THAT THE GFS/ECMWF ARE HANDLING THIS TROUGH...WITH THE
ECMWF HAVING IT FURTHER TO THE WEST AS IT CLOSES OFF A LOW ACROSS
NEVADA. THIS WOULD KEEP PRECIPITATION CHANCES SOUTH OF THE REGION
WHILE THE GFS HAS THE TROUGH DEEPENING OVER MONTANA. WILL SIDE
WITH THE ECMWF FOR NOW AND INTRODUCE A QUIETER PERIOD IN THE WAKE
OF THE WEEKEND SYSTEM AND IN ADVANCE OF THE NEXT.

REGARDLESS...EXPECT NORTHERLY WINDS ON THE BACKSIDE OF THE INITIAL
SYSTEM TO HELP BRING IN UNSEASONABLY COOL TEMPERATURES TO
CONTINUE INTO EARLY NEXT WEEK. IN FACT...SOME PLACES MONDAY
MORNING ALONG THE INTERNATIONAL BORDER AND IN SOME OF THE DEEPER
VALLEY LOCATIONS ALONG THE MILK/MISSOURI RIVER BASINS AND PERHAPS
THE YELLOWSTONE MAY SEE LOW TEMPERATURES DIPPING INTO THE UPPER
30S. THE REALIZATION OF COLDER TEMPERATURES WILL SOMEWHAT DEPEND
ON RADIATIVE COOLING SUNDAY NIGHT AND HOW QUICKLY CLOUDS/
PRECIPITATION EXIT. IF SKIES CAN CLEAR OUT...RADIATIONAL COOLING
WILL MAKE FOR A COLD START FOR MONDAY MORNING AND TEMPERATURES
ONLY RECOVERING TO THE 50S AND 60S DURING THE DAY.

DIFFERENCES IN MODEL SOLUTIONS INCREASE FROM TUESDAY INTO LATE
NEXT WEEK. BOTH GFS AND ECMWF SHOW AN OPPORTUNITY FOR SOME
RIDGING ACROSS NORTHEAST MONTANA TUESDAY INTO WEDNESDAY AND SO
THIS PERIOD MAY OFFER BENIGN WEATHER. RECALL THAT THE GFS HAS A
SECOND TROUGH INITIALLY ACROSS MONTANA ON MONDAY. IT TRACKS THE
TROUGH PROGRESSIVELY FURTHER EAST ALLOWING FOR A RIDGE AND DRY
WEATHER TO PERSIST INTO MUCH OF NEXT WEEK ACROSS THE NORTHERN
PLAINS. IN CONTRAST...THE ECMWF HAS THAT TROUGH FURTHER
WEST...WITH RIDGING OCCURRING OUT AHEAD OF IT WHICH WOULD OFFER
DRY WEATHER FOR TUESDAY AND WEDNESDAY ACROSS THE CWA. THE TROUGH
THEN TRANSLATES EAST WITH A SURFACE LOW TRACKING AHEAD OF IT
DOWNSTREAM LATE NEXT WEEK. PRECIPITATION CHANCES TO THE NORTH OF
THIS LOW WOULD EXTEND FROM WYOMING TO SOUTHEAST MONTANA AND INTO
THE DAKOTAS. IN SHORT...IT IS UNCLEAR WHICH SOLUTION MAY PLAY OUT
AND SO UNCERTAINTY BEYOND MONDAY IS QUITE LARGE. MALIAWCO


&&

.AVIATION...
A BROAD UPPER LEVEL TROUGH SLOWLY MOVING ACROSS THE PACIFIC
NORTHWEST AND MONTANA WILL BRING INCREASING CHANCES FOR
PRECIPITATION THIS AFTERNOON THROUGH THE WEEKEND.

THIS AFTERNOON AND TONIGHT: SCATTERED SHOWERS...ISOLATED
THUNDERSTORMS AND LOW LEVEL CLOUD COVER WILL BECOME MORE
WIDESPREAD ACROSS THE TAF SITES. AS A RESULT...PASSING
THUNDERSTORMS AND HEAVIER SHOWERS MAY PRODUCE TEMPORARY MVFR/IFR
CEILINGS AND VISIBILITIES...ALONG WITH GUSTY WIND.

OTHERWISE EXPECT OVERCAST TO BROKEN MID-LEVEL CLOUDS...ALONG WITH
LOW CLOUDS THAT INFREQUENTLY PRODUCE MVFR CEILINGS. FOG OR MIST IS
POSSIBLE BY MORNING...MOST LIKELY AT TAF SITES NEAR THE
YELLOWSTONE RIVER. LIGHT NORTHERLY WINDS ARE EXPECTED THROUGH
FRIDAY MORNING. WIND BECOMES EASTERLY AND INCREASES UP TO 15 KTS
FRIDAY AFTERNOON. SCT


&&

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

&&

$$

WEATHER.GOV/GLASGOW




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