Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 302025
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
225 PM MDT SAT AUG 30 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH MONDAY...

SYNOPTIC SET UP... HOT HIGH PRESSURE IS BOTTLED UP OVER THE FOUR
CORNERS AND DESERT SOUTHWEST. A WEAK RIDGE EXTENDS OUT TOWARD THE
CENTRAL US PLAINS. A COOL BROAD TROUGH IS CENTERED OVER THE COAST
OF THE PACIFIC NORTHWEST AND BRITISH COLUMBIA AND EXTENDS INFLUENCE
OVER MONTANA AND THE CANADIAN HIGH PLAINS. NORTHEAST MONTANA
CURRENTLY SETS AT THE EDGE OF THIS TROUGH IN SOUTHWEST FLOW ALOFT.

TONIGHT... PACIFIC MOISTURE ON THE SOUTHWEST FLOW IS CAUSING
RAIN SHOWERS THIS AFTERNOON WHICH SHOULD EXIT THE AREA TO THE
NORTHEAST OVERNIGHT. AS COOLER AIR FILTERS IN NEAR THE SURFACE A
SURFACE INVERSION WILL SET UP TRAPPING SOME OF THIS MOISTURE IN.
THIS COULD LEAD TO FOG WHICH HAS CURRENTLY HAS LOW CONFIDENCE OR
LOW LEVEL STRATUS ALONG THE NORTH DAKOTA BORDER WHICH APPEARS TO
MAINTAIN HIGHER CHANCES. THE BIG PROBLEM WITH FOG IS THAT MORE
MOISTURE IS EXPECTED TO MOVE THROUGH THE AREA IN THE FORM OF MID
LEVEL CLOUDS WHICH WHICH WOULD IMPEDE SURFACE RADIATION NEEDED FOR
FOG FORMATION.

SUNDAY THROUGH MONDAY... LARGE SCALE TROUGH WILL BECOME MORE
DOMINANT DURING THESE PERIODS... BUT AS THE CENTER OF THIS COLD AIR
ALOFT MOVES THROUGH IT MAY RECEIVE LARGE ENOUGH OPENING FOR
SURFACE HEATING BOTH SUNDAY AND MONDAY AFTERNOON. A WARM SURFACE
LAYER AND COLD AIR ALOFT WILL LEAD TO LIMITED AFTERNOON
INSTABILITY SHOWERS WHICH SHOULD SUBSIDE OVERNIGHT. FOR TUESDAY
AFTERNOON SPECIFICALLY MODELS POINT TOWARDS A MINOR SHORTWAVE IN
THE FLOW THAT MAY CLIP THE NORTHEASTERN CORNER OF THE CWA AND
CONTRIBUTE SOME THUNDERSTORMS TO THE RAIN SHOWERS TUESDAY AFTERNOON
WITH THE ADDED LIFT.

GAH


.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...
THE 30/12Z MODEL SUITE IS FAIRLY CONSISTENT WITH EARLIER THINKING
AND SO THE GOING FORECAST THROUGH THE EXTENDED WAS LEFT AS IS.
AGREEMENT BETWEEN THE ECMWF/GFS/NAM EXISTS ON HAVING A BROAD UPPER
TROUGH ACROSS THE NORTHERN HIGH PLAINS AND UPPER MIDWEST. THIS
WILL LEAVE NORTHEAST MONTANA IN NORTHWEST FLOW ALOFT WHICH WILL
NEAT TO BE MONITORED FOR SUBTLE SHORTWAVE DISTURBANCES TRACKING
THROUGH. WILL EXPECT COOLER THAN AVERAGE TEMPERATURES TO START OFF
THE PERIOD BUT 1000-500MB THICKNESSES RISE ON TUESDAY AS THE
TROUGH TRANSLATES EASTWARD. THIS WILL ALLOW FOR SLIGHTLY WARMER
TEMPERATURES AND DRIER CONDITIONS WITH LARGE SCALE SUBSIDENCE IN
PLACE UNDER WEAK RIDGING.

A VIGOROUS SHORTWAVE ALOFT WILL APPROACH ON WEDNESDAY BUT THERE
CONTINUES TO BE SOME UNCERTAINTY IN THE TRACK AND BEST FORCING FOR
ASCENT PERHAPS COULD BE NORTH ACROSS THE INTERNATIONAL BORDER.
HOWEVER...MODEL TRENDS HAVE THIS WAVE TRACKING SOMEWHAT FURTHER
SOUTH THAN EARLIER THINKING AND SO SHOWER/THUNDERSTORM ACTIVITY
MAY BE POSSIBLE ACROSS AT LEAST A PORTION OF THE CWA WEDNESDAY
AFTERNOON INTO THURSDAY AND FUTURE SHIFTS MAY HAVE TO ADD IN POPS.
LEFT THE WX GRIDS DRY FOR NOW UNTIL MODELS SHOW MORE RUN TO RUN
CONTINUITY OF SOLUTIONS. GIVEN POTENTIAL STRENGTH OF THIS WAVE AND
COLD AIR ALOFT...WILL NEED TO ASSESS SEVERE WX POTENTIAL AS THIS
PERIOD MOVES CLOSER TO THE SHORT TERM.

WEDNESDAY NIGHT ONWARD...TREND IS FOR COOLER TEMPERATURES AS
MIDWEEK WAVE AND ASSOCIATED SURFACE COLD FRONT LEAD TO DECENT COLD
AIR ADVECTION ACROSS NORTHEAST MONTANA. IT MAY BE THAT CURRENT
FORECAST IS STILL TOO WARM FOR THE SECOND HALF OF THE WEEK IN
TAKING AN INITIAL LOOK AT THE 12Z GUIDANCE. HOWEVER...AS ENSEMBLE
OF 500MB HEIGHTS SHOWS INCREASING SPREAD BY THIS TIME...AND MODEL
TRENDS ARE JUST STARTING TO BECOME ESTABLISHED...FORECAST CONFIDENCE
DROPS OFF.

IT SHOULD BE POINTED OUT THAT THE ECMWF SOLUTION TODAY SHOWS THAT
INITIAL MIDWEEK WAVE PUSHING EASTWARD ALONG THE INTERNATIONAL
BORDER/ALBEIT TRACKING SOMEWHAT FURTHER SOUTH IN COMPARISON TO
YESTERDAY/S SOLUTION/ BEFORE A DEEPER TROUGH BECOMES ESTABLISHED
ACROSS THE WESTERN CONUS BY THE END OF THE WEEK.  THIS WOULD LEAD
TO A PROLONGED COOLER PERIOD AND PROGRESSIVE PATTERN PROVIDING
PERIODIC CHANCES OF SHOWER ACTIVITY ASSOCIATED WITH TRACKING
SHORTWAVES. THIS IS SOMEWHAT CONSISTENT WITH PERSISTENCE GIVEN THE
CWA HAS NOT BEEN IN STATIC WX CONDITIONS RECENTLY. IN ANY
RESPECT...AS THIS IS THE SAME SCENARIO DEPICTED YESTERDAY FROM THE
ECMWF...THERE IS INCREASED CONFIDENCE IN THIS AND SO FUTURE SHIFTS
MAY WANT TO TREND TEMPERATURES DOWN FOR THE SECOND HALF OF THE
WEEK EVEN FURTHER ALONG WITH HONING IN ON POPS TO BETTER DEPICT
PRECIPITATION CHANCES. THE GFS SOLUTION WHICH JUST MAINTAINED A
BROAD TROUGH ACROSS THE REGION IN YESTERDAY/S SOLUTION NOW ALSO
SHOWS THAT SEPARATE MIDWEEK SHORTWAVE AND THUS IS COMING INTO
ALIGNMENT WITH THE ECMWF. HOWEVER...THE GFS IS FURTHER NORTH THAN
THE ECMWF WITH THAT INITIAL DISTURBANCE. GIVEN TREND IS TOWARD
ECMWF SOLUTION...WILL NEED TO WATCH INTERNATIONAL BORDER CAREFULLY
FOR POTENTIAL NEED TO INCREASE POPS FOR PORTIONS OF THE SECOND
HALF OF THE WEEK. MALIAWCO


PREVIOUS LONG TERM DISCUSSION...
OVERALL SYNOPTIC-SCALE PATTERN FLOW BETWEEN THE MODELS SHOW OK
AGREEMENT...BUT THE FINER DETAILS OF THE TIMING AND PLACEMENT OF
THE EMBEDDED WEAK DISTURBANCES GIVE RISE TO SOME DOUBT WHETHER
ANYTHING MORE THAN A TRACE OF PRECIPITATION WILL BE REALIZED
ANYWHERE IN THE CWA THROUGHOUT THE EXTENDED PERIOD.

NOT A LOT OF SUPPORT SEEN FOR PRECIPITATION IN THE EXTENDED
FORECAST PERIOD. IN FACT...MORE CONSENSUS SEEN FOR A DRY FORECAST
MORE THAN ANYTHING ELSE. GREATEST CONFIDENCE IS IN FLEETING
CHANCES FOR A TRACE OF PRECIP HERE OR THERE THROUGHOUT. IT COULD
BE THAT THE FORCING FOR ASCENT AND AVAILABLE MOISTURE IS JUST TOO
STRETCHED OUT THROUGH THE LOBES OF THE LARGE UPPER LEVEL TROUGH AS
IT PUSHES THROUGH THE REGION AT LARGE.

EXPECT TEMPERATURES SLIGHTLY BELOW NORMAL BUT NOT MUCH. BMICKELSON


&&

.AVIATION...
VFR PREVAILING CONDITIONS WILL CONTINUE OVERALL TONIGHT. SCATTERED
SHOWERS AND PERHAPS A THUNDERSTORM WILL COME TO AN END FROM WEST
TO EAST. AFTER SKIES CLEAR OUT THERE IS A LOW CONFIDENCE
POSSIBILITY OF PATCHY FOG OR LOW STRATUS THAT COULD AT TIMES
RESTRICT CIGS AND VSBYS. WEST WINDS THIS EVENING AT 5 TO 10 KTS
WILL BECOME LIGHT AND VARIABLE AFTER 06Z. MALIAWCO


&&

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


&&

$$

WEATHER.GOV/GLASGOW




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