Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 220900
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
300 AM MDT FRI AUG 22 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH SUNDAY...
AN UPPER TROUGH WILL CONTINUE TO DIG OVER THE PACIFIC NORTHWEST
TODAY WITH SOUTHWEST FLOW ALOFT OVER MONTANA. THIS SW FLOW ALOFT
WILL CONTINUE TO BRING MOISTURE INTO THE FORECAST AREA WITH
CHANCES FOR SHOWERS AND THUNDERSTORMS. THE BEST CHANCE WILL BE IN
THE SOUTHWEST ZONES WHERE THE BEST INSTABILITY IS EXPECTED. WITH
UPPER LEVEL DYNAMICS EXPECTED TO BE WEAK... THERE WILL ALSO BE DRY
PERIODS TODAY.

THE UPPER TROUGH BECOMES A CLOSED UPPER LOW BY THIS EVENING AS IT
MOVES INTO IDAHO. ALSO...DEEPER GULF OF MEXICO MOISTURE IN THE LOW
LEVEL STARTS TO FEED INTO THE SYSTEM. MEANWHILE... THE MAIN RAIN
SHIELD ASSOCIATED WITH THIS SYSTEM MOVES INTO NORTHEAST MONTANA.
EAST WINDS WILL ALSO INCREASE AS SURFACE GRADIENT TIGHTENS BETWEEN
A LOW PRESSURE SYSTEM IN WYOMING AND HIGH PRESSURE IN
SASKATCHEWAN. THE WIND SPEEDS WILL REACH LAKE WIND ADVISORY
CRITERIA BY MIDNIGHT TONIGHT AND CONTINUE INTO SATURDAY EVENING.
WILL ISSUE A LAKE WIND ADVISORY FOR FORT PECK LAKE.

THE UPPER LOW AND SURFACE LOW BECOMES STACKED ON SATURDAY AS IT
DRIFTS INTO MONTANA. RAIN... HEAVY AT TIMES... WILL CONTINUE. THE
LOW REMAINS OVER MONTANA SATURDAY NIGHT AND FINALLY EXITS THE AREA
ON SUNDAY. AT THIS POINT... EVENT TOTALS OF 2 TO 4 INCHES OF RAIN
IS POSSIBLE. SMALL STREAM FLOODING WILL BE POSSIBLE ESPECIALLY IF
RAINFALL TOTALS END UP BEING CLOSER TO 4 INCHES. SOIL MOISTURE
CONDITIONS IS HIGHLY VARIED AS SOME AREAS LIKE THE SIDNEY...
GLENDIVE AND WIBAUX AREAS HAVE HAD HEAVY RAIN RECENTLY WHILE MANY
OTHER AREAS HAVE HAD MUCH LESS RAIN. WILL WAIT TO SEE HOW THIS
SYSTEM EVOLVES BEFORE ISSUING ANY FLOOD WATCHES. FORRESTER

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

SYNOPTIC SET UP... LONG TERM BEGINS WITH HOT HIGH PRESSURE OVER
THE SOUTHERN US PLAINS... FOUR CORNERS... AND CALIFORNIA. A LARGE
TROUGH RUNS DOWN SASKATCHEWAN INTO MONTANA AND THE NORTHERN US
PLAINS. BEHIND THE TROUGH AND TO THE WEST A RIDGE RUNS UP THE
COAST OF THE PACIFIC NORTHWEST AND INTO NORTHERN BRITISH COLUMBIA.

SUNDAY NIGHT THROUGH MONDAY NIGHT... CENTER OF THE BASE OF THE
LARGE TROUGH WILL EJECT EAST OVER THE NORTHERN US PLAINS AND UPPER
MISSISSIPPI VALLEY. THIS WILL CARRY THE LAST OF THE RAIN SHOWERS
OUT OF THE AREA SUNDAY NIGHT BUT LEAVE BEHIND A COOL AIR IN PLACE
AT THE SURFACE ACROSS MUCH OF MONTANA THROUGH MONDAY NIGHT.

TUESDAY THROUGH THURSDAY... RIDGE TO WEST WILL MOVE ON SHORE AND
GAIN STRENGTH DURING THESE PERIODS. COLD AIR WILL BE WHITTLED OUT
AND A WARMING TREND WILL TAKE PLACE WITH TEMPERATURES WARMING TO
NEAR SEASONAL NORMS AT FIRST BUT TOPPING OUT WELL ABOVE NORMAL BY
THURSDAY WITH A RIDGE OVERHEAD. THESE PERIODS LOOK TO REMAIN DRY
THROUGH MOST OF THE TIME.

THURSDAY NIGHT ONWARD... MODEL BREAKDOWN BEHIND THE RIDGE SETTLES
IN AT THIS POINT. MODELS AGREE TO RIDGE BREAKDOWN BUT ARE UNSURE
OF THE WAVE FOLLOWING IT. CURRENT GUESS IS FOR ZONAL FLOW TO A
WEAK TROUGH TO PASS THROUGH. HOWEVER... THIS COULD QUICKLY CHANGE
WITH NEW RUNS.  GAH

&&

.AVIATION...
FLIGHT CATEGORY: IFR TO VFR

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

SCATTERED SHOWERS... ISOLATED THUNDERSTORMS... AND LOW LEVEL CLOUD
COVER WILL BECOME LESS WIDESPREAD ACROSS THE AREA TODAY AND THEN
TREND BACK UP OVERNIGHT. AS A RESULT EXPECT OVERCAST TO BROKEN
MID-LEVEL CLOUDS... ALONG WITH LOW CLOUDS THAT INFREQUENTLY
PRODUCE MVFR CEILINGS. TERMINALS NEAR THUNDERSTORMS COULD TEMPORARY
RECEIVE IFR VISIBILITIES.

FOG/MIST: IS POSSIBLE BY MID-MORNING...MOST LIKELY AT TERMINALS
NEAR THE YELLOWSTONE RIVER.

AREA WINDS: FROM THE NORTHEAST UNDER 10 KTS OVERNIGHT... VEERING
TO THE EAST AND INCREASING TO 10 TO 15 KTS AFTER SUNUP.

GAH


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
LAKE WIND ADVISORY FROM 9 PM THIS EVENING TO MIDNIGHT MDT
SATURDAY NIGHT FOR FORT PECK LAKE FOR CENTRAL AND SOUTHEAST
PHILLIPS...CENTRAL AND SOUTHERN VALLEY...GARFIELD...MCCONE...
PETROLEUM.

&&

$$

WEATHER.GOV/GLASGOW




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