000
FXUS65 KGGW 181540
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
940 AM MDT SAT MAY 18 2013

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

UPDATED FORECAST TO ACCOUNT FOR RADAR PPT TRENDS AND SHORT TERM
MODEL FORECASTS. MORNING SOUNDING IS SATURATED WITH PRECIPITABLE
WATER OF ABOUT AN INCH...WHICH IS CLOSE TO THE 99TH PERCENTILE FOR
THIS TIME OF YEAR. DEEP WET AND UNCAPPED SOUNDING IS
CHARACTERISTIC OF A PERSISTENT RAIN EVENT...WITH SOME THUNDER
POSSIBLE. HOWEVER...HAVE DEEMPHASIZED THE IMPACT FROM
THUNDERSTORMS AS RAIN IS THE MAIN IMPACT. DISORGANIZED UPPER FLOW
WITH WEAK TO MODEST DYNAMIC FORCING SUGGESTS PERIODS OF RAIN OFF
AND ON FOR THE NEXT 2 OR 3 DAYS WITH SPECIFIC LOCATIONS RECEIVING
THE MOST RAIN DIFFICULT TO PIN DOWN. MODELS DO DIFFER ON WHEN RAIN
WILL TAPER OFF WITH THE GFS MODEL MORE RAPIDLY PROGRESSING THE
SYSTEM EASTWARD...HOWEVER...TEND TO FAVOR THE EC AND NAM MODELS
WHICH HAVE HAD GREATER RUN TO RUN CONSISTENCY. MARTIN

PREVIOUS DISCUSSION...
TODAY THROUGH MONDAY...MAIN CONCERN WILL BE THE CONTINUATION OF
WET WEATHER ACROSS NORTHEAST MONTANA. CURRENT RADAR OBSERVATIONS
EARLY THIS MORNING ARE SHOWING A RATHER EXPANSIVE AREA OF SHOWER
ACTIVITY ACROSS THE CWA. SOME 40-50 DBZ REFLECTIVITY HAS BEEN
OCCURRING FROM TIME TO TIME IN VERY ISOLATED LOCATIONS AND SO
CANNOT RULE OUT A RUMBLE OF THUNDER THIS MORNING.

MODELS ARE IN EXCELLENT AGREEMENT WITH THE OVERALL SYNOPTIC
PATTERN KEEPING IN AN UPPER LEVEL TROUGH PERSISTING ACROSS THE CWA
WHICH WILL PROVIDE A CONTINUATION OF UNSETTLED WEATHER CONDITIONS.
HOWEVER...THERE ARE NOTABLE DIFFERENCES FROM THE MODELS IN THE DETAILS
AND HANDLING OF MESOSCALE CONVECTION THAT DEVELOPS. THE GFS IN
PARTICULAR HAS NOT BEEN PERFORMING WELL IN THE PLACEMENT OF QPF
WITH RECENT RAIN SHOWER ACTIVITY AND THEREFORE HAVE DISCOUNTED IT
FOR THE SHORT TERM FORECAST PERIOD. THE 00Z ECMWF AND THE LATEST
HRRR HAVE SHOWN TO HAVE A PRETTY GOOD HANDLE ON THE OVERALL
SITUATION AND LEANED WITH A COMPROMISE OF THEIR SOLUTIONS IN LARGE
PART FOR THE FORECAST. IN A NUTSHELL...UPPER LEVEL SHORTWAVE
FEATURES WILL PROPAGATE THROUGH SOUTHWEST FLOW ALOFT WHICH ALONG
WITH UPPER LEVEL DIFFLUENCE WILL HELP FORCE VERTICAL ASCENT. A
SURFACE LOW PRESSURE WILL ALSO SIT AND SPIN ACROSS THE DAKOTAS
THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK WHICH WILL CONTINUE
TO PROVIDE MOIST EASTERLY FLOW INTO NORTHEAST MONTANA. GIVEN THESE
CIRCUMSTANCES...FEEL VERY CONFIDENT IN WIDESPREAD MEASURABLE
RAINFALL ACCUMULATIONS.

THE CHALLENGE WITH THIS FORECAST WILL BE DETERMINING WHERE THE
HEAVIEST AMOUNTS OF RAINFALL WILL OCCUR...WHICH WILL LARGELY
DEPEND UPON MESOSCALE DETAILS THAT ARE DIFFICULT TO PINPOINT WITH
MUCH CONFIDENCE AT THIS TIME. AREAS WITH HEAVIEST RAINFALL MAY
CERTAINLY PICK UP OVER AN INCH OF RAINFALL...IF NOT MORE...THROUGH
EARLY NEXT WEEK. GIVEN THESE ARGUMENTS...WILL GO WITH CATEGORICAL
POPS IN MOST PLACES THROUGH SUNDAY NIGHT AND TAPER TO LIKELY POPS
ON MONDAY AS THE UPPER TROUGH BEGINS TO TRANSLATE EASTWARD AND THE
SURFACE LOW EXITS THE DAKOTAS AND HEADS FOR SW MN AND NW IA. NAM
BUFR SOUNDINGS CONTINUE TO INDICATE LI READINGS AROUND 0 OR
SLIGHTLY NEGATIVE ACROSS PARTS OF THE CWA AT TIMES GOING INTO
TONIGHT...AND INDICATE SMALL AMOUNTS OF CAPE AND SOME INSTABILITY.
DECIDED TO KEEP A SLIGHT MENTION FOR THUNDER IN THE GRIDS GIVEN
THESE ARGUMENTS. NO LARGE SWINGS IN TEMPERATURES ARE EXPECTED
THROUGH THE SHORT TERM SINCE THE OVERALL PATTERN WILL REMAIN
RATHER STATIC. THEREFORE WILL EXPECT SEASONAL HIGHS AND LOWS
THROUGH EARLY NEXT WEEK. MALIAWCO


.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...
THE EXTENDED FORECAST BEGINS MONDAY NIGHT WITH AN UPPER LOW
EXITING INTO THE UPPER MISSISSIPPI RIVER VALLEY AND WEAK RIDGING
BUILDING INTO NORTHEASTERN MONTANA.

BY WEDNESDAY MORNING ANOTHER UPPER LOW MOVES IN OVER THE PACIFIC
NORTHWEST SETTING UP DI-FLUENT SOUTHWEST FLOW ALOFT OVER THE AREA
THROUGH THE END OF THE EXTENDED.

THIS WILL CONTINUE THE COOLISH TEMPERATURES DURING THE DAY AND
NEAR NORMAL TEMPERATURES AT NIGHT. PRECIPITATION CHANCES SHOULD
RANGE SLIGHTLY ABOVE NORMAL... HOWEVER PIN POINTING ANY BETTER
DAYS THAN OTHERS WILL BE VERY HARD.

ENSEMBLES OF THE GFS AND EC SHOW HIGH CONFIDENCE IN AN UPPER LOW
OVER THE PACIFIC NORTHWEST...HOWEVER DO HAVE TROUBLE KEEPING THE
DAY TO DAY PLACEMENT OF THE UPPER LOW THE SAME. RMOP IS PRETTY
GOOD FOR UPPER LOWS OVER THE PACIFIC NORTHWEST. MODERATE TO HIGH
CONFIDENCE ON THE PATTERN. HOWEVER THE PATTERN IS MORE SHOWERY IN
NATURE NOT ALLOWING FOR THE CONFIDENCE TO DOUBLE OF CLIMO POPS AT
THIS TIME.              PROTON

&&

.AVIATION...
A MIX OF VFR WITH PERIODS OF MVFR CAN BE EXPECTED THROUGH THE
PERIOD AT ALL TERMINALS. SOUTHWEST FLOW ALOFT AND MOIST EAST TO
SOUTHEAST FLOW WILL KEEP SKIES BROKEN TO OVERCAST. CEILINGS WILL
BE TRICKY... GUIDANCE HAS A SPLIT WITH ONE GOING FOR SOLID
MVFR...THE OTHER SOLID VFR. WILL GO WITH THE PREDOMINATE OF VFR
AND PERIODS OF MVFR MAINLY FOR MORNING LOWER CEILINGS AND ANY
AFTERNOON CBS THAT FORM. LIGHT RAIN SHOWERS ARE EXPECTED ON AND
OFF THROUGHOUT THE ENTIRE TAF PERIOD.

KOLF ASOS IS NOT TRANSMITTING THE OBSERVATIONS FOR US TO SEE THEM
ONLINE AND INSTEAD WE ARE HAVING TO CALL EVERY HOUR. THEREFORE THE
TAF IS AMD NOT SKED.

PROTON/FRANSEN


&&

.HYDROLOGY...
THE NEXT FEW DAYS WILL BE RATHER WET AS AN UPPER-LEVEL TROUGH
AFFECTS THE AREA. SEVERAL DISTURBANCES ASSOCIATED WITH THIS TROUGH
WILL PASS THROUGH WHICH WILL KEEP CHANCES FOR RAIN WITH SOME
THUNDERSTORMS THROUGH EARLY NEXT WEEK. MODEL GUIDANCE DEPICTS HIGH
AMOUNTS OF MOISTURE WITH THIS SYSTEM. AT THIS POINT THE
ENVIRONMENT LOOKS FAVORABLE FOR SLOW- MOVING STORMS WITH HIGHER
PRECIPITATION IN LOCALIZED AREAS.

MOST OF THE BASINS IN NORTHEAST MONTANA WILL BE ABLE TO ACCOMMODATE
THIS AMOUNT OF MOISTURE... AT LEAST EARLY ON IN THE EVENT. THERE IS
SOME CONCERN FOR RAPIDLY RISING STREAMS AND LOCALIZED URBAN
FLOODING AS THE EVENT PERSISTS. SOME FLOODING MAY BECOME AN
ISSUE... ESPECIALLY FOR THE EASTERN AND SOUTHERN COUNTIES WHERE
THE POTENTIAL FOR STRONGER THUNDERSTORMS IS HIGHER.


&&

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

&&

$$

WEATHER.GOV/GLASGOW