Severe Thunderstorm Warning 7, NWS Glasgow, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
230 PM MDT FRI MAY 21 2004

.SHORT TERM...FOR NORTHEAST MONTANA TONIGHT THROUGH SUNDAY...
ACTIVE PATTERN EXPECTED TO CONTINUE ACROSS THE AREA THROUGH THE
PERIOD. ETA AND GFS HAVE COME FURTHER SOUTH WITH SYSTEM FOR SATURDAY
NIGHT INTO SUNDAY...WITH THE ETA FURTHER SOUTH THAN THE GFS. BOTH
SOLUTIONS SHOWING WIDESPREAD PRECIP ACROSS THE AREA FOR SUNDAY...AND
WILL LEAN TOWARDS GFS GIVEN ITS PERFORMANCE WITH LAST EVENT AND ETA
IS MORE OF AN OUTLIER. FORECAST IS IN PRETTY GOOD SHAPE AND WILL NOT
MAKE ANY MAJOR CHANGES TO GOING GRIDS.

TONIGHT...SHOULD SEE ANOTHER ROUND OF SHOWERS AND SOME THUNDERSTORMS
ACROSS THE AREA TONIGHT WITH MOISTURE CONTINUING TO STREAM
NORTHEAST. AREA OF PRECIP ACROSS WESTERN ZONES BECOMING MORE
ORGANIZED AT THIS TIME. WILL RAISE POPS TO LIKELY OR CATEGORICAL IN
THE WEST AND NORTH SINCE THESE WILL BE THE AREAS MOST LIKELY
AFFECTED. BEST CHANCE OF THUNDERSTORMS WILL COME ACROSS SOUTHEAST
ZONES WHERE PARTLY CLOUDY SKIES HAVE ALLOWED FOR BEST WARMING. DO
NOT EXPECT THUNDERSTORMS TO REACH SEVERE LEVELS...BUT GIVEN LOW WET
BULB ZERO HEIGHTS WOULD NOT BE SURPRISED IF ANY THUNDERSTORMS THAT
DO DEVELOP PRODUCE SMALL HAIL. TEMPERATURES TONIGHT SHOULD ONCE
AGAIN STAY IN THE 40S AND GOING FORECAST HANDLES THIS WELL. GIVEN
CLOUDY SKIES AND INCREASING PRESSURE GRADIENT WILL FOREGO MENTION OF
FOG...BUT IF WINDS DO NOT MATERIALIZE AS THOUGHT THIS WILL HAVE TO
BE REVISITED IN EVENING UPDATE.

SATURDAY AND SATURDAY NIGHT...SOUTHWEST FLOW CONTINUES ACROSS THE
AREA WITH CLOSED LOW DIGGING INTO WEST COAST. UPPER DIFFUENCE
INCREASES AS TROUGH TAKES SHAPE TO THE WEST...AND COMBINED WITH
MARGINAL INSTABILITY SHOULD SEE SHOWERS CONTINUING ACROSS THE AREA.
WILL RAISE POPS TO LIKELY ACROSS NORTHWEST WHERE BEST LIFT IS
PRESENT...AND KEEP CHANCE POPS ELSEWHERE. WITH LIMITED WARMING DUE
TO CLOUDS DO NOT EXPECT WIDESPREAD THUNDERSTORMS...BUT ENOUGH
INSTABILITY AND DYNAMICS PRESENT FOR MENTION DURING AFTERNOON AND
EVENING HOURS. DUE TO CLOUDY SKIES CURRENT HIGH FORECAST IN THE 50S
LOOKS ON TRACK. THIS IS ABOVE GUIDANCE...BUT GIVEN WARM OVERNIGHT
LOWS AREA WILL NOT HAVE TOO FAR TO WARM TO REACH THESE TEMPERATURES.
GRADIENT INCREASE ACROSS THE AREA SO EXPECT DECENT WINDS ACROSS THE
AREA...AND WILL RAISE TO 15 TO 25 MPH ACROSS NORTHERN ZONES. GLASGOW
AREA WILL SEE ENHANCEMENT DUE TO MILK RIVER AND WILL UP INTO WINDY
CATEGORY HERE.

SUNDAY...MAIN SYSTEM APPROACHES THE AREA WITH MODELS SHOWING MAIN
DIFFERENCES DURING THIS TIME. GFS IS FURTHER NORTH WITH THE FEATURES
ASSOCIATED WITH THIS SYSTEM AND WILL AGAIN LEAN TOWARD IT GIVEN ITS
PERFORMANCE EARLIER THIS WEEK. UPPER DIFFLUENCE INCREASES AS CLOSED
LOW APPROACHES...WITH JET STREAK NOSING INTO SOUTHEAST MONTANA ALSO
PROVIDING FOR BROAD AREA OF DIVERGENCE AROUND 300MB. SHOULD SEE BEST
CHANCE FOR RAIN NORTH OF 700MB...WHICH HAS MOVED MUCH FURTHER SOUTH
TODAY COMPARED TO 24 HOURS AGO. FOR NOW WILL NOT SPLIT HAIRS AND
JUST KEEP GOING LIKELY POPS...BUT NORTHERN AREAS MAY NEED TO BE
RAISED TO CATEGORICAL BY INCOMING SHIFTS. TEMPERATURES SUNDAY WILL
NOT WARM MUCH WITH PERSISTENT CLOUDS AND PRECIP SO GOING FORECAST IN
THE UPPER 40S TO MID 50 LOOKS ON TRACK. THUNDERSTORM POTENTIAL
LIMITED ON SUNDAY GIVEN LITTLE OR NOW LOW LEVEL WARMING AND ONLY
MARGINAL INSTABILITY SO WILL KEEP OUT OF FORECAST AT THIS TIME...BUT
GIVEN DYNAMIC NATURE OF SYSTEM THIS MAY NEED TO BE REVISITED AS
WELL. JZ

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...
ETA TRYING TO PULL OUT WITH DEEP UPPER LOW BY SUNDAY NIGHT. SIDED
WITH THE MORE REASONABLE AND SLOWER SPEED OF THE GFS AND ECMWF. THE
700 MB LOW TO TRACK RIGHT OVER NE MT WITH 850 MB TEMPERATURES
HOVERING RIGHT AROUND ZERO DEG C. OVER SUNDAY NIGHT. WITH PLENTY OF
LIFT AND MOISTURE WILL GO WITH AN INCREASE TO LIKELY FOR MIXED
PRECIPITATION IN THE FORM OF RAIN AND SNOW ACROSS NORTHEAST MONTANA.
ACCUMULATIONS ARE VERY UNCERTAIN GIVEN THE MARGINAL TEMPERATURE
PROFILES SO WILL NOT MENTION ANY SIGNIFICANT ACCUMULATIONS IN THIS
PACKAGE.

PRECIPITATION WILL TAPER OFF ON MONDAY AS MAIN UPPER LOW SLIDES
EAST. STRONG NEGATIVE VORTICITY ADVECTION FOR MONDAY WILL BE ONLY
SLIGHTLY OFFSET BY DECENT LAPSE RATES AND LINGERING MOISTURE BEHIND
THE EXITING SYSTEM. THEREFORE...WILL KEEP CHANCE POPS FOR EARLY
WEEK. NO OTHER MAJOR CHANCES MADE TO GOING FORECAST WITH COOL START
TO WEEK IN NORTHWEST FLOW...FOLLOWED BY A SLIGHT WARMING TREND
TOWARDS THE LATTER PART OF THE WEEK. ALTHOUGH SOME MINOR SHORT WAVES
TO MOVE THROUGH THE AREA...TIMING AND MOISTURE WILL BE UNCERTAIN SO
LEFT DAYS 6 AND 7 DRY AS IN GOING FORECAST. ADOLPHSON

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.GGW WATCHES/WARNINGS/ADVISORIES...NONE.

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