Hail and Damaging Wind in Montana, May 17, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
914 AM MDT TUE MAY 17 2005

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY
UPDATE SENT TO CANCEL LAKE WIND ADVISORY AT 8 AM...ELSE FORECAST
REMAINS ON TRACK. WINDS HAVE DIMINISHED ACROSS WESTERN AND CENTRAL
CWA...REMAIN SLIGHTLY STRONGER OVER EASTERN ZONES...BUT ALL WINDS
BELOW CRITERIA FOR LAKE WIND ADVISORY. COLD FRONT HAS REACHED INTO
EXTREME SOUTHWEST AND WEST ZONES...WILL SLOWLY PROGRESS EAST ACROSS
CWA TODAY...SHIFTING WINDS TO WEST OR NORTHWEST DURING AFTERNOON.
FAIRLY DENSE CLOUD SHIELD ACROSS MOST OF CWA...LIKELY TO INHIBIT
SOLAR WARMING. 12Z GGW SOUNDING SHOWS UNSTABLE ATMOSPHERE ABOVE
775MB...BUT CLOUDS LIKELY TO LIMIT HEATING TO OVERCOME INVERSION
BELOW. EXCEPTION MAY BE EXTREME EAST...WILL MONITOR AND CONSIDER 18Z
SPECIAL SOUNDING IF CONDITIONS SUGGEST IT WILL BE NEEDED. SPC SLIGHT
RISK AREA EXTENDS INTO SOUTHEAST ZONES...WHICH IS ALREADY COVERED BY
SPS. NO FURTHER UPDATES EXPECTED...BUT WILL REQUIRE VIGILANCE. DNS

PREVIOUS DISCUSSION...TODAY THROUGH THURSDAY...
COMPLICATED WEATHER PATTERN THROUGH THE NEXT 24 HOUR PERIOD
DEVELOPING. SMALL SCALE SHORTWAVES HARD TO PICK OUT...AND FRONT ALSO
A CHALLENGE TO PICK OUT DEFINITIVELY AT THE MOMENT. MODELS ARE
STRUGGLING WITH SMALLER SCALE FEATURES...BUT GENERALLY ADVERTISING
THE SAME PATTERN. WILL BASE NEAR TERM FORECAST ON CURRENT
TRENDS...AND USE A MODEL BLEND BEYOND THAT.

FIRST ORDER OF BUSINESS IS LAKE WIND ADVISORY ALREADY IN EFFECT.
WITH EAST WINDS STILL 20 TO 30 MPH...SEE NO REASON TO TOUCH IT.
STILL APPEARS THAT SURFACE GRADIENT WILL RELAX A LITTLE LATER THIS
MORNING...SO WILL LET 8 AM REMAIN THE EXPIRATION TIME.

STRONG SHORTWAVE CURRENTLY IN CENTRAL UTAH CONTINUES TO ROUND THE
BASE OF AN UPPER LEVEL TROUGH AND LIFT NORTHEAST INTO NORTHEAST
WYOMING BY THIS AFTERNOON. SURFACE TROUGH STILL SITTING THROUGH
CENTRAL MONTANA AT THIS HOUR. ANALYSIS SHOWING A FEW DISTINCTIVE LOW
PRESSURE CENTERS...AND HARD TO SAY WHICH ONE WILL WIN OUT FOR SURE.
MODELS THE PAST COUPLE OF DAYS HAVE SUGGESTED A NORTHERN LOW CENTER
IN ALBERTA AND SASKATCHEWAN...WITH ANOTHER CENTER TAKING SHAPE
ACROSS SOUTHEAST MONTANA. MODELS CONTINUE TO ADVERTISE THIS IDEA
THIS MORNING...SO WILL GO WITH IT. APPEARS THAT WESTERN PART OF THE
FORECAST AREA WILL BE AFFECTED BY BOTH LOWS...WHILE EASTERN PART OF
THE REGION WILL SEE GREATEST IMPACT FROM SOUTHEASTERN LOW. FRONT
WITH NORTHERN LOW TO APPROACH THE WEST LATER THIS MORNING.
ATMOSPHERE STILL UNSTABLE AND VERY MOIST...SO WILL CONTINUE WITH
IDEA OF 60S FOR POPS. OUT IN THE SOUTHEAST...FRONT ASSOCIATED WITH
SOUTHERN LOW TO PASS THROUGH EARLY THIS AFTERNOON. STILL LOOKS LIKE
AN ISOLATED THREAT OF A SEVERE STORM IN THE EXTREME SOUTHEAST WHERE
MORE WARMING TO OCCUR AHEAD OF FRONT. LIFTED INDEX VALUES TO DROP
BELOW ZERO ALONG WITH SOME DECENT CAPE...BUT WIND PROFILE
STILL NOT LOOKING TOO GREAT. THINK BIGGER PROBLEM WITH ANY
THUNDERSTORM DEVELOPMENT WOULD BE HEAVY RAIN WITH PRECIPITABLE WATER
VALUES REMAINING OVER AN INCH ACROSS THE ENTIRE AREA. WILL LEAVE OUT
SEVERE MENTION IN THE ZONES...BUT MORNING HWO WILL INCLUDE ISOLATED
THREAT. WILL PUT MENTION OF HEAVY RAIN IN THE FORECAST. BY LATER ON
THIS AFTERNOON...SOUTHEASTERN LOW BECOMES DOMINANT PLAYER AS IT
MINGLES WITH BOUNDARY FROM NORTHERN LOW. PRECIPITATION SHOULD STAY
RIGHT ALONG THAT BOUNDARY AND LOOKS TO UNDERGO SOME STRONG
FRONTOGENESIS AS UPPER LEVEL LOW BECOMES CUT OFF. LATEST NAM
SPITTING OUT SOME IMPRESSIVE QPF VALUES ACROSS THE EAST...WHICH
MAKES SENSE WITH ALL THINGS CONSIDERED. WILL THEREFORE KEEP MENTION
OF HEAVY RAIN IN THE EAST.

BY EARLY WEDNESDAY MORNING...SYSTEM CONTINUES TO SHIFT EAST INTO THE
DAKOTAS WHILE BECOMING STACKED UP. LINGERED SOME POPS IN THE
EAST...BUT IF SYSTEM BECOMES STACKED MAY SEE THINGS SLOW DOWN AND
THEREFORE NEED TO LINGER HIGHER POPS LONGER LATE TUESDAY NIGHT/EARLY
TUESDAY MORNING.

SHORTWAVE RIDGE WORKS IN BY WEDNESDAY ALLOWING FOR NICE DRYING AND
WARMER TEMPERATURES RETURNING. PATTERN REMAINS MUCH SIMPLER THROUGH
THE REST OF THE SHORT TERM AS ANOTHER UPPER LEVEL LOW HEADS TOWARD
THE WEST COAST...SLOWLY TURNING THE UPPER LEVEL FLOW TO THE
SOUTHWEST WITH ANOTHER COLD FRONT APPROACHING BY THE END OF THE
PERIOD. EVEN MORE WARMING EXPECTED BY THURSDAY AHEAD OF FRONT WITH
TEMPERATURES REBOUNDING INTO THE UPPER 70S TO NEAR 80. NO
PRECIPITATION EXPECTED BEYOND CURRENT WEATHER SYSTEM. JAZ

.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...
MODELS AGREE ON HAVING SOUTHWEST FLOW ALOFT TO START THE EXTENDED
PERIOD AHEAD OF AN UPPER TROUGH THAT AFFECTS MONTANA OVER THE
WEEKEND. HOWEVER...THEY DO DIFFER ON TIMING A COLD FRONT ACROSS
EASTERN MONTANA. ECMWF IS CURRENTLY THE FASTEST WITH FRI
MORNING...GFS MOVES THE FRONT THROUGH DURING THE DAY ON
FRIDAY...WHILE THE DGEX AND CANADIAN WAIT UNTIL FRI NIGHT. WILL MOVE
THE FRONT ACROSS THE AREA FRI AND FRI EVENING WITH A MIX OF THE GFS
AND DGEX FOR NOW. ADDED A SLIGHT CHANCE OF THUNDERSTORMS TO THE NW
ZONES FOR FRIDAY AND RAISED CHANCE OF THUNDERSTORMS FOR FRI NIGHT TO
AROUND 30 PERCENT IN MOST AREAS.

UPPER TROUGH LINGERS OVER THE AREA THROUGH THE WEEKEND...WILL LINGER
A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS UNTIL DURING THE DAY ON
SUNDAY.

MODELS STILL AGREE ON BRINGING AN UPPER RIDGE ACROSS FOR MONDAY AND
TUESDAY WITH DRY WEATHER. FORRESTER
&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
 LAKE WIND ADVISORY FOR FORT PECK LAKE IN EFFECT UNTIL 8 AM TUESDAY.

&&

WEATHER.GOV/GLASGOW

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
929 AM MDT TUE MAY 17 2005

MTZ024>027-181200-
RICHLAND-DAWSON-PRAIRIE-WIBAUX-
929 AM MDT TUE MAY 17 2005

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHEAST
MONTANA.

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS WILL DEVELOP THIS AFTERNOON OVER EASTERN MONTANA. A
FEW OF THESE STORMS MAY BECOME SEVERE WITH LARGE HAIL AND DAMAGING
WINDS. THE AREA WITH THE BEST POTENTIAL TO HAVE A SEVERE
THUNDERSTORM WILL BE ALONG AND EAST OF THE YELLOWSTONE RIVER.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

NO HAZARDOUS WEATHER EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.