Damaging Wind in Montana, May 1, 2001

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
930 AM MDT TUE MAY 1 2001
...UPDATE PLANNED FOR ZONES...
MAIN CHANGE TO FORECAST WILL BE TO CANCEL HIGH WIND WARNING FOR N
CENTRAL MT. MODELS INDICATE DECREASING TREND IN BOTH SURFACE PRESSURE
GRADIENTS AND NW WINDS ALOFT. OTHERWISE CURRENT FORECAST LOOKS IN GOOD
SHAPE AND PLAN TO MAKE SOME MINOR TWEAKS TO THE FIRST PERIOD. LATEST ETA
AND MESOETA KEEP PLAINS..EXCEPT FOR N CENTRAL MT..DRY TODAY WHEREAS
CURRENT FORECAST HAS A MENTION OF PRECIPITATION. LATEST ETA/MESOETA HAVE
A VORTICITY CENTER OVER THE NRN E SLOPES OF THE ROCKIES THIS AFTERNOON.
SO WITH THAT AND A WEAKLY UNSTABLE AIRMASS IT IS PROBABLY BEST TO LEAVE
IN THE MENTION OF SHOWERS. FOR SW MT...ETA INITIALIZED A VORTICITY
CENTER NEAR THE BORDER BETWEEN S CENTRAL WA AND N CENTRAL OREGON AT 12Z.
WATER VAPOR IMAGERY FOR 12Z INDICATED THE POSSIBILITY OF A CENTER IN
THIS AREA. ETA HAS ASSOCIATED SHORTWAVE CLIPPING FAR SW MT INTO EARLY
AFTERNOON. SO MENTION OF SCATTERED SHOWERS IN THIS REGION ALSO LOOKS
FINE. LATEST ETA/NGM ARE A LITTLE WEAKER WITH THE UPPER TROUGH MOVING S
OVER THE AREA WED BUT WITH A MORE FAVORABLE LOW LEVEL UPSLOPE DIRECTION
AND A MORE UNSTABLE AIRMASS CURRENT SCATTERED SHOWER FORECAST LOOKS
GOOD. BLANK

EXTENDED...LITTLE CHANGE IN MEDIUM RANGE MODELS ONCE AGAIN THIS
MORNING...SO WILL GENERALLY KEEP WITH CURRENT FORECAST. WILL MAKE ADD
MENTION OF WINDS...SHOWERS AND THUNDERSTORMS TO SATURDAY FORECAST...WITH
COLD FRONT PUSHING THROUGH THEN. OTHERWISE...WITH THE EASTERN PACIFIC
UPPER RIDGE BUILDING ON DAY 3 (THURSDAY)...THE BROAD UPPER TROUGH OVER
WESTERN/CENTRAL CONUS DIGS SOUTH...ALLOWING A CUT-OFF LOW TO FORM OVER
THE SOUTHWESTERN CONUS. MOSTLY UNSETTLED WEATHER DAY 3 TO GIVE WAY TO
MOSTLY DRY CONDITIONS DAY 4 (FRIDAY) AS EASTERN PACIFIC RIDGE NOSES OVER
INTO MONTANA...WITH WEAK HIGH PRESSURE AT THE SURFACE. THIS WILL ALSO
CONTINUE A WARMING TREND FROM DAY 3 INTO DAY 4. THE ONLY SIGNIFICANT
CHANGE IN CURRENT MODEL RUNS OVER PREVIOUS ONES IS THAT THE LATEST RUNS
MOVE AN UPPER TROUGH IN FROM THE EASTERN PACIFIC A LITTLE FASTER THAN
BEFORE. THIS UPPER TROUGH LINGERS OVER THE AREA THROUGH THE WEEKEND AND
INTO DAY 7 (MONDAY)...KEEPING UNSETTLED WEATHER ACROSS THE AREA. THE
RESULT OF THE FASTER TROUGH IS THAT THE UPPER LOW LIFTING OUT OF THE
SOUTHWEST THROUGH THE WEEKEND WILL MOVE TO THE EAST MORE AND HAVE LESS
OF AN EFFECT ON THE STATE. OTHERWISE...DAY 5 (SATURDAY) WILL SEE A COLD
FRONT MOVE THROUGH FOR GUSTY WINDS AND A BETTER CHANCE OF THUNDERSTORMS.
ALSO...WITH THE LINGERING UPPER TROUGH OVER THE AREA...TEMPERATURES WILL
BE A BIT COOLER FOR DAYS 6 (SUNDAY) AND 7 (MONDAY).  COULSTON

CCF NUMBERS
GTF EW 054/030 051/035 063 10223
CTB EW 050/028 048/030 060 10333
HLN WW 054/033 054/033 063 10434
BZN WW 055/030 054/031 063 10433
WEY WW 048/024 045/025 054 10533
DLN WW 054/028 052/029 061 10433
HVR EW 058/032 054/034 065 10333
LWT EW 054/028 052/028 064 10334