Damaging Wind in Montana, May 5, 2001

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
300 PM MDT SAT MAY 5 2001

MAIN FORECAST ISSUE THIS AFTERNOON IS THE STRONG COLD FRONT THAT IS
MOVING SLOWLY THROUGH THE CWA. STRONG SOUTHWEST WINDS AHEAD OF THE COLD
FRONT HAVE SWITCHED TO THE WEST AT CUT BANK WITH A BIT OF A DROP IN
TEMPERATURE...WITH SLIGHTLY DECREASING WINDS. FRONT SEEMS TO BE PUSHING
THROUGH GREAT FALLS AT THIS TIME. WINDS HAVE BEEN JUST BELOW HIGH WIND
CRITERIA ACROSS THE PLAINS ADJACENT TO THE ROCKY MOUNTAIN FRONT. THEY
SHOULD CONTINUE TO DECREASE AFTER SUNSET...BUT THEY SHOULD STAY BREEZY
THROUGHOUT THE NIGHT WITH THE UPPER TROUGH PASSING ACROSS NORTHERN
MONTANA. MOISTURE IS SOMEWHAT LIMITED WITH FRONTAL PASSAGE...SO
CLOUDINESS IS SCARCE AND PRECIPITATION IS ALMOST NON-EXISTENT.
HOWEVER...MODELS ALL AGREE IN BRINGING MOISTURE SOUTH OUT OF ALBERTA
OVERNIGHT ASSOCIATED WITH CHANNELED VORTICITY IN THE NORTHWEST FLOW ON
THE BACK SIDE OF THE UPPER TROUGH. WILL THEREFORE GO WITH SLIGHT CHANCE
POPS FOR AFTER MIDNIGHT ACROSS NORTHERN ZONES...WITH LESSER POPS IN THE
SOUTHWEST FOR WEAK EVENING CONVECTION. A FEW LIGHTNING STRIKES HAVE BEEN
INDICATED IN CENTRAL ALBERTA THIS AFTERNOON IN THE VICINITY OF THE BEST
VORTICITY...BUT WILL LEAVE MENTION OF THUNDERSTORMS OUT AS CONVECTION IS
LIMITED ACROSS THE CWA. OTHER THAN EASTERN ZONES...WILL GO WITH
DECREASING CLOUDINESS AFTER MIDNIGHT. AFTER TONIGHT (AND MORNING CLOUDS
ACROSS EASTERN ZONES)...EXPECT DIRTY UPPER RIDGE TO SLOWLY SHIFT INTO
THE PACIFIC NORTHWEST ON SUNDAY...ALLOWING THE FLOW ALOFT TO BECOME MORE
WESTERLY AND ANTICYCLONIC DURING THE AFTERNOON...FOR ONLY VARIABLE HIGH
CLOUDS AND MAYBE SOME CUMULUS DEVELOPMENT OVER THE MOUNTAINS. RIDGE AXIS
PROGRESSES FARTHER EAST INTO WESTERN MONTANA ON MONDAY...TO KEEP SKIES
MOSTLY CLEAR SUNDAY NIGHT AND MOSTLY SUNNY MONDAY. TEMPERATURES WILL
ALSO WARM ABOUT 10 DEGREES FROM SUNDAY TO MONDAY. COULSTON

EXTENDED...MRF AND EUROPEAN MODELS IN GENERAL AGREEMENT WITH SHORT TERM
DETAILS BUT AGAIN DIVERGE LATER IN THE WEEK. DAY 3 CONTINUES TO LOOK DRY
WITH H5 RIDGE OVER THE CWA. AVN MOVES A STRONG UPPER TROF OVER THE AREA
DAY 4 BUT THE THE MRF VERSION OF THIS EVENT IS WEAKER AND SLOWER. MRF
SOLUTION HAS INCREASING SOUTHWEST FLOW ALOFT WITH A CHANCE OF SHOWERS.
SHORT WAVE MOVES ACROSS DAY 5 WITH WEAK UPSLOPE SURFACE GRADIENTS AND A
CONTINUED CHANCE OF SHOWERS. ANOTHER WEAK UPPER TROF MOVES ACROSS DAY 6
WITH A STRONG WESTERLY SURFACE GRADIENT KEEPING PRECIPITATION CONFINED
TO THE MOUNTAINS. DAY 7 LOOKS DRY WITH DOWNSLOPE GRADIENTS.

CCF NUMBERS
GTF BU 034/058 036/069 046 10200
CTB BU 030/056 033/066 040 10200
HLN BB 032/060 032/070 040 10200
BZN BB 027/058 027/069 036 10100
WEY BB 018/053 018/064 028 10100
DLN BB 024/058 024/071 033 10100
HVR EU 034/064 034/071 043 10210
LWT EU 032/058 032/068 040 10210