Flooding in Montana, March 16 to 18, 2003

NORTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
233 AM MST SUN MAR 16 2003

...MAJOR WINTER STORM EXPECTED FOR NORTHEAST MONTANA STARTING ON
MONDAY...

.SHORT TERM...
SURFACE TROUGH LOCATED OVER CENTRAL MONTANA THIS MORNING WITH SW
FLOW ALOFT STARTING TO BRING MID AND HIGH LEVEL MOISTURE INTO THE
STATE. THE SURFACE TROUGH REMAINS STATIONARY TODAY WITH ANOTHER WARM
DAY TODAY BEFORE WINTER RETURNS ON MONDAY.

MEANWHILE...A SHORTWAVE MOVES ACROSS CALIFORNIA AND NEVADA TODAY AND
AN UPPER TROUGH STARTS DIGGING OVER THE CENTRAL ROCKIES. ALONG THE
SURFACE TROUGH AXIS...A LOW DEVELOPS IN COLORADO FORMING AN INVERTED
TROUGH INTO MONTANA. THIS INVERTED TROUGH SLIDES INTO EASTERN
MONTANA TONIGHT AND BECOMES STATIONARY.

ON MONDAY...A CLOSED UPPER LOW FORMS OVER THE SURFACE LOW IN
COLORADO WITH THE INVERTED SURFACE TROUGH REMAINING STATIONARY OVER
EASTERN MONTANA. EASTERN MONTANA BETWEEN 600 AND 800 MB BECOMES AN
AREA OF STRONG Q-VECTOR CONVERGE...STRONG FRONTOGENESIS...POTENTIAL
VORTICITY AND UPWARD OMEGA THAT LASTS INTO TUESDAY. ADD STRONG
400-500 MB DIVERGENCE...A MOISTURE FEED FROM THE GULF OF MEXICO AND
THETA-E RIDGING AND IT BECOMES A RECIPE FOR A LOT OF PRECIPITATION.
EXCEPT FOR THE ETA BEING SLIGHTLY WEST OF THE AVN WITH THE PLACEMENT
OF THE INGREDIENTS AND SOME DIFFERENCES IN TEMPERATURES ALOFT THAT
COULD AFFECT THE TYPE OF PRECIP ON MONDAY...THE MODELS ARE SIMILAR
WITH THIS SYSTEM.

ETA FORECAST SOUNDINGS SHOWS THAT PRECIPITATION SHOULD START AS RAIN
EITHER SUNDAY NIGHT OR MONDAY. THE COMBINATION OF COLD AIR ADVECTION
AND DYNAMIC COOLING WILL CHANGE THE PRECIP TO ALL SNOW BY MONDAY
NIGHT. ONE FORECAST PROBLEM IS THE MODELS LINGER SOME WARMER AIR
ALOFT ON MONDAY OVER THE EASTERN ZONES WHICH COULD RESULT IN A
PERIOD OF SLEET OR FREEZING RAIN IN THE TRANSITION FROM RAIN TO
SNOW. LOOKING AT THE MODEL SOUNDINGS FOR SDY...GDV AND PLENTYWOOD...
FREEZING RAIN IS MORE LIKELY THAN SLEET. WILL FORECAST A MIX OF
RAIN...FREEZING RAIN AND SNOW FOR THE EASTERN ZONES AND A MIX OF
RAIN AND SNOW CHANGING TO SNOW IN THE WEST FOR MONDAY. WILL FORECAST
ALL SNOW FOR MONDAY NIGHT AND TUESDAY. FORRESTER

.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY
POWERFUL SLOW MOVING STORM IN THE CENTRAL U.S. WILL CONTINUE TO
IMPACT OUR WEATHER INTO WEDNESDAY.  MODELS LOOK TO BE GOOD AGREEMENT
THAT A 990MB LOW WILL BE LOCATED IN NORTHERN TX OR WESTERN OK WITH
AN INVERTED SFC TROUGH EXTENDING NNW INTO EASTERN MT.  THE LOW IS
EXPECTED TO ROTATE AROUND THE UPPER LEVEL TROUGH THROUGH
WEDNESDAY...AND THE AVN HAS THE LOW POSITIONED IN JUST ABOUT THE
SAME LOCATION IN NORTHERN TX 24 HOURS LATER AT 00Z THURSDAY.  THERE
IS PLENTY OF MOISTURE WRAPPING BACK INTO EASTERN MONTANA TUESDAY
NIGHT...AND LIFT COMBINED WITH FRONTOGENESIS AT 700MB LOOK
SUFFICIENT TO CONTINUE CATEGORICAL POPS ACROSS THE EASTERN THREE
QUARTERS OF OUR CWA.

ON WEDNESDAY THE GFS HAS A SHORT WAVE MOVING FROM WEST TO EAST
ACROSS THE STATE WHICH SHOULD SHIFT THE DEFORMATION AREA TO OUR EAST
DURING THE DAY.  WILL CONTINUE WITH LIKELY POPS IN THE EAST...BUT
BEGIN TO DRY IT OUT DURING THE AFTERNOON ACROSS OUR WESTERN ZONES.
A SFC HIGH AND 500H RIDGE BUILD IN WEDNESDAY NIGHT AND THURSDAY
WHICH WILL PUT AN END TO THE PRECIPITATION.  TEMPERATURES WILL BE
TRICKY THURSDAY AS THERE WILL LIKELY BE EXTENSIVE SNOWCOVER AT THIS
POINT.  WILL GO ABOUT 10 DEGREES BELOW GUIDANCE NUMBERS TO ACCOUNT
FOR THIS.

ON FRIDAY THE SFC HIGH MOVES TO OUR EAST AND WE BEGIN TO GET INTO
MORE OF A ZONAL FLOW ALOFT.  A WEAK COLD FRONT APPROACHES
SATURDAY...BUT AT THIS POINT WILL KEEP IT DRY.  A DIURNAL CYCLE OF
ABOVE AND BELOW FREEZING TEMPERATURES WILL ALLOW FOR SNOWMELT AT THE
END OF THE WEEK INTO NEXT WEEKEND WHICH COULD LEAD TO FLOODING
PROBLEMS.  AT THIS POINT IT LOOKS LIKE A RETURN TO WELL ABOVE
TEMPERATURES IS NOT IN THE CARDS...SO HOPEFULLY THE SNOWMELT WILL BE
GRADUAL OR MAJOR FLOODING COULD BECOME A CONCERN.  CB

KGGW EOS /055 036/036 027/033 7903+++9
     SBEE 024/034 026/036 025/040 024/043 025/ 9280000000
KGDV EOS /057 037/039 027/034 7904+++9
     SBEE 026/035 025/038 024/040 023/043 024/ 9284000000

.GGW...WINTER STORM WATCH MONDAY THROUGH TUESDAY ALL ZONES.

MTZ016>027-059>062-171300-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GLASGOW MT
555 AM MST SUN MAR 16 2003

.DAY ONE...

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...

A WINTER STORM WATCH IS IN EFFECT FOR MONDAY THROUGH TUESDAY. A LATE
SEASON WINTER STORM IS EXPECTED TO DEVELOP OVER EASTERN COLORADO BY
LATE SUNDAY NIGHT AND EXTEND NORTHWARD OVER EASTERN MONTANA MONDAY.
THIS STORM IS EXPECTED TO BEGIN AS A MIX OF RAIN...FREEZING
RAIN...AND SNOW BEFORE TURNING TO ALL SNOW BY MONDAY EVENING. THIS
STORM IS EXPECTED TO BE VERY SLOW MOVING...THUS THERE IS POTENTIAL
FOR TOTAL SNOWFALL ACCUMULATIONS OF UP TO 8 INCHES ACROSS PORTIONS
OF THE WATCH AREA THROUGH TUESDAY. STRONG NORTH TO NORTHEAST WIND
WILL ACCOMPANY THIS STORM...LIKELY BRINGING SIGNIFICANT BLOWING AND
DRIFTING SNOW TO MANY AREAS. ADDITIONAL SNOWFALL IS POSSIBLE FROM
THIS STORM TUESDAY NIGHT INTO WEDNESDAY. PLEASE SEE GTFWSWGGW OR
WGUS45 KGGW FOR DETAILS.

A WINTER STORM WATCH IS ISSUED WHEN SEVERE WINTER WEATHER IS
POSSIBLE...BUT NOT IMMINENT. AT THE TIME...THERE IS A POTENTIAL FOR
UP TO 8 INCHES OF SNOW ACCUMULATION THROUGH TUESDAY. FUTURE DRIVING
AND WALKING CONDITIONS MAY BECOME HAZARDOUS...SO IT IS IMPORTANT TO
MONITOR THE LATEST FORECASTS AS REFINEMENTS ARE MADE.

STAY TUNED TO NOAA WEATHER RADIO AND OTHER LOCAL MEDIA OUTLETS FOR
FURTHER DETAILS OR UPDATES ON THIS POTENTIAL WINTER STORM.

.SPOTTER INFORMATION STATEMENT...

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

CB