Severe Thunderstorm Warning 48, NWS Glasgow, MT

NORTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
228 PM MDT THU JUL 4 2002

.SHORT TERM...TIMING ON AVN AND ETA FAMILY MODELS HINT AT ANOTHER
NOCTURNAL PRECIP EVENT.  ONCE AGAIN REVIEWING THE THETA E AND
CAPE...SHORTWAVES AND SURFACE TROUGHS...AND POSITION OF LOW LEVEL
JET AND QPF.  A SHORTWAVE WITH ENHANCED CAPE IN SOUTHWEST MONTANA IS
PROGGED TO ENTER THE SW CWA ZONES 0Z-02Z THIS EVENING.  SHORTWAVE
WILL PROGRESS ACROSS THE CWA AND GENERATE SHOWERS/TSTMS AS IT PASSES
OVERNIGHT.  MAIN INSTABILITY AND DYNAMICS INITIALLY ALONG THE BORDER
WITH NORTH DAKOTA THIS EVENING WILL DIMINISH BY MIDNIGHT.

AVN AND ETA HAVE SOME DIFFERENCES IN THE INTENSITY AND PROGRESSION
OF THE QPFS...THETA E RIDGE AND CAPE GRADIENT.  AVN TRACKS FURTHER
SOUTH AND WEST THAN THE ETA...LEAVING THE EXTREME EASTERN PART OF
THE CWA VULNERABLE TO SEVERE WEATHER.  ETA PROGS THE THETA E AND
CAPE NORTH AND EAST OF THE CWA WITH THE CAPE GRADIENT PULLING INTO
CANADA AROUND MIDNIGHT.  RESULT CAPS THE REGION AND WILL BE LESS
LIKELY TO FIRE CONVECTION.  SO FAR THE ETA MODEL HAS HANDLED THE
WEATHER PATTERN BEST...BUT WILL BLEND SOME OF THE POPS FOR A BETTER
OVERALL COVERAGE OF THE CWA.

18Z GGW SOUNDING THIS AFTERNOON SHOWS A MOIST AIR MASS WITH 1.10 PW.
SOUNDING ALSO SHOWS THE WESTERN CWA IS STILL CAPPED AND HAS A WEAK
SUBSIDENCE INVERSION AT 850MB.  IN ADDITION FORECAST SOUNDINGS OVER
THE EASTERN ZONES INDICATE THE CAP IS STILL PRESENT ALTHOUGH
WEAKENING.  MOIST ATMOSPHERE WILL HAVE MORE RAIN POTENTIAL SINCE THE
FREEZING LEVEL IS AROUND 15 KFT.  EVEN WITH CAPE 1100 J/KG AT MIDDAY
BELIEVE THE REGION WILL NEED A TRIGGER BEFORE CONVECTION DEVELOPS.
ANTICIPATE ACTIVITY WILL BE MORE OF A SINGLE CELL PULSE OR MULTICELL
DEVELOPMENT THAN SUPERCELLS.

MEANWHILE FRIDAY LOOKS FAIRLY DRY FOR NOW THOUGH THERE MAY BE SOME
ISOLATED TO SCATTERED SHOWERS LINGERING IN THE EASTERN HALF OF THE
CWA IN THE MORNING.  ANOTHER SHORTWAVE COMES THROUGH LATE SATURDAY
AFTERNOON WHICH MAY GENERATE SOME CONVECTION THROUGH THE EVENING.
FOR NOW WILL KEEP THE ISOLATED AND SILENT POPS FOR SATURDAY NIGHT.

.LONG TERM...HIGH AMPLITUDE RIDGE BUILDS OVER THE REGION WITH JET
STREAM DISPLACED WELL NORTH IN CANADA.  RIDGE WILL BE CONTAMINATED
WITH SHORTWAVES AND THERMALLY INDUCED GRAVITY WAVES WHICH MAY CREATE
ENOUGH INSTABILITY FOR LOCAL SHOWERS.  PRESENT SLIGHT CHANCE POPS
LOOK GOOD FOR NOW.  TEMPERATURES WILL CLIMB INTO THE 90S AS THE
SURFACE HIGH IS ENHANCED BY THE UPPER RIDGE.  MCNULTY

KGGW BBB 063/080 050/087 053/087 81410012
     BBBB 060/088 059/086 059/093 061/093 8122222222
KGDV BBB 066/085 053/086 054/087 81420012
     BBBB 062/090 060/088 057/095 059/095 8122222222

.GGW...NONE.