Severe Thunderstorm Warning 35, NWS Billings, MT

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
158 PM MDT MON JUL 3 2000

.TUE AND WED...

VERY UNSTABLE AND MOIST ATMOSPHERE IN PLACE OVER MOST OF THE COUNTY
WARNING AREA.  AT 18Z LAPS LIS ARE AS LOW AS -11...CAPES OF GREATER THAN
4000J IN SOUTHERN ROSEBUD COUNTY...DEW POINTS IN THE MID 60S IN THE
EAST...TO THE MID 50S IN THE WEST.  VAD WIND PROFILE AT 1740Z OVER
BILLINGS INDICATES GOOD LOW LEVEL DIRECTIONAL SHEAR WITH A 30 KT LOW
LEVEL SSE JET AT AROUND 850 MB.

WATER VAPOR IMAGERY INDICATES AN UPPER LOW OVER WASHINGTON...ONE OVER
THE QUEEN CHARLOTTE ISLANDS...AND A THIRD OVER NORTHERN ALBERTA WITH
SEVERAL SHORTWAVES ROTATING INTO THE STATE IN THE CYCLONIC FLOW.  A
COUPLE OF JET STREAKS WERE SEEN ON THE WATER VAPOR IMAGERY...WHICH IS
PROBABLY ENHANCING THE CONVECTION OVER SOUTHWEST MONTANA.  BASED ON THE
SATELLITE IMAGERY...AND THE LAPS MSL THE ETA SEEMS LIKE A BETTER CHOICE.
HOWEVER...FEEL THAT EVEN THE ETA SEEMS TO BE LIFTING THE SURFACE AND LOW
LEVEL FEATURES NNE TOO FAST.  FOR EXAMPLE...THE 850 MB PROG DOES NOT
INDICATE THE LOW LEVEL JET.  VISIBLE IMAGERY ALSO DEPICTS DEVELOPING
CONVECTION OVER THE BEARTOOTH MOUNTAINS AND THE BIG HORN MOUNTAINS.
WITH THE EJECTING SHORTWAVES AND THE FACT THAT THE MODELS ARE NOT
DEPICTING THE SITUATION WELL...WILL NOT BE TOO DETAILED. BELIEVE THE
AREA OF UPPER LEVEL DIFFLUENCE WILL BE FURTHER SOUTH THAN THE ETA HAS
DEPICTED. UPPER LOWS DO THE DANCE AND DUMBBELL AROUND EACH OTHER WITH
MAIN LONGWAVE TROF ALONG THE COAST.  SHORTWAVES CONTINUE TO EJECT INTO
THE AREA WITH PROBABLE GOOD UPPER LEVEL DIFFLUENCE...WHICH WILL LEAD TO
LEE SIDE SURFACE CYCLOGENESIS IN NORTHERN WYOMING.  WITH SUCH HIGH DEW
POINTS...WOULD EXPECT LOCALLY HEAVY RAIN...ESPECIALLY EAST WITH ANY
CONVECTION. SPC HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR THE CENTRAL
AND WESTERN COUNTIES.  SPC IS ALSO CONSIDERING A TORNADO WATCH FOR THE
EASTERN ZONES WITH THE VERY IMPRESSIVE DIRECTIONAL AND SPEED SHEAR.  IF
IT HAPPENS LATER THIS AFTERNOON...WILL UPDATE.  ETA HINTS THAT THE CWA
IS NOT GOING TO BE OUT OF THE WOODS ON TUESDAY...HOWEVER WILL NOT
MENTION SEVERE ON TUESDAY AT THIS TIME...WILL LET MID SHIFT TAKE A LOOK
AT THE 00Z MODEL RUNS.  CWA REMAINS UNDER CYCLONIC FLOW ON WEDNESDAY FOR
A CHANCE OF MORE CONVECTION.

AGAIN...THE CENTRAL AND WESTERN ZONES ARE UNDER A SEVERE THUNDERSTORM
WATCH UNTIL 800 PM.  THIS INCLUDES MUSSELSHELL...YELLOWSTONE...AND BIG
HORN COUNTIES WEST. STROBIN

.THU...FRI...AND SAT...
WARM PATTERN LOOKS TO CONTINUE ACROSS SOUTHERN MONTANA DURING THE
PERIOD. ALL MODELS INDICATING ONE MORE DAY OF SOUTHWEST FLOW ON
THURSDAY...THUS WILL LEAVE IN CHANCE OF THUNDERSTORMS. MRF AND ETA
700MB TEMPERATURES ARE ROUGHLY 8 TO 12 DEGREES...WHILE AVN IS A COUPLE
OF DEGREES WARMER. SINCE AVN IS HAVING PROBLEMS HANDLING TODAYS
SITUATION...ESPECIALLY MOISTURE...WILL STICK MORE WITH THE ETA FOR
THURSDAY AND LOWER HIGH TEMPS A COUPLE DEGREES. FRIDAY SHORTWAVE TROUGH
OVER WEST COAST EJECTS OUT AND RIDES OVER TOP OF THE RIDGE IN PLACE OVER
THE CENTRAL US AND IS QUICKLY REPLACED BY ANOTHER. THE TROUGH WILL ACT
TO BRING IN COOLER TEMPERATURES DUE TO SLIGHTLY COOLER MID LEVEL
TEMPS...BUT LOOKS TO BE TOO FAR NORTH TO BRING MUCH OF A CHANCE OF
PRECIPITATION TO THE CWA...SO WILL LEAVE FRIDAY DRY FOR NOW. SATURDAY
THE RIDGE BEGINS TO BUILD BACK IN TO THE AREA...WITH DRY NORTHWESTERLY
FLOW AND WARMING TEMPERATURES...DEPENDING ON WHETHER ECMWF OR MRF IS TO
BE FOLLOWED. ECMWF IS OLDER.  WILL FOLLOW THE NEWER MRF THIS TIME.
JZ/CHB

BIL TTTBB 059/079 055/084 058/087 057/086 058/089 634443 52
LVM TTTBB 054/078 052/083 055/085 055/084 056/087 634443 52
HDN TTTBB 058/081 053/086 058/088 055/087 057/090 634443 52
MLS TTTBB 063/085 057/088 061/090 060/088 059/090 634443 52
4BQ TTTBB 062/086 057/089 060/092 060/089 060/091 634443 52
BHK TTTBB 061/084 056/087 060/091 059/087 059/088 634443 52
SHR TTTBB 056/080 051/085 055/089 055/087 056/090 634443 52