Hail in Montana, June 21, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
924 AM MDT THU JUN 21 2007

.UPDATE...MAIN FORECAST CONCERN WILL BE PCPN CHCS TODAY AND
TONIGHT WITH VERY WARM TEMPS THROUGH SAT. MORNING KGGW SOUNDING
HAS PLENTY OF LLVL MOISTURE AND INSTABILITY BUT ALSO SHOWING WEAK
CAP ABOVE 700MB WITH WEAK FLOW UP TO 650MB. CURRENT WATER VAPOR
SAT IMAGERY SHOWS A WEAK SHORTWAVE CROSSING SCNTRL MT WITH THE
REFLECTION OF A SURFACE TROUGH. GFS AND NAM SHIFT 1ST SHORTWAVE
ACROSS SRN PORTIONS OF THE CWA IN THE AFTERNOON AND A FEW MORE
WEAK VORTICITY FEATURES TONIGHT AS THE UPPER RIDGE AXIS BEGINS TO
AMPLIFY. MODELS SHOWING GOOD DEAL OF WARMING ALOFT AS HEIGHTS
INCREASE FRIDAY AFTERNOON INTO SATURDAY AS RIDGE AXIS WILL BE
POSITIONED OVER ERN MT. VERY WARM SFC TEMPS FRI WITH +29C AND +31C
SAT WITH 586DM THICKNESS VALUES SO MID- UPPER 90S LIKELY. SFC
FRONT SAT NIGHT SHOULD BRING SOME COOLING AND ISOLD PCPN INTO
SUNDAY. CURRENT FORECAST LOOKS GOOD WITH MORNING POPS SOUTH AND
EAST AND ISOLD POPS ACROSS CWA THIS AFTN AND EVENING. SLA
&&

.PREVIOUS DISCUSSION...310 AM MDT..UPPER RIDGE WILL BRING WARM TO HOT
WEATHER THE NEXT 3 DAYS. A SHORTWAVE RUNNING THROUGH EASTERN
MONTANA HAS PRODUCED SOME ISOLATED SHOWERS AND THUNDERSTORMS SOUTH
OF THE MISSOURI RIVER. A FEW OF THESE CELLS WILL AFFECT THE
FORECAST AREA MAINLY IN THE EAST THIS MORNING.

ANOTHER WEAK SHORTWAVE SLIDES ACROSS THE RIDGE TONIGHT. WITH AN
UNSTABLE ATMOSPHERE WITH LIFTED INDEX AS LOW AS -5 AND CAPE AS
HIGH AS 1000 J/KG...MAY SEE AN ISOLATED THUNDERSTORM WITH THIS
WAVE TONIGHT.

ON FRIDAY...THERMAL RIDGE STRENGTHENS AND ATMOSPHERE BECOMES
CAPPED. THIS RIDGE AND CAP WILL PREVAIL THROUGH SATURDAY WITH HOT
AND DRY WEATHER. A DEVELOPING LOW PRESSURE SYSTEM ON SATURDAY WILL
BRING SOUTHEAST WINDS INTO THE FORECAST AREA WHICH MAY BECOME
STRONG ENOUGH FOR A LAKE WIND ADVISORY. FORRESTER

.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY... NO SIGNIFICANT
CHANGES MADE TO PREVIOUS FORECAST AS LIMITED REVELATIONS AROSE
FROM THE EVENING MODELS. OVERALL CONFIDENCE IN PATTERN EARLY ON IS
STILL QUITE HIGH...ALTHOUGH NOTEWORTHY DIFFERENCES REMAIN A FACTOR
BEYOND MONDAY. SATURDAY EVENING/NIGHT STILL BARES WATCHING FOR
POTENTIAL SEVERE WEATHER EPISODE AS HEIGHT FALLS WITHIN
SOUTHWESTERLY FLOW ALOFT BEGIN WEARING DOWN THE UPPER RIDGE ACROSS
EASTERN MONTANA. COLD FRONT WITH NOTICEABLY COOLER AIR SHOULD
CROSS THE CWA DURING THE DAY SUNDAY ALLOWING SOME RELIEF FROM THE
EARLY SUMMER HEAT. KEPT RELATIVELY LOW POPS SUNDAY GIVEN
CONSISTENT STRONG INHIBITION SIGNAL...THOUGH FRONTAL FORCING COULD
EASILY MITIGATE THIS MAINLY ACROSS THE EASTERN ZONES.

UPPER LOW THEN LIFTS INTO NORTHERN SASKATCHEWAN BY TUESDAY LEAVING
THE REGION IN AN UNSETTLED SOUTHWEST FLOW. ECMWF HAS DEVIATED
SUBSTANTIALLY FROM ITS PREVIOUS RUNS IN THE HANDLING OF THIS
FEATURE. LATEST RUNS FAVOR A MUCH FASTER AND MORE DYNAMIC
SOLUTION HOWEVER RUN TO RUN CONTINUITY IS MUCH BETTER WITH GFS.
POTENTIAL UPPER RIDGE AND RETURN TO UNSEASONABLE WARMTH BY MID
WEEK MAY STILL BECOME CONTAMINATED BY SEVERAL PACIFIC DISTURBANCES
FROM YET ANOTHER CLOSED UPPER LOW. GIVEN THIS...HAVE KEPT LOW
/SUB-CLIMO POPS GOING THROUGH THE REMAINDER OF THE EXTENDED. MCZ

&&

.AVIATION...
VFR. SURFACE WINDS BECOME SE BETWEEN 10 TO 15 KNOTS. ISOLATED
THUNDERSTORMS WILL BE POSSIBLE BY LATE THIS AFTERNOON INTO THE
EVENING AT ALL THE TAF SITES AHEAD OF A WEAK UPPER DISTURBANCE.
MCZ/SIMONSEN

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

WEATHER.GOV/GLASGOW