FXCN01 CWHF 080809

FORECAST DISCUSSION FOR OPS AREA ALPHA AND THE ECHOES, CFB HALIFAX
PROPERTIES AND 12 WING SHEARWATER ISSUED BY AVIATION AND DEFENCE
SERVICES OF ENVIRONMENT AND CLIMATE CHANGE CANADA AT 0830Z ON
FRIDAY 08 MAY

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KEY FORECAST POINTS:

- UNSTABLE AIRMASS WILL COMBINE WITH DAYTIME HEATING TO GIVE
   SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE REGION
   TODAY.
- CONVECTION IS EXPECTED TO DEVELOP ALONG THE SPINE OF NOVA SCOTIA
   AND TRACK OFF TO THE NORTHEAST SATURDAY AFTERNOON.
- DIGGING UPPER TROUGH WILL SPREAD IMPULSES OF SHOWERS/RAIN INTO THE
   REGION LATE SATURDAY INTO MID WEEK.. EXPECT WET CONDITIONS WITH
   THE HEAVIEST TOTALS OCCURRING MONDAY NIGHT INTO TUESDAY.

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SHORT RANGE DISCUSSION FOR 0600Z 08 MAY TO 0300Z 10 MAY.
MODEL DISCUSSION: USED RDPS/HRDPS.
CONFIDENCE: GENERALLY HIGH.
COMMENTS/IMPACTS: AN UNSTABLE AIRMASS LINGERS IN THE WAKE OF THE
 SYSTEM THAT AFFECTED THE REGION THURSDAY. EXPECT DAYTIME HEATING
 AND WEAK TROUGH TO ASSIST IN DEVELOPING SCATTERED SHOWERS AND
 ISOLATED THUNDERSTORMS ACROSS THE MARITIMES TODAY. MODELS HAVE
 CONTINUOUSLY PUSHED THE STRONGEST CONVECTION OFF TO THE NORTH AND
 EAST OF HALIFAX SO HAVE REMOVED THE RISK IN THE FORECAST. WHILE NOT
 ZERO, IT IS LESS THAN 20 PERCENT CHANCE OF THUNDERSTORMS AFFECTING
 THE REGION TODAY. EXPECT CONVECTION WILL BEGIN DISSIPATE AFTER
 SUNSET AND CLEAR SKIES ARE GENERALLY EXPECTED BY MIDNIGHT. ONCE
 AGAIN, CONVECTIVE CLOUD WILL DEVELOP BUT THE FOCUS APPEARS ALONG
 THE SPINE OF NOVA SCOTIA SATURDAY. WHILE AFTERNOON CLOUDY PERIODS
 WILL DEVELOP, SHOWERS AND THE THREAT OF THUNDERSTORMS ARE FORECAST
 TO REMAIN INLAND. CLOUDY WILL BEING TO INCREASE LATE IN THE DAY
 SATURDAY AHEAD OF A DEVELOPING TROUGH MOVING OFF THE EASTERN
 SEABOARD WITH SHOWERS MOVING INTO THE HALIFAX REGION NEAR MIDNIGHT.
 GENERALLY LIGHT TO MODERATE WEST TO SOUTHWEST WINDS ARE FORECAST
 THROUGH THE PERIOD WITH AFTERNOON AND EARLY EVENING GUSTS IN THE
 LOW 20 KNOT RANGE.  WIND ADVISORY FOR 12 WING SHEARWATER IS
 UNLIKELY.

LONG RANGE DISCUSSION FOR 0300Z 10 MAY TO 0300Z 13 MAY.
MODEL DISCUSSION: USED RDPS/GDPS.
CONFIDENCE: GENERALLY HIGH... MEDIUM WITH PRECIPITATION
 AMOUNTS/WHERE BAND OF HEAVIEST RAINFALL WILL LINE UP MONDAY INTO
 TUESDAY.
COMMENTS/IMPACTS: A DIGGING UPPER TROUGH WILL GRADUALLY MOVE INTO
 THE REGION BEGINNING LATE SATURDAY GIVING AN UNSTABLE AND WET
 FORECAST THROUGH THE EXTENDED. THE FIRST IMPULSE OF SHOWERS WILL
 MOVE INTO THE REGION NEAR MIDNIGHT SATURDAY. SHOWERS AND DRIZZLE
 WILL CONTINUE TO STREAM SOUTHWEST TO NORTHEAST ACROSS THE REGION
 THROUGH THE DAY SUNDAY. A FRONTAL TROUGH WILL APPROACH MONDAY
 GIVING SHOWERS, POSSIBLY AT TIMES HEAVY, THROUGHOUT THE DAY. A NEW
 LOW IS FORECAST TO DEVELOP ALONG THE TAIL END OF THE COLD FRONTAL
 TROUGH MONDAY INTO THE OVERNIGHT THEN INTENSIFY AND TRACK UP
 TOWARDS THE REGION TUESDAY GIVING PERIODS OF RAIN, LIKELY AT TIMES
 HEAVY.  MODEL RUNS FROM 24 HOURS AGO HAD THE GDPS GIVING THE
 HEAVIEST RAINFALL AMOUNTS. IT NOW GIVES SOME OF THE LEAST AMOUNTS
 AS IT HAS THE FURTHEST EAST TRACK OF THE MODELS. GFS/ECMWF TRACK
 THE LOW TOWARDS CAPE BRETON AND GIVE PERIODS OF SIGNIFICANT
 RAINFALL TUESDAY WHILE THE ICON TRACKS THE LOW JUST OFF THE COAST
 OF HALIFAX AND GIVES THE HEAVIEST AMOUNTS TO THE LOCAL REGION.  ALL
 THAT TO SAY.. WET CONDITIONS ARE EXPECTED THROUGH THE EXTENDED
 WITH SOME AREAS ALONG THE NOVA SCOTIA COAST GETTING POSSIBLY
 SIGNIFICANT RAINFALL, DEPENDENT UPON THE TRACK OF TUESDAYS LOW.

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