358
FXCN01 CWHF 210804
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
MONDAY 21 SEP
===================================================================
KEY FORECAST POINTS:
- LOW CONDITIONS IN SHOWERS/DRIZZLE AND PATCHY MIST/FOG IMPROVING
THIS MORNING.
- STRONG RIDGE BUILDING INTO THE REGION FROM THE NORTHWEST GIVING
COOL NORTHEAST FLOW OFF GULF OF ST.LAWRENCE GIVING PATCHY CLOUD
TUESDAY THROUGH WEDNESDAY.
- RIDGING OVERHEAD THURSDAY GIVING SUNNY SKIES.
- UNCERTAINTY WITH TIMING OF STRENGTHENING LOW PRESSURE SYSTEM
SLOWLY APPROACHING FROM THE SOUTH GIVING CLOUD AND POSSIBLY RAIN
FRIDAY.
===================================================================
SHORT RANGE DISCUSSION FOR 0600Z 21 SEP TO 0300Z 23 SEP.
MODEL DISCUSSION: USED RDPS/HRDPS.
CONFIDENCE: MEDIUM FOR CLOUD COVER BEYOND THIS AFTERNOON.
COMMENTS/IMPACTS: BROAD TROUGH OF LOW PRESSURE PASSING THROUGH THE
REGION THIS MORNING WITH A LOW PRESSURE SYSTEM DEVELOPING WELL TO
THE SOUTH. CLOUDY CONDITIONS WITH SHOWERS/DRIZZLE WILL TAPER TO A
CHANCE OF SHOWERS THIS MORNING. A DISSIPATED COLD FRONTAL TROUGH
TRACKS DOWN TOWARDS THE REGION GIVING FURTHER SUPPORT TO A FEW
SHOWERS LATE THIS AFTERNOON/THIS EVENING. HOWEVER, THIS RUN IS
CLOUDIER THAN PREVIOUS RUNS AND THE RDPS HAS MORE CLOUD THAN THE
HRDPS BEYOND THIS AFTERNOON. WHILE THE RDPS WOULD KEEP THE REGION
MAINLY CLOUD THROUGH MUCH OF TONIGHT, THE HRDPS BREAKS THE CLOUD UP
A BIT SO HAVE GONE WITH BECOMING A MIX OF SUN AND CLOUD LATE THIS
AFTERNOON AND CLOUDY PERIODS OVERNIGHT. ADDITIONALLY, WITH THE
TROUGHING MOVED OFF TO THE EAST AND A STRENGTHENING RIDGE BUILDING
IN FROM THE NORTHWEST, THE REGION WILL REMAIN UNDER A
NORTH/NORTHEAST FLOW THROUGH WEDNESDAY, BEGINNING THIS EVENING.
THIS COOLER FLOW WILL DRAW MOISTURE OFF THE WARMER GULF OF
ST.LAWRENCE GIVING PATCHY CLOUD/MIX OF SUN AND CLOUD THROUGH
WEDNESDAY. LASTLY.. A STREAM OF THICK CIRRUS WILL MOVE ACROSS LATE
TONIGHT INTO TUESDAY, SPILLING OFF A SYSTEM SOUTH OF THE GREAT
LAKES.
LONG RANGE DISCUSSION FOR 0300Z 23 SEP TO 0300Z 26 SEP.
MODEL DISCUSSION: USED RDPS/GDPS.
CONFIDENCE: MEDIUM FOR WEDNESDAY CLOUD COVER, HIGH FOR THURSDAY,
LOWER FOR FRIDAYS APPROACHING SYSTEM.
COMMENTS/IMPACTS: AS NOTED ABOVE.. A BIT OF UNCERTAINTY WITH HOW
MUCH MOISTURE/CLOUD STREAMS OFF THE GULF OF ST.LAWRENCE IN THE
COOLER NORTHEAST FLOW WEDNESDAY. HAVE GONE WITH A MIX OF SUN AND
CLOUD FOR NOW BUT COULD HAVE A DECENT DECK OF SC DEVELOP AND SHIFT
OVER THE REGION NEAR MIDDAY. BY THURSDAY, THE RIDGE IS MAINLY
OVERHEAD WITH NOW SIGNIFICANT DRAW OF MOISTURE OFF THE GULF OF
ST.LAWRENCE AND A FAIRLY SUNNY DAY. CIRRUS WILL BEGIN TO INVADE THE
REGION FROM THE SOUTH LATE THURSDAY/OVERNIGHT AND INTO FRIDAY AS A
SYSTEM DEVELOPS OFF THE MID-EASTERN US SEA BOARD THEN INTENSIFIES
AND TRACKS TOWARDS THE CAPE COD REGION FOR THE WEEKEND. AS THIS
SYSTEM DEVELOPS, IT WILL ROTATE A BAND OF RAIN, LIKELY ALONG A
TROWAL, UP TOWARDS NOVA SCOTIA. THE TIMING OF THIS BAND, HOW FAR
UP TO OR INTO NOVA SCOTIA THE BAND MOVES IN WILL BE GUIDED BY HOW
QUICKLY THE RIDGE OVERHEAD WEAKENS THURSDAY NIGHT INTO FRIDAY AND
HOW THE RIDGE AXIS SHIFTS TO THE NORTH. AT THIS TIME, THE GDPS IS
THE EARLIEST ONSET FOR RAIN, WITH THE GDPS NOT TOO FAR BEHIND. BOTH
THE ICON/ECMWF DRY OUT THE BAND AS IT DEFORMS ALONG THE SOUTHERN
EDGE OF THE RIDGE AND KEEP RAIN OUT OF THE REGION UNTIL LATER INTO
THE WEEKEND. LOWER CONFIDENCE WITH THE FORECAST AS MODELS CONTINUE
TO BATTLE THE WEAKENING OF A VERY STRONG HIGH, PEAKING
WEDNESDAY/THURSDAY WITH AN INTENSIFYING LOW MOVING UP THE EASTERN
SEABOARD LATE THIS WEEK INTO THIS WEEKEND.
END/METOC-HFX
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