406
FXCN01 CWHF 250810
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 25 AUG
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KEY FORECAST POINTS:
- INFLUX OF TROPICAL MOISTURE WILL GIVE SHOWERS, HEAVY AT TIMES,
LATER TODAY.
- 25 MM OF RAINFALL IS POSSIBLE WITH THIS EVENT, ESPECIALLY WITH
POSSIBLE THUNDERSHOWERS THIS EVENING.
- DRYING OUT WITH GUSTY WEST WINDS TUESDAY.
- VARIABLE CLOUD AMOUNTS BUT MAINLY DRY FOR THE LONG RANGE PERIOD.
===================================================================
SHORT RANGE DISCUSSION FOR 0600Z 25 AUG TO 0300Z 27 AUG.
MODEL DISCUSSION: USED RDPS
CONFIDENCE: HIGH
COMMENTS/IMPACTS: A TROUGH OF LOW PRESSURE TO THE WEST OF THE
MARITIMES WILL COMBINE WITH A SURGE OF TROPICAL MOISTURE MOVING UP
THE ATLANTIC SEABOARD OF THE UNITED STATES TODAY. A NEW AREA OF LOW
PRESSURE WILL FORM TO THE SOUTH OF NEW YORK IN THIS MOISTURE LATER
THIS MORNING AND TRACK OVER NOVA SCOTIA TONIGHT. SHOWERS OR PERIODS
OF RAIN WILL DEVELOP LATE THIS AFTERNOON AND BECOME HEAVY AT TIMES
THIS EVENING. THE LATEST RDPS MODEL RUN HAS NEARLY 50 MM OF
RAINFALL IN HALIFAX, BUT THIS AMOUNT IS EXPECTED TO BE HIGHLY
LOCALIZED. AS A MORE GENERAL RULE, MUCH OF THE AREA SHOULD GET 25
MM OF RAINFALL AND AN ADVISORY WILL BE ISSUED FOR THE EVENT. THESE
AMOUNTS LOOK TO BE CONFINED TO THE ATLANTIC COAST OF NS HOWEVER,
AND THE FIRE-PRONE AREAS OF NS LOOK TO GET MUCH LESS FOR AMOUNTS.
BEHIND THE NEW LOW, EARLY TUESDAY, A MODERATE TO STRONG WESTERLY
FLOW OF DRIER AIR MOVES OVER NS. THE CLOUDS SHOULD THIN OUT AND
DISPERSE DURING THE DAY.
LONG RANGE DISCUSSION FOR 0300Z 27 AUG TO 0300Z 30 AUG.
MODEL DISCUSSION: USED GDPS.
CONFIDENCE: HIGH-MEDIUM.
COMMENTS/IMPACTS: THERE IS A REDUCED CONFIDENCE IN THE FORECAST
CLOUD AMOUNTS OVER THE THREE LONG RANGE DAYS FROM WEAK SYSTEM
MOVING NEAR THE OPS AREA. THERE IS ALSO SOME TIMING DIFFERENCES
AMONGST THE MODELS FOR THE FORECAST ON FRIDAY.
ON WEDNESDAY, MODELS ARE DEPICTING A DENSE HIGH CLOUD SHIELD
ACROSS NOVA SCOTIA FROM A WEAK LOW PRESSURE SYSTEM PASSING WELL
SOUTH OF THE PROVINCE. HOWEVER, BOTH MODELS ARE SHOWING THIS
FEATURE, SO THERE IS A HIGH LIKELIHOOD THIS DAY COULD END UP QUITE
CLOUDY. ALSO HOWEVER, WITH THE FEATURE BEING SO WEAK AND SO FAR
AWAY FROM THE PROVINCE, THIS CLOUD SHIELD COULD BE QUITE OVERDONE
AS WELL.
ON THURSDAY, A FLAT RIDGE MOVES THROUGH THE PROVINCE. BUT DAYTIME
HEATING IS LIKELY TO GENERATE A FAIR BIT OF CUMULUS AS IT HEATS
THE UNSTABLE AIRMASS OVER THE PROVINCE.
ON FRIDAY, A TROUGH OF LOW PRESSURE MOVES INTO MAINE AND SPILLS
CLOUD INTO THE PROVINCE. THE GFS IS MUCH FASTER AND PUSHES THE
TROUGH INTO NOVA SCOTIA AND SHOWS A DECENT SHOT AT SOME SHOWERS
LATER IN THE DAY. THE ECWMF KEEPS THE TROUGH WEST OF NS, BUT ALLOWS
A SYSTEM FROM THE SOUTH TO PUSH CLOUDS AND POSSIBLE SHOWERS INTO
EASTERN PARTS OF THE PROVINCE. THIS IS THE MOST UNCERTAIN FORECAST
DAY OF THE THREE.
END/METOC-HFX
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