037
FXCN01 CWHF 131907
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 2030Z ON
WEDNESDAY 13 MAY
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KEY FORECAST POINTS:
- THE EDGE OF A WARM WILL GIVE A CHANCE OF SHOWERS THIS EVENING.
- VARIABLE MORNING THURSDAY WITH INCREASING SOUTHEAST FLOW.
- DOWNWARD WEATHER TREND THURSDAY EVENING WITH EAST FLOW.
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SHORT RANGE DISCUSSION FOR 1800Z 13 MAY TO 0300Z 15 MAY.
MODEL DISCUSSION: USED RDPS / HRDPS
CONFIDENCE: MEDIUM
COMMENTS/IMPACTS: THE EDGE OF A WARM FRONT IS FORECAST TO PASS WEST
OF HALIFAX THIS EVENING. INCREASING CLOUDS WILL OCCUR THIS EVENING
AND THERE IS A CHANCE OF SHOWERS AS THE FRONT PASSES. THE WINDS
WILL SHIFT FROM SOUTHWEST TO SOUTH AND DIMINISH IN THE WARM SECTOR.
SURPRISINGLY, THERE IS NO BIG PUSH OF LOW LEVEL MOISTURE THURSDAY
MORNING IN THE WARM SECTOR, AS A BIT OF RIDGE BUILDS BACK OVER
NOVA SCOTIA. THAT STARTS TO CHANGE IN THE AFTERNOON AND ESPECIALLY
IN THE EVENING AS A SUBTROPICAL MOISTURE REGIME PUSHES NORTHWARD.
THE MORNING WILL BE THE TOUGHEST PART OF THE FORECAST, AS THERE IS
SOME UNCERTAINTY IN THE AMOUNT OF CLOUDS THAT WILL BE LEFT BEHIND
AS THE RIDGE BUILDS OVER. THE MODELS ARE SHOWING A FAIR BIT OF
THINNING, BUT THE LOW LEVEL SOUTHERLY FLOW MAKES ME SUSPICIOUS.
BY AFTERNOON, THERE IS MORE CERTAINTY THAT THE CLOUD LAYERS WILL
THICKEN UP AND THE SOUTHEAST FLOW INCREASE. BY EVENING, THE FLOW
SHIFTS TO THE EAST AND THE LOW LEVEL MOISTURE LEVELS RISE.
LONG RANGE DISCUSSION FOR 0300Z 15 MAY TO 0300Z 18 MAY.
MODEL DISCUSSION: USED GDPS
CONFIDENCE: MEDIUM
COMMENTS/IMPACTS: THIS MODEL RUN OF THE GDPS IS QUITE CONSISTENT
WITH THE 00Z RUN OF THAT MODEL. THERE ARE SOME DIFFERENCES NOTED IN
THE GFS AND EURO HOWEVER.
ON FRIDAY, THE FIRST AREA OF LOW PRESSURE THAT WILL BE BRINGING
THE MOISTURE THURSDAY IS STARTING TO PULL OFF TO THE EAST, BUT A
SECOND IMPULSE FROM MAINE WILL ROTATE INTO NOVA SCOTIA DURING THE
DAY. THE GDPS IS SHOWING A FAIR BIT OF PRECIPITATION IN THE MORNING
AND AGAIN IN THE EVENING, WITH A MOIST AIRMASS DURING OTHER PARTS
OF THE DAY. HOWEVER, THE BULK OF THE HEAVIER PRECIPITATION ON OUR
MODEL LIES TO THE NORTH AND EAST OF HALIFAX. OUR MODEL ALSO HAS A
FAIRLY STRONG NORTHEAST WIND THAT BECOMES MODERATE NORTHERLY. THE
GFS DOES NOT PUSH THIS PRECIPITATION AS FAR NORTH AS HALIFAX WITH
THE FIRST LOW AND ALSO MOSTLY MISSES WITH THE SECOND FEATURE. THE
CANADIAN MODEL IS MORE OF AN OUTLIER AT THIS POINT, SO OUR FORECAST
MAY NEED SOME ADJUSTMENT SOON.
BY SATURDAY, MOST OF THE MODELS ARE THE SAME. THE SECONDARY
FEATURE DEPARTS IN THE MORNING. BUT THE MODELS DIFFER WITH TIMING,
AND HE CANADIAN ONE IS LIKELY THE SLOWEST. BY MIDDAY A MODERATE
NORTHWEST FLOW OF DRY AND WARM AIR BECOMES ESTABLISHED. FORECAST
HIGHS ARE 20C OR HIGHER EVEN ALONG THE COAST. A GOOD START TO THE
VICTORIA DAY WEEKEND.
BY SUNDAY, A RIDGE BUILDS SOUTH OF NOVA SCOTIA DEFLECTING THE
WINDS TO THE SOUTHWEST. LATE IN THE DAY A TROUGH APPROACHES FROM
THE NORTHWEST WITH A FEW SHOWERS. THE CANADIAN MODEL IS SLOWEST
WITH THESE SHOWERS. THE AMERICAN MODEL IS THE FASTEST. THE SHOWERS
WILL BE LEFT OUT OF THE FORECAST FOR NOW.
END/METOC-HFX
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