325
FXCN01 CWHF 222011
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
SATURDAY 22 AUG
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KEY FORECAST POINTS:
- VERY MOIST AND UNSTABLE AIRMASS MOVES INTO THE REGION THIS EVENING
GIVING RAIN/DRIZZLE WITH EMBEDDED HEAVY SHOWERS AND THE RISK OF
THUNDERSTORMS TONIGHT THROUGH MONDAY EVENING.
- SIGNIFICANT RAINFALL AMOUNTS QUITE POSSIBLE FOR THE REGION,
POSSIBLY UP TO 100 MM OR MORE AS WELL AS LOW CONDITIONS IN
STRATUS MIST AND FOG.
- IMPROVEMENT TUESDAY/WEDNESDAY WITH A CHANCE OF AFTERNOON SHOWERS
AS UNSTABLE AIRMASS LINGERS IN BROAD TROUGHING REMAINING OVER
REGION.
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SHORT RANGE DISCUSSION FOR 1800Z 22 AUG TO 0300Z 24 AUG.
MODEL DISCUSSION: USED RDPS/HRDPS.
CONFIDENCE: GENERALLY HIGH.
COMMENTS/IMPACTS: MODELS IN VERY GOOD AGREEMENT, ASIDE FROM EXACT
RAINFALL TOTALS. INTENSE ANCHORING LOW DEVELOPING OVER THE GREAT
LAKES REGION WILL SET UP A VERY MOIST AND UNSTABLE FLOW OVER THE
LOCAL REGION LATE THROUGH MONDAY EVENING. A SERIES OF TROUGHS/LOWS
WILL GUIDE BOUTS OF HEAVY RAIN/SHOWERS WITH A RISK OF THUNDERSHOWERS
THROUGH THE REGION BEGINNING NEAR MIDNIGHT TONIGHT. HEAVY
RAIN/SHOWERS WILL TAPER OFF TO DRIZZLE/SCATTERED SHOWERS NEAR NOON
SUNDAY THEN BECOME HEAVY ONCE AGAIN AHEAD OF THE NEXT TROUGH MONDAY
EVENING. THROUGHOUT THE PERIOD, THERE WILL BE A RISK OF
THUNDERSTORMS THOUGH THE GREATEST RISK WILL BE LATE TONIGHT INTO
SUNDAY MORNING AND ONCE AGAIN SUNDAY NIGHT INTO MONDAY. EXTENSIVE
LOW CONDITIONS WILL DEVELOP AFTER MIDNIGHT WITH STRATUS MIST AND
FOG PERSISTING INTO MONDAY EVENING. AS THIS IS GOING TO BE A VERY
CONVECTIVE SYSTEM, WITH A SOURCE REGION OF MOISTURE FROM THE
TROPICS/OFF THE FLORIDA COAST, RAINFALL TOTALS WILL VARY QUITE A
LOT OVER THE REGION. WHILE GENERAL AMOUNTS OF 40 TO 80 MM ARE
LIKELY, OVER ABOUT A 48 HOUR PERIOD, THERE ARE INDICATIONS THAT
INTENSE BANDS OF CONVECTION WILL TRACK OVER THE SAME LOCATIONS
GIVING POSSIBLY MUCH MORE SIGNIFICANT RAINFALL TOTALS, IN EXCESS
OF 100 MM.
LASTLY.. MODERATE TO STRONG SOUTHEAST WINDS WILL DEVELOP AHEAD OF
THE TROUGH TONIGHT THEN BECOME MORE SOUTHERLY LATE SUNDAY IN THE
WAKE OF THE SECOND TROUGH. AT THIS TIME, ASIDE FROM CONVECTIVE
WINDS MIXING DOWN, WINDS ARE EXPECTED TO REMAIN BELOW 25-30 KNOTS.
LONG RANGE DISCUSSION FOR 0300Z 24 AUG TO 0300Z 27 AUG.
MODEL DISCUSSION: USED RDPS/GDPS.
CONFIDENCE: GENERALLY HIGH.
COMMENTS/IMPACTS: RAIN, POSSIBLY WITH HEAVY SHOWERS AND THE RISK OF
THUNDERSTORMS, AS WELL AS EXTENSIVE MIST AND FOG WILL CONTINUE TO
AFFECT THE REGION THROUGH THE DAY MONDAY AND FINALLY BEGIN TO
IMPROVE NEAR MIDNIGHT MONDAY INTO TUESDAY. SEE ABOVE FOR RAINFALL
DISCUSSION OVER THE PERIOD. AS THE FINAL TROUGH MOVES EAST OF THE
REGION, EXPECT A CLEARING TREND TUESDAY MORNING. HOWEVER, THE
ANCHORING LOW FROM THE GREAT LAKES OVER THE WEEKEND WILL LIE OVER
QUEBEC/LABRADOR WITH BROAD TROUGHING LINGERING OVER THE LOCAL
REGION. EXPECT THIS TO COMBINE WITH DAYTIME HEATING TO GIVE A
CHANCE OF AFTERNOON SHOWERS TUESDAY AND ONCE AGAIN WEDNESDAY..BOTH
WITH A MIX OF SUN AND CLOUD AND A LIGHT TO MODERATE SOUTHWEST FLOW.
END/METOC-HFX
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