FXUS63 KGRR 230445
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1145 PM EST TUE DEC 22 2009
LATEST UPDATE...AVIATION...
.SYNOPSIS...(340 PM EST TUE DEC 22 2009)
AN UPPER AIR DISTURBANCE PASSING BY TO THE SOUTH OF MICHIGAN LATE
THIS AFTERNOON WILL CONTINUE TO BRING LIGHT SNOW SOUTH OF A LINE
FROM SOUTH HAVEN TO KALAMAZOO INTO EARLY THIS EVENING.
MEANWHILE A LARGE CANADIAN POLAR HIGH PRESSURE SYSTEM ANCHORED
BETWEEN LAKE SUPERIOR AND JAMES BAY WILL FEED COLD AND DRY AIR INTO
THE AREA FROM TONIGHT THROUGH WEDNESDAY NIGHT. SUNSHINE SHOULD BE
MORE PREVALENT NORTH OF INTERSTATE 94 WEDNESDAY AFTERNOON.
A STRONG WINTER STORM WILL MOVE FROM THE MISSISSIPPI RIVER VALLEY
TOWARD THE WESTERN GREAT LAKES BY FRIDAY. IT WILL BRING A MIX OF
WINTER TYPE PRECIPITATION TO THE AREA LATER THURSDAY INTO SATURDAY.
A MIX OF SNOW SLEET AND FREEZING RAIN WILL OVERSPREAD THE AREA LATE
IN THE DAY THURSDAY THEN CHANGE TO RAIN FROM SOUTH TO NORTH AFTER
EARLY CHRISTMAS MORNING. SIGNIFICANT SNOW WITH THIS SYSTEM WILL STAY
WELL TO OUR WEST. HOWEVER THE FREEZING RAIN ON CHRISTMAS EVE WHICH
COULD POTENTIALLY CREATE VERY HAZARDOUS TRAVEL CONDITIONS FROM
CHRISTMAS EVE INTO CHRISTMAS DAY. IT WILL TURN COLDER WITH SNOW
SHOWERS LATE FRIDAY THROUGH THE WEEKEND. AS A RESULT WE HAVE
ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM LATE THURSDAY
AFTERNOON TROUGH FRIDAY MORNING. FOR THE AREA NEAR AND NORTH OF
ROUTE 10 THE WINTER STORM WATCH GOES THROUGH FRIDAY AFTERNOON.
&&
.SHORT TERM...(1025 PM EST TUE DEC 22 2009)
(TONIGHT THROUGH WEDNESDAY NIGHT)
UPDATED TO REFLECT MORE IN THE WAY OF CLOUD COVER OVERNIGHT. IR LOOP
SHOWS MID CLOUDS MOVING INTO THE SRN CWA FROM THE WEST. STRATOCU WAS
ALSO DEVELOPING OVER LAKE HURON AND MOVING SSWWD. THUS...WE SHOULD
SEE THE CWA PINCH OFF IN CLOUD COVER. THE EXCEPTION MAY BE THE FAR
NORTH WHERE SKIES ARE CLEAR AND SHOULD REMAIN NORTH OF THE CLOUDS
ADVECTING IN FROM WISCONSIN.
OVERALL...UPSTREAM SHORTWAVE RIDGING WILL PREVAIL THROUGH WEDNESDAY
NIGHT. THAT IN TURN WILL CONTINUE TO DRY THE ATMOSPHERE OUT SO THAT
MOST OF THE CWA SHOULD SEE CLEARING OF MOST OF THE CLOUDS TONIGHT.
SOME LOW CLOUDS MAY PREVAIL NEAR AND SOUTH OF I-94 DUE TO EAST WINDS
OFF LAKE ERIE...INTO THIS EVENING BUT THAT SHOULD CLEAR TOO AS WINDS
BECOME MORE NORTHEAST. THIS WILL ALLOW FOR A VERY COLD NIGHT AS SNOW
COVER PREVAILS OVER MOST OF THE CWA. LOWS COULD BE BELOW ZERO NORTH
OR ROUTE 10 AND EAST OF BALDWIN.
THE ANTICYCLONIC CURVATURE IN THE LOW LEVEL FLOW FROM THE CANADIAN
HIGH WILL CONTINUE THE FEED OF DRY AIR AT LOW LEVELS THROUGH
WEDNESDAY NIGHT. THE UPPER RIDGING WILL CLEAR OUT THE MID AND HIGH
CLOUDS SO PARTLY CLOUDY TO MOSTLY SUNNY SKIES ARE EXPECTED
WEDNESDAY. INCREASING MID AND HIGH CLOUDS WILL BEGIN LATER WEDNESDAY
NIGHT. INCREASING WINDS IN THE BOUNDARY LAYER WILL KEEP THE LOWS
FROM GETTING AS COLD WEDNESDAY NIGHT.
&&
.MID TERM...(355 PM EST TUE DEC 22 2009)
(THURSDAY THROUGH FRIDAY NIGHT)
LITTLE HAS CHANGED IN OUR THINKING FOR THE HOLIDAY PERIOD STORM.
THE MODELS ARE INDICATING THE EVENT WILL UNFOLD A BIT SLOWER DUE TO
THE MOVEMENT OF THE UPPER LOW AND PERSISTENT DRY EASTERLY FLOW.
HOWEVER THE PCPN SHOULD ARRIVE BY LATE AFTERNOON THURSDAY IN THE
WEST...AND BY EVENING IN THE EAST. WITH THE LOW CENTER REMAINING TO
OUR WEST A WARM SURGE OF AIR WILL ARRIVE IN THE LOW/MID LEVELS WITH
COLD AIR PERSISTING OVER THE BOUNDARY LAYER. FREEZING RAIN AND
SLEET APPEARS TO BE THE MOST LIKELY PCPN TYPE...WITH A BIT OF SNOW
POSSIBLE AT THE ONSET.
DUE TO THE INCREASING LEVEL OF CONFIDENCE...HAVE GONE WITH A WINTER
STORM WATCH FOR THE ENTIRE CWA STARTING LATE THURSDAY AFTERNOON. WE
LOOKED AT THE RECORD BOOKS AND FOUND A VERY SIMILAR EVENT THAT
OCCURRED FEB 13-14 2005. THE TRACK AND TEMP PROFILE DURING THAT
EVENT MIRRORED THIS COMING EVENT. ICE ACCUMULATIONS WERE IN THE 0.1
TO 0.3 INCH RANGE. THE QPF EXPECTED WITH THE PENDING SYSTEM DURING
THE FREEZING RAIN PORTION IS HIGHER THAN THAT...BUT SOME OF THIS
WILL PROBABLY JUST RESULT IN RUNOFF AS THE PCPN INTENSITY INCREASES
THURSDAY NIGHT. SO WE FEEL THE ICE ACCUMS WILL BE NEAR THE FEB 2005
EVENT...WITH HIGHEST ICE ACCUMS IN THE NORTHERN CWA WHERE THE
FREEZING RAIN PERSISTS LONGER.
THESE ICE ACCUMS ARE BORDERLINE WATCH MATERIAL. HOWEVER WHAT TIPPED
THE SCALES ARE TWO THINGS: THE EASTERLY WINDS ARE EXPECTED TO GUST
TO 30 MPH AT TIMES. THESE WINDS AND THE ICE ACCUMULATION ON TREES
MAY RESULT IN BROKEN LIMBS THAT COULD RESULT IN SCATTERED POWER
OUTAGES. THE SECOND ITEM...OF COURSE...IS THE TIMING. ANY HOLIDAY
TRAVEL PAST NIGHTFALL ON CHRISTMAS EVE WILL BE IMPACTED. ISSUING
THE ADVANCED WATCH WILL GIVE THE STORM MORE CREDENCE AND AT LEAST
HAVE THE PUBLIC CONSIDER PLAN ADJUSTMENTS ACCORDINGLY.
THE FREEZING RAIN AND SLEET CHANGES TO RAIN SOUTH OF M46 ON
CHRISTMAS MORNING...BUT CONTINUES NORTH OF THERE INTO CHRISTMAS
AFTERNOON. THEN TOWARD NIGHTFALL WE WILL SEE COLDER AIR WRAP AROUND
THE SYSTEM AND COME IN FROM THE SW. THE RAIN WILL CHANGE TO SNOW
EARLY FRIDAY EVENING AND CONTINUE FRIDAY NIGHT.
.LONG TERM...(355 PM EST TUE DEC 22 2009)
(SATURDAY THROUGH TUESDAY)
MAIN CONCERN IS LAKE EFFECT POTENTIAL FROM LAKE SATURDAY INTO EARLY
SUNDAY. HAVE RAISED HPC GUIDANCE POPS SLIGHTLY DURING THIS TIME
FRAME. OTHERWISE FOLLOWED HPC GUIDANCE CLOSELY.
BY SATURDAY MORNING...GFS/ECMWF MODELS AGREE ON A STACKED CUTOFF LOW
IN THE VICINITY OF WISCONSIN. BY SATURDAY EVENING...GFS AND FIM
SOUNDINGS SHOW WINDS VEERING TO MORE W/SW DIRECTION WITH FAVORABLE
SATURATION/LAPSE RATES DEVELOPING IN THE DGZ ASSOCIATED WITH A
FAVORABLE LES PROFILE. GFS CONTINUES TO GROW THE CONVECTIVE
LAYER TO NEARLY 500 MB BY MONDAY MORNING. IF THIS WERE TO OCCUR IN
CONJUNCTION WITH THE EXITING UPPER PV ANOMALY...THERE WOULD BE
POTENTIAL FOR LOCALLY HEAVY LAKE EFFECT SNOW FROM LATE SUNDAY INTO
EARLY MONDAY BEFORE THE LOW EXITS THE LATER IN THE DAY ON MONDAY.
FOR NOW...HAVE ONLY NUDGED POPS SLIGHTLY DURING THIS VERY LATE TIME
FRAME.
&&
.AVIATION...(1145 PM EST TUE DEC 22 2009)
SATELLITE IMAGERY AND SURFACE OBSERVATIONS SHOW MVFR CLOUDS MOVING
SOUTHWEST OFF OF LAKE HURON. WHETHER THESE CLOUDS MOVE INTO KLAN OR
KJXN IS THE MAIN CHALLENGE IN THE AVIATION FORECAST.
FORECAST SOUNDINGS SUGGEST THIS LOW LEVEL MOISTURE FROM HURON WILL
MAKE IT INTO KLAN AND KJXN. COMPUTER DATA NOW SHOWS INCREASING LOW
LEVEL MOISTURE INTO TAF SITES FURTHER WEST INCLUDING KGRR AND KBTL
BY 18Z. WHILE THERE MAY BE A DIURNAL DECREASE TO THIS LOW LEVEL
MOISTURE AS IT TRACKS INTO WESTERN LOWER MI...AFT 00Z THU A MOISTURE
PLUME IS SHOWN FROM LAKE ERIE INTO KJXN TO KGRR. AT THIS POINT WILL
ADD MVFR CLOUDS ARRIVING PRIOR TO DAYBREAK FOR KLAN AND KJXN. A LOW
RISK FOR IFR IS THERE AS WELL. I AM NOT CONFIDENT ENOUGH TO ADD MVFR
CLOUDS TO TAF SITES FURTHER WEST...BUT WE WILL NEED TO MONITOR THIS
CLOSELY THROUGH THE NIGHT.
&&
.MARINE...(340 PM EST TUE DEC 22 2009)
WE ISSUED A GALE WATCH FOR THE ENTIRE NEAR SHORE FROM 12Z THURSDAY
THROUGH 18Z ON FRIDAY. THIS IS IN RESPONSE TO THE DEEP LOW THAT
MOVES THROUGH IOWA BY FRIDAY MORNING RESULTING IN GALE FORCE SOUTH
WINDS BY LATE IN THE DAY ON THURSDAY.
&&
.HYDROLOGY...(340 PM EST TUE DEC 22 2009)
CONCERN FOR ICE DEVELOPMENT THAT WOULD LEAD TO ICE JAMS IS MITIGATED
BY MAX TEMPS MAINLY IN THE 30S THROUGH FRIDAY... RESULTING IN LOW
ICE JAM POTENTIAL. PCPN THURSDAY THROUGH FRIDAY WILL NOT BE
SIGNIFICANT ENOUGH TO CAUSE HYDRO ISSUES. THE TEMPERATURES ARE NOT
EXPECTED TO BECOME WARM ENOUGH LONG ENOUGH TO SIGNIFICANTLY MELT THE
SNOW PACK EITHER.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY
AFTERNOON ALL ZONES.
LM...GALE WATCH FROM MID MORNING THURSDAY THROUGH FRIDAY MORNING FOR
THE ENTIRE NEAR SHORE.
&&
$$
SYNOPSIS: WDM
SHORT TERM: WDM 93
MID TERM: JK
LONG TERM: TJT
AVIATION: MJS
MARINE: WDM
HYDROLOGY: WDM
